West Nile Virus

West Nile Virus (WNV) is established as a seasonal epidemic in North America that flares up in the summer and continues into the fall. WNV is spread by the bite of an infected mosquito. Mosquitoes 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 directly from an infected person through blood transfusions, organ transplants, breastfeeding and during pregnancy from mother to baby. WNV is not spread through casual contact such as touching or kissing a person with the virus.

What Are the Symptoms of WNV?

Few people develop serious symptoms. About 1 in 150 people infected with WNV will develop severe illness. The severe symptoms can include high fever, headache, neck stiffness, disorientation, coma, tremors, convulsions, muscle weakness, vision loss, numbness and paralysis. These symptoms may last several weeks, and neurological effects may be permanent. There may be milder symptoms in some individuals. Up to 20 percent of the people who become infected will have 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 to as long as several weeks. A majority of people, approximately 80 percent, who are infected with WNV will not show any symptoms at all, but there is no way to know in advance if you will develop an illness or not.

How Soon Do Infected People Get Sick?

People typically develop symptoms between 3 and 14 days after they are bitten by the infected mosquito.

What Can I Do to Prevent WNV?

• The easiest and best way to avoid WNV is to prevent mosquito bites. When outdoors, use repellents containing DEET, picaridin, IR3535, some oil of lemon eucalyptus or paramenthane-diol. Follow the directions on the package.
• Many mosquitoes are most active from dusk to dawn. Be sure to use insect repellent and wear long sleeves and pants at these times or consider staying indoors during these hours.
• Make sure you have good screens on your windows and doors to keep mosquitoes out.
• Get rid of mosquito breeding sites by emptying standing water from flower pots, buckets and barrels. Change the water in pet dishes and replace the water in bird baths weekly. Drill holes in tire swings so water drains out. Keep children’s wading pools empty and on their sides when they are not being used.

How Is WNV Infection Treated?

There is no specific treatment for WNV infection. In cases with milder symptoms, people experience symptoms such as fever and aches that pass on their own, although illness may last weeks to months. In more severe cases, people usually need to go to the hospital where they can receive supportive treatment including intravenous fluids, help with breathing, and nursing care.

What Should I Do if I Think I Have WNV?

Milder WNV illness improves on its own, and people do not need to seek medical attention for this infection though they may choose to do so. If you develop symptoms of severe WNV illness, such as unusually severe headaches or confusion, seek medical attention immediately. Severe WNV illness usually requires hospitalization. Pregnant women and nursing mothers are encouraged to talk to their doctor if they develop symptoms that could be WNV.

What Is the Risk of Getting Sick from WNV?

People over the age of 50 are more likely to develop serious symptoms of WNV if they do get sick and should take special care to avoid mosquito bites. Being outside means you’re at risk. The more time you’re outdoors, the more time you could be bitten by an infected mosquito. Pay attention to avoiding mosquito bites if you spend time outside, either working or playing. Risk through medical procedures is very low as all donated blood is checked for WNV before being used. The risk of getting WNV through blood transfusions and organ transplants is very small, and should not prevent people who need surgery from having it. If you have concerns, talk to your doctor.

What Is MCHD Doing About WNV?

The Division of Communicable Disease Control and Prevention conducts surveillance activities on all reports of West Nile Disease to investigate and monitor the number of human cases in Montgomery County. Data on suspected and confirmed cases is shared with the Division of Environmental Field Services for the purpose of vector control. The Division of Environmental Field Services practices an integrated mosquito management (IMM) approach towards combating the spread of WNV. Our IMM program consists of public education, breeding source reduction, complaint response, and the control of both larval and adult mosquitoes.

The public plays a vital role in winning the battle over WNV. We ask the public to maintain their property in a manner that is not conducive to mosquito breeding. The presence of stagnate water is necessary for the immature stages (egg, larva, and pupa) of mosquito development. We recommend that residents take precautions to clear away mosquito breeding areas around their homes by eliminating standing water from their property. MCHD also encourages residents to mosquito-proof their homes by replacing torn screens in doors and windows; cleaning out gutters; and by emptying and turning over containers that could collect water allowing mosquitoes to breed. Anything that can hold water for four days can breed 1000’s of mosquitoes. Eliminating standing water has proven effective in controlling WNV.

Adult mosquito surveillance is conducted throughout the county utilizing three different types of traps. The traps give us information regarding mosquito population, species present, effectiveness of control measures, and viral activity. MCHD will soon begin routine larviciding of public properties throughout the summer months. If the WNV activity poses a risk to human health, adulticiding or spraying may be necessary in targeted areas.

Adapted from the CDC’s “West Nile Virus (WNV) Fact Sheet”