It's West Nile season: Don't forget the bug spray

(AP Photo/Centers for Disease Control and Prevention, James Gathany)

By Michael Yudell

With 7 cases of mosquito transmitted West Nile Virus recently confirmed in Pennsylvania, counties around the state are warning residents to protect themselves by taking steps to avoid infection and prevent mosquito breeding. But don’t let the low number of so-far-confirmed cases fool you. Of the thirty-nine counties in the state that are part of the Pennsylvania West Nile Virus Control Program, thirty-five are considered high-risk for the virus. Making matters worse is that as climate change brings hotter, wetter, and more humid summers, we are likely to see cases of West Nile on the rise.

Most people infected with West Nile experience no symptoms, while 25 percent contract West Nile Fever, a mild flu-like illness with symptoms including fever, headache, and body ache that generally last for just a few days. A small number of cases, less than 1%, are classified as West Nile neuroinvasive disease (WNND), a dangerous condition that results in severe illness, disability, and sometimes death. According to the Centers for Disease Control and Prevention, symptoms of WNND “include headache, high fever, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, and paralysis.”

Although there are no approved drugs to treat the virus, Karen Roos from the American Academy of Neurology and a Professor of Neurology in the Indiana University School of Medicine told me that it is important that patients experiencing symptoms should seek immediate medical care. For severe cases, Roos told me that supportive care can save lives by treating the brain swelling, seizures and high blood pressure often associated with the infection. In some of these cases, damage to the nervous system can be permanent or result in death. Roos reminded me “that people over the age of 50 get sicker than younger people” from West Nile, and that babies and the immunocompromised are also vulnerable.

Here in Pennsylvania, one study estimates that between 1999 and 2010 there have been more than 50,000 cases of West Nile virus, including 255 cases of WNND. Nationwide, Texas suffered the highest number of total cases—320,000 of the virus and almost 1500 WNND infections. Some smaller, less populous states have higher incidences of cases. South Dakota has it the worst with more than 13% of its population having been infected during this period, with Wyoming, North Dakota and Nebraska not far behind in terms of the cumulative incidence of the virus.

This year’s seven confirmed cases in the Keystone state, two of which were in Delaware County, have public health officials concerned. The Pennsylvania Department of Public Health reports that “the risk for more human infections is high and will remain high through the rest of the summer and into early fall.” Because mosquitos breed in standing and stagnant water, the Department is advising residents to take the following actions to protect themselves:

  • Remove tin cans, plastic containers, ceramic pots, discarded tires or any object that could collect standing water. Drill holes in the bottom of recycling containers left outdoors.
  • Have roof gutters cleaned every year, particularly if the leaves from nearby trees have a tendency to clog the drains.
  • Turn over plastic wading pools and wheelbarrows when not in use.
  • Do not let water stagnate in birdbaths.
  • Aerate ornamental pools, or stock them with fish.
  • Clean and chlorinate swimming pools, and remove standing water from pool covers.
  • Use landscaping to eliminate standing water that collects on your property.
  • Treat standing water that cannot be eliminated with Bti products which are sold at outdoor supply, home improvement and other stores. Bti is a natural product that kills mosquito larvae, but is safe for people, pets, aquatic life and plants.

The Department is also reminding people that mosquitos can bite anytime, but are particularly active at dawn and dusk, and that insect repellant can prevent bites. So make sure that mosquitos stay out of your home by checking and repairing screens, if necessary.

Here at home, the Philadelphia Department of Public Health’s fact sheet on West Nile has more suggestions, including wearing “shoes, socks, lightweight long pants and a long-sleeved shirt when you go outside for a long time.” Philadelphia and other counties around the state will be spraying pesticides and treating sewer catch basins to kill adult mosquitos and their larvae. If you have any questions about West Nile or about mosquito spraying, you can call the city’s “Mosquito Control Hotline” at 215-685-9027.

If the West Nile outbreak in the South and Midwest are a bellwether of what’s to come, then break out the bug spray. Texas is currently facing the worst outbreak in the nation, resulting in 16 deaths statewide so far this summer. Dallas County, where ten of those deaths occurred, has declared a state of emergency. In Houston alone, 95% of mosquitos tested carry the virus.

What’s causing the so-far-unusually-bad season? Some have speculated that the severe drought across much of the country is suppressing populations of the common mosquito, leaving the Culex mosquito, a carrier of West Nile that can survive on very little water and feed on birds, to thrive.

Another factor may be climate change.

David Fisman is an epidemiologist at the University of Toronto and was an author on a 2009 paper examining how weather patterns can influence West Nile virus. Fisman told me that climate change driven warming and increases in rain and humidity will cause "already endemic levels of West Nile to be elevated relative to what it would have been with cooler weather." Fisman sees these changes "playing out dramatically" with other vector borne diseases, including lyme disease.

So put on the bug spray, dump out any standing water, wrap yourselves in mosquito netting, and educate yourself about the changing climate and its current and future impact on your life.

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