Dermatophytoses are superficial infections of the skin and hair caused by keratinophilic fungi of the genera Microsporum, Trichophyton and Nannizzia. In dogs and cats, Microsporum canis predominates by a wide margin. The condition is contagious, infectious and transmissible to humans, which gives it a place apart in the dermatology consultation. The veterinary surgeon treats an animal and protects its household.
About half of the people exposed to an infected cat, whether or not it shows signs, acquire the infection, and in 30 to 70 % of households keeping an infected cat at least one person is affected (Miller et al., 2013). Treatment, however, has changed. Not in its principles, set out in international consensus guidelines, but in the means available: several licensed products have disappeared and a resistance mechanism has emerged. That is why, in 2026, it was time to take full stock both of the molecules still available and of the updated protocols.
Note to the reader: the regulatory framework described in this article, in particular the products withdrawn from the market, the marketing authorisations and the prescribing cascade, is the French one. The molecules, dosages and therapeutic principles remain valid everywhere, but the commercial availability of each product must be checked on your own national market.
Dermatophytosis in humans
1 Developments since the reference protocols
1.1 Why treat a disease that resolves on its own?
Dermatophytosis is not life-threatening and resolves without intervention. If we treat, it is to shorten the course of the disease and limit transmission (Moriello, 2019a).
Five dogs aged 6 to 18 months with generalised dermatophytosis received an inert substance orally once daily with food. Signs resolved in 3 of them after 4 to 8 weeks. The other 2, showing no improvement, recovered after 6 weeks of ketoconazole (Medleau et al., 1992). In the cat, the disease is described as self-limiting in a large number of cases, with hair loss and scaling as the only manifestations; multifocal or generalised forms are seen mainly in kittens and in immunocompromised animals (Frymus et al., 2013).
The cure rates in control groups are therefore not artefacts. The 6 of 40 cats that recovered on placebo in the pivotal itraconazole trial illustrate this natural course. It is against that course that the effect of a treatment is measured. Moreover, since the animal would recover anyway, the therapeutic aim is to shorten the infectious period and to decontaminate the environment.
1.2 The 2017 consensus guidelines and what they established
The reference text for the discipline remains the clinical consensus document of the World Association for Veterinary Dermatology, published in 2017 (Moriello et al., 2017).
No diagnostic test is recognised there as a reference method. The Wood’s lamp and direct hair examination have good predictive value, both positive and negative.
On treatment, cure requires the simultaneous use of an oral systemic antifungal and of a topical antifungal on the coat. Since the animal carries infective spores on hairs that are not all lesional, neither route is sufficient on its own. Systemic antifungals are further described as having a wide safety margin, and physical cleaning together with the application of an antifungal in the environment as essential in decontaminating premises. Finally, the authors recall that serious complications of transmission to humans are exceptional.
1.3 Products withdrawn from the French market and practical consequences
Several of the products cited in older international guidelines are no longer available for purchase, particularly in France.
First, griseofulvin. The veterinary tablet formulation of griseofulvin, FULVIDERM ND (Virbac), retains a valid marketing authorisation in the European veterinary medicines register, but can no longer be ordered. Only an oral powder remains, DERMOGINE ND (Dopharma France), containing 100 mg of griseofulvin per gram, authorised in dogs, cats and horses under authorisation FR/V/8551428, of unlimited duration (ANSES-ANMV, 2026). In human medicine, Sanofi announced on 19 July 2021 that it was discontinuing the GRISEFULINE ND 250 mg and 500 mg products, owing to unresolved manufacturing difficulties (ANSM, 2021).
Next comes decontamination of premises. The enilconazole smoke generator, CLINAFARM ND (Elanco France), long the reference tool in catteries and shelters, is no longer marketed in France. This product has biocide status rather than that of a veterinary medicine, and so does not appear in the national veterinary medicines register. Its disappearance leaves a gap that nothing strictly equivalent fills, and renders obsolete part of the cattery protocols written before it.
To these two withdrawals is added a lasting constraint: lime sulphur, the cornerstone of the entire North American literature on topical treatment, corresponds to no veterinary medicine authorised in the European Union. In the United States, the marketed preparations carry a statement that the federal agency has not established their safety or efficacy and has not approved their labelling. The molecule is registered there with the environmental protection agency, for agricultural uses and for topical application against livestock mites. The French practitioner therefore reads recommendations built on a product that is inaccessible to him, and that the authority of the country where it is used has never evaluated. Enilconazole, by contrast, remains available in France as a concentrate for cutaneous spray emulsion at 100 mg/ml, IMAVERAL ND (Audevard). This product holds an unlimited authorisation granted in 1982 and is not subject to prescription. Its indication covers dermatophytoses due to Microsporum canis, Microsporum gypseum, Trichophyton verrucosum, Trichophyton mentagrophytes and Trichophyton equinum, in dogs, cats, cattle and horses (ANSES-ANMV, 2026). The molecule is not marketed in the United States (VCA, 2026), which explains the marginal place it occupies in American publications; it does, however, remain authorised in other member states, under different trade names. It is this product that may be applied in the environment at a concentration 5 times higher than that applied to animals.
Extensive dermatophytosis in a dog
1.4 The emergence of allylamine-resistant dermatophytes
The most striking new development since 2013 concerns not a molecule but a fungus. Trichophyton indotineae, first described as genotype VIII of the Trichophyton mentagrophytes complex, emerged from the Indian subcontinent and has spread internationally (Ahmad, 2026).
Point mutations in the squalene epoxidase gene alter the target of terbinafine. Three substitutions are named: Leu393Phe, Phe397Leu and Ala448Thr. These mutations confer high minimum inhibitory concentrations for terbinafine, and they have been detected in both human and animal isolates, indicating the circulation of stable and transmissible resistant clones (Ahmad, 2026).
Whole genome sequencing of 13 Indian isolates, 9 of human and 4 of canine origin, showed small differences in polymorphisms between the two origins, which argues for zoonotic transmission and rapid spread over long distances (Thakur et al., 2025). However, two canine strains from northern India characterised separately proved susceptible to terbinafine, with no substitution at positions 393 or 397 (Thomas et al., 2025). Resistance therefore does not accompany the species, it accompanies certain clones.
In Europe, two T. mentagrophytes isolates from Polish hedgehogs carried the Leu393Phe substitution, with a minimum inhibitory concentration of 2 µg/ml for terbinafine (Gnat et al., 2021).
Microsporum canis, the agent of almost all canine and feline cases, also develops resistance, but by another route. The first terbinafine-resistant strain isolated from a cat was reported in 2018: a two-year-old exotic shorthair with alopecia and mild scaling of the trunk, whose strain showed a minimum inhibitory concentration above 32 µg/ml for terbinafine and of 0.023 µg/ml for itraconazole. The animal recovered on systemic itraconazole (Hsiao et al., 2018). The mechanism involved is not a squalene epoxidase mutation but an overexpression of ABC transporters: in a resistant strain, expression of the PDR1, MDR1, MDR2 and MDR4 genes was two to four times higher than in susceptible strains, and adding the efflux blocker FK506 lowered the minimum inhibitory concentration from above 32 to 8 µg/ml (Kano et al., 2018). Efflux-mediated resistance therefore does not necessarily spare the azoles, unlike a mutation of the terbinafine target.
