West Nile virus Agent Information Sheet

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

Agent

West Nile virus (WNV) is single-stranded RNA virus of the Flaviviridae family, genus Flavivirus. It is transmitted to humans primarily through the bite of an infected Culex mosquito. WNV was first isolated from a febrile patient in the West Nile district of Uganda in 1937 during a large epidemiologic study of Yellow Fever virus. Outbreaks in the Mediterranean basin were identified in the early 1950s and 1960s. It was identified in North America in 1999. WNV is now one of the most widely distributed arboviruses.

  • Disease/Infection
    About 1 in 5 persons infected with WNV virus become ill. Illness is usually mild with symptoms lasting for several days to a week; however, about 1 in 150 persons infected with WNV develop severe neuroinvasive disease, including meningitis, encephalitis, and acute flaccid paralysis.
  • Pathogenicity
    Causes self-limited disease. Fatality rate is approximately 10% in those with neuroinvasive disease.

      1. Special Populations at Risk
        People over 60 years of age and those with certain medical conditions, such as cancer, diabetes, hypertension, kidney disease, and people who have received organ transplants, are at greater risk for severe disease. WNV is not known to cause birth defects, but WNV infection during pregnancy may result in fetal demise.
  • Biosafety Information
    1. Risk Group/BSL
      Risk Group 2
      Biosafety level: BSL2/ABSL2
    2. Modes of Transmission
      By bite of infectious mosquitoes, mainly Culex spp. mosquitoes. Transmission may occur through blood transfusion, organ transplantation, breast-feeding, or intrauterine exposure. Lab-acquired infection also reported.

      Transmission
      Skin Exposure (Needlestick, animal bite, or scratch):Accidental parenteral inoculation, direct or indirect contact with broken skin
      Mucous Membrane Exposure Splash to Eye(s), Nose or Mouth:Direct or indirect contact with mucous membranes
      Inhalation:Uncommon but potential source
    3. Host Range/Reservoir
      Birds are primarily amplifying host. Humans are “dead-end” hosts for WNV. Horses and other vertebrates act as incidental hosts.
    4. Symptoms
      Persons infected with WNV virus are predominantly asymptomatic or have a mild illness, including abrupt onset of fever with other symptoms such as headache, body aches, joint pains, vomiting, diarrhea, or rash. Symptoms of severe illness include high fever, headache, neck stiffness, stupor, disorientation, coma, tremors, seizure, muscle weakness, vision loss, numbness, and paralysis. Recovery from severe illness may be prolonged.
    5. Incubation Period
      3 to 14 days
    6. Viability
      Susceptible to common disinfectants; 70% ethanol, 1% sodium hypochlorite, 2% glutaraldehyde, potassium permanganate, ether, and temperatures >60°C.
    7. Survival Outside Host
      Virus stable in dried blood and exudates up to several days at room temperature

Information for Lab Workers

      1. Laboratory PPE
        PPE Personal protective equipment includes but is not limited to laboratory coats or gowns, disposable gloves, safety glasses, face shield if risk of splash, and respirator (PAPR or N-95) if aerosol risk.
      2. Containment
        Research should be conducted using Biosafety Level 3 practices, equipment, and facility design. Animal studies may be performed at ABSL-3.
      3. In Case of Exposure/Disease
        1. For injuries in the lab which are major medical emergencies (heart attacks, seizures, etc…):
          1. Medical Campus: call or have a coworker call the Control Center at 617-414–4144.
          2. 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.
        2. 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.
        3. Under any of these scenarios, always inform the physician of your work in the laboratory and the agent(s) that you work with.
        4. Provide the wallet-size agent ID card to the physician.
      4. Vaccination
        None available.

Information for First Responders/Medical Personnel

    1. Public Health Issues
      Not directly transmitted from person-to-person. Standard precautions should be used.
    2. Diagnosis/Surveillance
      Monitor for symptoms. Laboratory diagnosis of WNV is accomplished by testing serum or cerebrospinal fluid to detect WNV-specific IgM antibodies. Immunoassays for WNV-specific IgM are available commercially and through state public health laboratories. WNV-specific IgM antibodies are detectable 3 to 8 days after onset of illness and persist for 30 to 90 days. If testing is performed early in the course of an illness, tests may need to be repeated on a later sample. Viral culture, RT-PCR, immunohistochemistry, and plaque-reduction neutralization tests (PRNTs) are additional tests that may be performed in reference laboratories to help determine the specific infecting flavivirus.
    3. First Aid/Post Exposure Prophylaxis
      Perform one of the following actions:

      Skin Exposure (Needlestick or scratch):Immediately go to the sink and thoroughly wash the wound with soap and water for 15 minutes. Decontaminate any exposed skin surfaces with an antiseptic scrub solution.
      Mucous Membrane Splash to Eye(s), Nose or Mouth:Exposure should be irrigated vigorously.
      Splash Affecting Garments:Remove garments that may have become soiled or contaminated and place them in a double red plastic bag.
    4. Treatment
      There is no specific medication for treatment of a WNV infection. Laboratory personnel who have been exposed to WNV should be asked to monitor for symptoms. They should also rest, drink plenty of fluids, and consult a physician. If they feel worse (e.g., develop headache, neck stiffness, disorientation, muscle weakness), they should go immediately to the hospital for evaluation. Immediate care of those with severe disease would include fluid resuscitation and supportive management of associated symptoms.
    5. References
      CDC. Laboratory-Acquired West Nile Virus Infections — United States, 2002. MMWR 2002;51(50):1133-5. (https://www.cdc.gov/mmwr/preview/mmwrhtml/mm5150a2.htm)CDC. West Nile Virus. Available at: https://www.cdc.gov/westnile/index.html. (accessed 3/9/18)Colpitts TM, Conway MJ, Montgomery RR, Fikrig E. West Nile Virus: biology, transmission, and human infection. Clin Microbiol Rev. 2012 Oct;25(4):635-48. doi: 10.1128/CMR.00045-12. Review.Yeung MW, Shing E, Nelder M, Sander B. Epidemiologic and clinical parameters of West Nile virus infections in humans: a scoping review. BMC Infect Dis. 2017 Sep 6;17(1):609. doi: 10.1186/s12879-017-2637-9.

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