Plague is primarily a disease of rodents which can affect humans. It is transmitted between rodents by rodent fleas and can be transmitted to people through infected rodent flea bites. It can also be transmitted to humans through direct contact with infected animal tissue. As with many primarily zoonotic diseases, where the disease is transmitted from vertebrae animals to humans, plague is a very severe disease in people, with a case-fatality ratio of 50%-60% if left untreated.

There are three main forms of plague in humans: bubonic, septicaemic and pneumonic.

• Bubonic plague is the result of an insect bite in which the plague bacillus travels through the lymphatic system to the nearest lymph node. The lymph node then becomes inflamed and is followed by bubo formation, a reaction in the body which occurs following the entrance of Yersinia pestis, the plague bacillus, through the skin and in the lymph nodes;
• The septicaemic form of plague occurs when infection spreads directly through the bloodstream. This form is usually fatal in the absence of antibiotic therapy;
• Pneumonic plague is an infection of the lungs caused by the plague bacillus and also has a very high case-fatality ratio.

Treatment

Effective treatment methods enable almost all plague patients to be cured if diagnosed in time. These methods include antibiotics and supportive therapy.

Prevention

The objective of preventive measures is to reduce the likelihood of people being bitten by infected fleas, of having direct contact with infective tissues, or of being exposed to patients with pneumonic plague. Important preventive measures include the following:

Case recognition and medical intervention

• Ensure dissemination of information concerning clinical features and case definition to health workers;
• Verify that patients have been placed on appropriate antibiotic treatment and that local supplies of antibiotics are adequate to handle further cases;
• Isolate pneumonic plague patients.

Plague vaccines are available worldwide, but are not recommended for immediate protection in outbreak situations. Vaccination is only recommended for high-risk groups, e.g. health workers and laboratory personnel who are constantly exposed to the risk of contamination.

Epidemiological and epizootical investigation and emergency control:

• Identify the rodent and flea species most likely to be sources of infection in the area where the human case(s) was exposed;
• Identify areas of potential risk to humans.

• Conduct research to identify which local rodent and flea species should be targeted for extensive surveillance and control;
• In endemic areas, long-term surveillance of zoonotic foci may be valuable. Management of plague foci comprises long term surveillance and control. Long-term environmental management is also strongly encouraged. This focuses on the elimination or reduction of areas in workplaces or near homes that are attractive to plague-susceptible rodents.

Thanks to the World Health Organisation
for much of this information.