Its frequency nonetheless remains low. Among 348 M. canis isolates from mainland China studied over 27 years using method M38-A3 of the Clinical and Laboratory Standards Institute, in a human series including in particular 54 cases of tinea capitis in children, two strains proved resistant to griseofulvin with a minimum inhibitory concentration of 64 µg/ml, one to fluconazole at the same value, and two to terbinafine at 16 µg/ml. The great majority of strains retained low minimum inhibitory concentrations for the 11 molecules tested, and analysis of their distribution revealed no clear resistance profile (Liang et al., 2025). In Central Asia, among human clinical isolates, all 57 M. canis strains tested by the EUCAST method remained susceptible to terbinafine, whereas 4 of the 33 Trichophyton strains were resistant (Aimoldina et al., 2026). These two series cannot be compared point by point: the minimum inhibitory concentration values produced by the American and the European methods are not interchangeable, and only the order of magnitude of the resistance frequency can be read across the studies.
Resistance in M. canis therefore exists, but is rare, and arises through a mechanism distinct from that of T. indotineae. Moreover, no clinical series to date links squalene epoxidase mutations to treatment failures in dogs or cats in Europe. The immediate consequence is therefore diagnostic before it is therapeutic: it concerns species identification in cases of failure, not first-line choice. It weighs all the more heavily because culture-based identification does not distinguish T. indotineae from the other Trichophyton species: this requires sequencing of the ITS region supplemented by that of the HMG gene, which encodes an HMG-box transcription factor whose sequence separates the species that the ITS region alone does not distinguish, mass spectrometry with an updated library, or sequencing of the squalene epoxidase gene (Ahmad, 2026).
2 Pharmacology of the usable antifungals
2.1 Azoles: mechanism, spectrum and activity in keratin
Azoles inhibit 14-alpha-demethylase, a fungal cytochrome P450 enzyme that converts lanosterol into ergosterol. The fungal membrane is thereby deprived of its structural sterol and enriched in methylated precursors. Its permeability is disrupted and fungal growth stops. The effect is fungistatic at the concentrations achieved in practice.
This inhibition is not perfectly selective, however, and that is where the adverse effects of the class come from. The same cytochrome P450 enzymes are involved in mammalian steroidogenesis and in the hepatic metabolism of numerous drugs, hence the hormonal disturbances and drug interactions observed, especially with ketoconazole.
Itraconazole accumulates in hair and skin, where it persists at concentrations above the therapeutic threshold during the weeks when treatment is interrupted, and beyond the last dose. It is this tissue persistence, and nothing else, that permits the alternate-week regimen.
2.2 Allylamines: fungicidal action and persistence
Terbinafine acts further upstream in the same chain. It inhibits squalene epoxidase, the fungal enzyme that converts squalene into squalene epoxide. Two consequences add up: ergosterol is no longer produced, and squalene accumulates in the fungal cell to a toxic level. This accumulation kills the fungus rather than merely preventing it from growing. Terbinafine is therefore fungicidal against dermatophytes, where the azoles are fungistatic.
It is this same enzyme that the mutations described above modify, which explains why resistance acquired through target mutation affects terbinafine and spares the azoles. This reservation does not apply to efflux-mediated resistance, which exports several classes of molecules indiscriminately and therefore does not necessarily spare the azoles.
2.3 Griseofulvin: residual place and constraints
Griseofulvin is a fungistatic antibiotic produced by Penicillium griseofulvum. It binds to the intracellular microtubules of the dermatophyte and blocks their polymerisation, halting mitosis at metaphase. It reaches the cells that synthesise keratin precursors and binds to keratin in the adnexa. Its metabolism is essentially hepatic and its elimination mainly urinary. Its spectrum is limited to dermatophytes, principally Microsporum spp. and Trichophyton spp. (ANSES-ANMV, 2026).
Its intestinal absorption is poor and depends on dietary lipids, which requires it to be given with a fatty food. Its safety constraints, set out below, have relegated it behind the azoles wherever these are available.
3 Systemic treatment
3.1 Itraconazole
Itraconazole is today the first-line molecule in the cat. The European feline guidelines already gave it that place (Frymus et al., 2013), and subsequent data have left it there.
The 10 mg/ml oral solution intended for cats, ITRAFUNGOL ND (Virbac), is authorised in France under authorisation FR/V/7569820 granted on 9 August 2004, of unlimited duration, for the treatment of dermatophytoses due to Microsporum canis in the cat. It is given at a dose of 5 mg/kg once daily, that is 0.5 ml/kg, on alternate weeks, for three cycles: administration in weeks 1, 3 and 5, interruption in weeks 2 and 4 (ANSES-ANMV, 2026).
The product is not given to cats with hepatic or renal insufficiency, nor to pregnant or lactating queens. Two interactions have been observed in the cat: combination with cefovecin caused vomiting and hepatic and renal disorders, and combination with tolfenamic acid caused motor incoordination, faecal retention and dehydration. To these are added the interactions linked to cytochrome P450 3A4 and P-glycoproteins, described in human medicine, which increase the plasma concentrations of midazolam, ciclosporin, digoxin, chloramphenicol, ivermectin and methylprednisolone (ANSES-ANMV, 2026).
The summary of product characteristics states that cats treated with itraconazole may continue to contaminate other animals, dogs included, until mycological cure is achieved. The pivotal study involved 80 cats infected with M. canis, allocated between the itraconazole solution and a placebo, with no associated topical treatment. Cure on Wood’s lamp examination, defined as absence of fluorescence at the base and mid-shaft of the hair, was achieved in 39 of the 40 treated cats against 6 of the 40 controls, and the time to mycological cure was significantly shorter in the treated group. In the two cats that failed, the minimum inhibitory concentrations of itraconazole remained within the susceptible range, which rules out resistance as an explanation.
The review of published studies sets out the expected timeframes: itraconazole at 10 mg/kg once daily, or on the combined continuous then pulse regimen, cured infected animals in 56 to 70 days, whereas low-dose protocols of 1.5 to 3 mg/kg in 15-day cycles required one to three cycles, that is 15 to 45 days (Moriello, 2004).
Earlier data under natural conditions had already established the efficacy of the molecule, at lower doses and with poorer tolerance. Of 15 cats with dermatophytosis due to M. canis, treated with oral itraconazole at 1.5 to 3 mg/kg once daily for 15 days, 8 recovered completely, 6 of them after a single course. Five cats vomited or became anorexic at the higher doses, which required the dose to be reduced progressively. Six of the 15 animals had previously failed on griseofulvin at 10 mg/kg for 60 days (Mancianti et al., 1998).
The combined continuous then pulse regimen was assessed in 9 cats: itraconazole at 10 mg/kg once daily for 28 days, then on alternate weeks at the same dose, stopping after two consecutive negative cultures. Eight of the 9 cats were cured at 56 days (Colombo et al., 2001). The number is small and the authors themselves present these results as preliminary, pending a controlled study that did not follow.
