Abstract

Histoplasma is a dimorphic fungal organism found worldwide and has caused granulomatous disease in both humans and animals. The organism has a high nitrogen requirement and thus is commonly found in soils contaminated with bird or bat feces. The most common site of infection in humans and domestic animals is the respiratory system due to inhalation (rarely orally) of contaminated aerosols. Treatment in animals is efficacious if started at a timely basis.

Starting in 1998, the Houston Zoo experienced an outbreak of histoplasmosis. The disease was found in 25 mammals of six different species (Table 1), all housed at some point in their life in the zoo’s small mammal house. The majority of the animals were found dead in their enclosure with no prior illness detected. Lesions containing Histoplasma organisms were found on gross necropsy and confirmed with histopathology. Several cases were confirmed Histoplasma capsulatum by culturing.

Table 1. Species, necropsy date, and Histoplasma lesion location of the animals of the Houston Zoo found to have histoplasmosis

A trend of histoplasmosis cases was noted at the end of 1999. After the first group of animals succumbed to the disease at the small mammal house, a review of husbandry protocols was conducted. Changes in husbandry practices were made, although by this time, many animals in the small mammal house had possibly already been exposed to fungal spores. It is unknown how the histoplasma organism was introduced into the building but, it was suspected that the organisms were present in the mulch used as substrate for many of the exhibits.

There was a lapse of 1 year, from November 2001 to December 2002, when no cases of histoplasma were detected. This was attributed to major changes in husbandry methods, personal protection protocols, and prophylactic treatment of all animals housed in the area. Treatment was attempted first in the Egyptian fruit bat group using ketoconazole (June 2000, approximately 30 mg/kg PO, SID x 1 month) mixed in the food. When additional cases of histoplasma were discovered on necropsy, oral itraconazole (June 2001, 10 mg/kg PO in food SID x 4 months) was initiated for the Egyptian fruit bats. An Artibeus bat, a flying fox, and the sugar glider group were also treated with oral itraconazole for a total of 2 months.

It is unknown if any additional animals from this building harbor or will succumb to histoplasmosis. Antemortem disease testing in these species thus far has been unrewarding. Further diagnostic testing is being investigated.