Abstract
In December 1998 at Audubon Zoo, a 27-year-old female colobus (Colobus guereza caudatus) was diagnosed with a spontaneous infection of Dirofilaria immitis at necropsy. The day of death it was found down in its exhibit with profound dyspnea and died while in transport to the hospital. Historically, it had no record of cardiopulmonary disease. Two months prior to its death, it had an episode of nasal discharge and rostral edema.
At necropsy, the animal had abundant subcutaneous edema in all tissues, particularly in dependent regions like perineum, limbs, hands, and feet. Abundant straw-colored fluid was found in the abdomen, thorax and pericardium. The liver was rounded and heavy. The lungs were heavy and edematous as well. The heart was flaccid, thin walled and enlarged. Multiple, coiled nematodes were found within the right atrium and ventricle of the heart, the longest measuring 20 cm in length. Both male and female worms were mature. The female worm was gravid.
Identification as Dirofilaria was made based on the histologic features seen, as well as on the location they were found. The cuticle of the worms was thick, smooth, and bulged into the pseudocoelom in the region of the lateral chords forming lateral internal ridges. These features are consistent with that of a Dirofilaria. D. immitis is the only member of that species that has been found in the circulatory system of nonhuman primates (C. Gardiner, personal communication).
Naturally occurring infections with D. immitis (the canine heartworm) are a very rare occurrence in nonhuman primates, and in fact, its presence in humans is more common (C. Gardiner, personal communication).5,6,8 Reports on D. immitis infection in orangutans, a rhesus monkey, and a gibbon have been published.1,4 Microfilaremia has been found in pale-headed saki monkeys, which suggests a patent heartworm infection had occurred.2 Experimental infections have been attempted in gibbons and macaques with some success.4,7
Heartworm infections have occurred in humans in regions of the world where canine heartworm is endemic.6,8 Infection with D. immitis most often results in an immature worm that does not survive in the heart, and embolizes to the lung. Once embedded in lung parenchyma, it creates a granuloma that can be seen radiographically.3
The case seen at Audubon Zoo in a colobus indicates D. immitis can infect nonhuman primates and cause clinically relevant disease and death similar to that seen in its natural canine host.
Literature Cited
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