The adverse effects reported after marketing are, in decreasing order of reporting frequency, anorexia, vomiting, raised liver enzymes, lethargy, weight loss, jaundice, raised total bilirubin and diarrhoea. Deaths, including euthanasia, have been reported. Safety is not established in the pregnant queen. Use requires caution in renal dysfunction or hepatic impairment.
The authorisation does not cover the dog, in which no controlled trial has assessed itraconazole alone. A retrospective study of 64 dogs infected with the Trichophyton mentagrophytes complex in the central United States, over the period 1997-2020, concludes that ketoconazole, itraconazole and terbinafine appear equivalent as systemic options in this indication (Pieper et al., 2023). The level of evidence is that of a retrospective series, but it is the most substantial canine dataset available.
Few authorised systemic treatments exist for the dog
The American agency has reported substantial variation in absorption between compounded itraconazole preparations depending on the pharmacy producing them, and recommends prescribing the veterinary product rather than a compounded formulation.
3.2 Terbinafine
Terbinafine holds no veterinary marketing authorisation and is therefore prescribed, in France, under the cascade provided for in article L.5143-4 of the public health code.
The cascade only opens if no authorised medicine is suitable for the species and indication concerned. Now, ketoconazole is authorised in the dog and griseofulvin in both dog and cat, both for the treatment of dermatophytoses: the justification for using terbinafine cannot therefore be the absence of an authorised alternative. The same reasoning applies to itraconazole in the dog, authorised only in the cat. The place of terbinafine has nonetheless become established, for two reasons: its fungicidal action, and its availability where itraconazole is expensive or lacking.
The most robust data come from work carried out in a shelter on 85 cats with spontaneous dermatophytosis due to M. canis, monitored by weekly toothbrush culture with colony-forming unit counts. The toothbrush technique consists of methodically combing the entire coat with a new sterile toothbrush and then inoculating the brush itself onto the culture medium: it collects infected hairs from the whole body, including outside visible lesions, which makes it superior to lesional sampling for both screening and monitoring. Counting colonies on the plate makes it a semi-quantitative test: a fall in the number of colony-forming units accompanies the response to treatment, whereas a stable or rising number signals a poor response. The animals received oral terbinafine for 14 days in 21 of them, or 21 days in the other 64, in both cases with lime sulphur dips twice weekly and daily disinfection of the premises with 5.5 % sodium hypochlorite diluted one in ten. Dosing was set by weight band, for convenience in splitting the 250 mg tablet: a quarter tablet, that is 62.5 mg, for cats under 2.8 kg; half a tablet, that is 125 mg, from 2.8 to 5.5 kg; a whole 250 mg tablet above 5.5 kg, in a single daily dose with the morning meal. Lime sulphur was applied at 236 ml per 3.8 litres of water, by sprayer, with no collar to prevent licking. The cats treated for 14 days responded at first, the number of animals with a positive culture falling from 21 to 6 within two weeks, then relapsed, 15 of the 21 becoming positive again at week 6, and they required rescue with itraconazole at 10 mg/kg once daily for 21 days. The cats treated for 21 days responded as they did on itraconazole given for 21 days, with a mean and median time to mycological cure of 22.7 days, individual values ranging from 13 to 39 days. Mycological cure was defined there as two consecutive negative weekly cultures. Tolerance was good, and no cat developed oral lesions after grooming the topical product (Moriello et al., 2013a).
An older series under natural conditions had used a high dose over a short period: oral terbinafine at 30 mg/kg once daily for two weeks in 15 cats infected with M. canis, of which 12 could be followed to the end. Eleven of these 12 animals recovered completely, with checks on the last day of treatment, at one month and then at three months (Mancianti et al., 1999). Terbinafine was proposed there as an alternative to griseofulvin in cases of fungal resistance or idiosyncratic intolerance, with faster cure and fewer relapses, a proposal that the withdrawal of griseofulvin makes topical again today.
Canine data are thinner but consistent. The retrospective series of 64 dogs already cited places terbinafine on the same level as ketoconazole and itraconazole (Pieper et al., 2023). A comparative study of 35 animals, dogs and cats together, set griseofulvin against terbinafine under three protocols: griseofulvin at 50 mg/kg once daily was effective in 100 % of cases, with no adverse effects, and a mean time to cure of 41 days; terbinafine at 5 mg/kg once daily was effective in 81.3 % of cases, with no adverse effects, and a mean time of 21 days; at 20 mg/kg, efficacy was comparable but the time lengthened to 33 days and adverse effects appeared in 16.6 % of animals, vomiting, diarrhoea, raised transaminases and alkaline phosphatases (Balda et al., 2007). The authors conclude that terbinafine is a good therapeutic alternative, but that griseofulvin remains in their view the first-line drug in dogs and cats, a position that must be reported even though French availability has since made it hard to follow.
These two series do not contradict each other: the first concerns shelter animals, the second owned cats, and the reinfection pressure is not the same. The finding that governs prescribing, however, is Moriello’s: 14 days are not enough.
Two earlier experimental studies had already bracketed the dose. Carried out in 27 cats experimentally infected with M. canis, they showed that 10 to 20 mg/kg was insufficient and that 30 to 40 mg/kg was required (Kotnik et al., 2001; Kotnik and Černe, 2006). These animals were inoculated in the laboratory, which carries less weight than a series under natural conditions, but the threshold they identify agrees with that of the review.
The review of published studies provides the range of doses and durations actually used, dogs and cats together: terbinafine doses of 5 to 40 mg/kg have been used, doses above 20 mg/kg being necessary to achieve mycological cure, and the number of treatment days to cure ranged from 21 to more than 126 days (Moriello, 2004). This spread makes it impossible to announce a duration to the owner and requires cultures to be followed.
One hundred and sixty-five European hedgehogs with spontaneous dermatophytosis due to Trichophyton erinacei were allocated between oral itraconazole and terbinafine for 28 days. Mycological cure rates were 36.6 % at 14 days and 65.9 % at 28 days on itraconazole, against 92.8 % and 98.8 % on terbinafine (Bexton et al., 2016). The number is substantial and the study randomised, but the species and the agent differ from ours: the result suggests superiority of terbinafine in dermatophytoses due to Trichophyton, it does not transfer unchanged to feline M. canis infections.
3.3 Ketoconazole
Ketoconazole is, in France, the only azole holding a veterinary marketing authorisation in this indication in the dog. Griseofulvin holds one as well, but belongs to another class. Two 200 mg tablet products are authorised: KETOFUNGOL ND (Elanco, authorisation FR/V/0086228 granted in 1983) and FUNGICONAZOL ND (Dechra). The indication names infections due to Microsporum canis, Microsporum gypseum and Trichophyton mentagrophytes in the dog. The dose is 10 mg of ketoconazole per kg of body weight per day, that is one 200 mg tablet per 20 kg, for three to four weeks, preferably given with a meal in order to obtain maximum absorption (ANSES-ANMV, 2026).
