 Reference Base  Fungal pneumonia in black rhinoceros (Diceros bicornis) |
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Weber, M.; Miller, R.E., 1996. Fungal pneumonia in black rhinoceros (Diceros bicornis). Proceedings of the American Association of Zoo Veterinarians 1996: 34-36
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Diseases |
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Black Rhino |
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Fungal pneumonia in Diceros bicornis. Black rhinoceros in captivity are affected by a number of unusual diseases that have been previously, including hemolytic anemia, mucocutaneous ulcers, and encephalomalacia. The etiologies of these diseases are not fully understood and at this time treatment is largely supportive, consisting of variable courses of antibiotics, corticosteroids and nutritional supplements. A review of necropsy results from black rhinoceros showed that a seemingly large number of animals that had died or were euthanatized had evidence of invasive pulmonary fungal disease at necropsy. As fungal pneumonias are rare in domestic animals, including equids, a survey was sent to veterinarians at U S. institutions holding black rhinoceros asking for information regarding occurrence of pulmonary fungal disease in their collections. Information was also requested regarding the use of corticosteroids in black rhinoceros at these institutions because of the potential immuno-suppressive effects of these drugs and because of one previously reported case of a black rhinoceros that died of a systemic mycotic infection after a long course of corticosteroid therapy.
Results
Thirty surveys were sent out; at the time of writing 22 institutions had responded. Between the years 1980-1994 eight animals were reported to have had evidence of fungal respiratory disease at necropsy or on histopathology. During the same time period the North Arnerican Regional Studbook for black rhinoceros lists 57 animals greater than 1 yr of age that died, an incidence of 14%. Seven of the eight animals died between 1988-1994, a time period in which 28 black rhinoceros greater than 1 yr-old died, an incidence of 25%. All rhinoceros with fungal respiratory disease were affected with concurrent disease (anemia, mucocutancous ulcers, tuberculosis). Corticosteroid use in the affected animals was sporadic, with two animals reported to have been on long-term steroid therapy immediately prior to death. Institutions reporting steroid use in black rhinoceros generally used corticosteroids as a single dose as an adjunct to anesthesia or as part of a short-term therapeutic regime. Most affected animals had been treated with broad spectrum antibiotics.
The most common findings on gross necropsy were multifocal firm nodules distributed throughout the long lobes. Some nodules were foci of mineralization or fibrosis while others contained purulent debris. One animal had mats of fungi present in the trachea but no other reported gross evidence of fungal pneumonia. Microscopic lesions included extensive pulmonary necrosis with granulomatous inflammation, fibrosis, and mycotic emboli. Most fungi seen on histopathology were morphologically determined to be Aspergillus spp. These fungi (Aspergillus spp.) were also the organisms most frequently cultured, one animal had concurrent infections with Mucor spp. and Aspergillus spp.
Discussion
Systemic fungal infections in most animals are rare and fungal pneumonia is infrequently reported. One retrospective study examined necropsy results from 7,020 horses and confirmed 19 cases of fungal pneumonia, an incidence of 0.27%. In the above study some cases may have been missed on histopathologic examination as fungal pneumonias are often localized. However, there is still an apparently increased incidence of fungal pneunonia in black rhinoceros when compared to their most closely related domestic species. Possible explanations include increased environmental exposure to fungi, increased incidence of severe disease, and/or an inherent immunologic abnormality. The change in incidence from 14% to 25% between 1980-1994 and 1988-1994 is most likely due to improved institutional record keeping and more intensive postmortem diagnostic testing.
The majority of domestic mammals with fungal pneumonia have a serious primary disease such as enterocolifis, organ failure, neoplasia, or septicemia. Others are predisposed to infection by the use of corticosteroids or broad spectrum antibiotics. All the black rhinoceros identified in this survey had severe concurrent disease. Most had suffered bouts of mucocutaneous ulceration and many had had episodes of hemobac anemia. Two animals were determined to be infected with Mycobacterium spp. The affected rhinoceros may have been immunocompromised by their concurrent disease, however further studies are necessary to evaluate the black rhinoceros immune system and response to stress. The use of corticosteroids is not definitively related to the presence of fungal pneumonia but caution should still be exercised with the use of long-term or high-dose corticosteroid in sick rhinoceroses.
Due to the alteration of bacterial flora, the use of broad spectrum antibiotics may also be an area of concern.
Premortem diagnosis of fungal pneumonia in black rhinoceros is difficult. Aspergillus spp. are ubiquitous in the environment and tracheobronchial lavage of normal horses can reveal the presence of fungal hyphae, either free or within mononuclear cells. Radiography is not likely to be a useful option because of the size of the animals. Percutaneous lung biopsy may miss a site of infection due to the localized nature if fungal pneumonias. Srelogy has been shown to be of questionable value. Normal horses can have high titers against Aspoergillus spp. due to environmental exposure, and animals that are immunosuppressed may not develop effective antibody titers.
Systemic antifungal agents such as amphotericin B, ketoconazole, miconazole, or itraconazole have been considered for treatment. These agents have not been especially effective in humans with invasive pulmonary aspergillosis and the cost of long-term therapy with these drugs in black rhinoceros would be prohibitive.
At the present time, invasive fungal pulmonary disease appears to occur with unusually high frequency in black rhinoceros. The association with other severe diseases, the difficulty of preinortem diagnosis, and the lack of effective and available therapy combine to create a clinical challenge. It is important to be aware of fungal pneumonia as a potential complicating factor when treating a sick black rhinoceros.
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