Systemic blastomycosis in a horse.

The research article discusses a case of systemic blastomycosis in a 17-year-old Quarter horse broodmare, a disease caused by the fungus Blastomyces dermatitidis, which is usually rare in horses but was found extensively in this case, affecting the horse’s skin, mammary gland, lungs, and other tissues.

Case Background and Symptoms

• The horse initially started showing symptoms three months after giving birth, which was initially diagnosed as mastitis, an infection of the mammary gland, and was treated with antibiotics.
• However, the treatment was ineffective as the disease, later identified as blastomycosis, progressed into severe cutaneous lesions affecting the horse’s ventrum, pectoral region, and limbs. This condition was also associated with a noticeable weight loss over several months.

Disease Identification and Diagnosis

• The horse was referred for further inspection due to the severity of conditions. Here, yeast bodies typical to blastomycosis were observed in the swabs taken from the cutaneous exudate, indicating the likely presence of the disease.
• Additional examination revealed pleural effusion (a condition where excess fluid fills the area between the lungs and the chest wall), cavitated lung lesions and hyperproteinemia (an abnormally high level of protein in the blood). Given the poor prognosis, the horse was euthanized.

Necropsy and Histology Results

• Postmortem examination provided deeper insights into the extent of the disease. Extensive pyogranulomas were found in the mammary glands, skin, subcutaneous tissues, and lungs, indicating chronic inflammation due to body’s reaction to the persistent fungal pathogens.
• Thrombi, clots that impede blood flow, were identified within major blood vessels of the lungs and hind limbs, suggesting that the disease had a systemic impact.
• On microscopic examination, the tissue samples from various parts showed pyogranulomatous inflammation and the presence of fungal organisms, confirming the presence of blastomyces dermatitidis. This fungus was also cultured from the mammary gland, lungs, lymph node and an inguinal abscess.

Discussion and Conclusion

• Despite being endemic in the area of origin of the horse, Northwestern Wisconsin, blastomycosis is rarely a cause of disease in horses, and therefore, can be easily misdiagnosed.
• The particular case under study stands out due to the extent to which the mammary gland was involved and the presence of multiple thrombi sites, not typically observed in equine blastomycosis.
• This case sheds light on the possibility of such rare fungal infections in horses, necessitating further research into this matter for better understanding and effective treatment of the disease.