STORY BYNo new cases of West Nile Virus (WNV) have yet been diagnosed in Americans in 2003. However, its confirmation in other species in at least 20 states is causing speculation as to what to expect in terms of human cases, especially during August and September when the majority of human cases occur.
“I think it’s going to become an endemic disease, which we’ll learn to manage as we have other communicable infections,” said Luis Ostrosky-Zeichner, MD, assistant professor of medicine, Division of Infectious Diseases at the University of Texas Medical School at Houston.
“WNV spread to just east of the Rocky Mountains last year, so it will be interesting to see what happens this year,” said Kristy M. Lillibridge DVM, assistant professor in epidemiology at the UT School of Public Health at Houston, who previously worked on WNV for the US Centers for Disease Control. “There are many environmental factors that will determine the extent of virus activity this year.”
Last year 4,161 Americans were reported to have been infected with WNV, with 277 fatalities. While an estimated 80 percent of infected individuals do not even develop symptoms, about one in every 150 becomes seriously ill. Those at special risk include the elderly, individuals with compromised immune systems, diabetics and people with hypertension. About one in 1,000 infections leads to fatal encephalitis (inflammation of the brain).
WNV is a mosquito-borne virus transmitted to humans, birds, horses, and other animals through mosquito bites. While simple preventive measures can be taken to minimize risk, the association of WNV transmission through blood transfusions and organ transplants during the past year identified a new area of concern. Since most people do not develop symptoms, individuals could donate blood without knowing they are infected. Some data suggest the virus is present in the blood from one to 11 days after the infecting mosquito bite.
To address this issue, the US Food and Drug Administration (FDA) last year called for development of blood-donor screening tests for WNV, held a scientific meeting, and issued an updated guidance for industry in May. The FDA is currently allowing the investigational new drug applications for products of two companies to proceed. Both are starting clinical trials this summer.
As a result, most of the US blood supply will be tested for the presence of WNV, which should minimize the risk of acquiring the virus via transfusion. One screening product, a fully automatic polymerase chain-reaction-based system developed by Roche Molecular Diagnostics, will be tested at the Gulf Coast Regional Blood Center in Houston. Beginning the week of June 16, the blood of all donors will be tested, with approximately 1500 to 2000 samples tested each night. Another trial to begin in July will investigate a nucleic acid test developed by GenProbe, Inc., a San Diego-based company. Test sites for this investigation cover approximately 80 percent of the US blood supply.
Clinical trials for a vaccine are also underway. Current studies are investigating the effectiveness of immunoglobulin and interferon. Supportive measures continue to be the mainstay of treatment.
“If a vaccine becomes available, it would be worthwhile to use it in areas where there are a lot of cases,” said Ostrosky-Zeichner. “Another area of interest is genetics. There may be a genetic explanation for the susceptibility of some individuals to extreme symptoms.”
Mosquito-control organizations are currently testing dead wild birds as part of a national monitoring effort to collect data on this year’s outbreak. No one knows how many wild birds were affected last year, but 14,122 dead birds tested positive. Only 27 percent of dead birds in 2002 were submitted for testing. Estimates suggest the actual number of dead birds to be probably 100 to 1000 times higher. Some states also monitor domestic chicken flocks.
In addition, mosquito surveillance and prevention are being undertaken on a local basis. Harris County has one of the most extensive testing plans in the country, with weekly monitoring of 200 storm-sewer and gravid traps to be implemented by July.
To minimize risk, the best course of action, according to Lillibridge, is to observe the four D’s: Deet (insect repellent), dress (long sleeves and pants), dusk and dawn (avoidance of these high-risk times outdoors) and drain (standing water). It’s also good to make sure window screens are in good repair to avoid mosquitoes inside the house.
“Don’t forget preventive measures,” she said. “We’ll all be better off.”
UPDATED: 7-07-2003
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Dr. Luis Ostrosky-Zeichner is an assistant professor in the Division of Infectious Diseases at the UT Medical School.
See Dr. Ostrosky also at:
Dr. Kristy Murray is an assistant professor in epidemiology at the UT School of Public Health.
See Dr. Murray also at:
Men: Pay Attention
to Your Bicycle Seat
Men who bike more than three hours a week should be aware that standard bicycle seats, ridden for extended periods, can cause temporary numbness and, in some, more serious problems, such as erectile dysfunction.
Such problems are caused by compression of an artery and a nerve connected to the penis. New seat designs to minimize compression are now available.
Other preventive measures you can incorporate:
