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Plague is a zoonotic disease circulating mainly among small animals and their fleas. The bacteria Yersinia pestis can also infect humans. It is transmitted between animals and humans by the bite of infected fleas, direct contact, inhalation and rarely, ingestion of infective materials. Plague can be a very severe disease in people, with a case-fatality ratio of 30%-60% if left untreated.
Infected persons usually start with "flu-like"� symptoms after an incubation period of 3-7 days. Patients typically experience the sudden onset of fever, chills, head and body-aches and weakness, vomiting and nausea. Clinical plague infection manifests itself in three forms depending on the route of infection: bubonic, septicaemic and pneumonic.
Plague is endemic in many countries in Africa, in the former Soviet Union, the Americas and Asia. In 2003, 9 countries reported 2118 cases and 182 deaths. 98.7% of those cases and 98.9% of those deaths were reported from Africa. Today the distribution of plague coincides with the geographical distribution of its natural foci.
Rapid diagnosis and treatment is essential to reduce complications and fatality. Effective treatment methods enable almost all plague patients to be cured if diagnosed in time. These methods include the administration of antibiotics and supportive therapy.
The objective of preventive measures is to inform people to be aware of the areas where zoonotic plague is active and to take precautions against flea bites and handling carcass while in plague-endemic areas. People should avoid having direct contact with infective tissues, or from being exposed to patients with pneumonic plague.
Case recognition, medical intervention and field investigation
Diagnosis and confirmation of plague requires laboratory testing. Recovery and identification of Y. pestis culture from a patient sample is optimum for confirmation. Depending on the presentation of the form on plague: bubo aspirates, blood, and sputum are the most appropriate specimens for rapid testing and culture. Serum taken during the early and late stages of infection can be examined to confirm infection. Rapid dipstick tests have been validated for field use to quickly screen for Y. pestis antigen in patients. Specimens should be collected and forwarded to laboratories for plague testing.
Plague vaccines at one time were widely used but have not proven to be an approach that could prevent plague effectively. Vaccines are not recommended for immediate protection in outbreak situations. Vaccination is only recommended as a prophylactic measure for high-risk groups (e.g. laboratory personnel who are constantly exposed to the risk of contamination).
Surveillance and control
Sources: US Department of Health; The World Health Organization