West Nile Virus: Here to Stay

As Wisconsin reaches the end of its annual trudge into summer, the remnants of cabin fever send a lot of us outdoors. Beaches, parks, hiking trails and backyards beckon; soon they’ll be packed with Midwesterners doing whatever they do when parkas and boots become irrelevant. But while we’re outside basking in our day in the sun, local health authorities are reminding us to be aware of a threat that’s become part of our standard medical vocabulary.

West Nile virus has found its way to Wisconsin, and apparently it’s here to stay. According to Mohammad Almoujahed, MD, Assistant Professor of Medicine in the Medical College of Wisconsin’s Division of Infectious Diseases, “The expansion of West Nile virus indicates that it is permanently established in the Western Hemisphere.”

West Nile virus (WNV) was first discovered in 1937 in the West Nile area of Uganda – thus the name – but it didn’t make its way to North America until the summer of 1999, when it was found in the New York City area. Sixty-two people were hospitalized with the infection and 7 died. By the summer of 2001 the disease had spread to several southeastern states; sixty-six people contracted the virus and 9 died. Although no cases of human infection were confirmed in Wisconsin, the virus was found in 58 birds, most of them in Milwaukee County.

Last year, in the summer of 2002, the Centers for Disease Control and Prevention (CDC) recorded 4,156 human cases of West Nile virus in the US, with 284 deaths. Wisconsin had 52 documented human cases and 3 deaths.

Infection Rare and Usually Mild
Dr. Almoujahed reports that in most people, WNV brings on mild flu-like symptoms such as fever, body aches or headache and sometimes a rash or swollen glands. But in rare cases, the virus can enter the brain and cause encephalitis. In these cases, the infection can be fatal. There is currently no human vaccine against West Nile virus, and no specific medicine available to treat the infection.

“The chance that you will become severely ill from one mosquito bite is extremely small,” he notes. "In areas where West Nile virus has been found, very few mosquitoes (less than 1%) become infected with the virus, and less than 1% of people who get bitten and become infected will become severely ill.” As with many illnesses, the elderly and those with weakened immune systems run the highest risk of severe disease. When illness from WNV does occur, it takes from 3 to 15 days after being bitten by an infected mosquito for symptoms to appear. Although there may be a few infections reported through the year, medical facilities typically start seeing infections in July and the case count tends to peak in August and September.

Dr. Almoujahed recommends that anyone who develops symptoms such as high fever, confusion, muscle weakness and severe headaches contact their health care provider immediately.

WNV and Blood Transfusions
Because of the potential for blood transmission of WNV, Froedtert & Medical College doctors have added new parameters for transfusing blood products. “Last year during the WNV outbreak, it became clear there was a relationship between blood transfusion and the transmission of WNV infection,” says Jerome Gottschall, MD, Medical College Professor of Pathology and Medical Director of the Transfusion Service. “The CDC confirmed 21 cases of transfusion transmission of WNV by blood components from 14 donors,” he notes, with six deaths among the 21 cases.

A new blood donor screening test is expected to be available by July, before extensive human infection is expected. However, Dr. Gottschall says that if the risk of transfusion-transmitted WNV becomes significant in our community before the screening test is available, physicians may want to consider limiting non-urgent transfusions.

“It is critical to recognize that the risk of transfusion-transmitted WNV infection will always be small,” says Dr. Gottschall. “It is also critical to recognize that the life-saving benefits of medically necessary transfusions will outweigh the risk of transfusion-transmitted WNV infection in nearly all cases.”

DNR Continues Studies
In May 2003, the Wisconsin Division of Public Health (DPH) and the Wisconsin Department of Natural Resources (DNR) resumed sick/dead bird surveillance for WNV. They are collecting information on sick or dead crows, blue jays and ravens.

It’s important to remember that the virus is only transmitted by the mosquitoes that feed on birds and animals, not by the birds and animals themselves. There has not been a documented case of person-to-person or animal-to-human transmission of WNV. Despite this, and despite the rarity of serious WNV infections, caution is still very important. Authorities urge people either to stay away from dead birds or animals, handle the bodies without touching them or wear rubber gloves when handling sick or dead birds.

The DNR will also be collecting and testing bald eagles and other raptors; songbirds (not house sparrows); water birds (cranes, herons, shorebirds, pelicans, gulls, and terns); game birds (mourning dove, ruffed grouse, and wild turkey [not hunter harvested]); gray squirrels and chipmunks.

Call the Wisconsin WNV Hotline at 800-433-1610 to report a dead bird or mammal. Hotline staff will refer you to a local Wildlife Biologist to report animals other than crows, blue jays and ravens.

Protect Yourself from Mosquitoes
The most important way to prevent West Nile virus is to avoid being bitten by mosquitoes. Mosquito repellants with the ingredient DEET (N,N-diethyl-3-methyl-benzamide) have been shown to be the most effective in keeping mosquitoes away from humans.

Use a repellant that’s appropriate to your environment and activities. More mosquitoes means higher risk, so choose your product carefully. Some contain higher concentrations of DEET than others; labels will typically specify how to use the product and how long it will last once applied.

Additionally, Dr. Almoujahed recommends wearing protective clothing such as long pants, loose-fitting long-sleeved shirts and socks when outdoors, and keeping window screens in good repair when indoors. Getting rid of any standing water is also a very important step, as it eliminates a prime breeding ground for mosquitoes. Taking common-sense steps to avoid mosquito bites will greatly reduce your chances of being infected.

This article includes information from:
Medical College of Wisconsin Division of Infectious Diseases
Medical College of Wisconsin Pathology Department
US Centers for Disease Control and Prevention (www.cdc.gov)
Wisconsin Department of Natural Resources (www.dnr.state.wi.us)
National Institute of Allergy and Infectious Diseases (www.niaid.nih.gov/)
US Geological Survey (ww.usgs.gov)