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Maddie's® Shelter Medicine Program at Cornell

 

Dermatophytosis (Ringworm) and Shelter Cats

kittens suspected of ringworm Dermatophytosis is the most common skin infection of cats (Moriello, 1995). It can infect cats of all ages and breeds, although kittens and long-haired cats may be at greater risk (Fortney, 1994). Dermatophytosis is caused by infection of the skin, hair, and nails with microscopic fungal organisms that cause varying degrees of hair loss and dermatitis. The dermatophyte that causes the majority of cases in felines is Microsporum canis which causes greater than 96% of all cases of dermatophytosis (Carney et al., 1993). M. canis not only infects cats but can also infect humans, thereby creating a zoonotic risk for owners and shelter workers. Studies have shown that if there is an infected cat in a household, the humans in the household are also infected almost 70% of the time (Moriello, 1995).

Dermatophytosis is common when cats are housed at high densities and under stressful circumstances. Risk factors associated with M. canis include:

Since most shelters possess many, if not all of these risk factors, they present a unusually difficult situation to try to control the spread of dermatophyte infections. Studies conducted in shelter cats reveal that up to 38% of cats housed in shelters were culture positive (Reberg, et al., 1999). Also of note, is the fact that the incidence of dermatophytosis is higher in warm, humid climates (Boyanowski, et al., 1998, Moriello, et al. 1994).

kittens suspected of ringworm The arthrospore, the naturally infective stage of M. canis, is formed from segmentation and fragmentation of fungal hyphae. Dermatophyte arthrospores are transmitted by contact with infected hair and scales or fungal elements on animals, in the environment, or on fomites (Sierra et al, 2000). In experimental models of M. canis infection, the incubation period between inoculation and development of clinical lesions is usually 7-14 days (Moriello, 1994), however in some cases it may be as long as 4 weeks (Fortney, 1994). If left untreated, most infections will spontaneously resolve within 12 to 14 weeks post-infection. However, during this time, the infected cat will infect the surrounding environment and other animals or humans in the household (Moriello, 1994). Still, many cats infected with dermatophytosis do not develop lesions. These asymptomatic carriers (despite the presence of lesions) can transmit dermatophytosis to other animals, including humans (Fortney, 1994). Infection in some cats with dermatophytosis (those with lesions and those that are asymptomatic carriers) does not spontaneously resolve and persists for months or years without aggressive treatment (Moriello 1995).

kittens suspected of ringworm Control of dermatophytosis is difficult because the spores formed by M. canis can survive in the environment for 18 months or even longer and are extremely resistant to disinfectants and detergents (Muller, 2001). In addition, the presence of asymptomatic carriers makes it difficult to readily recognize all infected cats without the use of culture techniques. Dermatophyte spores can be destroyed, however, of all the commercially available disinfectants, only a 1:10 solution of sodium hypochlorite (bleach) kills the spores (Moriello, 1994). At this concentration, the bleach solution is not suitable for use on many surfaces and is a severe respiratory irritant. Animals must be removed from the area before the solution can be applied. Therefore, in the shelter environment, the application of 1:10 bleach solution is impractical. (Solutions of 1:30 bleach solution readily kill a wide variety of common infectious pathogens, may be used on surfaces, are less noxious, but do not kill ringworm spores). Thus, dermatophytosis is nearly impossible to control in a shelter setting.

Although M. canis is an important zoonotic fungus, there is no known practical means of controlling or preventing the infection in a shelter setting. Studies have shown that M. canis can be cultured in an infected environment on furnace filters, dust, and heating vents. Many shelters are housed in older buildings with old ventilation ducts. Thus, many shelters are chronically infected with dermatophyte spores that cannot be removed (Muller, 2001).