The molecule is not used in animals with hepatic insufficiency. Its safety has not been established in pregnancy or lactation, and studies in laboratory animals have shown teratogenic and embryotoxic effects: its use is therefore not recommended during pregnancy. It is not given at the same time as antacids or antihistamines, which alter its absorption, nor with anticoagulants. The summary of product characteristics further notes that repeated use of ketoconazole may induce, albeit rarely, cross-resistance to the other azoles.
These constraints, together with poorer tolerance than that of itraconazole, explain why ketoconazole has lost its first-line place even though it remains, in the dog, the only authorised azole.
3.4 Griseofulvin
Griseofulvin is given to dogs and cats at a dose of 20 mg per kg of body weight per day, that is one gram of oral powder per 5 kg mixed into the ration, for three to four consecutive weeks (ANSES-ANMV, 2026).
It is prescribed first and foremost according to its safety constraints. The molecule is teratogenic. It is therefore not given to pregnant animals, nor to animals under 12 weeks of age. It is not given to an animal with hepatic disease. It requires particular caution in cats infected with feline immunodeficiency virus, because of the risk of iatrogenic neutropenia. In overdose, hepatic toxicity is seen, and rare cases of neurotoxicity have been described in the cat. The person administering the product must not be pregnant, and anyone hypersensitive to griseofulvin must avoid all contact with the drug.
Griseofulvin at 50 mg/kg cured infected animals in 41 to 70 days (Moriello, 2004). This dose exceeds that of the French authorisation, set at 20 mg/kg, which must be pointed out to the prescriber. The difference matters, because underdosing is the leading cause of relapse.
The summary of product characteristics finally recommends disinfecting the premises at the same time.
3.5 Comparative tolerance and laboratory monitoring
Laboratory monitoring is set as much by the animal treated as by the molecule. A complete blood count and platelet count are strongly recommended in all cats on griseofulvin, and particularly in the Persian, the Abyssinian and the Siamese (Miller et al., 2013). Given the profile of the adverse effects reported on itraconazole, raised liver enzymes, jaundice, raised bilirubin, hepatic monitoring is equally required as soon as treatment is prolonged or the animal shows anorexia or lethargy.
Terbinafine stands out for its tolerance. In the shelter series it was well tolerated by 85 animals (Moriello et al., 2013a). In a report on two cats treated for 12 to 14 weeks, only mild to moderate lethargy was observed in one of them, with no other adverse effect and no change in blood parameters (Nuttall et al., 2008). Vomiting and facial pruritus have nonetheless been reported in the cat.
3.6 Summary of systemic prescribing
The data scattered through the preceding subsections are brought together in Table 1, which gives for each molecule its French status, the established dose, the schedule, the expected duration and the monitoring it requires.
Table 1. Systemic antifungals for dermatophytosis in dogs and cats: status in France, doses and monitoring
|
Molecule |
Status in France |
Species |
Dose |
Schedule and duration |
Monitoring |
|
Itraconazole |
Oral solution 10 mg/ml, French veterinary authorisation in the cat (FR/V/7569820); off-licence in the dog |
Cat (authorised); dog (cascade) |
5 mg/kg, that is 0.5 ml/kg (authorisation); 10 mg/kg (published protocols); 1.5 to 3 mg/kg (low-dose protocol) |
Alternate weeks, 3 cycles; or 28 continuous days then alternate weeks; or 15-day cycles, 1 to 3 cycles. Cure in 56 to 70 days, or 15 to 45 days at low dose |
Liver enzymes, bilirubin; anorexia and vomiting common at high doses. Contraindicated in hepatic or renal insufficiency, pregnancy and lactation. Interactions: cefovecin, tolfenamic acid, CYP3A4 substrates |
|
Terbinafine |
No veterinary authorisation, prescribed under the cascade |
Cat and dog |
62.5 mg below 2.8 kg; 125 mg from 2.8 to 5.5 kg; 250 mg above. Published doses of 5 to 40 mg/kg, above 20 mg/kg for mycological cure |
Once daily with food, 21 days minimum, 14 days carry a risk of relapse. Cure in 21 to more than 126 days |
Good tolerance; vomiting and facial pruritus in the cat; vomiting, diarrhoea and raised transaminases and alkaline phosphatases in 16.6 % of animals at 20 mg/kg |
|
Ketoconazole |
200 mg tablets, veterinary authorisation |
Dog |
10 mg/kg |
Once daily with food, 3 to 4 weeks per cycle |
Liver function; contraindicated in hepatic insufficiency and pregnancy; do not combine with antacids, antihistamines or anticoagulants |
|
Griseofulvin |
Oral powder 100 mg/g, veterinary authorisation; the only formulation still available |
Dog, cat, horse |
20 mg/kg (authorisation); 50 mg/kg in published studies |
Once daily in a fatty meal, 3 to 4 weeks per cycle. Cure in 41 to 70 days |
Blood count and platelets, particularly in the Persian, the Abyssinian and the Siamese; teratogenic; caution in the FIV-positive cat |
The duration given in the table is that of one cycle or the order of magnitude observed, never a treatment duration: that is set by the cultures, according to the criterion set out in 7.2.
3.7 Lufenuron: an abandoned avenue
Lufenuron, a chitin synthesis inhibitor, raised hopes that the data have not borne out. Efficacy has been reported anecdotally in the rabbit at a dose of 135 mg/kg orally every four weeks, but studies in other species have failed to demonstrate it (Miller et al., 2013). No protocol based on current data uses it, and it has no place in the treatment of dermatophytosis in dogs and cats.
4 Topical treatment
4.1 Why topical treatment is not optional
Dermatophytosis is an infection of the hair and not of the skin surface alone. Infected hairs are not all lesional, so that a coat of healthy appearance carries arthrospores. These spores detach, contaminate the environment and reinfect the animal and those around it. Treating the visible lesion therefore leaves the source of dissemination in place.
The consensus guidelines require the simultaneous use of an oral systemic antifungal and of topical disinfection of the coat (Moriello et al., 2017). A topical treatment applied to the lesion alone is therefore not a treatment for dermatophytosis: the focal topical is additional to whole-body treatment. The literature itself classes focal application products as adjuvants (Moriello, 2020).
Likewise, the leaflet for the itraconazole product intended for cats recalls that the molecule is not sporicidal, and recommends for that reason a treatment of the coat and of the environment in order to reduce zoonotic potential and environmental contamination.
The pivotal itraconazole trial nonetheless achieved cure in 39 of 40 cats with no topical treatment at all, and the Mancianti series are likewise systemic monotherapies. The contradiction is only apparent: a systemic antifungal alone is sufficient to achieve mycological cure of the treated animal, and that is what these trials establish. It does not thereby render the coat non-contaminating during treatment, since it is not sporicidal: the arthrospores already present on the hairs continue to seed the environment and those around the animal. Topical treatment therefore aims not at cure of the individual but at halting dissemination, and it is on that ground that the consensus holds the two routes to be inseparable. The shorthand “no topical, no cure” is false; the exact wording is that without a topical the animal recovers but those around it remain exposed, and the risk of reinfection from a reseeded environment remains entire.
