Sylvatic Plague Immunization in Black-footed Ferrets and Prairie Dogs

Sylvatic plague is a bacterial disease of wild rodents that is transmitted by fleas. It can afflict numerous species of mammals, including humans. Prairie dogs are highly susceptible to plague and are the primary food source of the highly endangered black-footed ferret, which is also susceptible to the disease. Sylvatic plague can decimate prairie dog colonies, with mortality rates of 90 percent or more, resulting in local extinctions and population reductions. Because of the susceptibility of prairie dogs to sylvatic plague, coupled with the potentially devastating effect the disease can have on black-footed ferrets, plague control is a vital concern for ferret recovery programs and conservation efforts.

Scientists at the USGS National Wildlife Health Center (NWHC), in collaboration with colleagues at the University of Wisconsin, state agencies, and other Federal agencies, have tested the feasibility of vaccinating black-footed ferrets and prairie dogs against sylvatic plague infections. The plague vaccine was developed for humans by the U.S. Army Medical Research Institute for Infectious Disease and is being tested for use on animals at the USGS National Wildlife Health Center. Vaccination of ferrets by injection was shown to be highly successful both in the laboratory and in the field. However, injectable vaccines are not practical for field use in free-ranging animals, such as prairie dogs. Ultimately, management of the disease in ferrets will depend on managing the disease in prairie dogs.

Currently, efforts to halt the spread of plague rely on dusting individual prairie dog burrows with pesticides that kill plague-infected fleas, but pesticide application is labor intensive, costly and difficult to sustain over time.

Sylvatic Plague Vaccine (SPV)

Immunizing entire populations of free-ranging prairie dogs and other rodents is highly challenging, but preliminary NWHC studies indicate prairie dogs can be successfully immunized by voluntarily eating vaccine-laden baits. These studies suggest that plague in prairie dogs could be managed through oral immunization, which would be especially useful in areas where black-footed ferrets reside and in populations of prairie dogs of conservation concern.

The Sylvatic Plague Vaccine Subcommittee of the Black-footed Ferret Recovery and Implementation Team is acting to coordinate efforts to complete development and delivery of SPV as a management tool to combat plague in grassland ecosystems. Currently, the NWHC is working with USDA’s Center for Veterinary Biologics to register SPV for use in the field. Field safety trials with SPV are scheduled to begin in summer 2012 in Colorado. Field efficacy studies for free-ranging prairie dog populations are planned to begin in 2013. Ultimately, SPV would be used as a plague management tool to reduce the occurrence of plague outbreaks and thus to enhance ferret recovery and prairie dog conservation in targeted areas.