Information for Healthcare Providers

Clinical Evaluation and Disease

Jamestown Canyon virus is a California serogroup orthobunyavirus that was first isolated in 1961 from mosquitoes in Colorado. The virus is widely distributed throughout much of North America and can be transmitted by a variety of mosquito vectors, depending on geographic location and time of year (e.g., Culiseta, Aedes, and Anopheles species). Deer are the likely animal reservoir. Jamestown Canyon virus is related to other California serogroup orthobunyaviruses, such as La Crosse, Keystone, and snowshoe hare viruses.

Many Jamestown Canyon virus infections are asymptomatic, but the specific symptomatic-to-asymptomatic ratio is not known. Among patients who are symptomatic, initial symptoms are non-specific, including fever, fatigue, or headache. Some patients also report respiratory symptoms, such as cough, rhinitis, or pharyngitis. Some individuals with Jamestown Canyon virus disease might develop meningitis or encephalitis may develop with possible meningismus, seizures, altered mental status, and cerebrospinal fluid pleocytosis. About half of known Jamestown Canyon virus disease cases have been hospitalized, but deaths have been rare.

Most cases of Jamestown Canyon virus infections occur from April through September. Unlike La Crosse virus infections which occur mostly in children, there is no clear age predilection for Jamestown Canyon virus disease, although most cases have been reported among adults.

Diagnostic Testing

Healthcare providers should consider Jamestown Canyon virus and other arboviral infections in patients with acute fever, meningitis, or encephalitis during spring through fall in the United States, particularly when tests are negative for other more common infections (e.g., herpes simplex virus, enteroviruses, West Nile virus). Diagnosis is usually made by serology, typically by a Jamestown Canyon virus-specific immunoglobulin (Ig) M test followed by a confirmatory plaque reduction neutralization test (PRNT). However, it is not known how long IgM antibodies can be detected in serum following a Jamestown Canyon virus infection; therefore, a positive IgM antibody test may reflect past infection. Healthcare providers should contact their state or local health department for assistance with Jamestown Canyon virus testing, which is done at CDC and some state health departments.

Treatment and Prevention

Treatment of Jamestown Canyon virus disease is supportive only. Some patients diagnosed with the disease have required hospitalization but most patients recover without long-term sequelae. Deaths have been rare.

The best way to prevent Jamestown Canyon virus infection is to avoid mosquito bites. Protective actions people can take include using an EPA-registered insect repellent and wearing long-sleeved shirts and pants when outdoors. More information about reducing exposure to mosquito bites is available on the CDC Prevent Mosquito Bites website.

Page last reviewed: November 27, 2019
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