Friday, September 7, 2012

How hard should I worry about West Nile virus?

West Nile virus has taken lives in several states, but how worried should we be? What can we do beyond stocking up on Deep Woods Off and staying away from ponds?

On the one hand, West Nile fever and severe West Nile disease are scary, having caused 87 deaths nationwide. The 1,993 infections so far this year represent the highest number ever reported through the first week in September. The virus is carried by 64 different species of mosquito and has now spread through 48 states, including all of Alabama. Furthermore, the CDC says the number of West Nile virus infections is “grossly underreported.”

On the other hand, most people infected with WNV have no symptoms at all, let alone become ill, and you can protect yourself with insect repellant. To put the WNV numbers in perspective, even the low end of the CDC’s estimate for annual flu-related deaths is 3,000, with the average closer to 10 times that.

Maybe what makes WNV so distracting is that it’s unpredictable from year to year and from person to person based on their age and other factors. I have kids aged five and eight, and my WNV worry meter amped down when I saw that cases in children are rare. But with a mother approaching 70 and a grandma in her 90s, my concern grew again when I learned than more than half of West Nile deaths are in people aged 70 or older, who have weaker immune systems.

The severity of WNV infection in any given year depends on things like the number of mosquitoes out there, which depends on how cold the previous winter was, says Qianjun Li, Ph.D., assistant professor in the UAB School of Medicine’s Division of Infectious Diseases. Last winter was warm, so the mosquito population has swelled.

Also important is the outcome of the annual evolutionary battle between the virus and the immune defenses of birds and humans, says Li. Viruses change their makeup with every generation, forcing immune defenses to scramble to recognize the new versions. One side may gain the upper hand in any given year. Complicating matters, some people’s bodies and brains react to viral invasion so strongly that that the reaction itself threatens to become life-threatening. The fever and inflammation that come with viral infections are the body’s doing.

Despite the media coverage, WNV disease is rare. That means that government funding for related research is limited, and the willingness of pharmaceutical companies to invest in therapies or vaccines is even more constrained, says Li. Thus, the work moves slowly, with the arrival of both vaccines and antiviral medications, in Li's estimation, more than five years away.

A visit to Clinical Trials.gov reveals six vaccine trials and two antiviral drug trials underway in WNV, but none of them will deliver immediately. As pointed out in a recent piece by my colleague Nicole Wyatt, self-protection will be the key during the many WNV seasons that will pass before vaccines and treatments arrive.

Li’s research focuses on mosquito-transmitted viruses, such as yellow fever, dengue fever and WNV. He is exploring the theory that human immune response against WNV infection may become deadly as chemicals released by immune cells to fight the infection — chemokines and cytokines — build up to the point that they kill surrounding human tissue.

He is also working to develop tests that can accurately measure whether WNV drugs currently under development are nontoxic and effective, lessons that may apply to WNV relatives like the dengue virus. The ultimate goal of Li’s work is to understand the interactions between viruses, mosquitoes and the immune systems of birds and humans, and to develop new anti-viral therapeutics that prevent and control infections.

Li recommends that those interested in learning more visit the CDC West Nile page or the West Nile Virus Information Exchange.

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