West Niles Virus Begins to Appear in Humans - Kansas, S. Dakota, Missouri

June 28, 2005 – The Centers for Disease Control and Prevention says the first human case of West Niles virus (WNV) for 2005 was confirmed last week in Kansas. By week’s end health officials in South Dakota said they had confirmed two cases there and one case was identified by officials in Missouri. This seasonal mosquito-born disease is most dangerous for senior citizens and baby boomers over the age of 50.

Since 1999, when WNV was first identified in the United States, WNV has caused nearly 17,000 cases of human illness, including more than 650 deaths. Although people of any age can become severely ill, the risk is highest for persons age 50 and over or recipients of solid organ transplants.

In 2004, 2,535 total human cases and 98 deaths were reported to CDC, with the largest number of cases in Western states. Cases reported to CDC were highest in 2003, with 9,862 human illnesses and 264 deaths.

While Kansas is the first state to report human WNV activity, infection in birds, mosquitoes or horses has already been reported from fourteen states this year, according to the CDC.

"This season’s first human case of West Nile virus reminds us of the importance of taking precautions to avoid becoming ill," said Dr. Lyle Petersen, director of CDC’s Division of Vector- borne Infectious Diseases. "It’s impossible to predict what this year’s season will hold. So everyone who spends time outdoors should take steps to protect themselves from mosquito bites and West Nile virus."

Simple measures can help prevent infection: avoid mosquito bites by using insect repellents and protect your home by emptying standing water and installing screens. People can also help their communities by supporting community-based mosquito control programs. In many places, people can report dead birds to local health authorities to help with disease monitoring activities.

CDC recently expanded the list of active ingredients it recommends for protection against mosquito bites. In addition to DEET and permethrin, repellents containing picaridin and oil of lemon eucalyptus have recently been found to provide reliable and long-lasting protection from mosquito bites.

As of 2005, WNV had been reported at some time in all states except Hawaii and Alaska. (Washington state has reported only animal activity one year, in 2002.) The "hot spots," that is, places with high numbers of human cases, of WNV activity have changed each year, but virus activity has generally continued locally each year after cases are reported.

Mosquitoes become infected with WNV when they feed on infected birds, and the virus may be transmitted when an infected mosquito bites a human. WNV transmission through transplanted organs, transfused blood, from mother to fetus and likely transmission to infants through breast milk were also identified in 2002. Routine screening of blood donations for WNV since 2003 has greatly reduced the risk of WNV infection through transfused blood.

About two of every 10 people infected by a mosquito develop milder WNV symptoms such as fever, aches, nausea and vomiting. About 1 in 150 people infected with WNV develop more serious symptoms and West Nile virus can be fatal.

Promising New West Nile Therapy Cures Disease in Mice

A newly published paper by researchers at Washington University in St. Louis points to a promising treatment for West Niles virus. This research, published by Nature Medicine, was funded in part by the National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health.

The research team developed an infection-fighting antibody that mimics one produced by people whose immune systems successfully fend off the West Nile virus. The researchers tested their antibody in mice and say its success warrants further development and testing in people with West Nile disease.

Scientists do not know why some people infected with West Nile virus have no symptoms or a mild flu-like illness, while in others the virus invades the central nervous system and causes paralysis or coma. "We could give this antibody to mice as long as five days after infection, when West Nile virus had entered the brain, and it could still cure them," says Washington University senior investigator Michael Diamond, M.D., Ph.D., who headed the research team. It also completely protected the mice against death."

The researchers decided to develop the potential treatment — known as a monoclonal antibody — after finding that antibodies taken from the blood of people who recovered from West Nile fever could cure mice infected with West Nile virus.

The Washington University scientists made 46 monoclonal antibodies against West Nile virus and then eliminated the less effective ones through a tedious molecular-level screening process. They then turned to Rockville, Maryland-based MacroGenics Inc., to create a human-like version of the most effective antibody. Macrogenics stitched the part of the antibody that cripples the West Nile virus into the scaffold of a human antibody. The monoclonal antibody was several hundred times more potent in cell culture tests than antibodies obtained from people who had recovered from West Nile virus infection.

What you need to know about protection from West Niles virus

When dealing with West Nile virus, prevention is your best bet. Fighting mosquito bites reduces your risk of getting this disease, along with others that mosquitoes can carry. Take the commonsense steps below to reduce your risk:

avoid bites and illness;
clean out the mosquitoes from the places where you work and play;
help your community control the disease.

Something to remember: The chance that any one person is going to become ill from a single mosquito bite remains low. The risk of severe illness and death is highest for people over 50 years old, although people of all ages can become ill.

Avoid Mosquito Bites
Apply Insect Repellent Containing DEET (Look for: N,N-diethyl-meta-toluamide) to exposed skin when you go outdoors. Even a short time being outdoors can be long enough to get a mosquito bite. For details on when and how to apply repellent, see Insect Repellent Use and Safety in our Questions and Answers pages. See also Using Insect Repellent Safely from the EPA.
Clothing Can Help Reduce Mosquito Bites When possible, wear long-sleeves, long pants and socks when outdoors. Mosquitoes may bite through thin clothing, so spraying clothes with repellent containing permethrin or DEET will give extra protection. Don't apply repellents containing permethrin directly to skin. Do not spray repellent containing DEET on the skin under your clothing.
Be Aware of Peak Mosquito Hours The hours from dusk to dawn are peak mosquito biting times for many species of mosquitoes. Take extra care to use repellent and protective clothing during evening and early morning -- or consider avoiding outdoor activities during these times.

Mosquito-Proof Your Home
Drain Standing Water Mosquitoes lay their eggs in standing water.Limit the number of places around your home for mosquitoes to breed by getting rid of items that hold water. Need examples? Learn more on the Prevention of West Nile Virus Question and Answer page.
Install or Repair Screens Some mosquitoes like to come indoors. Keep them outside by having well-fitting screens on both windows and doors. Offer to help neighbors whose screens might be in bad shape.
Help Your Community
Report Dead Birds to Local Authorities Dead birds may be a sign that West Nile virus is circulating between birds and the mosquitoes in an area. Over 130 species of birds are known to have been infected with West Nile virus, though not all infected birds will die. It's important to remember that birds die from many other causes besides West Nile virus. By reporting dead birds to state and local health departments, you can play an important role in monitoring West Nile virus. State and local agencies have different policies for collecting and testing birds, so check the Links to State and Local Government Sites page to find information about reporting dead birds in your area. Click here for more info about reporting dead birds and dealing with bird carcasses.
Mosquito Control Programs Check with local health authorities to see if there is an organized mosquito control program in your area. If no program exists, work with your local government officials to establish a program. The American Mosquito Control Association can provide advice, and their book Organization for Mosquito Control is a useful reference. More questions about mosquito control? A source for information about pesticides and repellents is the National Pesticide Information Center, which also operates a toll-free information line: 1-800-858-7378 (check their Web site for hours).
Clean Up Mosquito breeding sites can be anywhere. Neighborhood clean up days can be organized by civic or youth organizations to pick up containers from vacant lots and parks, and to encourage people to keep their yards free of standing water. Mosquitoes don't care about fences, so it's important to control breeding sites throughout the neighborhood.
Find out more about local prevention efforts Find state and local West Nile virus information and contacts on the Links to State and Local Government Sites page.

More information about WNV can be found at www.cdc.gov/westnile.

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