ACVIM 2017: Opportunistic Fungal Infections in Dogs With Immune-Mediated Diseases

Dogs receiving immunosuppressive treatment for immune-mediated diseases can develop opportunistic fungal infections (OFIs). These infections may cause small skin lesions or severe disseminated disease. The incidence of and risk factors for OFIs in dogs receiving immunosuppressive medications are currently not well understood.

In a poster presentation at the ACVIM Forum in June in National Harbor, Maryland, Brigitte McAtee, DVM, reported the results of a study of OFIs in dogs being treated for immune-mediated diseases. In this study, dogs receiving cyclosporine and male dogs were at increased risk for developing OFIs.

OFIs can be serious and are “something that clinicians need to look out for,” said Dr. McAtee, an internal medicine resident at Texas A&M University Veterinary Medical Teaching Hospital, in an interview with American Veterinarian^®.

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Dr. McAtee and her colleagues conducted a retrospective study to investigate the incidence of OFIs in dogs receiving immunosuppressive therapy. Their secondary aim was to explore risk factors for OFI associated with particular immunosuppressive drugs.

The investigators reviewed the records of dogs seen at Texas A&M between January 2008 and December 2015. Dogs included in the study had immune-mediated hemolytic anemia, immune-mediated thrombocytopenia, immune-mediated polyarthritis, or Evans syndrome (concurrent immune-mediated hemolytic anemia and thrombocytopenia). Dogs were excluded from the analysis if they died or were lost to follow-up within 30 days of beginning immunosuppressive therapy.

The researchers analyzed the records of 246 dogs. Of these, 16 (6.5%) were diagnosed with an OFI. The percentage of dogs with fungal infections surprised the team, said Dr. McAtee. “It was kind of a shock for us.”

The most common immune-mediated disease in the study population was immune-mediated hemolytic anemia. Over half of the dogs included in the study had this condition.

In some dogs, fungal lesions were small and subtle. Other dogs developed large cutaneous ulcers. About half the lesions were described as nodules and half were described as ulcerative lesions (all cutaneous or subcutaneous).

One dog had only a single nodule on a distal extremity. A dog with multiple ulcerative nodules also had a renal capsule lesion caused by disseminated fungal infection; this dog died 6 days after diagnosis of the fungal infection.

The median time from initiation of immunosuppressive treatment to diagnosis of an OFI was 42.5 days (range, 7—390 days). Methods used to diagnose fungal infections included the following:

• Skin lesion cytology alone: 5 dogs
• Skin lesion cytology and culture: 4 dogs
• Skin lesion culture and biopsy: 3 dogs
• Skin lesion culture alone: 1 dog
• Hair culture: 1 dog
• Lymph node aspirate culture: 1 dog
• Biopsy of renal capsule and dermal lesions: 1 dog

The dogs in the study were treated with prednisone, cyclosporine, and other immunosuppressive drugs. Dogs receiving cyclosporine were more than 4 times as likely to develop an OFI than those not receiving cyclosporine (odds ratio, 4.4; 95% CI, 1.2—16.2; P = .02).

Male dogs were significantly more likely than female dogs to have an OFI (odds ratio, 4.1; 95% CI, 1.4­­—12.4; P = .01). Dr. McAtee speculated that lifestyle factors might account for the sex difference, but the retrospective nature of the study did not allow for further investigation of possible explanations.

“Small, subtle nonulcerated/ulcerated cutaneous lesions may represent an OFI in dogs receiving immunosuppressive therapy,” conclude the study authors. They recommend that skin or subcutaneous lesions in these dogs be tested with cytology, culture, and/or histopathology.

Dr. Laurie Anne Walden received her doctorate in veterinary medicine from North Carolina State University. After an internship in small animal medicine and surgery at Auburn University, she returned to North Carolina, where she has been in small animal primary care practice for over 20 years. Dr. Walden is also a board-certified editor in the life sciences and owner of Walden Medical Writing, LLC. She works as a full-time freelance medical writer and editor and continues to see patients a few days each month.