Thursday, August 16, 2012

West Nile Virus in NC, by Mike Waldvogel

Many of you probably saw or read reports about increased incidences of West Nile Virus across the U.S. with the notable exception of a few states, including North Carolina. However, Wayne County has reported a death attributed to West Nile Virus. At this point, there are only a few details being provided about the person which is to be expected due to health records privacy laws. However, the announcement from the Wayne County Health Director’s office (as reported by the Goldsboro News-Argus) described the victim as “elderly."

Only about 1% of people who become infected develop severe illness, and many people may not become sick at all. In cases of people who do develop symptoms (which takes 3-14 days), many of them may not attribute it to the virus until it becomes severe. Among people that develop severe illness (i.e., excluding those individuals who exhibit minimal or no symptoms), the mortality rate ranges from about 3% to 15%, with the rate being highest among the elderly (as likely the case mentioned above).

West Nile Virus occurs far less frequently in people in North Carolina as compared to other nearby states and it is far less frequent here than other mosquito-borne diseases such as Eastern Equine Encephalitis (EEE) and LaCrosse Encephalitis (LAC). EEE is more common in eastern NC while LAC is found primarily in western NC. Birds are the “amplifying hosts” for the virus, which basically means that infected mosquitoes transmit the virus to birds which are in turn bitten by other mosquitoes which acquire the virus and spread it to even more
birds. Some mosquitoes species feed primarily on birds but the species that will readily feed on both birds and mammals are the ones that pose the risk of spreading the disease to people. The mosquito species that transmit West Nile Virus tend to breed in wastewater
collection areas and stagnating catch-basins. You can also find them breeding where water collects after storms and begins to stagnate with the abundant organic matter present. So, one obvious approach for residents is to make sure that they clear stagnating water sources on their property. It doesn’t matter if this water is on a 1000 acre farm or on a 0.1 acre home lot; water that collects and stagnates has the potential to become a mosquito breeding site. Across most of North Carolina, the Asian tiger mosquito remains our most common pest species and it will exploit similar pools of stagnating water on the ground and in man-made objects.

As I mentioned a few weeks ago, substantial rainfall (as we have seen recently in many areas) is inevitably going to lead to a rise in mosquito activity and the first response by individuals should focus on disrupting those breeding pools rather than worrying about what to spray in their yard. These were some of the particular points I mentioned previously, but they're worth noting again:

  • Bird baths - simply flush them out with a garden hose and you flush out the mosquito larvae in the process. Plus, the birds will appreciate the fresh water. For horse owners with water troughs near stalls or out in pastures, one option is to use a product such as "Mosquito Dunks" which contain the bacteria Bacillus thuringiensis israelensis, which kills the mosquito larvae (not the adults). Although you can use them in outdoor water bowls for pets, it is far simpler (and better for your animals) if you “tip and toss” the water from the bowl and replenish it with fresh water *daily*.
  • Old cans, tires, etc. - empty them and get rid of them (legally, don't simply toss them along the highway to become someone else’s problem).
  • Outdoor flower pots - empty the water from the dishes/trays underneath them. Your plants have plenty of water without the overflow. This also helps reduce fungus gnat problems in the plant soil.
  • Remove all of that built-up debris from your gutters. The water and decaying material attract mosquitoes.
  • Rain barrels – if you collect water from your gutters or some other system, make sure the barrel is screened to keep out debris and mosquitoes.
  • Tarps that cover your boat, grill, firewood, etc. also collect pockets of water that can remain for 1-2 weeks.
  • The bed of that '57 Ford pickup that you've been “restoring” for the last 25 years can collect water particularly if the tailgate faces uphill in your yard.
  • Kids' pools - if they're not being used by kids, they're probably being used by the mosquitoes (and maybe some toads) – empty them. The same thing applies to pools (in ground or above ground) that aren't maintained (e.g., pools on abandoned or foreclosed properties).
  • Drainage ditches - they're meant to collect storm water temporarily. Keep them free of debris so that water flows and has time to filter into the soil.
  • Decorative fish ponds can be a source of mosquitoes if they contain a lot of vegetation that provides hiding places for the mosquito larvae. “Mosquito Dunks” are an option here.
  • Tree holes - when limbs fall off trees, the remaining hole in the trunk can collect water. Flush that out or put a small piece of a mosquito dunk into it.
Another critical matter – personal protection. The majority of mosquito-borne disease incidences, whether they’re human or equine, are due to a lack of personal protection. Horse owners need to spend the time and money to get their horses vaccinated against EEE. For
us two-legged creatures, we simply need to take precautions when we’re outdoors for work or recreation. If it’s too uncomfortable to wear long-sleeved shirts and long pants, then cover all *exposed* areas of the skin with an insect repellent (see 

A few other important points about using repellents:
  • Do not put repellent on skin that will be covered by clothing.
  • Children spend a lot of time outdoors, particularly when school is not in session. The greater the amount of time spent outdoors can increase the likelihood of getting bitten by a mosquito (and potentially a higher likelihood of being bitten by an infected mosquito). Before applying a repellent to a child, read the label carefully to make sure that it contains concentration appropriate for use on children.
  • When using repellents on children - you should apply the product to your hands and then rub it on their arms, legs, neck, etc. If you allow your child to rub repellent on their arms and legs, they need to wash their hands immediately afterwards because they will inevitably forget and either rub their eyes or stick their fingers in their mouths.
One other point that I mentioned a few weeks ago - mosquitoes have no concept of property lines. They are simply out there looking for a blood meal whether it's you or your neighbor. Mosquito "control" may be a matter of spraying chemicals to reduce the population below
nuisance levels. On the other hand, mosquito *management* is what is often needed. It is a long-term proactive project that requires a community effort in order to succeed.

We have information on mosquito control on the web at
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