What is Fungal Infections (Mycoses)?
While there are over 70,000 species of fungi, only 50 can cause disease in animals and humans. Of these, there are four classes, which are superficial, cutaneous, subcutaneous, and deep mycosis. Superficial fungi affect the skin. Cutaneous fungi attack skin as well, but also affect the hair. Subcutaneous fungi are able to spread from the surface of the skin to deep tissue. Deep mycosis is the most serious, attacking the upper and lower respiratory systems. In addition, there are two kinds of fungi, primary and opportunistic. Primary fungi are those that can affect any horse, healthy or sick. Opportunistic fungi attack horses that are immunocompromised by another illness.
There are many types of fungal infections, but there are only about 10 that are common in horses. Some of the most often reported are Conidiobolus coronatus, Cryptococcus neoformans, Blastomyces dermatitidis, Histoplasma capsulatum and Coccidioides immitis in healthy horses. In immune compromised horses, the most common are Pneumocystis carinii, Aspergillus spp., Candida spp, Fusarium spp and Emmonsia crescens. If your horse has nasal discharge, any kind of skin problems (rash, redness, lesions), or a cough, you should see the veterinarian to check for a fungal infection.
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Symptoms of Fungal Infections (Mycoses) in Horses
The symptoms of fungal infections will vary, depending on the type of fungi, but the most common signs are:
- Rapid breathing
- Nasal discharge (may be mucous or blood)
- Lack of appetite
- Respiratory distress
- Weight loss
- Lesions on skin
- Ulcerated skin
- Facial deformation (from partial blockage of nasal passages)
There are many types of fungi, but these are the 10 most common in horses:
- Conidiobolus coronatus (conidiobolus)
- Cryptococcus neoformans (cryptococcosis)
- Blastomyces dermatitidis (blastomycosis)
- Histoplasma capsulatum (histoplasmosis)
- Coccidioides immitis (coccidioidomycosis or Valley fever)
- Pneumocystis carini (pneumonia)
- Aspergillus spp (aspergillosis or guttural pouch mycosis
- Candida spp (candidiasis)
- Fusarium spp (fusarium)
- Emmonsia crescens (adiaspiromycosis)
Causes of Fungal Infections (Mycoses) in Horses
The causes of fungal infections can be attributed to about 50 different species, hundreds of types, and thousands of subtypes of fungi. The skin surface and deep tissue are affected, as is the hair. The respiratory system can be affected as well. The fungi can cause illness in healthy horses, but are particularly dangerous to equines with compromised immunity.
Diagnosis of Fungal Infections (Mycoses) in Horses
A definitive diagnosis includes your horse’s medical history, a physical examination, imaging, and several diagnostic tests. The physical exam includes checking your horse’s skin and hair from head to tail, looking for any abnormalities such as rashes or lesions. The veterinarian will also step back and watch your horse’s stature, attitude, conformation, and behavior. Once that is finished, the veterinarian will check your horse’s lung sounds with a stethoscope and palpation and have you walk and trot your horse in a circle and on a straightaway to watch the muscle and joint function in motion. To continue, your horse’s weight, height, blood pressure, heart rate, respirations, and body condition score will be recorded.
An endoscopy will be done to get a good look at your horse’s throat and upper airway and may be used to get a tissue sample for biopsy. Cytology, histopathology, and microbiologic culture will also be performed on the samples gotten from the endoscopy and lesions. To rule out other conditions some blood tests are needed such as fungal and bacterial cultures, complete blood count (CBC), blood chemistry panel, blood urea nitrogen (BUN), glucose level, and packed cell volume (PCV). Some of the most important tests are imaging, which can show the fungi wherever it is in the tissues and the organs. Regular and digital radiographs (x-rays) can show some of the areas of infection, but it takes an ultrasound and a cross-sectional CT scan to see a much more detailed view.
Treatment of Fungal Infections (Mycoses) in Horses
There are different treatments for each type of fungal infection.
Fluconazole, posaconazole, voriconazole, itraconazole, and ketoconazole are just some of the most common antifungal medications that are prescribed to horses. Also, topical medications such as nystatin or miconazole are used for some cutaneous and subcutaneous fungal infections.
In some cases, surgery to use curettage to remove lesions or plaques is necessary. Cryotherapy and endoscopic laser surgery can also be helpful in debulking surgery to remove fungal granulomas, which are growths of fungi usually found in one or both nasal passages.
Recovery of Fungal Infections (Mycoses) in Horses
Your horse’s prognosis depends on what type of fungal infection and side effects or complications are involved. Many of the fungi are not fatal if treated, but some can be hard to treat. In severe fungal infections such as guttural pouch mycosis or aspergillosis, the chance of a full recovery may be guarded to poor. An equine veterinarian can offer you the best treatment for the type of fungal infection your horse has, but since some of the medications and surgery have dangerous side effects, many owners do not treat their horses as they should.