Plague is a deadly infectious disease that is caused by the enterobacteria Yersinia pestis, named after the French-Swiss bacteriologist Alexandre Yersin. Primarily carried by rodents (most notably rats) and spread to humans via fleas, the disease is notorious throughout history, due to the unrivaled scale of death and devastation it brought. Depending on lung infection, or sanitary conditions, plague also can be spread in the air, by direct contact, or by contaminated undercooked food or materials. The symptoms of plague depend on the concentrated areas of infection in each person: such as bubonic plague in lymph nodes, septicemic plague in blood vessels, pneumonic plague in lungs, and so on. It is treatable if detected early. Plague is still endemic in some parts of the world.
Historically, plague destroyed entire civilizations. In the 1300s, the "Black Death," as it was called, killed approximately one-third of Europe's population. Today plague is uncommon. This is largely due to better living conditions and antibiotics.
Clinical plague infection manifests itself in three forms depending on the route of infection: bubonic, septicaemic and pneumonic.
Bubonic form is the most common form of plague resulting from the bite of an infective flea. Plague bacillus enters the skin from the site of the bite and travels through the lymphatic system to the nearest lymph node. The lymph node then becomes inflamed because the plague bacteria, Yersinia pestis or Y. pestis, will replicate here in high numbers. The swollen lymph node is called a "bubo" which is very painful and can become suppurated as an open sore in advanced stage of infection;
Septicaemic form of plague occurs when infection spreads directly through the bloodstream without evidence of a "bubo". More commonly advanced stages of bubonic plague will result in the presence of Y. pestis in the blood. Septicaemic plague may result from flea bites and from direct contact with infective materials through cracks in the skin.
Pneumonic form of plague is the most virulent and least common form of plague. Typically, pneumonic form is due to a secondary spread from advanced infection of an initial bubonic form. Primary pneumonic plague results from inhalation of aerosolized infective droplets and can be transmitted from human to human without involvement of fleas or animals. Untreated pneumonic plague has a very high case-fatality ratio.
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.
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).