Zika, Mosquitoes, and Repellents

[From the August 2016 issue of the UC IPM Retail Newsletter]

The Zika virus is spread to people mainly through the bite of an infected mosquito, mostly Aedes aegypti and Aedes albopictus. People can also get the Zika virus through sexual contact with an infected person, and the virus can also be passed from a pregnant woman to her developing fetus, which can cause a serious birth defect called microcephaly.

According to the Centers for Disease Control and Prevention (CDC), there is currently no vaccine to prevent the disease or any drugs to treat it. The best way to prevent Zika and other mosquito-borne diseases, including West Nile virus, is to protect yourself and your family from mosquito bites. Aedes mosquitoes are considered day biters, so it's important to limit exposure to mosquitoes, which may include clothing and use of mosquito repellents. See the box for tips on how to avoid mosquito bites.

Effective Mosquito Repellents

Consumer Reports, a nonprofit educational and consumer product research group, recently tested 16 mosquito repellent products containing a variety of ingredients to find out which were the most effective. Products tested included those with the active ingredients DEET, picaridin, oil of lemon eucalyptus (also known as PMD or para-menthane-diol), as well as a variety of plant oils, such as cedar, citronella, geraniol, lemongrass, and rosemary. See Table 1.

The most effective products against Aedes mosquitoes were those containing 20% picaridin and 25% DEET. These concentrations of active ingredients kept mosquitoes from biting for about 8 hours. Furthermore, one product (Sawyer Fisherman's Formula Picaridin) was reportedly the only one among those tested that also kept Culex mosquitoes (which can spread West Nile virus), as well as deer ticks away for at least 8 hours.

DEET is the most effective mosquito repellent if you will be out for long periods where mosquitoes are abundant. However, DEET is an irritant to some people, and repellents containing high DEET concentrations can damage synthetic materials such as clothing or plastics.

Consumer Reports suggests avoiding products made with natural oils such as citronella, lemongrass oil, cedar oil, geraniol, rosemary oil, cinnamon oil, and others. According to their analyses, many of these products were only effective against Aedes mosquitoes for 1 hour or less.

Click here to read the full article and find the ratings of all products tested.

Tips to Protect Yourself from Mosquito Bites

• Wear long-sleeved shirts and long pants.
• Stay in places with air conditioning and window / door screens.
• Empty, cover, or clean up any items outside of your home that can hold water. For specific tips, see the resources at the end of this article.
• If traveling overseas to areas where mosquito-borne diseases are common, sleep under a mosquito bed net.
• Use EPA-registered insect repellents with one of the following active ingredients: DEET, picaridin, IR3535, oil of lemon eucalyptus (PMD).

o   Always follow the product label instructions.
o   Reapply insect repellent as directed.
o   Do not spray repellent on the skin under clothing.
o   If you are also using sunscreen, apply sunscreen before applying insect repellent.

• To protect your child from mosquito bites:
  o   Do not use insect repellent on babies younger than 2 months old.
  o   For children younger than 3 years old, do not use products containing oil of lemon eucalyptus or PMD.
  o   Dress your child in clothing that covers arms and legs.
  o   Cover cribs, strollers, and baby carriers with mosquito netting.
  o   Do not apply insect repellent onto a child's hands, eyes, mouth, or cut or irritated skin.
  o   Adults: Spray insect repellent onto your hands and then apply to a child's face.

Using Mosquito Repellent

CDC recommends using products containing active ingredients registered by the U.S. Environmental Protection Agency (EPA) for use as repellents applied to skin and clothing. An EPA registration indicates the active ingredients of repellents have been tested for human safety when applied according to the instructions on the label. When used as directed, EPA-registered insect repellents are proven safe and effective, even for pregnant and breast-feeding women.

To see if a mosquito repellent is registered by the EPA, look for its registration number on the package, which usually is written as "EPA Reg." or check the EPA Web site.  

Learn more about the Zika virus and find information on prevention, symptoms, and risks on the CDC Web site and on the American Mosquito Control Association Web site.

For general information about managing mosquitoes, reducing breeding habitats, and using insect repellent, see the UC IPM Pest Notes: Mosquitoes.