Shelter Snapshot: Evidence-based answers to your dermatophytosis questions
One patchy kitten with ringworm can send a shelters veterinary team into a panic. Before you start scrambling, review the research so you can manage this pesky dermatologic problem effectively.
As a practicing shelter veterinarian, I get a jolt of panic when I see that bright green glow under the Wood's lamp on my intake exam of a patchy kitten.
So many questions need answers right now: Do we have any other kittens from this litter (or hoarding house or transport vehicle)? Where have they been in our shelter? What about before that? Is there room in isolation? Do we have dip and antifungals in stock? Is further testing needed? Who's willing to socialize this little one (and its friends) for the next several weeks? Is (informed, experienced) fostering possible? What concentration of disinfectant have we been using-and which one? What about laundry? When is it safe to spay/neuter and send this happy, bright, fluffy thing home?
A significant body of literature investigating dermatophytosis risk factors, diagnosis, treatment, testing for cure, and follow-up has been published steadily over the last 15 years, giving us evidence-based answers to many of the dermatophytosis management questions asked by shelters over the years. Here's a closer look.
Who gets dermatophytosis?
Many studies cite an increased risk in cats less than a year old, and a recent study found that kittens under 6 months old had an eight times greater risk.1-3 Warm seasons and climates increase incidence, but seasonal intake of kittens may confound this observation.3,4 A history of living in catteries, shelters or outdoors has also been implicated.4,5
In one shelter, transport cats were twice as likely to present with dermatophytosis as owner surrenders.3 Elsewhere, hoarding and cruelty cases make up the majority of dermatophytotic shelter intakes. Hoarded cats are also less likely to follow the risk patterns (age, season, climate) just mentioned.6
Microsporum canis is far more common than any other dermatophyte species, responsible for more than 90% of all infections.3,7 Microsporum gypseum and especially Trichophyton species seem to be more common in the West, harder to spread, and easier to cure.8
What's up with Wood's lamps?
The importance of using a Wood's lamp at shelter intake and whenever skin lesions are noted cannot be overstated. Sensitivity is much higher than many think; the World Association for Veterinary Dermatology undertook a massive rereading of the literature in 2017 and calculated an overall figure of greater than 72% sensitivity for M. canis. For experimentally infected animals, sensitivity was 100%.4 Furthermore, even though not all kittens in a litter may fluoresce at the time of exam, a recent study found that 80% of the time, all kittens in that litter were infected.3
How do I confirm infection?
The following methods have advantages and disadvantages.
1. Trichogram. Microscopic examination of the hair is the only definitively diagnostic technique for M. canis, according to dermatologists, because it actually demonstrates the presence of infective spores within the hair of the cat.4 No further confirmation is needed. However, trichogram does not identify fungal species and is not sensitive or specific in asymptomatic cats.
2. PCR. Polymerase chain reaction (PCR) confirms the presence of dermatophyte spores, but because of its unparalleled sensitivity, uninfected fomite carriers also show positive results.9 This test has an excellent turnaround time of two to three days,10 and it's especially useful for diagnosis for cats that are probably negative but have potential for infection (i.e., for ruling out infection). When negative results are confirmed, these healthy cats can be moved swiftly through the sheltering system.
3. Culture. In-house dermatophyte test medium (DTM) culture has been the inexpensive mainstay for ringworm diagnosis confirmation for many years. In 2006, researchers described a system for using culture (along with physical exam and Wood's lamp) to determine whether cats were fomite carriers or truly infected.11 Under this system, cats with fewer than 10 fungal colonies per culture and no visible symptoms at re-examination are considered carriers. Others have used stricter criteria (such as fewer than four colonies per culture).3 This system has been used by shelters across North America with consistently good results for many years.
Once inoculated, fungal cultures grow fastest in a darkened incubator (or cabinet) at 75-85 F (25-30 C) and at least 30% humidity.12 Daily monitoring for color or growth and identification of fungal species is always recommended, but waiting 14 to 21 days when no growth is seen is unnecessarily long. In 2006, a study reported that of more than 4,000 cultures, all were positive by day 10 of inoculation (median days 5 to 7);13 a 2019 study involving 291 cultures identified all infected cats by day 7 (median day 5).3 For shelters with reliable culturing technique and consistent incubation, negative cats can be moved through after seven to 10 days.
How can I tell when the cat is cured?