4.2 Whole-body application: comparative persistence of the active substances
The work that separates whole-body products is an in vitro study on hairs taken from naturally infected kittens, which measured both the immediate and the residual activity at 24, 48 and 72 hours of 14 products (Moriello, 2020). Beyond the classic test on a suspension of isolated spores, toothbrushes loaded with whole infected hairs were treated repeatedly until negative cultures were obtained.
Three products were assessed for whole-body application. Lime sulphur and enilconazole showed residual activity; the shampoo combining 2 % miconazole nitrate and 2 % chlorhexidine showed none, which the authors expected of a rinsed product. The persistence measured was comparable at 24, 48 and 72 hours for each of the products that possessed it. The authors draw from this the recommendation of twice-weekly application of enilconazole and lime sulphur.
A randomised non-inferiority trial in 76 shelter cats has since compared three whole-body products, lime sulphur, a miconazole and chlorhexidine shampoo, and hydrogen peroxide, and concludes in favour of lime sulphur (DeTar et al., 2025). It is the highest level of evidence available on topical treatment of the coat, and it designates precisely the product that is not accessible in Europe.
Lime sulphur corresponds to no veterinary medicine authorised in the European Union: it is inaccessible here while it underpins the entire North American literature, where it is used at 8 ounces per gallon, that is a one in sixteen dilution, about 60 ml per litre (Miller et al., 2013; Moriello, 2004). Enilconazole is available in France and is used after diluting one volume of concentrate in fifty volumes of lukewarm water, that is a final concentration of 2 mg/ml. The leaflet specifies that the first application is made over the whole body, in order to reach subclinical lesions (ANSES-ANMV, 2026). Of the two validated products with residual activity, the French practitioner therefore has only enilconazole.
The review of published studies had already identified the same three products as consistently antifungal on isolated infected hairs and in controlled or field studies: lime sulphur diluted one in sixteen, 0.2 % enilconazole rinses and the shampoo combining 2 % miconazole and 2 % chlorhexidine, applied once or twice weekly (Moriello, 2004). Review and persistence measurements agree, and underpin twice-weekly application.
The miconazole and chlorhexidine shampoo retains its full place despite its lack of persistence: it provides a one-off disinfection of the coat, not prolonged protection. The schedule set out in the review of published studies is one to two applications per week (Moriello, 2004); its actual frequency is governed above all by how many baths the animal tolerates. A recent comparative study in 16 cats set a lime essential oil shampoo against the classic formulation combining 2 % miconazole and chlorhexidine, both groups also receiving itraconazole at 5 mg/kg on a pulse regimen of alternate weeks for 56 days. No difference appeared between the groups at 56 days on cytology, direct hair examination and Wood’s lamp, and both significantly reduced the total lesion score, which aggregates the extent and severity of lesions, and the fungal score, which grades the abundance of fungal elements observed, from day 28 onwards (Chuenngam and Chermprapai, 2026). The number is small and both groups received systemic treatment, which precludes attributing the result to the topical alone.
4.3 The question of clipping
Clipping remains debated, and two situations that are often confused must be distinguished.
In the short-haired pet with limited lesions, no data require it. In the long-haired cat and in group housing, it is part of established protocols: the classic recommendation covers clipping the entire coat of all culture-positive cats and of all animals with lesions, whiskers included, in a room that is easy to decontaminate, with the person clipping wearing disposable protection, the infected hair burned or placed in biohazard bags and autoclaved before disposal, and the procedure repeated monthly until the infection is eliminated (Miller et al., 2013).
Close surgical clipping is avoided: its microtrauma promotes the spread of lesions.
5 Environmental decontamination
5.1 Survival of arthrospores and what actually contaminates
Arthrospores present in the environment remain infective for 12 to 24 months. Contamination reaches high levels in households keeping infected kittens: up to 1,000 arthrospores per square metre have been measured in homes housing cats infected with M. canis (Miller et al., 2013). These figures come from a single, old source, not updated since.
A contaminated environment distorts follow-up cultures. A cured animal living in premises that have not been decontaminated will give positive cultures through simple passive carriage of spores on its coat, without being infected. That is the first reason to decontaminate, ahead even of preventing reinfection.
5.2 Mechanical cleaning
Literature aimed at the public repeats that a home cannot be decontaminated. That is false.
In total, 70 foster homes that had housed cats infected with M. canis for varying periods were followed over ten years. The procedure applied was simple: removal of gross debris from the rooms occupied by the cats, cleaning of surfaces with commercial household detergents, rinsing, then disinfection of hard surfaces with household bleach diluted one in a hundred or with accelerated hydrogen peroxide, a hydrogen peroxide formulation containing surfactants and chelating agents that increase its activity and stability, common in North America as ready-to-use surface disinfectants. Thirty-eight homes were completely decontaminated after a single cleaning following the departure or recovery of the cat. Among the others, decontamination was achieved after one further cleaning in 28 cases, two in 2 cases, three in 1 case. A single home could not be decontaminated, the foster family itself acknowledging that it had not followed the procedure. No transmission to other animals or to people was observed (Moriello, 2019b).
Decontaminating a home is not difficult, and the disinfectant kills what mechanical cleaning has not removed. The consensus guidelines indeed place physical cleaning first among the means of decontaminating exposed premises (Moriello et al., 2017).
5.3 Comparative efficacy of disinfectants on hard surfaces and textiles
Eight commercial products were assessed directly against infective spores of Microsporum and Trichophyton isolated from cat hair, with a contact time of 10 minutes and three tests of increasing difficulty (Moriello et al., 2013b).
In the classic suspension test, at a one in ten dilution, all 8 products completely inhibited growth. On contaminated fabric, 4 of the 8 products completely inhibited growth of both agents after application of one millilitre or one spray; but all 8 products achieved this after five millilitres or five sprays. The quantity applied therefore matters more than the molecule: vigorous removal of the contaminated material, followed by generous application of a ready-to-use disinfectant claiming fungicidal activity against Trichophyton mentagrophytes, is a valid alternative to diluted sodium hypochlorite.
Bleach diluted one in ten remains the economical reference available everywhere, and features in the classic surface cleaning protocols (Miller et al., 2013).
The claim to look for on the label is that of established fungicidal activity against Trichophyton mentagrophytes, the species that standardised tests use as the test organism for dermatophytes.
The enilconazole fumigant held a place apart in French group-housing protocols; its withdrawal leaves the practitioner without an equivalent, and requires the effort to be shifted onto mechanical cleaning and surface disinfection.
5.4 Textiles, bedding and grooming equipment
Textiles concentrate the difficulty, and it is on them that the preceding test was most demanding. The quantity of disinfectant applied determines the result there, a single spray having proved insufficient for half the products tested (Moriello et al., 2013b).
Grooming equipment provides passive transport of spores from one animal to another. Clippers, brushes and combs are cleaned and disinfected after each animal, and the clipping room is chosen so as to be easy to decontaminate (Miller et al., 2013).
5.5 What messages to give the owner
The owner should take away three messages.
The first is reassuring, and it is evidenced: serious complications of transmission from animal to human are exceptional (Moriello et al., 2017), and decontaminating a home is achievable, 38 of the 70 homes followed having been decontaminated with a single cleaning (Moriello, 2019b). An owner who has read that ringworm is impossible to eliminate from a house must be told the opposite.
