La Crosse encephalitis virus (LACV, LAC) Agent Information Sheet

Boston University
Research Occupational Health Program (ROHP)
617-358-7647

Agent

La Crosse encephalitis is a rare disease that is caused by a virus spread by infected mosquitoes and contaminated lab water. La Crosse (LAC) encephalitis virus (LACV) is one of a group of mosquito-transmitted viruses that can cause inflammation of the brain (encephalitis). La Crosse virus (LACV) is a California (CAL) serogroup virus, in the genus Bunyavirus, family Bunyaviridae.

Disease/Infection

LaCrosse encephalitis.

Pathogenicity

In nature, LACV is transmitted to humans through the bite of an infected mosquito (Aedes triseriatus, the eastern tree hole mosquito). Less than 1% of LAC encephalitis cases are fatal.

• Special Populations at Risk
  Outside of the laboratory, most cases of severe LACV disease occur in children under 16 years of age. People who live in or visit woodland habitats and those who work outside or participate in outdoor recreational activities in areas where the virus is circulating are at increased risk due to mosquito exposure.

Biosafety Information

Risk Group/BSL
Risk Group 2
Biosafety Level 2 Practices

Modes of Transmission
Humans contract LAC from the bite of an infected mosquito, primarily Aedes triseriatus, the eastern tree hole mosquito. The virus is maintained and amplified in Aedes triseriatus populations through transovarial and venereal transmission. Humans are dead-end hosts for the virus, i.e., they do not circulate sufficient numbers of the LAC virus in the blood stream to infect a mosquito, and the disease cannot be spread from person to person.

Host Range/Reservoir
Tree hole mosquito, squirrels, chipmunks, humans dead-end host

Symptoms
Most persons infected with LACV have no apparent illness. Initial symptoms in those who become ill include fever, headache, nausea, vomiting, and meningeal signs. Severe disease (involving encephalitis, an inflammation of the brain) occurs most commonly in children under age 16, and is often accompanied by HA, meningeal signs and seizures occur in 46% of infected individuals. Coma and paralysis occur in some cases.

Incubation Period
The incubation period is usually 5-15 days

Viability
Susceptible to disinfectants – 1% sodium hypochlorite, 2% glutaraldehyde, 70% ethanol, formaldehyde. Sensitive to heat (infectivity lost at 50-60°C for at least 30 min)

Survival Outside Host
Does not survive for long periods out of host

Information for Lab Workers

Laboratory PPE

Personal protective equipment includes but is not limited to laboratory coats or gowns, disposable gloves, and safety glasses.

Containment

BSL-2 facilities, equipment, and operational practices for work involving infectious or potentially infectious materials, animals, or cultures. Procedures that are likely to generate aerosols should be conducted in a biosafety cabinet. Practices may be enhanced based on risk assessment.

In Case of Exposure/Disease

• For injuries in the lab which are major medical emergencies (heart attacks, seizures, etc…):
  • Medical Campus: call or have a coworker call the Control Center at 617-414–4144.
  • Charles River Campus: call or have a coworker call campus security at 617-353-2121.
    You will be referred to or transported to the appropriate health care location by the emergency response team.
• For lab exposures (needle sticks, bite, cut, scratch, splash, etc…) involving animals or infectious agents, or for unexplained symptoms or illness call the ROHP 24/7 hour number (1-617-358-ROHP (7647); or, 8-ROHP (7647) if calling from an on-campus location) to be connected with the BU Research Occupational Health Program (ROHP) medical officer. ROHP will refer you to the appropriate health care location.
• Under any of these scenarios, always inform the physician of your work in the laboratory and the agent(s) that you work with.
• Provide the wallet-size agent ID card to the physician.

Vaccination

There is no vaccine.

Information for First Responders/Medical Personnel

Public Health Issues

Person to person transmission is not documented. Standard precautions should be utilized.

Diagnosis/ Surveillance

Preliminary diagnosis is often based on the patient’s clinical features and known exposures. Laboratory diagnosis of arboviral infections is generally accomplished by testing of serum or cerebrospinal fluid (CSF) to detect virus-specific IgM and neutralizing antibodies. Only a few state laboratories or other specialized laboratories, including those at CDC, are capable of doing this specialized testing.

First Aid/Post Exposure Prophylaxis 

Perform one of the following actions:

Prevention of mosquito bites is key.

Treatment

Patients with suspected LAC encephalitis should be hospitalized, appropriate serologic and other diagnostic tests ordered, and supportive treatment (including seizure control) provided. No specific antiviral treatment for clinical LACV infection is available, Ribavirin may be considered.

References

Biosafety in Microbiological and Biomedical Laboratories; Deborah E. Wilson, DrPH, CBSP Director Division of Occupational Health and Safety National Institutes of Health Bethesda, Maryland L. Casey Chosewood, M.D. Director Office of Health and Safety Centers for Disease Control and Prevention Atlanta, Georgia; US Government Printing Office, Washington DC. 5^th Edition; 2007 

Control of Communicable Diseases Manual. David L. Heymann. Washington DC, USA: American Public Health Association Press, 19^th edition, 2008

CDC BMBL: https://www.cdc.gov/labs/pdf/SF__19_308133-A_BMBL6_00-BOOK-WEB-final-3.pdf

Revised: 7/20/2012