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Bug of the Week is written by "The Bug Guy," Michael J. Raupp, Professor of Entomology at the University of Maryland.

Zika and yellow fever mosquitoes, Take 2: Where in the US is the Yellow Fever Mosquito, Aedes aegypti?

 

Female mosquitoes like this yellow fever mosquito biting my hand use human blood to produce eggs. While feeding, viruses like Zika are transmitted from the mosquito to the human in saliva injected into the wound by the mosquito. Blood loss credit: M. J. Raupp.

 

Several months ago we visited the yellow fever mosquito, Aedes aegypti, and learned of its role in transmitting the nasty arbovirus called Zika. In the January episode we explored the history of the virus, where it was first discovered, when it arrived in the Western Hemisphere, who was most at risk, some of Zika’s effects on human health, and ways to prevent contracting Zika. Part of my spiel included a brief discussion on the distribution of the primary vector of Zika, the yellow fever mosquito, and where it was found in the United States. Many published accounts placed the mosquito primarily in southern states lining the Gulf of Mexico and Caribbean. Within days of my posting, I received a fascinating article that provided evidence of a population of yellow fever mosquitoes that successfully overwinters in the Capital Hill neighborhood of Washington, DC. These remarkable scalawags have made a hibernal home in the relative warmth of yet unknown subterranean redoubts somewhere beneath the city. During summertime and early autumn when scientists conducted their studies, larvae of yellow fever mosquitoes were collected from water-containing vessels, including a birdbath, fountain, trash can, plant saucer, and from a storm water basin. This clever human-loving species spends winter snug underground and then bubbles up in late spring to breed in the warmth of the Washington summer and dine on humans and likely other mammals in the heart of DC.

Historical records certainly support the finding of yellow fever mosquitoes in our nation’s capital. As early as the 1700s, many cities in the US were plagued by yellow fever mosquitoes and the diseases they carried. In 1793, Philadelphia was struck with an outbreak that killed some 5,000 people. Baltimore experienced yellow fever in 1794 and in nearby Norfolk and Portsmouth more than 3,000 died in the yellow fever epidemic of 1855. A quick perusal of our entomology museum at College Park revealed specimens of Aedes aegypti collected in Virginia likely in the 1960s. As mentioned in our previous Zika episode, there is a growing concern in the scientific community that Aedes albopictus, the pesky daytime biting Asian tiger mosquito, may also be a competent vector of Zika here in the US. Some mosquito experts say there is no reason to assume that the Asian tiger will not be able to vector the virus.

CDC recently updated range maps of the potential distributions of the yellow fever mosquito and the Asian tiger mosquito in the US. Please note that these maps do not indicate risk that mosquitoes will spread viruses in these areas.

What can you do to avoid contracting this potentially dangerous illness? My first suggestion is to consult a physician or reputable website such as the CDC website for travel advisories regarding illnesses before you travel abroad. For pregnant women or women who plan to become pregnant living in or traveling to countries with Zika, beware of significant health risks to your unborn child.  Excellent advice for women concerning Zika and unborn children can be found at these two links:

http://www.cdc.gov/zika/pregnancy/question-answers.html

http://www.nytimes.com/interactive/2016/health/what-is-zika-virus.html

If your destinations include locations where Zika is endemic, be sure to use personal protection when you are outdoors. Some municipalities are recommending continued use of mosquito repellents after you return from Zika locations. This will help prevent the local transmission of Zika here in the US. Although mosquito bites are most common at dawn and dusk, Aedes aegypti and Aedes albopictus seek blood during daylight hours. Protect yourself from aggressive biters by wearing light-weight, long-sleeved shirts and pants when working or playing outdoors. Certain brands of clothing are pretreated with mosquito repellents such as permethrin. I have worn these in tropical rainforests where mosquitoes were fierce and the clothing really did help. Permethrin aerosols can be purchased and applied to clothing. Permethrin is not to be applied to skin. Many insect repellents can be applied to exposed skin before you go outdoors. Some will provide many hours of protection, while others provide virtually none. The “gold standard” of mosquito repellents is the compound DEET. Higher percentages of DEET in a product generally result in greater levels and duration of protection. However, surveys indicate that some people avoid using DEET for a variety of reasons. In recent years many botanically-based products have come to the marketplace. Scientists discovered that wild tomato produces a compound, 2-undecanone, and created a product which prevents mosquitoes from landing on humans. Picaridin is another active ingredient that provides long lasting protection against mosquitoes. Other products containing oils extracted from lemon eucalyptus, Corymbia citriodora, and products combining oils of soybean, geranium, and caster bean protected people from mosquito bites as effectively as products containing DEET in field trials, but often for shorter time intervals. One new repellent with the cryptic moniker IR3535 has also made the CDC preferred active ingredient list. Products based on citronella and other essential oils derived from plants vary greatly in repellency with average protection times ranging from 5 minutes to 2 hours. So, you may have to apply these products more frequently to be protected.

Questions always arise regarding the use of repellents on children. Repellents carry precautionary statements on their labels. Always read the label carefully and follow directions and precautions exactly. You should help children apply repellents and consult a pediatrician before applying any product to the very young. Some products state that children should not handle the product and even some botanically-based products warn against use on kids under the age of 3. If your travel destinations include places that will be clothing light, be sure to use sunscreen to protect your beautiful skin from harmful UV and use insect repellent. Repellent is applied after, not before, sunscreen and should be replenished after swimming.

 

This video provides tips for reducing problems with mosquitoes around the home.

References

The excellent CDC web sites on Zika virus, the information rich “Mosquito Information Web Site” of the University of Florida, and the fascinating articles, “Evidence for an Overwintering Population of Aedes aegypti in Capitol Hill Neighborhood, Washington, DC” by Andrew Lima, Diane D. Lovin, Paul V. Hickner, and David W. Severson, and “American Disasters: 201 Calamities That Shook the Nation” edited by Ballard C. Campbell, were used in the creation of this episode.

To learn more about Zika and yellow fever mosquitoes please visit the following web sites:

http://www.cdc.gov/zika/

http://mosquito.ifas.ufl.edu/Mosquito_Management.htm