All dogs are at risk for ringworm, but the condition is most common in puppies less than a year old, and in older dogs with compromised immune systems. It is contagious to humans and causes a crusty, itchy skin rash. In humans, ringworm typically displays as round, ring-like sores.
What Is Ringworm?
Ringworm is a fungal parasite that causes skin disease in pets and people. It is a member of skin fungi called dermatophytes. The parasite feeds on keratin, the outer dead surface of growing skin and nails. There are many types of dermatophytes, but most cases of canine ringworm are caused by one of three species. The most common species is Microsporum canis. Another type of ringworm, carried by rodents, may infect pups that dig through rodent burrows. The third kind of ringworm lives in the soil.
Ringworm easily spreads to humans but most healthy adults won't become infected. Young children, the elderly, or anyone with a depressed immune system are most susceptible.
As the inside central sore heals, the “ring” of reddened inflammation surrounding the area gives it its characteristic look and name.
Symptoms of Ringworm in Puppies
Puppies suffering from ringworm infection won’t necessarily show a ringed skin pattern. Areas without hairs (alopecia) and sores expand but may not be in rings, and can look like a variety of other pet skin diseases such as skin allergies.
Typically there is scaling and crusting at the margins of bald patches, with broken or stubbled hair in these areas along with variable itchiness. The dermatophyte lives only on hairs that actively grow. The infected hairs break off and leave a stubby patchwork fur pattern, and mild to severe crusty sores also can develop.
Some pets become itchy, others do not. The inner hairless regions appear clear as they start to heal. The face, head, and forelimbs are typically the first areas affected, but in very severe infections, the fungus potentially can spread and affect the pup's whole body.
Cause of Ringworm
The immune system of healthy adult dogs is often strong enough to prevent ringworm infection. However, some healthy pets can become asymptomatic carriers, meaning they have no health problem themselves, but spread the infection to others. Once a pet becomes infected with ringworm, spores contaminate the environment, thus propagating the spread of infection.
The condition is transmitted by direct animal-to-animal contact usually from infected hair or skin debris. However, ringworm is also transmissible from contaminated grooming equipment, toys, bedding, and contaminated furniture and clothing.
If one pet in the house is diagnosed, all should be treated whether showing signs or not. Infected pets should be quarantined from those not showing signs.
Canine ringworm is diagnosed by identification of the fungus. The veterinarian may use a Wood's Lamp to screen suspect cases; about half of M. canis cases will glow when exposed to its ultraviolet light. However, because not all cases will show up under this special lighting, a negative result should not be presumed to be a true negative and further diagnostic testing should be conducted.
Other times, a skin scraping collects debris from the lesions, which is then examined microscopically. The best way to definitively diagnose ringworm is to take a sample of skin/fur and send it to the lab to culture. A sample from the lesion is placed in a special medium designed to grow ringworm. It may take up to three weeks before the test indicates a positive result.
Confirmed cases of ringworm in pets should be treated to prevent further spread of the disease. Most successful therapeutic regimens for ringworm involve both topical medicated shampoos and oral antifungal medication. Both treatment types need to be continued for several weeks; it's very important for the success of the treatment to follow your vet's instructions and not stop treatment prematurely.
Longhaired puppies should be clipped first to reduce the amount of contaminated hair (remember to disinfect the clipper blades afterward). Your veterinarian will recommend the best choice for your situation.
Be cautious about medicating sores with anything prior to a veterinary examination. That may interfere with an accurate diagnosis. Treat only after your veterinarian diagnoses the condition, and follow post-treatment recommendations.
How to Prevent Ringworm From Spreading
In addition to treating your puppy, for treatment to be effective, you must also clean its environment. This is easier said than done because ringworm spores are not visible to the naked eye and can spread easily throughout a home.
Currently, experts recommend environmental control by daily cleaning of all surfaces using a diluted bleach solution (one part bleach to 10 parts water), along with thorough vacuuming.
Get rid of disposable spore reservoirs such as pet bedding. A high-temperature steam cleaning is recommended for carpets and sometimes drapery. Vacuum repeatedly, but remember to toss out the bag every time, or you’ll simply spread the spores. Disinfect the vacuum, too, with the bleach and water spray.
You must treat the puppy and continue disinfecting the environment until follow-up cultures of the pet are negative. In a single pet home, treatment may be needed for six to eight weeks and sometimes longer in multi-pet households with multiple infections.