Authors: L.Larsuprom et al. (2017)
Histoplasma capsulatum is a dimorphic soil-borne fungus. It forms mycelia in the environment and changes to be a yeast form in the host’s body. It can affect both humans and animals (dogs and cats). Besides, it is the second most reported fungal infection in cats following cryptococcosis. H. capsulatum grows in soils contaminated with bird or bat droppings. The primary route of infection is inhalation of mycelium from contaminated areas. The endemic areas of H. capsulatum include North, Central, and South America, Africa, India, and Southeast Asia.
The case was a 2-year-old, neutered female domestic shorthaired cat, mostly living indoor but with access to outdoor areas contaminated with a great amount of pigeon feces. She was referred to the Kasetsart University Veterinary Teaching Hospital with a history of multiple papules on surface of the pinnae and nodules on the nose for four months. In addition, a chronic wound was presented on the lateral surface of the left radial area. According to physical examination, the cat had no clinical signs of systemic involvements e.g., gastrointestinal or respiratory signs. On day 0, the general health condition was good, together with pink mucous membrane and normal hydration. Complete blood count and serum chemical profiles were in normal ranges. Serological examination was negative for feline leukemia virus and feline immunodeficiency virus.
Samples from nasal swab and chronic wound area were collected for cytology. The cytological findings demonstrated hypocellularity of intracellular narrow-based budding yeasts with thin wall capsules, indicating fungal infection. Skin biopsy was conducted from the pinnae for histopathology; the results revealed that the samples were positively stained with Periodic Acid Schiff (PAS). The organisms were identified as 2–5 µm in diameter, oval-to-round shape, narrow based budding yeasts in the macrophages. These characteristics were consistent with Histoplasma spp. PCR was performed using extracted DNA from paraffin embedded tissues of the pinnae.
After 10 mg/kg itraconazole was prescribed twice a day, a chronic wound at the left forelimb showed an obvious improvement, and were completely healed within 28 days. This demonstrated that itraconazole at 10 mg/kg twice a day was more efficient than that at 5 mg/kg twice a day. After 35 days of treatment with 10 mg/kg itraconazole twice a day, the cat started to have recurrent skin nodules at the bridge of the nose and both ear pinnae. The recurrence of those lesions might have been caused by an incomplete clearance of infection or development of drug resistance. Subcutaneous injection of amphotericin B at 0.5 mg/kg twice a week was performed, together with itraconazole treatment, resulting in some improvements. Unfortunately, a firm nodule was subsequently developed at the injection site. It was suspected that the firm nodule was caused by either an adverse effect of amphotericin B or an irritation from injection.
This case report confirmed that histoplasmosis could occur in any young cat with a history of contact with contaminated bird feces. Furthermore, histoplasmosis should be considered as a differential diagnosis in cat with chronic skin wounds in endemic areas.
The treatment protocol was changed to fluconazole 50 mg PO once a day. Although the number of papules and nodules did not further decreased, no new lesions developed. The cat still ate and had normal daily activities. Subsequently, the owner did not further bring the cat for follow up to the hospital. However, by the phone communication, the owner gave the information that the cat was still stable after a month of fluconazole treatment.
Reference / full text: http://www.sciencedirect.com/science/article/pii/S2211753917300416#f0005