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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 virus and its vector: Yellow Fever Mosquitoes, Aedes aegypti


Concern exists that Asian tigers like this one in my backyard may serve as vectors for Zika virus in the US.


This week we turn our attention from chilly Maryland to Hawaii where a serious illness called Zika virus raised its ruthless head two weeks ago, and to yellow fever mosquitoes, tiny vampires that transmit the virus from person to person. For most people, Zika virus is not a serious health risk. Only about 20% of those infected will show symptoms, and for those that do fall ill symptoms are usually mild and include fever, rash, joint pain, red eyes, muscle pain, and headache. These symptoms usually pass in a few days to a week. However, for pregnant women, Zika poses serious health risks.

On January 19, a women in Oahu gave birth to a baby with a condition known as microcephaly (micro = small, cephaly = head). These babies with abnormally small heads sometimes suffer several related problems including seizures, developmental delays, impaired balance, hearing and vision, and reduced intellectual capacity. The mother who gave birth to the child tested positive for exposure to the Zika virus and had recently traveled to Brazil where the incidence of microcephaly has increased dramatically during an outbreak of Zika that began in 2015. Scientists and physicians around the world are concerned with the possible link between exposure of pregnant women to the Zika virus during pregnancy and children born with microcephaly.

Microcephaly is not the only disease linked to Zika virus. Scientists in French Polynesia suggest that the autoimmune disease of the nervous system called Guillain–Barré syndrome could also be associated with Zika virus. Zika belongs to a group of viruses called arboviruses owing to the fact that they are transmitted from one host to another by arthropods such as mosquitoes. A group of nasty arboviruses, known as the flaviviruses, pose serious threats to humans. Flaviviruses include Zika, West Nile, dengue, yellow fever, and several others.  Zika virus was first described in Africa in 1947 and is found in Africa, Asia, and Indonesia. It appeared in the Western Hemisphere in 2015 and as of January 26th the Centers for Disease Control (CDC)  reported Zika in Barbados, Bolivia, Brazil, Colombia, Dominican Republic, Ecuador, El Salvador, French Guiana, Guadeloupe, Guatemala, Guyana, Haiti, Honduras, Martinique, Mexico, Panama, Paraguay, Puerto Rico, Saint Martin, Suriname, U.S. Virgin Islands, and Venezuela.

Concern about Zika arriving and establishing in the US have arisen. In years past cases of another virus, the Chikungunya virus, involved US travelers who contracted the virus in a foreign destination and returned home with it. However, the ingredients for flaviviruses to establish in the US are present, as evidenced by West Nile and other nonnative viruses that arrived from foreign shores and now maintain themselves in the United States. Two important vectors for flaviviruses like Zika are common along the gulf coast of the United States. The yellow fever mosquito, Aedes aegypti, made famous by Walter Reed, has been in the United States for centuries. There is a growing concern in the scientific community that a related mosquito, Aedes albopictus, the Asian tiger mosquito, may also be a competent vector. Mosquito experts say there is no reason to assume that the Asian tiger will not be able to vector the virus. While the yellow fever mosquito has been with us for many years, the Asian tiger is a newcomer having arrived in Texas in 1985 in a boatload of water-filled tires from Asia.

Distributions of the yellow fever mosquito (Aedes aegypti) and the Asian tiger mosquito (Aedes albopictus) cover broad swaths in warmer regions of the US. The yellow fever mosquito is widely distributed in southern states, and the Asian tiger is found from Florida to New England in the eastern United States and as far west as California. [Source: Centers for Disease Control]


Other nonnative flaviviruses like West Nile virus have become established in the US.  Could the same scenario happen for the Zika virus? Only time will tell. Fortunately, here in the continental US in chilly January, breeding of Aedes mosquitoes nationwide is at a minimum. I suspect the real test will come in summer and early autumn when heat shrinks mosquito generation times from many weeks to a matter of days in many parts of the country. For tips on how to prevent or reduce problems with mosquitoes around the home, watch Mosquito Protection: Bite Them before They Bite You!

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:

If your destinations include locations where Zika is endemic, be sure to use personal protection when you are outdoors. 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.


Female mosquitoes like this one biting my ankle 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.

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 a cryptic moniker called 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 also use insect repellent. Repellant is applied after, not before, sunscreen and should be replenished after swimming.


We thank Lauren Dunn for providing the inspiration for this episode. The excellent CDC web sites on Zika virus, the information rich “Mosquito Information Web Site” of the University of Florida, and the fascinating article, “A new mosquito-borne threat to pregnant women in Brazil” by Marcia Truinfol were consulted in preparation of this episode.

Please visit the web sites below to learn more: