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Plague

Plague, caused by Yersinia pestis (PDF) , has not been recognized as an important disease entity in the laboratory animal setting. However, focal outbreaks of this once devastating disease continue to be recognized worldwide, including the United States, where the disease (PDF) exists in wild rodents in the western one-third of the country. In the United States, most human cases are related to wild rodents, but cats, dogs, coyotes, rabbits, and goats have also been associated with human infection.

The prairie dog (Cynomys Iudovicianus), along with rats, rabbits and squirrels, have been implicated in many cases of human plague. Plague is transmitted to humans via an infected-animal flea bite or exposure to infected-animal flea feces that is laden with the Yersina pestis organism.

Most cases are the result of bites by infected fleas, or contact with infected rodents. In human plague associated with nonrodent species, infection has resulted from bites or scratches, handling of infected animals (especially cats with pneumonic disease), ingestion of infected tissues, and contact with infected tissues. Nonrodent species can serve as transporters of fleas from infected rodents into the laboratory.

Human plague has a localized (bubonic) form and a septicemic form. In bubonic plague, patients have fever and large, swollen, inflamed, and tender lymph nodes, which can suppurate. The bubonic form can progress to septicemic plague, with spread of the organism to diverse parts of the body, including lungs and meninges. The development of secondary pneumonic plague is of special importance because aerosol droplets can serve as a source of primary pneumonic or pharyngeal plague, creating a potential for epidemic disease.

Preventivemeasures in a laboratory animal facility should encompass the control of wild rodents and the quarantine, examination, and ectoparasite treatment of incoming animals with potential infection. Those measures need to be applied continuously for animals that are housed outdoors, and therefore have an opportunity for contact with plague-infected animals or their fleas. Vaccines are available for personnel in high-risk categories, but confer only brief immunity.

Animal Biosafety Level 2 (PDF) practices, as well as containment equipment and facilities, are recommended for personnel working with naturally or experimentally infected animals.