The second concerns exposure. Human lesions of animal origin most often occur on the areas that touch the animal, arms, scalp, trunk (Miller et al., 2013). The most exposed people in a household are those who handle the animal most, and severe forms are seen in individuals with a debilitating or immunosuppressive disease, as well as in the elderly (Miller et al., 2013). Wearing gloves during topical applications, washing hands after contact and avoiding a shared bed make up the essentials of prevention. It must be added that the summaries of product characteristics exclude handling of griseofulvin by a pregnant woman, and application of enilconazole without eye and clothing protection, since the concentrated emulsion is irritant to skin and eyes (ANSES-ANMV, 2026).
The third message is that of referral: the veterinary surgeon does not diagnose or treat humans, and faced with a suspicious lesion in a member of the household he refers to the family doctor, a recommendation that the leaflet for the itraconazole product itself sets out. The human medical context has moreover changed in the same direction as the veterinary one: the discontinuation of griseofulvin led the French learned societies to revise urgently the management of scalp dermatophytosis in children (ANSM, 2021).
6 Management in group housing
6.1 Screening and sorting of the population
In catteries and multi-cat households, Microsporum canis is involved in almost all infections, particularly in long-haired breeds. Microsporum gypseum and Trichophyton mentagrophytes have only occasionally been responsible, where cats were housed in wire-screened verandas or outdoor runs (Miller et al., 2013).
Screening relies on toothbrush or sterile carpet-square culture, performed on all cats in the cattery and on all animals in the household. In catteries where M. canis infection has been present for more than 60 days, the dermatophyte is isolated from the brushings of every cat, whether or not they show clinical lesions. In other words, beyond that point the distinction between healthy and infected animals loses all meaning and treatment becomes collective.
Animals found free of infection, with no lesions and a negative culture, are bathed with a shampoo combining miconazole and chlorhexidine or ketoconazole and chlorhexidine, where available, or with enilconazole, then placed in quarantine in a separate room. They must be retested, because they may prove infected on the second culture (Miller et al., 2013).
6.2 Mass treatment protocol
Three approaches have been described, and the choice between them is as much a matter of the economics of the cattery as of medicine (Miller et al., 2013).
The first is to depopulate the cattery entirely, decontaminate the premises, then restock with animals negative on 3 consecutive brush cultures taken 15 days apart. Most breeders refuse this because of the loss of their bloodlines.
The second treats the whole colony and the premises, with appropriate topicals, systemic treatment and environmental decontamination, with isolation of the colony and suspension of breeding and shows. It is the option most often chosen.
The third treats only the kittens, and is conceivable only in establishments producing kittens for the pet market.
Whichever option is chosen, eliminating the infection requires separating carriers from non-carriers, treating or removing infected animals, and measures preventing recontamination of the premises. It requires vigorous systemic and topical treatment, suspension of breeding programmes and shows, isolation of the colony, environmental decontamination, and screening followed by isolation of every new arrival. Such programmes run up against the cost of care, loss of income, the time they demand, and fear of lasting damage to the cattery’s reputation, an obstacle the authors describe as the hardest to overcome.
In practice, clipping of all positive animals precedes treatment, topical dips are ideally applied twice weekly, and systemic treatment is started in all non-pregnant queens and in kittens over 12 weeks of age.
6.3 Monitoring and lifting of measures
Monitoring follows the same principle as in practice, with a stricter requirement: three consecutive negative cultures are recommended in multi-cat households and catteries, where two are sufficient for a single animal (Miller et al., 2013).
The lifting of measures is therefore decided not on the appearance of the animals but on the series of cultures, and it presupposes that the environment has been decontaminated, failing which the checks will remain positive through passive carriage.
7 Stopping criteria and definition of cure
7.1 Clinical cure and mycological cure
Most apparent failures arise from confusion between the two. Fungal cultures can remain positive for several weeks after clinical cure (Miller et al., 2013). Stopping treatment when the lesions disappear therefore amounts to stopping it too early.
The stopping criterion is mycological. Treatment continues until complete resolution of clinical signs and until the fungus is no longer isolated from coat cultures.
Establishing a diagnosis and establishing a cure are two distinct operations. No test prevails over the others in confirming the disease, where Wood’s lamp, direct examination and culture complement one another; in confirming cure, only culture counts: it alone shows that the hair no longer carries living fungus.
7.2 Successive cultures: how many, at what interval
Treatment continues until at least two consecutive negative fungal cultures have been obtained, taken a week apart by the toothbrush technique, three consecutive cultures being recommended in multi-cat households and catteries. This usually requires 4 to 20 weeks of treatment (Miller et al., 2013).
A recent retrospective study eases this requirement in the otherwise healthy pet. Among 371 cats treated for dermatophytosis due to M. canis and monitored by weekly culture, the first negative culture was indicative of cure in 335 of them, that is 90.3 %, with very good agreement between the one-culture and the two-culture criterion, kappa coefficient 0.903. The 36 cats in which the first negative culture did not mark cure fell into two groups: 19 healthy animals whose early negative result stemmed from a sampling error, and 17 animals with a concurrent condition, which took longest to recover, 11 weeks on average, from 8 to 28 weeks, cure occurring only after the associated problem was resolved (Stuntebeck et al., 2020). The authors conclude that in an otherwise healthy cat, whose owner has properly followed the instructions on cleaning, topical treatment and systemic treatment, two consecutive negative cultures are not necessary.
This result does not remove the need for a second culture in the animal that is otherwise unwell, nor in group housing; it does allow it to be dispensed with in the owned cat in good general condition, provided the sampling technique is beyond reproach, the authors’ main reservation concerning the risk of a false negative through inadequate sampling.
The durations written into the marketing authorisations are, however, closed and short, three cycles for the itraconazole solution, three to four weeks for ketoconazole as for griseofulvin, whereas the stopping criterion set out here requires 4 to 20 weeks. The mycological criterion prevails: the authorised duration fixes the schedule of one cycle, it does not define the end of treatment. The pivotal itraconazole trial illustrates this: the 2 cats not cured after the 3 cycles carried susceptible strains, and their failure called for treatment to be continued, not stopped. When the planned cycles are exhausted and the culture is still positive, treatment therefore continues beyond the authorisation, under the cascade, after reviewing compliance, dose, topical treatment and environmental decontamination.
The claws are an exception: their involvement requires a systemic antifungal, generally for 6 to 12 months, or onychectomy (Miller et al., 2013).
7.3 PCR: real speed, frequent false positives, useless for monitoring cure
The most direct field study compared a commercial real-time PCR panel with culture in 132 shelter cats with suspicious skin lesions or presumed exposure. Twenty-eight animals were culture positive for M. canis and 104 negative. PCR correctly identified all culture-positive animals and 92 of the 104 negatives, that is 12 false positive results. Sensitivity was 100 % and specificity 88.5 % (Jacobson et al., 2018).
However, among the 17 cats in which mycological cure could be assessed, 14 remained PCR positive at the time of the first negative culture, and 11 were still positive at the time of the second. The authors conclude that PCR is not reliable for establishing mycological cure.
