An Overview of Jamestown Canyon Virus Disease

Jamestown Canyon virus is a mosquito-borne California serogroup orthobunyavirus first isolated from Culiseta insornata mosquitoes near Jamestown, Colorado, in 1961. ^{1 -3} It is closely related to La Crosse, snowshoe hare, and California encephalitis viruses (and may have been historically mistaken for these given significant antibody cross-reactivity within the California serogroup). ² It has subsequently been identified in other mosquito species, with principal mosquito vectors likely varying by region. ^{1 -5} White-tailed deer are likely the primary amplifying hosts, though moose, elk, bison, and pronghorns may also play a role. ^1,2,4,5 Jamestown Canyon virus-specific neutralizing antibodies have been found in mammals and humans throughout North America suggesting a widespread geographic distribution. ^2,3

Since the 1960s, human cases of Jamestown Canyon virus disease have been reported throughout the United States, though there appears to be a geographic predilection for northern states. ^1,2,3,5 Case detection improved in 2013 when the Centers for Disease Control and Prevention (CDC) began routine testing of all domestic arboviral disease samples with a Jamestown Canyon virus-specific immunoglobulin (Ig) M test. ^1,3 Approximately 10–75 cases per year have been reported throughout the United States since then, though many other cases have likely gone unidentified. ^1,3 Interestingly, Wisconsin and Minnesota have reported more than half of these known cases, likely due to both increased surveillance and disease incidence. ^1,3,5 Most cases have symptom onset from April through September with bimodal peaks in spring and late summer (likely reflecting different mosquito populations involved throughout the year). ^2,3,5 Similar to other arboviral diseases, reported cases are more likely to be male. ^1,3,5 Unlike La Crosse virus disease which has a predilection for children, there is no such age predilection with Jamestown Canyon. ^1,3,5 Neuroinvasive disease has been reported in children, young adults, and older adults. ^3,5

Many Jamestown Canyon virus infections are thought to be asymptomatic, but the proportion is unknown. ^1,3,5 Symptomatic Jamestown Canyon virus disease cases may present with fever, fatigue, myalgia, and/or headache. ^1,2,3,5 Some patients may present with upper respiratory symptoms (e.g., cough, rhinitis, pharyngitis), which is uncommon for arboviral infections. ^1,2 About half of reported cases are neuro-invasive presenting with meningitis or meningoencephalitis. ^1,2,3,5 Lumbar puncture in neuroinvasive cases may show a lymphocytic cerebrospinal fluid (CSF) pleocytosis with normal glucose and elevated protein. ^5,6 Magnetic resonance imaging (MRI) of the brain may show bi-hemispheric lesions, basal ganglia lesions, or meningeal enhancement. ⁵ Approximately 50% of reported cases have been hospitalized, but deaths are rare. ^1,3,5 More chronic progressive courses may occur in those immunocompromised. ⁶

Diagnosis is typically made by serology (i.e., a positive Jamestown Canyon virus-specific IgM test in serum and/or CSF). ^1,3 Due to significant antibody cross-reactivity among the California serogroup, any positive IgM should be followed by a confirmatory plaque reduction neutralization test (PRNT). ^1,3 Rarely, Jamestown Canyon virus infection may be diagnosed through reverse transcription-polymerase chain reaction (RT-PCR) tests on serum or CSF samples from immunocompromised patients or on infected tissue. ^3,6

Treatment of Jamestown Canyon virus disease is supportive since no specific anti-virals are available. ^1,5 Intensive care may be necessary for those with refractory seizures, cerebral edema, and/or decreased consciousness.

Jamestown Canyon virus infection can be prevented by avoiding mosquito bites (e.g., wearing insect repellant, avoiding outdoors between dusk and dawn, wearing long-sleeved shirts and pants). ¹ Clinicians can contact their local and/or state health departments for questions regarding Jamestown Canyon virus disease and for assistance with testing.