False-positive PCR tests from dead spores14 and the high expense of serial testing mean that weekly culture is the preferred instrument for confirmation of cure. Shelters are encouraged to hold in-treatment DTMs for 14 days15 and to begin weekly testing after seven days of treatment, since in many cases this is the first negative culture. Furthermore, when cats are treated with appropriate oral antifungals daily and 8 oz/gal lime sulfur baths twice weekly, that first negative fungal culture in an otherwise healthy cat likely indicates successful cure.16
How do I treat ringworm in the shelter?
While speed might not be the top priority in a home or foster home setting, the length of time a kitten spends in “ringworm isolation” directly affects its welfare and the shelter's ability to serve more animals. Isolating and starting treatment whenever a cat (or its litter) is Wood's-lamp-positive or lesions are characteristic is strongly recommended. Experts advise simultaneous administration of the following treatments:
1. Oral antifungals. The fastest protocols to cure dermatophytosis from any fungal species include generic terbinafine at 30-40 mg/kg daily or commercially prepared itraconazole at 5-10 mg/kg daily. Both oral medications provide statistically similar efficacy and time to cure; both accumulate in fat and likely continue to have residual effects up to a week after stopping treatment.
2. Topical antifungals. Using lime sulfur at 8 oz/gallon (twice the bottle recommendation) has been shown to consistently decrease time to cure for cats with any species of dermatophytosis when paired with oral antifungals. Fomite cats also benefit from bathing to eliminate spore carriage. Miconazole/chlorhexidine (0.2%/0.2%) shampoo has also been shown to be effective against M. canis, but it takes twice as long to achieve cure.17 Accelerated hydrogen peroxide shampoos have not been adequately tested to date; daily bathing may be necessary to achieve a similar effect.
3. Welfare provisions. Social cats require human contact, especially during early life. Primary enclosures should be appropriate for long-term housing (we don't want to treat dermatophytosis only to cause herpes recrudescence).18,19 Double-compartment housing and daily enrichment in isolation are musts. If a shelter can't perform these treatments or house the cat in a manner that provides good welfare, cats should be sent to foster care, returned to the field to cure on their own, transported to a shelter that can provide good welfare, or euthanized.
How do I decontaminate the shelter?
The most important part of decontamination is the aggressive removal of contaminated hair and dander. Once the facility is debris-free, 1:32 sodium hypochlorite, 3.2% benzalkonium chloride (Lysol), 2% potassium peroxymonosulfate (Trifectant) and 1:16 accelerated hydrogen peroxide products are effective with 10 minutes' contact time.20,21 Washing of laundry in cold water performed twice (without bleach)22 or washing once in hot water (>30 C) is effective.23 Washing machine basins should be disinfected after use. Thoroughly drying laundry on the hottest setting will kill any remaining spores.
What about ringworm kittens in foster?
A foster home is a great place for a ringworm kitten socially, and it reduces the burden of treatment on shelter staff. However, the foster family must be informed of the zoonotic potential and prepared for administration of medication, bathing and rechecks. Although foster programs also have a capacity affected by length of stay, better compliance in foster care may be achieved by using liquid formulations of oral medication and miconazole-chlorhexidine shampoo. Foster homes can be safely decontaminated using aggressive removal of hair and routine household cleansers labeled as effective against Trichophyton species.24 When infected kittens leave a foster home, sweeping pads may be used to culture the foster's kitten area to ensure future litters have a clean, safe environment.25
Although most of these studies were specifically performed in shelters, their application to owned cats diagnosed with dermatophytosis is obvious. It behooves us to remember that the intensity of our treatment, diagnostics, housing and decontamination far outweighs the impact of dermatophytosis itself on cat welfare. Ongoing studies continue to help shelters and veterinarians strike the best balance between biosecurity and animal welfare, and help us reduce that panic we feel (and the cat's length of stay) when we see that characteristic glow.
1. Cafarchia C, Romito D, Sasanelli M, et al. The epidemiology of canine and feline dermatophytoses in southern Italy. Mycoses 2004;47:508-513.
2. Lewis DT, Foil CS, Hosgood G. Epidemiology and clinical features of dermatophytosis in dogs and cats at Louisiana State University: 1981-1990. Vet Dermatol 1991;2:53-58.
3. DeTar LG, Dubrovsky V, Scarlett JM. Descriptive epidemiology and test characteristics of cats diagnosed with Microsporum canis dermatophytosis in a northwestern U.S. animal shelter. J Feline Med Surg Feb. 19, 2019. doi: 10.1177/1098612X19825519. [Epub ahead of print]
4. Moriello KA, Coyner K, Paterson S, et al. Diagnosis and treatment of dermatophytosis in dogs and cats. Vet Dermatol 2017;28:266-e68.
