Plague is a disease caused by the bacteria Yersinia pestis. The bacteria can be transmitted to humans from infected rodents or other small mammals by fleas. The fleas enjoy a blood meal on an infected animal and ingest the bacteria. If the flea then feeds on a human’s blood, the bacteria can be
passed to the human. Rodents like roof rats or Norway rats typically live in close proximity to humans are historically the culprit, but prairie dogs, rabbits, and domestic pets can carry the disease as well. It is possible to contract the disease by eating an infected animal or by inhaling the bacteria, but this is very rare. Septicemic plague, where the bacteria invades the body through the blood stream, and pneumonic plague, where the lungs are infected by inhaling the bacteria are both considered 100% fatal if untreated with the appropriate antibiotics. Bubonic plague, a bacterial assault on the lymphatic system is less fatal, but still a very serious condition if not treated.
The disease is best known for its outbreaks in Europe during the middle ages, but it does persist today. Annually, approximately 2,000 cases are reported worldwide. In the U.S. the most recent reports of the disease were from the western states where prairie dog and ground squirrel populations are known to carry the disease. In all cases, spread of the disease from animals to humans can be prevented by eliminating the vector, biting fleas, from the human environment – especially in areas where the disease is known to be a problem.