Bubonic Plague

Bubonic plague is an infectious disease. Thus, it is a concern in forensic science as a possible cause of death during an occurrence or outbreak featuring an unknown pathogen (illness-causing agent).

The bacterium that is responsible for bubonic plague is Yersinia pestis, named after one of its co-discoverers, Alexandre Yersin, and is also known as Pasteurella pestis. Typically, the bacterium is passed from rodents to other animals and humans via the bite of a flea. The flea acquires the bacterium as it lives on the skin of the rodent. Humans can also acquire the disease by direct contact with infected tissue or fluids.

Pneumonic plague (infection with Yersinia pestis bacteria in the lungs) results from inhaling minute droplets of moisture in the air that are contaminated with the bacteria, usually from being near another person with pneumonic plague who is coughing.

With bubonic plague, Yersinia pestis invades the lymphatic system. Bubonic plague is named because of the symptoms. The bacterial infection produces a painful swelling of the lymph nodes. These are called buboes. Often, the first swelling is evident in the groin. During the Middle Ages, a large epidemic of bubonic plague was referred to as the Black Death, because of the blackening of the skin due to the dried blood that accumulated under the skin's surface.

The bubonic plague has been a significant cause of misery and death throughout recorded history. The Black Death was only one of many epidemics of plague that extend back to the beginning of recorded history. The first recorded outbreak of bubonic plague was in 542–543. This plague destroyed the attempts of the Roman emperor of the day to reestablish a Roman empire in Europe. This is only one example of how bubonic plague has changed the course of history.

The plague of London in 1665 killed over 17,000 people (almost twenty percent of the city's population). This outbreak was quelled by a huge fire that destroyed most of the city.

The disease remains present to this day. In North America, the last large epidemic occurred in Los Angeles in 1925. With the advent of the antibiotic era, bubonic plague has been controlled in the developed world. However, sporadic cases (e.g., 10–15 cases each year) still occur in the western United States. In less developed countries (e.g., in Africa, Bolivia, Peru, Ecuador, Brazil), thousands of cases are reported each year.

The infrequent outbreaks of bubonic plague do not mean the disease disappears altogether. Rather, the disease normally exists in what is called an enzootic state. That is, a few individuals of a certain community (e.g., rodents) harbor the disease. Sometimes, however, environmental conditions cause the disease to spread through the carrier population, causing loss of life. As the rodent populations dies, the fleas that live on them need to find other food sources. This is when the interaction with humans and non-rodent animals can occur. Between outbreaks, Yersinia pestis infects rodents without causing much illness. Thus, the rodents become a reservoir of the infection.

Symptoms of infection in humans begin within days after contamination with the plague bacterium. The bacteria enter the bloodstream and travel to various organs (e.g., kidney, liver, spleen, lungs) as well as to the brain. Symptoms include shivering, nausea with vomiting, headache, intolerance to light, and a whitish-appearing tongue. Buboes then appear, followed by rupture of blood vessels. The released blood can coagulate and turn black.

If the infection is untreated, the death rate from plague in humans approaches 75%. Prompt treatment most often leads to full recovery and a life-long immunity from further infection. Prevention is possible, since a vaccine is available. Unfortunately, the vaccine is protective for only a few months. Use of the vaccine is usually reserved for those who will be at high risk for acquiring the bacterial infection (e.g., soldiers, travelers to an outbreak region). Antibiotics such as tetracycline or sulfonamide are used more commonly as a precaution for those who might be exposed to the bacterium. Such use of antibiotics should be stopped once the risk of infection is gone, to avoid the development of resistance in other bacteria resident in the body.

The most effective way to prevent bubonic plague is the maintenance of adequate sanitary conditions. This acts to control the rodent population, especially in urban centers.