Biologists Monitor Jamestown Canyon Virus Spread in Pennsylvania Mosquitoes

In Pennsylvania, researchers are actively monitoring the presence of Jamestown Canyon virus within local mosquito populations, alongside the already well-known West Nile virus. Although West Nile remains the primary mosquito-borne threat in the state, recent findings indicate that Jamestown Canyon virus is increasingly appearing in different regions. As of July 18, health officials reported that 23 mosquitoes tested positive for this virus, with the highest concentration—13 cases—found in Luzerne County. A solitary positive case was also identified in Westmoreland County near Pittsburgh.

Originally discovered in a Colorado town bearing the same name in 1961, Jamestown Canyon virus was added to Pennsylvania’s West Nile Virus mosquito monitoring program last year. Experts, such as Elizabeth McGraw from Penn State University, emphasize that climate change is significantly altering the geographic distribution of mosquitoes and the viruses they carry. Rising temperatures and increased rainfall facilitate the expansion of mosquito habitats into previously unaffected areas, thereby increasing the potential for virus transmission.

Jamestown Canyon virus can cause febrile illness, meningitis, and inflammation of the brain (encephalitis). Uniquely, it can also lead to respiratory symptoms, setting it apart from other mosquito-borne illnesses. Interestingly, many infected individuals show mild or no symptoms, making it difficult to track actual case numbers. Severe cases are often identified only when hospitalization occurs, triggering more comprehensive testing.

While there is no specific treatment for Jamestown Canyon virus, symptoms typically include fever, headaches, and fatigue, which can be relieved through rest, fluids, and pain management. The virus circulates primarily between mosquitoes and animal hosts such as deer, bison, or moose, but humans are considered dead-end hosts — meaning they do not transmit the virus back to mosquitoes.

Pennsylvania’s Department of Environmental Protection conducts mosquito surveillance across various counties, including Allegheny, Beaver, Butler, Westmoreland, Washington, and Fayette, testing mosquitoes at their Harrisburg laboratory. Historically, the virus infects about 23 people annually across the United States, predominantly in the Midwest, with states like Minnesota and Wisconsin reporting the majority of cases. The CDC reports over 330 cases in the U.S. from 2011 to 2024, with 12 deaths, though no human cases have been reported so far in 2025.

Preventative measures include reducing standing water around properties, avoiding flooded areas with dense deer populations, and wearing protective clothing and insect repellents containing DEET, picaridin, or lemon eucalyptus oil. Limiting outdoor activity during dusk and dawn, when mosquitoes are most active, is also recommended.

As climate change continues to influence disease patterns, public awareness and prevention strategies become increasingly vital for safeguarding health against emerging mosquito-borne viruses like Jamestown Canyon.