Systemic antifungal drugs (such as griseofulcin and itraconazole) have been cited as the treatment of choice for existing infections (Moriello, 1995). These drugs are very expensive, thus they are usually not practical in the treatment of shelter animals due to the large number of animals that require treatment and the limited financial resources of most shelters. Furthermore, systemic therapies do not prevent other animals from exposure before the infection is cleared. Historically, topical treatments were once widely recommended; however, recent studies indicate that they are inadequate in the treatment of feline dermatophytosis as sole therapies (Moriello, 1995). Dermatophyte vaccines have been developed and are now available for treatment of dermatophytosis. However, these vaccines have limited efficacy in treatment and studies indicate that the vaccines are ineffective in the prevention of dermatophytosis (Moriello, 1995). Lufenuron was found in one retrospective study to aid in the treatment and possible prevention of dermatophytosis (Ben-Ziony and Arzi, 2000), however this was demonstrated to be a spurious finding based on a controlled study (DeBoer, et al. 2003). Thus, there is no known successful method for preventing dermatophytosis.

Lime sulfur is a common antifungal agent that has been used extensively in the topical treatment of feline dermatophytosis. It is very safe, readily available and inexpensive. Solutions of lime sulfur (1:16) can be applied to cats quickly and non-stressfully (Moriello, 1995). Although recent studies indicate that it is not the most effective therapy for feline dermatophytosis, they reveal that it is the most sporicidal of all approved topical agents used in the treatment of dermatophytosis (Moriello, 1995). Because of its excellent sporicidal effects, lime sulfur may prevent the infection of dermatophytosis in cats housed in enzootic environments.

For cats sheltered in endemic environments (such as animal shelters), the author recommends weekly lime sulfur dips of all resident cats for the purpose of preventing infection of cats, decreasing zoonotic transmission and reducing spore contamination in the environment. In the authors experience, this has been the most useful and cost-effective tool in the shelter environment. If done appropriately, it can be cost and time effective with little stress on feline residents. Of course, there is the smell...

References
Boyanowski KJ, Ihrke PJ, Moriello KA, Kass PH. Isolation of Fungal Flora from the Hair Coatsof Shelter Cats in the Pacific Coastal United States. AAVD/ACV Proceedings, 1998; 31-32.
Carney HC, Moriello KA. Dermatophytosis: Cattery Management Plan. In: Current Veterinary Dermatology. Ed Griffin CE, Kwochka KW, MacDonald JM. St. Louis: Mosby, 1993; 34-43.
DeBoer DJ, Moriello KA, Blum JL, Volk LM. Effects of lufenuron in treatment in cats on the establishment and course of Microsporum canis infection following exposure to infected cats. JAVMA. 222(9): 1216-20, 2003.
Fortney WD. Control of Dermatophytes in Catteries. In "Consultations in Feline Internal Medicine 2" (JR August, Ed.) W.B. Saunders Co., Philadelphia; 1994; 627-635.
Moriello KA, DeBoer DJ. Feline Dermatophytosis recent Advances and Recommendations for Therapy. Veterinary Clinics of North America: Small Animal Practice. 1995; 25(4), 901-921.
Moriello KA, Kunkle G, DeBoar DJ. Isolation of Dermatophytes from the Hair Coats of Stray Cats from Selected Animal Shelters in Two Different Geographic Regions in the United States. Veterinary Dermatology, 1994; 5: 57-61.
Muller GH. Dermatophytosis. In: Muller & Kirk's Small Animal Dermatology. Scott DW, Miller WH, Griffin CE. W.B. Saunders Co. Philadelphia; 2001; 339-361.
Reberg SR, Blakemore JC, Thorpe RJ. Dermatophytosis in Shelter Cats in Northeastern Indiana: A Survey of Disease Prevalence and the Influence of Shelter Management Practices. AAVD/ACVD Proceedings, 1999; 39-40.
Sierra, P et al. Fungal Flora on Cutaneous and Mucosal Surfaces of Cats Infected with FelineImmunodeficiency Virus or Feline Leukemia Virus. AJVR, 2000; 61: 158.
Ben-Ziony Y, Arzi B. Use of Lufenuron for treating fungal infections of dogs and cats: 297 cases (1997-1999), JAVMA, 217 (10)1510-3, 2000.

