Ringworm In Horses
Around here, there's been a huge outcry about a ringworm outbreak in dogs and cats in an animal shelter. Since I've spent the better part of the day talking about about ringworm control in small animals, I thought I might as well write about some horse ringworm issues as well.
Ringworm basics:
- Ringworm is a fungal disease caused by dermatophytes. The most common dermatophyte fungus that causes ringworm in horses is Trichophyton equinum.
- This fungus is spread through direct contact with infected horses, as well as contact with items contaminated by hair and skin cells from infected horses (e.g. tack, blankets, grooming supplies). People can move the fungus between horses, as can insects, but direct contact between horses and shared use of contaminated items account for the vast majority of infections.
- Not all horses that are infected have signs of disease. That's good for the individual horse but it also means that there can be "silent" carriers that are sources of infection for other people and animals.
- Young horses are more likely to develop infection than older horses.
Ringworm infection in horses:
- Ringworm typically causes fairly mild skin disease, characterized by patchy areas of hair loss, redness and scaling. Sometimes the lesions are itchy and the horse may cause more damage to the skin by scratching/rubbing, but most often ringworm doesn't seem to bother horses.
- Lesions are more common in the girth and shoulder areas, often because contaminated equipment was the source of infection, and because the warm, moist environment under the tack is perfect for ringworm to invade the skin and grow..
Diagnosis of ringworm in horses:
- The appearance of the skin lesions (when present) is quite suggestive, but other problems like dermatophilosis (rain scald) and staphylococcal skin infections can produce similar signs.
- A Wood's lamp (UV light) is sometimes used to detect the fungus because some dermatophytes will glow when exposed to UV light. However, most strains found in horses don't glow, so the test is not very useful.
- Culture is the best method of diagnosis, but it can take a few days to a few weeks to grow dermatophytes.
Treatment of ringworm in horses:
- Ringworm should go away on its own, given time.
- Topical treatment with substances like povidone iodine, lime sulfur, enilconazole or other antiseptics and antifungals can be used to try to speed up the process. All of them have good and bad points, and there is no consensus about which is best and whether it is even needed.
Infection control for ringworm:
- Affected horses should be isolated to prevent spreading ringworm to other horses and people. This is a zoonotic disease that can be easily spread to people in contact with the horse or items the horse has contaminated.
- Tack should be cleaned and disinfected after every use. Tack is difficult to properly disinfect. A dilute (1:50) bleach solution should be used whenever possible. There is an eniconazole preparation that is intended for environmental use, and that might be a good option for more sensitive items. Cheap items that cannot be properly cleaned and disinfected should be discarded.
- Remember that dermatophytes can survive in the environment for many months, so even equipment that has not been used for a long time may still be contaminated with infectious fungus if it was not properly cleaned before being put away.
Equine sarcoids are skin tumours that affect horses, donkeys, mules and zebras. They are the most common type of tumour found in horses, and account for 35-90% of all equine skin tumours. Sarcoids are generally not life-threatening – unlike some other tumours, they do not metastasize (i.e. spread to other organs or tissues). However, they can be locally aggressive growths, meaning they may invade deep into the tissues immediately surrounding the primary tumour. They are also very difficult to treat, and therefore can affect a horse’s welfare or quality of life, depending on the size and location of the sarcoid. There is some evidence of a genetic predisposition to sarcoids in some horses as well. Involvement of bovine papillomavirus in the development of sarcoids was first suggested by Olson and Cook in 1951, who were able to reproduce sarcoid-like lesions in horses by inoculating them with tissue from bovine warts. Since then, researchers have used PCR to show that the vast majority of sarcoids contain BPV DNA, whereas normal horses and non-sarcoid skin tumours do not. Although BPV DNA has been found in healthy horses living in close contact with sarcoid-bearing animals, there is currently no evidence that BPV or sarcoids are transmissible horse-to-horse.
No, not dental plaque like you get on your teeth - in this case we’re talking about aural plaques, which are a type of skin lesion that some horses develop on the inside surface of their ears. These plaques are usually depigmented, meaning the skin cells of which they are made do not have the same pigment in them as the cells of the surrounding skin, making the lesions appear pale grey or off-white. Other than being considered unsightly in some cases, aural plaques usually don’t cause problems for the horse – they’re not itchy, sensitive or painful. They can occur in any horse, no matter the age, breed or sex. Occasionally some horses may develop similar plaques on the udder or around the anus or vulva (under the tail). The diagnosis of an aural plaque is typically made based on the horse’s clinical signs alone (i.e. a raised, depigmented skin lesion inside the ear that is not associated with any inflammation or discomfort).
Papillomaviruses (PVs) are small DNA-based viruses that are recognized causes of disease in many animal species and humans. More than 100 different human papillomavirus types (HPV) have been identified, which can cause a range of problems from annoying (but benign) warts to malignant cervical cancer. The ability of papillomaviruses to cause cancer was first recognized in animals, specifically with cottontail rabbit papillomavirus (CRPV), bovine papillomavirus (BPV) and canine oral papillomavirus (COPV). In general, PV infection causes benign disease in the vast majority of individuals, but the viruses have the potential to cause malignant disease in a small proportion of the mammals they infect as well.
