Plague

Plague is a reportable disease in Oklahoma. Plague is an infectious disease caused by the bacterium Yersinia pestis. Plague is known as the infamous Black Death of medieval Europe, which is believed to have killed approximately one-third of the world’s population in the 14th century. Currently in the United States, plague occurs mostly in the western United States from the Great Plains to the Pacific Coast. Most reported cases occur in New Mexico, Arizona, and Colorado. Plague is a rare disease in Oklahoma; the last case of human plague was reported in 1991 and was associated with exposure to prairie dogs in the Oklahoma panhandle.

In Oklahoma, only the panhandle is west of the 100th meridian of longitude, which is a remarkably precise boundary of the rodents involved in the natural plague cycle. Accordingly, in Oklahoma plague is only found in prairie dogs in certain parts of the panhandle. The rat and mouse species found around human dwellings and within towns and cities in the United States are not part of the natural plague cycle, and there have been no cases of human plague acquired in an urban environment in the United States since the 1920’s.

Symptoms of plague include a painful, swollen lymph node (called a bubo), fever, chills, tiredness, muscle aches, nausea, sore throat, and headache. Symptoms appear between one and seven days after being infected, but a person usually becomes ill with plague within two to six days. The bacteria in some cases can spread to the lungs causing a severe respiratory illness called pneumonic plague. Another rare form is called plague septicemia, in which the bacteria enter the bloodstream. When a bubo occurs, the form is called bubonic plague.

In nature, plague is a disease of wild rodents, but can also infect humans and other mammals. Fleas become carriers of the bacteria by feeding on chipmunks, prairie dogs, ground squirrels, and other rodents that are infected with the bacteria. Less often, other mammals may become accidentally infected with plague, but they play no significant role in the disease cycle. Rarely, humans are bitten by plague-carrying fleas from rodents and become infected. In addition, humans may become infected after handling tissue or body fluids of sick or dead animals infected with plague, for example, while hunting. The species of fleas that infest dogs and cats do not transmit plague; however, rodent fleas may attach themselves to domestic pets that are allowed to enter the habitat of wild rodents. When brought into the home, these fleas may then bite humans and cause disease.

A rare form of the disease, pneumonic plague, is spread from person-to-person. Pneumonic plague can spread from person to person by sneezing or coughing. People must have face-to-face contact with the ill person. Pneumonic plague can also be spread to people by cats with pneumonic plague. Bubonic plague does not usually spread from person to person unless the person with bubonic plague also develops pneumonic plague.

Treatment with antibiotics is very effective, especially if started in the early stages of the disease. If left untreated, the bubonic form of the disease has a fatality rate of about 40%. No commercial vaccine currently exists in the United States.

How to prevent exposure to plague:

If you live in or visit the Oklahoma Panhandle, or participate in outdoor activities in the western United States (roughly west of the east-west Texas-Oklahoma border) the following tips will reduce your chances of becoming infected:

• Reduce the risk of fleabites by regularly treating pets (cats and dogs) with recommended flea control products.
• Avoid direct skin contact with sick or dead animals, especially rodents.
• Exercise caution to avoid cutting yourself when skinning wild animals.
• Prairie dogs will die when infected with plague, and their hungry fleas will bite passing people and animals. Therefore, it is advisable for people and pets to avoid prairie dog towns, especially if there appears to be a die-off.
• Do not allow domestic pets to range into rural or wild areas where they may pick up fleas from rodents or rodent burrows.
• Use of insect repellants containing DEET will prevent fleabites along with many other diseases spread by insects and ticks.

Plague Fact Sheets and Information:

Plague Fact Sheet (42k.pdf)
Pneumonic Plague Fact Sheet (41k.pdf)
   Pneumonic Plague Hoja Informativa (42k.pdf)

External Plague Resources:

Plague (CDC)