Genesee County Health Department

Better Life Through Better Health

West Nile Virus Update

West Nile virus (WNV) is a potentially serious illness. Experts believe WNV is established as a seasonal epidemic in North America that flares up in the summer and continues into the fall.  In 2003, there were a total of 9862 cases of WNV in the U.S. , with 264 deaths; Colorado had the highest number of cases in 2003 with 2947 WNV cases and 63 deaths.  Michigan had 19 WNV cases in 2003 with 2 deaths.  As of June 1, 2004 , 2 cases of WNV have been reported in the U.S, one each from Arizona and New Mexico . 

About one in 150 people infected with WNV will develop severe illness. The severe symptoms can include high fever, headache, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, vision loss, numbness and paralysis. These symptoms may last several weeks, and neurological effects may be permanent.  Up to 20 percent of the people who become infected will display symptoms which can include fever, headache, body aches, nausea, vomiting, and sometimes swollen lymph glands or a skin rash on the chest, stomach and back. Symptoms can last for as short as a few days, though even healthy people have been sick for several weeks.  Approximately 80 percent of people (about 4 out of 5) who are infected with WNV will not show any symptoms at all.

Most often, WNV is spread by the bite of an infected mosquito. Mosquitoes are WNV carriers that become infected when they feed on infected birds. Infected mosquitoes can then spread WNV to humans and other animals when they bite.  In a very small number of cases, WNV also has been spread through blood transfusions, organ transplants, breastfeeding and even during pregnancy from mother to baby.  WNV is not spread through casual contact such as touching or kissing a person with the virus.

There are no commercially available vaccines for the prevention of West Nile virus. Prevention of arboviral diseases like West Nile virus centers around controlling exposure to mosquitoes and avoiding mosquito bites. 

Patients presenting with 1) viral encephalitis or meningitis, 2) Guillain-Barre syndrome, especially with atypical features, such as fever, altered mental status, and/or a pleocytosis and 3) febrile illness of sudden onset often accompanied by malaise, anorexia, nausea, vomiting, headache, myalgia, rash, lymphadenopathy and eye pain need testing for arboviral serology.  The Michigan Department of Community Health (MDCH) conducts testing for the 4 mosquito-borne viruses that can cause illness in humans in Michigan .  This Arbovirus Serology panel includes West Nile virus (WNV), St. Louis encephalitis virus (SLE), La Crosse encephalitis virus (LC), and Eastern Equine encephalitis virus (EEE).  The laboratory test most commonly used for WNV measures antibodies (IgM antibodies) that are produced at an early stage in a person infected with WNV.  These IgM antibodies can be measured in blood serum or in cerobrospinal fluid.  Cerobrospinal fluid is the preferred specimen for testing.  The initial testing takes two days to perform and is repeated in duplicate if a positive result is obtained.  A preliminary report is generated within 72 hours of receipt of the sample and a confirmed positive result is released within 5 days of receipt of the sample.

Presence of IgM antibodies in a single serum sample will not confirm a recent infection, because IgM antibodies can persist in serum for up to 500 days post-onset. Patients who have been recently vaccinated against or recently infected with related arboviruses or those who had a WNV infection in the 2002 outbreak might have positive WNV results unrelated to recent WNV infection. A single serum sample will be held for testing until submission of a convalescent serum sample.  Both an acute serum sample (2.5 ml each) drawn at least 8 days post onset of symptoms and a convalescent serum specimen drawn at least 22 days post onset should be submitted.  Specimens should be submitted to the Michigan Department of Community Health (MDCH) via U.S. postal service, FedEx, UPS, or courier. Transportation may be at ambient temperatures. Specimens must be submitted in plastic tubes only.  Glass tubes are not accepted. For specific information on specimen submission, contact MDCH at 517-335-8059.