New Knowledge on Zika and Mosquito Control

Mosquitoes Spread Disease
Mosquitoes Spread Disease. Jim Occi, BugPics,

In February, I posted about the mosquito-borne Zika virus Zika Hits the US - How to Prevent Mosquito Bites and How to Protect Yourself from Mosquitoes that Spread Zika Virus. The articles discussed the fact that U.S. citizens were getting the virus, but only during travels. At that point it was not yet being spread by mosquitoes in the continental U.S. or North America as a whole.

While this is still true, with only those who traveled to countries in Central America, South America of the Caribbean contracting the virus, it is expected that mosquito season will bring some virus-carrying mosquitoes to some parts of the southern U.S., with the Gulf Coast states (Florida, Louisiana, and Texas) most at risk.

CDC is seeing the rate of illness increasing on a weekly basis, and it expects it to continue to increase substantially, especially in U.S. territories. Thankfully, even as the spread of infected mosquitoes and the rate of human infection increases, so, too, is the knowledge of the Centers for Disease Control and Prevention (CDC) continuing to grow and be spread to states and local departments who are responsible for mosquito control. In fact, CDC itself noted that it is "just at the beginning of the response and its rapidly evolving," thus its priorities also continue shift as more is learned each day.

Why is all this knowledge so important? Because it is only through reducing mosquito populations that we can reduce the spread of Zika.

All Mosquitoes Are Not Alike.

For any pest control effort to be successful, it is essential that the person attempting that control – whether it be the homeowner, a pest control professional, or a government agency – understand the pest, its biology and its behavior.

And, although all mosquitoes look pretty much the same to the naked eye when you are trying to swat it off your arm before it bites, different species of mosquitoes have different habits and spread different diseases.

For example, the Aedes aegypti mosquito spreads Zika (as well as the Chikungunya virus that was the hot topic of news in 2015).

Unlike most mosquitoes this species is active and bites during the day. Once the sun sets, it tends to hide out in shrubbery, tall grasses, or other areas near the home. For this reason, a city-sponsored mosquito-insecticide fogging from a truck will do little to reduce populations of this mosquito, as it is unlikely to penetrate all the way to the perimeter areas of the home where these mosquitoes are harboring.

Control of the Zika Mosquito

So if we can't control this mosquito the way we traditionally control mosquitoes, what do we do? That is exactly what CDC is working on learning and teaching. On April 1, 2015, CDC hosted a Zika Action plan Summit, which was attended by more than 300 public health experts. The purpose was to help ensure a coordinated response to the mosquito-borne illness across the U.S.

A key point of the summit was that planning needs to begin now so action can be taken to reduce mosquitoes right from the start of mosquito season. As such, CDC discussed new state guidelines for the development of risk-based Zika action plans, through a phased jurisdictional response based on where Zika was occurring.

For example, if only localized cases of Zika begin to appear, such as a few cases in a household, the best control may mean

  • spraying insecticides labeled for mosquito larvae (larvacide) and for adult mosquitoes (adulticides) specifically around the perimeter of that home with a protective radius out from it.
  • reducing the conditions that attract the mosquitoes and enable them to live – specifically water resources.
  • Potentially adding applications from truck-mounted sprayers and/or aerial sprays specifically in this area.

The specific control implemented would be based on a local decision, dependent on a number of factors. But these should all be thought out ahead of time and plans built around them, so we are all ready should Zika mosquitoes appear in our neighborhoods.

In fact, the environmental modifications to reduce water and mosquito attractants should be conducted ahead of mosquito season to help deter them from gaining a foothold in the first place.

Why is Zika so Serious?

Mosquitoes have been around longer than humans, and they, likely have been biting us for as long as we've been in existence. So why are we suddenly so concerned about this mosquito? Following are a number of facts from CDC:

  • Zika Symptome. Zika is spread primarily through the bite of an Aedes mosquito infected with the virus. In most cases, the virus is not serious with only 1 person out of 5 who are infected having any symptoms. The most common symptoms, which last several days to a week are fever, rash, joint pain and conjunctivitis.
  • Pregnancies. However, Zika can be very serious for pregnant women and their infants, as it is suspected (but not proven) to cause the birth defect microcephaly, which leads to an abnormally small head and brain. It also is suspected to cause other congenital problems for the baby such as eye problems and impaired growth, or even lead to miscarriage. It is currently unknown whether women who deliver a baby with Zika complications or have a Zika-related miscarriage are at risk in future pregnancies related to her Zika infection.
  • Other diseases. Zika also has been linked to Guillain-Barre syndrome, a nervous system illness which causes muscle weakness and can lead to paralysis.

More Zika Facts

  • No vaccine or treatment. There currently is no vaccine or treatment for Zika. Thus the best protection is preventing mosquito bites. (See How to Prevent Mosquito Bites.)
  • Insecticide Resistance. Some mosquitoes are showing resistance to certain insecticides, with the greatest issue being that different mosquitoes in different areas are resistant to different insecticides.
  • Sexual Intercourse. Zika has been shown to be able to be spread through sexual intercourse from males, thus CDC recommends that men who travel to any areas that has an active Zika infection should use a condom for at least six months after the travel.
  • Blood Transmission. Zika has also been shown to be able to be transmitted through blood. As such, the U.S. Food and Drug Administration has approved a new test to screen donated blood.
  • Zika Protection. On the positive side, those who are infected with Zika, even if they have no symptoms, are likely to be immune from future infections.
  • Travel Risk. The potential for being infected with the Zika virus during travel is dependent no only on being in the area where the infection is known to be active, but also on the length of time one spends in areas with Zika and whether the person took steps to prevent mosquito bites. 

Preparing for the Possibility of Zika in the U.S.

In addition to the prevention tips (cited and linked above) to keep mosquitoes from biting, CDC recommends the following to prepare for the possible expansion of Zika in the U.S.:

  • Pregnant women are advised not to travel to areas with active Zika virus transmission. Those who live in or must travel to one of these areas should talk to their health care provider and strictly follow steps to prevent Zika virus infection acquisition from mosquito bites (Avoid Bug Bites).
  • Pregnant women should consistently and correctly use condoms during sex (i.e., vaginal intercourse, anal intercourse, or fellatio) or abstain from sex throughout the pregnancy with male partners who reside in or have traveled to areas with active Zika virus transmission (See Areas with Zika and Zika and Sexual Transmission.
  • Travelers should visit CDC’s Travelers' Health site prior to travel to get up-to-date information on areas with active Zika virus transmission. These are likely to change over time and might include locations not yet listed, so the list should be checked each time one travels..

For more information on Zika and CDC efforts and recommendations, see