wildlife and zoo assay data sheet

Yersinia pestis (Plague)

Test code: B0065 - Ultrasensitive qualitative detection of Yersinia pestis, the etiologic agent of plague, by real time polymerase chain reaction.

Yersinia pestis is a gram-negative rod-shaped bacterium belonging to the family Enterobacteriaceae. Formerly called Pasteurella pestis, it is a facultative anaerobe that can infect humans and other animals. Stained, it has a “safety pin” appearance.

Three main forms of infection can occur in humans, referred to as pneumonic plague, septicemic plague and bubonic plague. All three forms have caused high mortality rates in epidemics throughout human history, including the Black Death (the bubonic form) that accounted for the death of at least one-third of the European population in 1347 to 1353.

Rodents are a common reservoir of these bacteria; their fleas help disseminate the disease. When humans or other animals live in close proximity to infected rodents, the bacteria can be transmitted via flea bites. Once the bacteria enter the bloodstream, they migrate to the lymph nodes. The ability of Yersinia pestis to inhibit phagocytosis allows it to avoid destruction by immune system cells such as macrophages and thereby to proliferate in lymph nodes, causing lymphadenopathy.

In North America, fleas infected with Yersinia pestis have been found on wild rodents and other animal species from the Pacific Coast to the Great Plains, and from southwestern Canada to Mexico. Most human cases in the United States occur in two regions: 1) northern New Mexico, northern Arizona, and southern Colorado; and 2) California, southern Oregon, and far western Nevada (Adjemian et al., 2007).

Domestic cats and dogs in endemic areas can easily be infected with these bacteria if exposed to infected rodents. Dogs are generally resistant to plague. Although they may become infected, they usually develop very mild symptoms, such as swollen lymph nodes, and they can become carriers of the bacteria. Wild and domestic cats can become infected and develop any of the three forms of the disease (bubonic, septicemic or pneumonic). About 50% of cats infected with Y. pestis will die soon after developing the disease.

Airborne transmission results in pneumonic plague, whereas patients infected by the bubonic or septicemic forms seldom exhibit pneumonic characteristics. After an incubation period, patients with pneumonic plague show sudden onset of coughing, high temperature, and lack of energy; these symptoms increase in severity over time. In pneumonic form, Y. pestis can be transmitted person-to-person or cat-to-person through aerosols from coughing (Gage et al., 2000). Due to its high replication rates, plague proves fatal in roughly 50% of cases even with medical treatment, and is almost universally fatal without treatment.

Traditionally, the "gold standard" for testing fleas for Y. pestis infection has been the inoculation of mice with ground flea suspensions. Inoculated mice are monitored for death, which usually takes at least 21 days; tissues from these dead mice are then tested by fluorescent antibody analysis for evidence of Y. pestis infection. This testing approach, however, requires considerable time and personnel involvement. False negative results can occur when death is used as the assay endpoint, because some mice occasionally survive the infection. Molecular detection is a rapid, sensitive, specific and safer alternative for identification of Y. pestis.

Utilities:

• Confirm the disease causing agent
• Shorten the time required to confirm a clinical diagnosis of Yersinia pestis
• Ensure that animals and facilities are free of Yersinia pestis
• Early prevention of spread of Yersinia pestis
• Minimize human exposure to Yersinia pestis
• Safety monitoring of biological products that derive from susceptible animals

References:
Adjemian, J.C., Foley, P., Gage, K.L. and Foley, J.E. (2007) Initiation and spread of traveling waves of plague, Yersinia pestis, in the western United States. Am J Trop Med Hyg. 76:365-375.
Engelthaler, D.M., Gage, K.L., Montenieri, J.A., Chu, M. and Carter, L.G. (1999) PCR Detection of Yersinia pestis in fleas: Comparison with mouse inoculation. J. Clin. Microbiol., 37:1980-1984.
Gage, K.L., Dennis, D.T., Orloski, K.A., Ettestad, P., Brown, T.L., Reynolds, P.J., Pape, W.J., Fritz, C.L., Carter, L.G.., and Stein, J.D. (2000)  Cases of human plague associated with exposure to infected domestic cats. Clin. Infect. Dis. 30:893-900.

Specimen requirements: 0.5 ml whole blood in EDTA (purple top) or ACD (yellow top) tube, or nasal swab, or skin swab, or lesion swab.

For specimen types other than those listed here, please call to confirm specimen acceptability and shipping instructions.

For all specimen types, if there will be a delay in shipping, or during very warm weather, refrigerate specimens until shipped and ship with a cold pack unless more stringent shipping requirements are specified. Frozen specimens should be shipped so as to remain frozen in transit. See shipping instructions for more information.

Turnaround time: 2 business days

Methodology: Qualitative polymerase chain reaction

Normal range: Nondetected