Mosquitoes and West Nile Virus

Many of you may have seen the report that someone in NC has died from West Nile Virus (WNV). Although the NC Department of Human and Health Services does not release patient-specific information in these situations, the person was subsequently identified by his family as being a 76 year old man in Durham County.

Only about 1% of people who become infected develop severe illness, and many people may not become sick at all. The symptoms of West Nile Virus can take 3-14 days to present themselves. Therefore, many people may not attribute their illness 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 here).

As we've seen in previous years, West Nile Virus occurs far less frequently in people in North Carolina as compared to other nearby states. We did not have a human case of WNV in 2014 and only about three in 2013. Those numbers are not intended to trivialize the fact that people were affected (some fatally). It's just a matter of making sure that people don't panic about the disease and just use common sense. West Nile Virus is far less frequent here than other mosquito-borne diseases, such as Eastern Equine Encephalitis (EEE) and LaCrosse Encephalitis (LACE). EEE is typically more common in eastern NC and occurs most commonly in horses that were not inoculated against the disease.

Birds are the "amplifying hosts" for West Nile 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 waste water collection areas and stagnating catch-basins. You can also find them breeding where water collects after storms and begins to stagnate with an abundance of 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 always, rainfall will dictate a lot of ebbs and flows of mosquito activity but with a multitude of urban water sources as breeding grounds, we will continue to see mosquito activity continuing into the early fall as long as temperatures are favorable (although the shortening day lengths and declining temperatures will send some mosquitoes into diapause). Although pesticides have their use in mosquito management, the first response by individuals should focus on "source reduction" (i.e., disrupting/eliminating those breeding sources rather than worrying first about what to insecticide to spray).

Follow these tips below for a good source reduction program:

• Bird baths - simply flush them out with a garden hose, and the mosquito larvae is flushed out 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 (but 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.

• All of that built-up debris in your gutters that you've been planning to clean out? It's time to actually do it and get rid of the water and decaying material that 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 covering boats, grills, 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 the yard.

• Kiddie pools - if they're not being used by kids, they're probably being used by the mosquitoes (and maybe some toads). So, empty them. The same thing applies to pools (in ground or above ground) that aren't maintained. In some of our western states where drought has been a major issue, swimming pools have become mosquito magnets (and the swimming pool owners have become the object of attention for emerging female mosquitoes looking for a blood meal).

• Drainage ditches - they're meant to collect storm water runoff 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 issue - 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 (seehttp://insects.ncsu.edu/Urban/repellents.htm). 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 even when school is back in session because the weather has been favorable. 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.

In terms of yard treatments for mosquitoes, the idea is to treat mosquito resting spots on the lawn and surrounding landscaping. These treatments can help reduce mosquito populations and are certainly a choice for individuals to make. With regard to fogging outdoors for mosquitoes (e.g., with the hand-held or backpack fogging machines available at hardware stores), these pieces of equipment produce a fine aerosol mist. So, bear in mind a few things if you decide to go that route:

• Spray when there is little (if any) wind. Otherwise, the chemical simply drifts off your property rapidly and may not kill as many mosquitoes are you expect.

• Remove or cover children's toys, pet water & food bowls, barbecue grills, etc.

• Avoid spraying flowering plants during the day when bees and other pollinators are out there. We're already losing enough honey bees and you don't need to contribute to the toll. 

• Stay upwind of any application that you're doing and take precautions by wearing proper Personal Protective Equipment (PPE) - long-sleeved shirts, long pants, hat, goggles, and preferably some respiratory protection. 

• More importantly, watch out for drift off of your property. The chemical may end up on someone else's property, whether that's private property or a park, school, or some other public property. Your neighbor's may or may not be receptive to the chemical mist and you need to be aware in particular what is going on at the adjoining property so you don't contaminate people/children, pets, food, honey bee hives, etc. 

And along that line, one other very important point - mosquitoes have no concept of property lines. They are simply out there looking for a blood meal whether it's you or your neighbor. Chemicals may knock down mosquito populations right now and provide some "control." However, mosquito management is what is really needed and that requires a proactive community effort in order to succeed. "It takes a village" applies to mosquito management and you only need one "village idiot" to make that program be unsuccessful. Communication and cooperation are as important (or more important) to make mosquito management work.

We have information on mosquito control on the web at
http://insects.ncsu.edu/Urban/mosquito.htm.