Fungal skin infection in a horse caused significant illness, say researchers

Distribution of hair loss and crusting seen during the second veterinary examination. (a) Bald areas, with thick keratin-rich crusts, distributed over the head; (b) baldness over the neck and shoulders, with some areas spared; (c) skin erosion on the left knee. Photos: Padalino et al.

A veterinarian should be called promptly in cases of skin disease in horses, according to researchers, who have described a case of fungal dermatitis that resulted in the gelding becoming very unwell.

The researchers, writing in the journal Animals, have reported on what they describe as a rare case of generalized fungal dermatitis in a horse caused by Geotrichum candidum.

There are 13 species of this yeast-like fungi, commonly found in soil, air, water, milk, silage, and plant tissues. It can be isolated from the digestive tract, skin, vagina, and mouth of humans and other mammals.

On occasion, it is known to cause localized skin disease in humans and animals.

Barbara Padalino and her colleagues said the 11-year-old bay saddle horse developed a well-defined area of non-itchy nodules, about 1 to 2cm across, on the neck.

The lesions appeared a week after standing surgery to remove a fracture from the splint bone, after which the horse received antibiotics to reduce the risk of infection.

Following surgery, the horse was boxed and wore a winter waterproof wool blanket with a neck cover to stay warm. He was bedded on straw.

On the development of the skin lesions, the owner did not consult with a veterinarian, as they were suspected to represent an allergic reaction. The owner gave corticosteroids orally for a week.

No improvement occurred and the horse lost weight — an estimated 50kg over three weeks, which was attributed to reduced appetite.

A week after stopping the steroids, a veterinarian was consulted.

The veterinarian identified further skin nodules, devoid of hair, on the upper part of the front legs.

Parental corticosteroids and antihistamine were prescribed for a week, as an allergic reaction was still clinically suspected.

During this second treatment regimen, and continuing for an additional two weeks, dermatitis spread to the head, shoulders and legs.

Macroscopic (a) and microscopic (b) features of Geotrichum candidum. Photos: Padalino et al.

The horse’s appetite remained poor and he became lethargic, with clinical signs of colic, which were then treated with flunixin meglumine.

A second veterinarian was then consulted, about a month after the initial nodules developed over the neck.

The horse had a fever and increased heart and respiratory rates. Hair was shedding or easily pulled from the head, neck, shoulder, chest and all four legs, with severe swelling of the hind limbs and carpal region.

Yellow exudate could be easily squeezed from the surface of a skin erosion on the left knee.

Large white loosely adherent scales coated the developing bald areas, with thick keratin-rich crusts.

Blood, hair samples and skin biopsies were taken for analysis.

Blood analysis revealed mildly elevated levels of white cells and excess globulins. There was further evidence of inflammation.

Testing of the collected samples ruled out parasites and bacteria. Further analysis identified yeast-like structures and Geotrichum candidum was isolated on culture.

The horse was successfully treated with an antifungal solution and antioxidants.

Three weeks after topical treatment, the horse had gained weight — about 80kg, according to a body-weight tape — and the bald regions showed new hair growth with fewer crusts.

Blood and biochemical parameters had returned to the normal range.

The antifungal treatment was continued twice a week for three more months.

The horse recovered completely. Antioxidant supplementation was recommended as an ongoing dietary supplementation as prescribed.

The authors said the infection had caused chronic skin disease and significant illness, partly attributed to incorrect clinical management.

“The goal of this case report is to educate horse owners, trainers and veterinarians to consider utilizing various diagnostic tools to enable accurate diagnosis of disease, especially where the initial clinical response to treatment is poor.”

Discussing the case, the authors say the early corticosteroid treatment may have impaired the immune system of this horse, making the horse susceptible to contracting a fungal infection.

“This case report highlights the importance of collecting appropriate samples to enable a thorough clinical workup of skin diseases in horses.

“Due to the initial lack of appropriate treatment when the skin disease first developed, this horse experienced prolonged sufferance for more than two months, developing chronic, spreading skin disease, with systemic signs of illness including weight loss, inappetence, fever, and colic.”

The horse at three-week follow-up. Bald regions showed new hair growth with fewer crusts on the abdomen and back. Photos: Padalino et al.

They say equine skin diseases are often challenging to diagnose and successfully treat.

“But this case demonstrates that appropriate laboratory tests should always be conducted as part of the basic principles of responsible pet ownership and proper veterinary duty of care, which are important to safeguard animal health and well-being.”

The said the housing conditions of this horse may have been beneficial for fungal infection to become established.

“The waterproof wool blanket may have created a humid microenvironment and increased sweat production as previously reported, favoring the growth and spread of the fungus.

“Moreover, the horse was stabled day and night, with little exposure to direct sunlight, which is vital for vitamin D production, important to keep skin healthy.

“Glucocorticoid and antibiotic usage, and perhaps some debilitation induced from the previous surgery, may have further predisposed the horse to developing fungal infection.”

They said the failure to identify the disease early in its course also played a role in the development of extensive skin disease.

While there are 13 species of Geotrichum, Geotrichum candidum is one of the most important species reported to cause infection in animals.

Geotrichum candidum had been isolated in 28.1% of the horses in a retrospective study of 64 horses presenting with skin lesions referable to fungal infection, the authors noted.

The case report team said a veterinarian should be promptly called in cases of skin disease in horses, and appropriate samples should be collected for testing.

“In the case of suspected fungi disease, multiple skin biopsy samples and crusts should be collected and submitted to the pathology laboratory.

“Late intervention, incorrect diagnosis, and inappropriate treatment regimens may lead to poor health and sufferance of patients, which should and can be avoided.”

The study team comprised Padalino, who is with the Department of Agricultural and Food Sciences at the University of Bologna in Italy; Jeanine Rhoda Sandy, with the Veterinary Diagnostic Laboratory at the City University of Hong Kong; and Roberta Barrasso, Adriana Trotta, Giancarlo Bozzo and Claudia Cafarchia, all with the Department of Veterinary Medicine at the University of Bari in Italy.

Padalino, B.; Sandy, J.R.; Barrasso, R.; Trotta, A.; Bozzo, G.; Cafarchia, C. Rare Generalized Form of Fungal Dermatitis in a Horse: Case Report. Animals 2020, 10, 871.

The study, published under a Creative Commons License, can be read here

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