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Essential Facts About Mosquito Control and Zika Virus

The primary mosquito vectors of Zika virus in Mississippi. (A) Aedes aegypti and (B) Aedes albopictus. Note the difference in white markings on the back. Figure courtesy of the Mississippi Department of Health.

The primary mosquito vectors of Zika virus in Mississippi. (A) Aedes aegypti and (B) Aedes albopictus. Note the difference in white markings on the back. Figure courtesy of the Mississippi Department of Health.

The threat to persons living in the southern United States from Zika virus (ZIKV) is both significant and ongoing. Although there are several modes of transmission of ZIKV to humans, mosquito transmission is the primary avenue by which persons become infected. Only 2 mosquito species are likely able to transmit ZIKV to humans in the United States, and information about their biology and control is important to physicians and public health officials. This article discusses ZIKV mosquito vector ecology and control, with emphasis on source reduction and personal protection.

There are at least 75 different species of mosquitoes occurring in the southern United States. Only a few of them are significant pests of humans, whereas many others are quite obscure, being found in unique and limited habitats. For example, there are some species of mosquitoes that only feed on frogs, and some that only live inside pitcher plants occurring along the southeastern coast.

Different Species of Mosquitoes Breed in Different Places

One of the common mistakes people make is thinking that all mosquitoes are the same and behave the same way. Mosquitoes can be roughly grouped into categories according to their breeding sites. Many Aedes species breed in artificial containers around the house or holes in trees. Others, like the Anopheles, breed in permanent water such as swamps or lakes. The West Nile virus (WNV) vector in southern states, Culex quinquefasciatus, prefers water with high organic matter content, such as that in septic ditches and storm drains. Some of our worst biting mosquito species come from groups such as Psorophora and Aedes, which breed in floodwaters or woodland pools after heavy rains.

Not All Mosquito Species Are Vectors of Disease Agents

Interestingly, not all species of mosquitoes have the capability to pick up and later transmit disease agents, a concept called vector competence. There are lots of examples of this. In places with malaria, only Anophelesmosquitoes are the vectors, despite the fact that there are many other mosquitoes in those areas. Additionally, after heavy spring rains, people get concerned about excessive mosquito biting from floodwater mosquitoes, but these mosquitoes are not carrying disease agents. The same is true for Zika virus (ZIKV); not all mosquitoes in southern states are able to transmit the virus to humans (see next section).

Only 2 Species of Mosquitoes in Southern States Are Likely Competent Vectors of ZIKV

Zika is primarily transmitted by the yellow fever mosquito, Aedes aegypti, and the Asian tiger mosquito, A. albopictus. Both species are very similar in appearance and habits. Aedes aegypti is a small black species with prominent white bands on its legs and a silver-white lyre-shaped figure on the upper side of its thorax (Figure 1). It breeds in artificial containers around buildings, such as tires, cans, jars, flowerpots, and gutters, and usually bites during the morning or late afternoon. They may readily enter houses and seem to prefer human blood meals (as opposed to animals), biting principally around the ankles or back of the neck. Interestingly, in many places in the United States where A. albopictus was accidentally introduced, this species has virtually disappeared, apparently being displaced.

 

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-Jerome Goddard, PhD

This article originally appeared in the November 2016 issue of The American Journal of Medicine.

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