Lime Sulfur Dip for Ring Worm
Instructions for Use

  1. Mix dip in bucket
         Use warm water
         1 cup lime sulfer dip per gallon of water
         best to mix up 2-3 gallons so bucket is filled enough to dip cats easily
  2. Cut x-ray film to make E-Collars
  3. Apply collar to cat-staple in place
  4. Put on gloves
  5. Hold cat two legs in each hand
  6. Lower cat into warm dip in bucket
  7. Second person should sponge dip on head and face (very important)
  8. Return cat to cage to drip dry (remove bowls and litter from cage)
  9. Do not towel dry (must drip dry)
  10. After drip dried, can remove e-collar. cat does not have to be 100% dry
  11. NOTE: if cats swallow a lot of dip, they may vomit; if dip gets in eyes, may cause irritation.some will invariable get in the eyes of some cats---just try to avoid it

It smells bad!!!!!!!!

Key Points for Shelters

Control measures recommendations:

If a ringworm outbreak has been documented in your shelter based on the presence of multiple cats with typical lesions and positive culture results, aggressive action is key to preventing massive facility contamination.

  1. Begin dipping all cats in your facility with LSD mixed at 1 cup per gallon (ideally twice a week, once may suffice)-- You could dip once a week and spray cats with a spray bottle of LSD in between. Dipping will need to be ongoing for weeks to months and should only be discontinued based on negative culture results over time.
  2. Remove cats with lesions or Treat cats with lesions with Itraconazole as well as LSD. Purchase brand name itraconazole (called Sporonox) from a Canadian internet pharmacy (they have the best prices). Dose is 10 mg/kg by mouth once a day for 30 days. It comes in 100 mg capsules-- empty out capsule and divide the little microencapsulated beads to dose. Put the dose in a pat of butter to administer to the cat. Most cats will need 1/2 to 1/3 capsule.
  3. Vacuum using heppa filters daily. Change filters every week. Clean regularly. Once a week, disinfect with 1:10 bleach. Measure it-- use a big sprayer to soak down all surfaces and allow it to air dry. Ventilation and removal of cats is required for application of 1:10 bleach.
  4. After a few dips, dispose of anything disposable-- and replace with clean baskets and blankets. I would advise getting the local hospital to donate new bedding. If this is not an option, be sure you are washing bedding in hot water with bleach added-- best to run it thru twice. Limit bedding until things are under control.
  5. Be sure you notify your adopters and visitors of the ringworm. Immunocompromised people should not enter the shelter. Add a waiver to your adoption paperwork.
  6. Repeat cultures 3-6 weeks after implementing shelter-wide control practices.
  7. Any new cats that enter the facility should be dipped in LSD weekly to prevent them from becoming infected.
  8. Start with a very thorough, deep cleaning (think: spring cleaning type of scrubbing) of your entire facility. You will need to temporarily move all of the cats from the room to do this, and if possible you should try to take the cages outside for the cleaning/disinfection because of the better ventilation.
    • Move all the cages (unless built in) to thoroughly clean behind and around them
    • Vacuum up all dust and dander
    • Clean with a detergent and degreasing agent to remove all the accumulated dirt and debris
    • Use "elbow grease"-scrub, scrub, mechanical cleaning is very important.
    • After cleaning and rinsing, disinfect with bleach diluted 1:10 in water (this is the only exception to the 1:32 rule).
    • Use a sprayer to apply the bleach to all surfaces and allow at least 10 minutes of contact time. (Canister sprayers with a pump and a wand-such as those used to apply pesticide-work well.)
    • At 1:10, bleach kills ringworm spores in addition to viruses and bacteria, but it is a severe respiratory irritant. Trifectant does NOT kill ringworm spores (despite the fact that the label says it does.) Therefore, bleach (at 1:10 dilution) is the best disinfectant for periodic "super disinfection" following deep cleaning.

B. Griffin 2003