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Fight the Bite SloganCalifornia serogroup viruses

(California encephalitis, La Crosse encephalitis, Jamestown Canyon)

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California serogroup viruses including California encephalitis, Keystone, La Crosse, Jamestown Canyon, snowshoe hare, and trivittatus are all mosquito-borne arboviral infections. In the United States, La Crosse virus (LACV) is the most common of the California serogroup viruses. Both LACV and Jamestown Canyon virus (JCV) infections have been reported in Wisconsin. People infected with California serogroup viruses may have no apparent symptoms. Some people have symptoms of illness that may range from mild fever to encephalitis or mengioencephelitis.

La Crosse encephalitis disease mostly occurs in the Midwestern, mid-Atlantic, and southeastern states of the United States. LACV was first isolated in1963 in children from La Crosse, Wisconsin. From 2002 to 2008, 68 cases of La Crosse encephalitis (average 10 cases/year) were reported in Wisconsin. Initial symptoms of illness may include fever, headache, nausea, vomiting, and tiredness. Some people may develop severe neuroinvasive disease (disease that affects the nervous system). Severe symptoms often involve encephalitis (an inflammation of the brain) and can include seizures, coma, and paralysis. Historically, most of the LACV infections in Wisconsin have been reported in children less than 16 years old; however, recent surveillance data show that both adults and children can become ill with La Crosse encephalitis.

Jamestown Canyon virus was first recognized as causing human illness in 1980 and occurs throughout temperate climate regions of North America. JCV infections have been rarely reported in Wisconsin, but because of the unavailability of a commercial test to detect the virus, the infection may be unrecognized and under reported.

Wisconsin acquired diseases Travel related diseases

California encephalitis 
La Crosse encephalitis
Jamestown Canyon

Snowshoe hare 

Arboviral diseases home

General information

Arboviral infections fact sheet - Hmong - Spanish

Data and statistics

Graph of total cases of California serogroup viruses in Wisconsin from 2008 to 2013 by year of onset.


Some tips to protect yourself:

  • Use effective mosquito repellant and apply according to the label instructions.
  • Wear long-sleeved shirts, long pants, socks, and shoes.
  • Mosquitoes may bite through thin clothing, so spraying clothes with a repellent containing permethrin or DEET will give extra protection. These repellants are the most effective and most studied.
  • Avoid being outside during times of high mosquito activity, specifically around dawn and dusk.
  • Keep window screens repaired so that mosquitoes cannot enter your home.
  • Dispose of discarded tires, cans, or plastic containers left outside that may contain standing water.
  • Drain standing water from pool or hot tub covers.
  • Turn over plastic wading pools and wheel barrows when not in use.
  • Change the water in bird baths, pet dishes and wading pools every 3-4 days.
  • Keep drains, ditches and culverts clean of trash and weeds so water will drain properly.
  • Clean gutters to ensure they drain properly.

For more information, Using Insect Repellants Safely - CDC

Information for health professionals

This is a Wisconsin disease surveillance category II disease: 
Report to the patient's local public health department electronically, through the Wisconsin Electronic Disease Surveillance System (WEDSS), by mail or fax using an Acute and Communicable Disease case report F-44151 or by other means within 72 hours upon recognition of a case.
Information on communicable disease reporting

Wisconsin case reporting and public health follow-up guidelines Arboviral diseases EpiNet 
Arbovirus case report form
2014 Arbovirus management protocol  

Laboratory guidance

  • Specimens should be tested using an arbovirus panel because arboviruses have similar clinical symptoms and serologic testing often results in cross-reactive antibodies among agents. Positive arbovirus specimens tested by a commercial laboratory should be forwarded to the Wisconsin State Laboratory of Hygiene (WSLH) for confirmatory panel testing (WNV, SLE, LAC, EEE, and WEE). Due to unavailability of a commercial test for Jamestown Canyon virus (JCV), the WSLH will forward JCV testing requests to the CDC.
  • Additional laboratory guidance 

Training and additional resources 


Wisconsin Local Health Departments - Regional offices - Tribal agencies

Diep Hoang Johnson Vectorborne Disease Epidemiologist
Wisconsin Division of Public Health 
Bureau of Communicable Diseases
(Phone 608-267-0249)  (Fax 608-261-4976)

    Last Revised: August 01, 2014