No false negative was observed in that series. Later and larger studies do show them, however. A commercial quantitative PCR assay evaluated in 52 shelter cats correctly identified mycological cure in only 39 of the 46 animals treated for the Microsporum canis assay, that is 84.8 %, and in 30 of 46 for the Microsporum spp. assay, that is 65.2 % (Moriello et al., 2018). A retrospective analysis of 615 dogs and cats seen in 16 referral practices, and of 667 paired samples, gives an overall sensitivity of 74.1 % for a specificity of 98.1 %; for treatment monitoring alone, sensitivity is 77.8 % and specificity 92.0 % (Frost et al., 2022). A series of 246 shelter animals gives similar values, with a sensitivity of 86.1 % (Cheung et al., 2024).
PCR is indeed highly specific and poorly sensitive: a positive result indicates the presence of fungal DNA, a negative result does not exclude infection. It does not replace culture, either for diagnosis or for establishing cure, and using it alone to rule out a suspicion risks missing one infected animal in four. Both diagnosis and cure rest on the combination of complementary tests (Frost et al., 2022). Its own advantage remains speed, one to three days, and the frequency of its false positives also risks treating uninfected animals.
In France, the technique is offered by veterinary laboratories, which quote a result within 48 hours.
7.4 Wood’s lamp in follow-up
The consensus guidelines have moreover restored the Wood’s lamp: together with direct hair examination, it has good predictive value, both positive and negative (Moriello et al., 2017).
Its use in follow-up rests on a precise criterion, the one adopted by the pivotal itraconazole study in the cat: cure on Wood’s lamp is defined as absence of fluorescence at the base and mid-shaft of the hair. On that criterion, 39 of the 40 treated cats were cured, against 6 of the 40 controls.
The reservation concerns the agent: only some M. canis strains produce fluorescence, and dermatophytes of the genus Trichophyton produce none. The lamp therefore points the way, it does not conclude, and it does not remove the need for culture to establish cure.
8 Treatment failures and particular situations
8.1 Analysing a failure
Faced with a dermatophytosis that drags on or recurs, resistance is the last hypothesis to consider, not the first. Chronic and recurrent cases are usually explained by four categories of cause (Miller et al., 2013).
The first is inappropriate treatment, and it alone accounts for the bulk of failures: wrong molecule, insufficient dose, too short a duration, absence of topical treatment, absence of clipping where it was indicated, untreated animals in the household, undecontaminated environment. The summary of product characteristics for griseofulvin puts it in one sentence: where underdosing occurs, relapses are frequent (ANSES-ANMV, 2026).
The second is underlying disease: hyperadrenocorticism, diabetes mellitus, infection with feline leukaemia virus or feline immunodeficiency virus, neoplastic process.
The third is another concurrent treatment, for example corticosteroids prescribed for pruritus, and the fourth the animal’s genetic background.
It is therefore compliance, dose and duration that must be reviewed before anything else, and then reinfection from the environment or from an untreated companion animal.
8.2 True resistance and determination of minimum inhibitory concentrations
Resistance exists and is better documented than ten years ago. M. canis strains resistant to ketoconazole and fluconazole had been reported, and Trichophyton spp. infections in the dog could already prove difficult to clear on griseofulvin (Miller et al., 2013). The recent data set out above add a feline strain resistant to terbinafine through overexpression of ABC transporters, and a low but measured frequency in large series.
Treatment failure nonetheless reaches up to 40 % of patients treated for M. canis infection, and the absence of a standardised reference method for assessing the susceptibility of this species is the major obstacle to appraising resistance in non-responding cases (Aneke et al., 2018).
Determining minimum inhibitory concentrations therefore runs into three difficulties. The first is methodological: correlation between the in vitro result and the clinical course was observed only when incubating conidia for three days at 30 °C, and not with other inocula or other durations. Under those precise conditions, strains from animals cured on itraconazole showed minimum inhibitory concentrations at or below 1 µg/ml, and those from animals not cured showed values above 1 µg/ml (Aneke et al., 2020). The second is interpretative: no clinical breakpoint is validated in dogs and cats, and establishing a breakpoint for M. canis is presented as an urgent necessity (Liang et al., 2025). The third concerns the very nature of the activity measured: in 8 M. canis strains, minimum fungicidal concentrations proved far higher than minimum inhibitory concentrations, from 2 to more than 32 mg/l for itraconazole against less than 0.03 to 0.125 mg/l as inhibitory concentration, which confirms the fungistatic nature of the molecule and is a reminder that a low inhibitory concentration does not mean the fungus is killed (Nojo et al., 2026).
Finally, 30 % resistance to terbinafine has been reported among dermatophytes isolated from human patients and cattle in Iran, with a minimum inhibitory concentration of 16 µg/ml for one of the species (Mohammadifard et al., 2022). The context is remote from ours and the population is neither canine nor feline.
In practical terms, determining minimum inhibitory concentrations is justified only once the causes of failure in the preceding section have been ruled out. It requires a specialised laboratory and precise technical conditions, and the sample to send is the strain isolated in culture, not a swab. Molecular species identification takes precedence over it, since it is the species involved that indicates the likelihood of resistance.
An 8-year-old entire male Spitz weighing 10 kg had persistent alopecia, scaling, erythema and pruritus despite several courses of itraconazole and topicals based on 2 % miconazole and terbinafine. Diagnosis was confirmed by microscopy, culture and punch biopsy. The choice of posaconazole, based on susceptibility testing, produced marked clinical improvement with no adverse effects (Tiwari et al., 2026). This is an isolated case, which precludes drawing a recommendation from it; it does, however, illustrate the sequence to follow, identification, susceptibility testing, salvage molecule, and the fact that a molecule outside the usual repertoire may respond where the three common ones have failed.
8.3 Deep nodular forms and predisposed breeds
Dermatophytic pseudomycetoma is a deep, nodular form in which the fungus develops in the dermis and subcutis within a granulomatous reaction. It preferentially affects the Persian, which has suggested a breed predisposition without the mechanism being established.
Two cats, a Persian and a Maine Coon, had generalised dermatophytosis with M. canis pseudomycetoma, the strain being susceptible in vitro to both itraconazole and terbinafine. Itraconazole was withdrawn in one for lack of efficacy and in the other for unacceptable adverse effects. Both animals achieved clinical and mycological cure after 12 to 14 weeks of terbinafine at 26 to 31 mg/kg every 24 hours orally. In the Maine Coon, clinical signs resolved after 7 weeks. In the Persian, 4 weeks of additional treatment with weekly baths of a shampoo combining 2 % chlorhexidine and 2 % miconazole, after clipping, reduced the pseudomycetoma by 98 %, the residual lesion then being excised surgically. The recurrent generalised dermatophytosis of this Persian was subsequently controlled with pulse treatment, 26 mg/kg of terbinafine every 24 hours one week per month. No predisposing underlying condition was identified in either cat despite extensive investigation (Nuttall et al., 2008).
