Information for Healthcare Providers

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

Clinical Evaluation and Disease

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 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.

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 or enteroviral infections).

Diagnostic Testing and Reporting

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.

Contact your state or local health department for assistance with diagnostic testing. They can assist you with determining if samples should be sent to the CDC Arbovirus Diagnostic Laboratory for further testing.

ALL RESULTS WILL BE SENT TO THE APPROPRIATE STATE HEALTH DEPARTMENT. Specimens should be submitted to CDC through state health departments.

Jamestown Canyon virus disease is a nationally notifiable condition. All cases should be reported to local public health authorities in a timely manner. Reporting can assist local, state, and national authorities to recognize outbreaks and to implement control measures to reduce future infections.

Treatment and Prevention

Treatment of Jamestown Canyon virus disease is supportive only. Patients with severe meningeal symptoms often require pain control for headaches and antiemetic therapy and rehydration for associated nausea and vomiting. Patients with encephalitis require close monitoring for the development of elevated intracranial pressure, seizures, and inability to protect their airway.

No Jamestown Canyon virus vaccines are available for use in humans. In the absence of a vaccine, prevention of Jamestown Canyon virus infection depends on personal protective measures to decrease exposure to infected mosquitoes. This includes using EPA-approved insect repellent, wearing long-sleeved shirts and pants, treating clothing and gear with 0.5% permethrin, and taking steps to control mosquitoes indoors and outdoors. More information about reducing exposure to mosquito bites is available on the CDC Prevent Mosquito Bites website.