RESOURCE RAMBLINGS Vol 6. No. 7
Wind Cave National Park Resource Management News Briefs July 2008
Plague is an infectious disease of animals and humans caused by the bacterium Yersinia pestis. Plague occurs throughout much of the world. In the United States, scattered cases primarily occur in rural areas in the West and Southwest. Infection is quite rare, and only about 10-15 individuals in the United States become infected each year. The three states with the highest prevalence of plague in North America are New Mexico, Arizona and Colorado. The primary areas of plague activity include northern Arizona and northern New Mexico, the panhandle of Texas, southern Colorado, and to a lesser extent southern Utah. A recent outbreak of plague in the Conata Basin near Badlands National Park has wildlife biologists concerned for the survival of endangered blackfooted ferrets. Modern antibiotics for humans are effective against plague if treated promptly.
Plague is usually transmitted through the bites of infected fleas. Animals that can become infected with plague include prairie dogs, wood rats, chipmunks, ground squirrels, rats, rabbits, squirrels, and cats. During plague outbreaks, many of the infected animals will die, causing the fleas to seek other sources of blood to survive, including humans. People can become infected by visiting areas where rodents or other animals have recently died from plague and the infected fleas are still present. People can also become infected by handling infected rodents or the wild carnivores that prey on these animals, since the virus can enter the human body through small breaks in the skin. House cats can also become infected with plague, or dogs and cats may bring infected fleas into the home. Inhaling the droplets expelled by the coughing of a plague-infected person or animal (especially house cats) can result in a plague infection of the lungs, which is known as pneumonic plague. Person-to-person transmission of plague pneumonia is rare and was last reported in the United States in 1924.
The typical sign of the most common form of human plague is a swollen and very tender lymph gland, accompanied by pain. (The swollen gland is referred to as a “bubo”, which is where the term bubonic plague comes from.) The incubation period for bubonic plague usually ranges from and rarely exceeds 2-6 days. Plague should be suspected when a person develops a swollen gland, fever, chills, headache, and extreme exhaustion, and has a history of possible exposure to rodents, rabbits, cats, or fleas.
When plague is left untreated, plague bacteria can invade the bloodstream. As the plague bacteria multiply, they can spread rapidly throughout the body and cause a severe and often fatal condition. Plague patients should receive antibiotic therapy as soon as possible following diagnosis.
Rodents and other animal carriers and their fleas may need active control around places where people live, work, and play. When possible, preventive measures should be taken to minimize rodent and other wild animal activity in areas occupied or frequented by people. Reduce food sources and nesting areas used by rodents, and rodent-proof homes, buildings, and storage areas. Do not apply insecticides or rodenticides unless approval is obtained from the NPS Integrated Pest Management (IPM) team.
If employees anticipate being exposed to fleas from rodents or other animal carriers, they should apply an insect repellent such as DEET to clothing and exposed skin. Employees who are more likely to be exposed include field researchers, biologists, and facility management staff who work directly with rodents or in areas occupied by rodents. Wear disposable gloves, such as nitrile, when handling potentially infected animals. Wildlife workers, hunters and trappers should wear rubber gloves when skinning game. DEET should be washed off of the skin once the employee returns indoors and there is no longer a risk of exposure. For employees who must regularly spend time in the field when plague-infected fleas may be present, permethrin may be used to treat clothing. Once on the fabric, it will last through several machine washings for about 6 weeks. Treated clothes should be washed separately from untreated clothes.
Anyone exposed to the blood or tissues of dead rodents, mountain lions or cats in plague areas should take precautions to prevent skin contact with their blood or body tissues and prevent inhalation of aerosolized droplets of the body fluids from such animals.
Although plague has not been identified within Wind Cave National Park, be aware that it could show up in the Park at any time. Park staff will be participating in management efforts this year to keep plague from infecting the Park, staff, visitors and Park wildlife. You as employees should be aware of the signs and symptoms of plague and understand the importance of seeking medical treatment immediately if any of these symptoms occur. Because of the short incubation period for plague, serious illness can develop very quickly.
Plague vaccination is not generally available and not recommended for NPS employees because of uncertainties over the effectiveness of the vaccine.
Please be alert, watch for and report rodents that are sick or dying for unexplained reasons. If multiple rodent deaths in the same area are noted or a rodent die off is discovered, contact Dan Roddy in Resource Management immediately.
Centers for Disease Control and Prevention.
NPS Inside Public Health. Illnesses and Diseases Website, Bubonic Plague.