Vector-Borne Diseases

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Vector-borne diseases are transmitted from one animal to another by vectors, including insects, such as mosquitoes or fleas, and arachnids, such as ticks. The USGS National Wildlife Health Center investigates wildlife diseases, including vector-borne diseases, such as West Nile virus and sylvatic plague.

The following are vector-borne diseases currently being studied by the USGS National Wildlife Health Center (NWHC).


West Nile Virus

West Nile virus, a mosquito-transmitted virus, was introduced into the New York City area of North America in 1999. Since then the virus has been transmitted throughout the continental U.S., southern Canadian Provinces, Mexico.  The virus has also been transmitted on the Caribbean islands, Central and South America. West Nile virus causes disease symptoms, including encephalitis, in humans and horses, but has been devastating to North American wild bird populations, particularly the corvids, raptors, and songbirds. Population declines in members of these bird groups have been documented and linked to the year West Nile virus emerged in states or geographic areas of the U.S.

Mosquito, species not verified

Mosquito, species not verified

(Public domain.)

The NWHC has been involved with West Nile virus surveillance in wild birds and research since the entry of the virus into the U.S.  In recent years we have assisted states and Tribes in monitoring for virus transmission in ruffed grouse (Bonasa umbellus), snow shoe hares (Lepus americanus), and wild wolves (Canus lupus).  Experimentally, the NWHC has been working to develop models of West Nile virus susceptibility in passerine, or song birds, using domesticated zebra finches (Taeniopygia guttata) and canaries (Serinus canaria), which show lower and higher susceptibility to the virus, respectively.  Since the genome of these domesticated birds has been published studies on molecular basis of disease susceptibility are possible.

West Nile virus continues to circulate every summer in the U.S. An uptick in human, domestic animal, and avian cases, might be related to weather, with hot and dry conditions being permissive, and also cycles of immunity in birds, the primary host for the virus. 

To see disease reports of West Nile virus, search WHISPers (Wildlife Health Information Sharing Partnership event reporting system.

To check out historic fact sheets on West Nile virus, see – NWHC Fact Sheets.



Sylvatic Plague

Sylvatic plague, caused by Yersinia pestis, is a bacterial disease transmitted by fleas that afflicts many mammalian species, including humans. For many species of wildlife, plague mortality is a serious conservation issue. Current efforts to halt the spread of plague in prairie dog colonies typically rely on dusting individual prairie dog burrows with pesticides to kill plague-infected fleas. Although flea-control insecticides, such as deltamethrin, are useful in stopping plague outbreaks in these prairie dog colonies, dusting of burrows is labor intensive and time consuming and may affect other insects and arthropods.

Image: Checking a Prairie Dog for Fleas

National Park Service veterinarian Kevin Castle checks an anaesthetized prairie dog for fleas in Wind Cave National Park. 

Over 30 organizations and agencies are testing a USGS-developed oral vaccine to prevent the spread of plague in prairie dogs. If successful, the sylvatic plague vaccine could help protect endangered black-footed ferrets in the western U.S. because the ferrets rely on prairie dogs for food. Castle tags each trapped prairie dog and takes hair, whisker, and blood samples before scientists release the animals back into the wild.

(Credit: Marisa Lubeck, U.S. Geological Survey. Public domain.)

Scientists at the USGS National Wildlife Health Center (NWHC), in collaboration with colleagues at the University of Wisconsin (UW), have developed a sylvatic plague vaccine that shows great promise in protecting prairie dogs against plague. Controlling plague is a vital concern for ongoing management and conservation efforts for prairie dogs.

To learn more about sylvatic plague and read related publications, see – Sylvatic Plague and Vaccines.