5. Moriello KA, Kunkle G, DeBoer DJ. Isolation of dermatophytes from the haircoats of stray cats from selected animal shelters in two different geographic regions in the United States. Vet Dermatol 1994;5:57-62.
6. Gordon E, Idle A, DeTar LD, BC SPCA, unpublished data.
7. Boyanowski KJ, Ihrke PJ, Moriello KA, et al. Isolation of fungal flora from the hair coats of shelter cats in the Pacific coastal USA. Vet Dermatol 2000;11:143-150.
8. Moriello KA, Stuntebeck R, Mullen L. Trichophyton species and Microsporum gypseum infection and fomite carriage in cats from three animal shelters: A retrospective case series. J Fel Med Surg May 9, 2019. doi: 10.1177/1098612X19846987. [Epub ahead of print]
9. Jacobson LS, McIntyre L, Mykusz J. Comparison of real-time PCR with fungal culture for the diagnosis of Microsporum canis dermatophytosis in shelter cats: A field study. J Feline Med Surg 2018;20(2):103-107.
10. Ringworm (Dermatophyte) RealPCR Panel. Westbrook, ME: IDEXX Laboratories.
11. Moriello KA, Newbury S. Recommendations for the management and treatment of dermatophytosis in animal shelters. Vet Clin North Am Small Anim Pract 2006;36(1):89-114.
12. Kaufmann R, Blum SE, Elad D, et al. Comparison between point-of-care dermatophyte test medium and mycology laboratory culture for diagnosis of dermatophytosis in dogs and cats. Vet Dermatol 2016;27:284-e68.
13. Newbury S, Moriello KA. Skin diseases of animals in shelters: Triage strategy and treatment recommendations for common diseases. Vet Clin North Am Small Anim Pract 2006;36(1):59-88.
14. Moriello KA, Leutenegger CM. Use of a commercial qPCR assay in 52 high-risk shelter cats for disease identification of dermatophytosis and mycological cure. Vet Dermatol 2018;29(1):66-e26.
15. Stuntebeck R, Moriello KA, Verbrugge M. Evaluation of incubation time for Microsporum canis dermatophyte cultures. J Feline Med Surg 2018;20(10):997-1000.
16. Stuntebeck RL, Morello KA. One vs two negative fungal cultures to confirm mycological cure in shelter cats treated for Microsporum canis dermatophytosis: A retrospective study. J Feline Med Surg Jul 3, 2019. doi: 10.1177/1098612X19858791. [Epub ahead of print]
17. Newbury S, Moriello KA, Kwochka KW, et al. Use of itraconazole and either lime sulphur or Malaseb Concentrate Rinse to treat shelter cats naturally infected with Microsporum canis: An open field trial. Vet Dermatol 2011;22(1):75-79.
18. Newbury S, Blinn MK, Bushby PA, et al. Guidelines for standards of care in animal shelters. The Association of Shelter Veterinarians, 2010.
19. Wagner DC, Kass PH, Hurley KF. Cage size, movement in and out of housing during daily care, and other environmental and population health risk factors for feline upper respiratory disease in nine North American animal shelters. PLoS One 2018; 2;13(1):e0190140.
20. Moriello KA, Kunder D, Hondzo H. Efficacy of eight commercial disinfectants against Microsporum canis and Trichophyton spp. infective spores on an experimentally contaminated textile surface. Vet Dermatol 2013;24(6):621-623, e151-152.
21. Moriello KA. Kennel disinfectants for Microsporum canis and Trichophyton sp. Vet Med Int 2015;2015:1-3.
22. Moriello KA. Decontamination of laundry exposed to Microsporum canis hairs and spores. J Feline Med Surg 2016;18(6):457-461.
23. Amichai B, Grunwald M, Davidovici B, et al. The effect of domestic laundry process on fungal contamination of socks. Int J Dermatol 2013;52(11):1392-1394.
24. Moriello KA. Decontamination of 70 foster family homes exposed to Microsporum canis-infected cats: A retrospective study. Vet Dermatol 2019;30:178-180.
“Shelter Snapshot” is a collaborative column between the Association of Shelter Veterinarians (ASV) and dvm360.com to help inform veterinarians and team members involved in veterinary shelter medicine and in related aspects of veterinary general practice. To learn more about the ASV and to find more information on these and other animal sheltering terms, visit sheltervet.org.
Dr. Lena DeTar is an assistant clinical professor with the Department of Population Medicine and Diagnostic Sciences and the Maddie's Shelter Medicine Program at Cornell University College of Veterinary Medicine