The nodular form does respond, but at the cost of treatment durations counted in months rather than weeks. And failure of an azole against a strain susceptible in vitro is not necessarily resistance: it may relate to penetration of the product into granulomatous tissue.
8.4 Pregnant or lactating queens and animals under 12 weeks
The contraindications brought together in Table 1 leave a population without systemic treatment. Griseofulvin is teratogenic: it is given neither to pregnant animals nor to animals under 12 weeks. Ketoconazole is teratogenic and embryotoxic in laboratory animals, and its use is not recommended during pregnancy. Itraconazole is not given to the pregnant or the lactating queen. Terbinafine has no veterinary authorisation, and safety data in these populations were not found in the literature.
No systemic molecule is therefore usable in the pregnant queen, the lactating queen and the kitten under 12 weeks, that is precisely in the animals of a cattery in full breeding season, and in those that develop the most severe forms.
No study has assessed what should be done in this situation. What follows is therefore a line of reasoning, not published data. Treatment is then reduced to the topical and environmental side, disinfection of the whole coat with a product having residual activity, environmental decontamination, isolation of affected animals, to which the argument in section 1.1 is added: the disease resolves spontaneously, and deferring systemic treatment until weaning or until the end of pregnancy costs infectious time, not a chance of cure. The decision rests with the clinician, case by case, weighing the severity of the lesions against the teratogenic risk.
8.5 The immunocompromised animal
Immunosuppression is among the classic causes of chronicity, in both spontaneous and iatrogenic forms (Miller et al., 2013). In the cat, co-infection with feline immunodeficiency virus further imposes a pharmacological constraint of its own: griseofulvin is used there with caution because of the risk of iatrogenic neutropenia (ANSES-ANMV, 2026). This restriction further narrows the usable molecules in precisely those animals whose infection is most resistant.
Management consists of looking for the underlying disease before blaming the treatment, withdrawing the current immunosuppressant as far as possible, and planning from the outset a treatment duration longer than that of an immunocompetent animal.
8.6 Canine particularities
The dog is not a large cat, and three differences govern management.
First, the agent differs. Although Microsporum canis also predominates in the dog, the Trichophyton mentagrophytes complex occupies a place there that feline practice scarcely knows. Of 90 dogs with skin lesions examined in Egypt, 47 were culture positive, with M. canis in 60 % of isolates and T. mentagrophytes in 20 % (Zineldar et al., 2025). To this must be added a reversal of the direction of contamination: an Indian series of 30 dogs isolated 14 M. canis, 8 Trichophyton rubrum, 6 M. gypseum and 2 Epidermophyton floccosum, the frequency of T. rubrum reflecting transmission from human to dog (Vadakkoot et al., 2024).
Second, the presentation differs. Of 64 dogs infected with the T. mentagrophytes complex in the central United States, lesions were on the bridge of the nose in 48 % of cases and on the head excluding the pinnae in 21 %. Incidence was higher in the sporting dog group, at 43 % of cases, and in terriers, at 20 %. A seasonal influence was noted, with onset of signs peaking in October (Pieper et al., 2023). This facial distribution and this breed profile point back to the mode of contamination: the digging dog meets the rodent’s dermatophyte.
Finally, treatment does not differ. In that same series, ketoconazole, itraconazole and terbinafine appeared equivalent as systemic options (Pieper et al., 2023). The dog therefore requires no particular molecule, but does require remembering that Trichophyton infections may resist griseofulvin (Miller et al., 2013), which shifts the choice towards the three preceding molecules.
Lastly, the first detection of Trichophyton indotineae in a dog in Africa was reported in Egypt (Zineldar et al., 2025).
9 Vaccination: the state of the question
Vaccination against dermatophytosis presents a paradox: it has worked, but not in dogs and cats.
In ruminants, vaccines using live attenuated fungal cells induce a cell-mediated response that gives lasting protection against homologous challenge. In Norway and a few other countries, systematic vaccination against bovine dermatophytosis has all but eliminated the disease, and human infection with Trichophyton verrucosum has become nearly non-existent there (Lund and Deboer, 2008). In Europe, freeze-dried modified live fungal vaccines have made it possible to control endemic dermatophytoses in cattle and in the fox (Miller et al., 2013).
In the cat, the vaccine failed. A killed vaccine against M. canis was marketed in 1994 for the treatment and prevention of feline dermatophytosis; clinical experience showed only limited benefit and the product was withdrawn (Miller et al., 2013).
In the laboratory cat, intradermal injection of a killed M. canis vaccine produced immediate and delayed hypersensitivity reactions in animals with active infection and in those that had recovered from it, but not in normal unexposed animals. In placebo-controlled studies, vaccinated cats developed high titres of anti-M. canis immunoglobulin G, comparable to those induced by natural infection, together with increased lymphocyte blastogenic responses to the antigen, weaker however than those of natural infection. Despite this immune response, all the cats developed dermatophytosis when they were inoculated or when an infected cat was introduced into the colony (Miller et al., 2013).
The available vaccines all belong to the first generation, the scientific literature is too thin to conclude on their efficacy and indications, and attempts at subunit vaccines based on keratinases have met with only limited success. The avenue that remains open is to identify the major T epitopes capable of specifically triggering a delayed hypersensitivity reaction, a strong T helper 1 response being the condition of protection (Lund and Deboer, 2008). A benefit comparable to that obtained in cattle could be expected if a safe and effective vaccine against M. canis became available for dogs and cats, but it is not.
That said, although fungal vaccines have not proved effective against infectious challenge, there are indications that they might be of use within treatment protocols (Moriello, 2004). This avenue has not since produced an available product.
In 2026, vaccination therefore forms no part of the treatment or the prevention of dermatophytosis in dogs and cats.
Conclusion
The principles of treatment have not changed: a systemic antifungal, topical disinfection of the whole coat, mechanical and antifungal decontamination of the environment, and a stopping decision based on successive negative cultures rather than on the appearance of the lesions. What has changed are the means and the context. In France, itraconazole has established itself as first-line in the cat, where it alone holds an authorisation in the indication. Terbinafine is becoming the fungicidal alternative, provided 21 days and not 14 is taken as the minimum duration: the actual duration is set by the cultures. Ketoconazole remains the only azole holding a veterinary authorisation in the dog, and griseofulvin survives in a single, impractical oral powder. In the dog, finally, the only reasonably substantial series places ketoconazole, itraconazole and terbinafine on the same level, which leaves the clinician the choice of molecule but obliges him to prescribe two of them off-licence. Of the two whole-body topicals with established residual activity, only one is accessible in France: enilconazole as an emulsion.
PCR, attractive for its speed, produces false positives and says nothing about cure. And resistance has ceased to be a theoretical concern: a squalene epoxidase mutation mechanism is circulating in the Trichophyton mentagrophytes complex, while Microsporum canis rarely develops efflux-mediated resistance, of which one feline case has been reported. Neither mechanism is to date linked to documented clinical failures in companion animals in Europe, and treatment failure, which reaches up to 40 % of cases, is almost always explained by dose, duration, absence of a topical or an undecontaminated environment. The practical consequence is therefore to review the protocol before blaming the fungus, and then to have the species identified by molecular methods if failure persists.
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