Yes, prairie dogs are involved with the plague, serving as both highly susceptible hosts and indicators of its presence in the environment. This disease, known as Sylvatic Plague when it occurs in wild animals, is an ongoing public health and wildlife conservation challenge in the Western United States. The transmission of the disease is mediated primarily by fleas, which carry the infection between prairie dogs and other susceptible species.
What Causes the Plague
The plague is caused by the bacterium Yersinia pestis, a small, rod-shaped organism responsible for historical pandemics like the Black Death. This bacterium is maintained in nature primarily within fleas and rodents, where it circulates silently in some populations. In humans, infection with Y. pestis can manifest in three main forms. The most common is bubonic plague, characterized by painful, swollen lymph nodes called buboes near the site of the flea bite.
A more severe systemic form is septicemic plague, where the bacteria multiply directly in the bloodstream, often without forming buboes. The rarest but most rapidly progressing form is pneumonic plague, which infects the lungs and is the only type transmissible directly between people through airborne droplets. This ancient disease remains endemic in specific regions of the world, including rural areas of the Western United States, particularly New Mexico, Arizona, and Colorado. The disease primarily spreads to new hosts when infected fleas seek a new blood meal.
The Role of Prairie Dogs in the Epizootic Cycle
Prairie dogs function as highly susceptible hosts within the natural disease cycle, often called the sylvatic cycle. Unlike some other rodents that can carry the disease without quickly succumbing to it, prairie dogs typically experience extremely high mortality rates during outbreaks. Colonies can be nearly wiped out, with die-offs sometimes reaching 90 to 100 percent of the population in a short period.
The high density and social nature of prairie dog colonies are what make them such effective amplifiers of the plague bacteria. When a prairie dog contracts the infection and dies, the fleas living on it lose their host and quickly seek a new source of blood. This phenomenon, known as “flea-swarming,” forces a large number of infected fleas to jump onto the nearest available host, which is often another prairie dog in the densely packed colony.
These widespread, rapid die-offs, known as epizootics, are a clear indicator of active plague in a region and are a major factor in the conservation of keystone species. The loss of entire colonies impacts dependent predators, such as the endangered black-footed ferret, which relies on prairie dogs for both food and shelter.
Pathways of Human Exposure
The transfer of plague from an infected prairie dog colony to humans is a form of zoonotic transmission, requiring specific types of contact. The most frequent route of human infection is through the bite of an infected flea that has recently fed on a sick or deceased prairie dog. When the original host dies, the newly hungry, infected flea will readily bite a human, injecting the Y. pestis bacteria into the bloodstream.
A second pathway involves direct physical contact with an infected animal, such as handling a sick or dead prairie dog without proper precautions. Transmission can occur if the bacteria enter the body through breaks in the skin, like cuts or abrasions. While much less common, humans can also contract the disease by inhaling infectious droplets expelled by a person or animal with pneumonic plague, which is a rare but severe complication.
Domestic animals can serve as a bridge, carrying the disease from wild colonies to human homes. Cats are particularly susceptible to plague, often contracting it by hunting infected rodents or from flea bites. An infected cat can then transmit the disease to its owners through flea bites or, in the case of pneumonic plague in the cat, through respiratory droplets. This highlights the importance of using effective flea control on pets, especially in areas where plague is endemic.
Control and Prevention in Wild Colonies
Wildlife managers utilize several strategies to stabilize prairie dog populations and mitigate the spread of plague in the wild. The most widely employed and immediate response involves the application of insecticide dust directly into the prairie dog burrows. Insecticides like deltamethrin are dusted into the tunnels to kill the flea vectors, effectively breaking the transmission cycle between hosts.
This dusting is labor-intensive but has proven effective in preventing a complete population collapse in threatened colonies and is often used in areas where endangered species, like the black-footed ferret, depend on the prairie dogs. Researchers are also developing and field-testing an oral vaccine, often delivered via peanut butter-flavored baits, which provides a long-term preventative measure. This vaccine aims to protect the prairie dogs before an outbreak begins, rather than reacting to a crisis.
Surveillance efforts are continuously used to monitor for signs of plague activity, such as unexplained die-offs or the presence of the bacteria in fleas. The public plays a role in prevention by avoiding contact with wild prairie dogs and their burrows, especially in known plague areas. Reporting sick or dead wildlife to local health authorities is another simple action that helps track and manage the disease’s presence in the ecosystem.