West Nile virus is making its return in the warm weather. Rockland County in New York is one of a number of areas over 35 states in which there have been reports of infection or signs that mosquitoes are carrying the disease. As of this week, New York has joined Arizona, California, Colorado, Georgia, Iowa, Louisiana, Mississippi, Missouri, Nebraska, New Mexico, Oklahoma, South Dakota, Tennessee, Texas, and Wisconsin in having reported West Nile virus infections in human beings to the Centers for Disease Control. In 2012, there were 107 cases of West Nile in New York State, and nine resultant deaths. Health officials say the appearance of the virus in Rockland was the first in the state this year.
West Nile virus doesn’t usually affect human beings; other than the mosquitoes that are carriers, birds are the most commonly infected animals. Infection with the virus may not have any symptoms. Only about one in every 150 people to become infected with the virus actually gets sick from it, mostly children and the elderly. When symptoms do appear, they are often mild—headache and skin rash, most commonly. It was strictly a tropical disease until the very end of the 20th century, only coming northward in the 1990s. There were more than 25 times as many cases in the United States in 2002 as in the three previous years combined, and nearly 16 times as many deaths. The good news is that the mortality rate is dropping; only four percent of people who got sick in 2012 died, compared to 15 percent in 2001.
There is no cure for West Nile disease. Preventing it means eliminating the mosquitoes responsible for spreading the disease. On an individual level, window screens and insect repellant are the tools people use, protecting themselves from the insects. Elimination of standing water—birdbaths, tire swings, persistent puddles—denies them a place to gather. In addition, health officials in many places conduct eradication campaigns, eliminating the mosquitoes for good.
Interestingly, while West Nile virus is related to the pathogen responsible for Dengue fever, the same prevention methods don't necessarily work on both. In fact, a mosquito bacteria that blocks transmission of Dengue fever to humans has the exact opposite effect on West Nile virus. In a study, mosquitoes protected against Dengue virus had higher than normal West Nile infection rates, the opposite of what the researchers had expected.