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An Outbreak of Listeriosis in a Breeding Colony of Chinchillas

Listeria monocytogenes is a facultatively anaerobic short gram-positive rod-shaped bacterium that infects a wide range of animals, including ruminants, monogastric animals, birds, fish, rodents, and humans. Infection with this obligate intracellular pathogen causes 3 distinct clinical entities, septicemia, encephalitis, and abortion, which rarely occur simultaneously in the same animal. The septicemic form affects the viscera with or without meningoencephalitis and is common in monogastric animals, whereas encephalitis and abortion occur principally in adult ruminants. Chinchillas are considered one of the species more susceptible to visceral listeriosis, especially when reared in confinement. Listeriosis in chinchillas has been described in many areas of the United States during a period (1949-1955) when chinchilla pelts were prized commodities in the fur industry. More recently, chinchillas have become a widely used animal model for studies of noise-induced hearing loss. An outbreak of disseminated visceral listeriosis occurred in a breeding colony of 130 chinchillas located in northern Idaho. The chinchillas in this operation were raised for pelts. Polygamous breeding was practiced; 1 male had access to 8 females. The feed, open sacks of commercially formulated chinchilla pellets and a bale of hay, was stored on a wood pallet. To promote maintenance of their hair coats, a dust bath pan was provided for the animals. During December 1995, there was an unusually large influx of mice into the chinchilla building, and on several occasions the owners noted mouse droppings in the feed. By January 1996, the colony experienced a 23% mortality (30 of 130) in breeding animals of various ages. Approximately 4 days prior to death, the animals were anorectic and hunched, and some had torticollis. Many animals were found dead without premonitory clinical signs. Four chinchillas (2 dead males, 1 dead female, 1 moribund female) were submitted to the Washington Animal Disease Diagnostic Laboratory for necropsy. All 4 chinchillas were emaciated and lacked subcutaneous and retroperitoneal fat. Consistent gross lesions in the 3 dead chinchillas included multifocal 0.1-0.3-cm-diameter whitetan foci affecting the capsular surfaces and parenchyma of the liver, mesenteric lymph nodes, and the serosa of the small and large intestines, particularly the cecum and colon. Individual differences in postmortem lesions are listed in Table 1. Animal A, a dead female, had a 2-cm rectal prolapse and colonic intussusception in addition to the visceral foci. The intussusception consisted of a 3-cm segment of dark red prox-