West Nile Virus
What is it?
West Nile Virus (WNV) is a viral illness transmitted by mosquitoes; it is not transmitted person to person. WNV infection may produce mild flu-like illness symptoms, but it can also cause encephalitis and death. There is neither a vaccine nor a specific treatment for this illness; therefore, prevention is the only rational strategy. During 2002 to date, there have been 22 cases in Texas with no known fatalities. Because the mosquito season lasts until October and possibly longer in some Texas counties, more cases are expected.
Since mosquitoes are the vector for WNV, birds and mammals other than humans (horses, livestock, and household pets) can become infected too. Although the risk of becoming infected through contact with an infected (usually dead) animal is minimal, carcasses should be handled with gloves.
Why is this a concern in the elderly?
Although less than 1% of persons infected with WNV develop severe illness, case fatality rates range between 3% and 15%. The majority of serious WNV infections and deaths occur in persons over the age of 50; the typical age of those that develop encephalitis is 68 years and older. Advanced age and the presence of diabetes are independent risk factors that make Long Term Care (LTC) residents vulnerable to this disease. Except for children with immune disorders who are also at high risk for severe infection, younger persons who become infected tend to fare much better.
A large study in Connecticut showed that individuals over the age of 50 and those that did not speak English were also the least likely to take appropriate precautions against mosquito bites. This emphasizes the importance of the role that LTC facility staff must play in actively protecting residents from exposure to mosquitoes.
What are the signs and symptoms of infection?
The signs of WNV infection include common viral infection symptoms such as fever, muscle aches, and rash as well as more severe symptoms. Severe cases manifest signs and symptoms of central nervous system infection such as high fever, stiff neck, confusion, sensitivity to light, seizures, and coma, as well as profound muscular weakness with respiratory failure due to axonal polyneuropathy.
What can a Long Term Care Facility do to prevent WNV infections?
Work conducted by the Centers for Disease Control shows that serological evidence of infection with WNV is most common among individuals who report either spending more time outside or seeing mosquitoes indoors.
Diseases such as WNV that are transmissible by insects make having intact window screens a matter of disease prevention, and DADS reminds all Long Term Care facilities that State regulations require that facilities have screens on all operable windows.
MQA offers the following recommendations to Long Term Care facility operators on the strength of similar public health recommendations from the Centers for Disease Control, the Texas Department of Health and other state health departments:
Sources of Information:
1. Texas Department of Health Zoonosis Control Division's web page for West Nile Virus (includes reporting procedures)
2. Centers for Disease Control Division of Vector-Borne Diseases
Last updated: August 19, 2002