An infection of keratinized tissue as in skin, hair, and claws, by fungi.

Clinical Signs

May observe the following:

  • Scaly ovoid type lesions with crusty edges in places where there is patchy hair loss. This is most often seen on the back , neck, and base of tail in rats, but can also appear on other places of the body.
  • Pruritus (itching) that may or may not be present.
  • Elevated patch of hair overlying scabbed area without patchy hairloss.
  • Clinical signs may not be present if the rat is an asymptomatic carrier.


Dermatophytes are fungi ( a plant parasite) that cause dermatophytosis, a disease of the epidermis. The genera is Microsporum and Trichophyton. It is seen in many animals including man and rodents. The organism that is typically seen in rodents most often is trichophyton mentagrophytes, however, other isolates that have been seen are T. aJell-Oi, T. schoenleini, T. terrestre, M. gallinae, M. gypseu, and M. cookei (listed in Infectious Diseases of Mice and Rats, National Research Council).

These organisms can cause diseases such as ringworm (tinea), and favus (T. schoenleinli) which is synonymous with crusted ringworm. The spores of these organisms are very hardy and can survive for years in the environment. They are transmitted via direct contact with the spores from infected animals, household pets, or humans, or by indirect contact via contaminated fomites such as bedding, litter, or cage supplies where spores have been shed. It is referred to as ringworm (though has nothing to do with worms) because it often presents as a red, itchy, and sometimes scaly ring of tiny bumps in humans.

Animals can be asymptomatic carriers. Just having direct contact does not always result in clinical signs of infection, a lot may depend on the following: the type of fungal species, if the animal is immunosuppressed, conditions where chronic or aggressive steroid therapy has been used, the condition that the animal’s skin is in, the condition of the animal’s nutritional status, cage cleanliness, and the environmental temperatures and humidity.

Treatment of symptomatic animals should include not only the presenting lesions, but the elimination of the fungal infection itself. The reason being is that even though the infection is often self-limited, clearing on its own in several weeks, the animal can continue to harbor the infection only to have it reoccur when conditions are again met. Other household pets residing in the home should be checked as well, and treated as necessary. Also important in the prevention and treatment program is for pet owners to remember to wash hands and materials that have come in contact with an infected animal.

In addition, pet owners (often those who are immunocompromised, or those with an open scratch or cut) who come in contact with this fungal infection usually see symptoms within 4 to 7 days. It is not dangerous and is often easily cured with over the counter anti-fungal creams applied twice daily for 2 to 4 weeks. Owners should check with their own physicians regarding appropriate treatment for themselves.


Case History of Dermatophytosis

  • Fig 1:  Ringworm in 4-month-old male rat (Petey)


Obtain history to determine cause.

Signs of characteristic lesions.

Woods ultraviolet lamp examination. Some, though not all, species of ringworm will fluoresce under the light aiding in diagnosis.

Skin scrapings from lesion periphery.


If scales are loose gently remove and wash area with chlorhexiderm at a concentration of not more than 1% before applying medicated cream or lotion daily.

Antifungals such as Nystatin (may need prescription), or creams containing clotrimazole (can be purchased OTC), can be applied. Gently cleanse affected area, and apply cream to skin rubbing in thoroughly. Do this once or twice a day. *Note: treatment often more effective when used in conjunction with an oral antifungal agent. Verify appropriateness of topical agent with vet prior to using.

Antifungal shampoos reportedly do not seem to work as well alone either, and should be used in conjunction with other treatment prescribed.

A dip, such as Lime Sulfur 2%, may be used once a week. Mix dip according to label or vet direction, bathe rat (taking care not to get in and around eyes or nose), do not rinse but towel dry.


  • Dip will stain clothing and jewelry
  • Dip may cause white fur to yellow temporarily
  • Dip does have strong odor similar to rotten eggs

Griseofulvin, an anti-fungal medication, whose primary use is for Trichophyton, can be given at 25 mg/kg PO for 30 to 60 days.


Ketoconazole, also an anti-fungal agent, given at 4 mg/lb TID, PO, given for 3 to 4 weeks .

Treatment may take several weeks and sometimes as long as 3 months. Fungus thrives on sugar, so a rat with a fungal infection should receive only a limited amount of sugar, including fruits, in his diet.

For secondary infections where moist or purulent lesions are present see Pyoderma.

Nursing Care

  • Assess skin daily for improvement of condition or decreased signs of inflammation, irritation, or lesions.
  • Prevent using chlorhexiderm to cleanse skin at a concentration of more than 1%, or even more than once a day. Diluted solution should appear lighter than a robin’s egg blue.
  • Keep nails clipped.
  • Strict handwashing before care and after care to prevent further spread of infection. Cleaning materials (e.g., towels) should be kept separate from other pets and yourself. All towels should be washed thoroughly and dried
    after each use.
  • Continue treatment until resolved or treatment changed.
  • Disinfect cage and wash all articles, which come in contact with pet, with a dilute bleach solution followed by rinsing well with water and drying thoroughly.
  • If condition worsens seek advice from a veterinarian.


  • The pruritus (itching) is alleviated.
  • Lesions that are present are resolved.
  • No secondary infection, or if present, condition controlled.


  • Maintain rat’s overall general health.
  • Use of prepackaged processed litter, and the freezing of litter where bags have been breached prior to purchase, may be of help.
    • *Please note: that any bags of litter/bedding that have been noted to have a row of holes in the top of the bag or any bag that has been breached during storage in pet stores and feed/tack warehouses, where possible contamination through contact of skin cells or hairs from residing infected animals, can be a potential risk. Freezing the litter before using in cages may be a helpful preventative measure. The spores causing ringworm are very hardy and have been known to survive in the environment up to a year or more.
  • Provide a clean cage environment.
  • Assess skin on a daily basis and seek treatment advice from a vet if signs and symptoms present.
  • Ensure prompt treatment of other infected animals living in the same house.
  • Quarantine all new rats for a minimum of three weeks and treat for infestation or infections if present prior to introducing to existing colony.
  • When holding or playing with rats other than your own, it is recommended that you wash and change clothes prior to handling your own rats.

  1. Diseases: Ringworm | CDC Healthy Pets Healthy People. (n.d.). Retrieved November 21, 2008, from
  2. The Ringworm Page. (2005, December 20). Retrieved November 21, 2008, from


Links to

Linked from


The Rat Guide and its affiliates accept no responsibility for misuse or misunderstanding of its information. This guide in whole or part, exists solely for the purpose of recognizing and understanding the care and illnesses in the pet rat. Please seek advice and treatment from a qualified Veterinarian if your rat is ill.

2000 - 2024 by Karen Grant RN. All rights reserved.
All other written and visual materials used by permission of specific authors for the sole use of the Rat Guide. Please visit our Privacy Policy for details.
Brought to you by KuddlyKorner4u
See Logos page for linking to the Rat Guide.
Contact us here: Rat Guide Team
Please note: Rat Guide email is not checked daily. Send e-mail to if you have an urgent medical problem with your pet rat. When possible, it is always best to take your rat to a qualified rat veterinarian.