Zika and Pesticides: How to Take Sensible Precautions

Dog sniffing mosquito repellent spray

The Zika virus poses serious public health threats of microencephaly and other neurodevelopmental abnormalities. There’s also concern about its possible links to Guillain-Barré syndrome in adults. That’s a condition in which the body’s immune system attacks its own nerves and may cause paralysis.

My previous blog for more on Defeating Zika using more common sense and less toxic chemicals, and the blog from NRDC climate health expert Dr. Kim Knowlton, Zika Goes Viral, has more information about Zika, but I’d like to offer some additional tips here to avoid unnecessary pesticide exposures.

The first line of defense is prevention. This includes avoiding mosquito bites by covering up with clothing, making sure that windows and doors are screened to keep out mosquitos, eliminating all standing water that could provide mosquito breeding grounds, and, of course, using mosquito repellant (Consumer Reports offers insect repellent ratings; I use a DEET-free lemon eucalyptus one that works well and smells nice).

Consider alternatives to spraying pesticide. The CDC and others are exploring this with some success, and these include: traps to capture and kill adult female mosquitoes, introducing genetically-modified male sterile mosquitoes to curb population growth, and new lower-risk biopesticides.

Still, we understand that even after taking these steps, it may be necessary to apply pesticides to control mosquitos near homes, schools or playgrounds. Here’s how to prevent potentially harmful exposures:

For individuals, communities, and local authorities when applying pesticide:

  • Use the least toxic pesticides that will be effective, at the lowest application rate that will be effective;
  • Try to reduce larval populations, rather than spray adult populations, which is more likely to lead to non-targeted spraying of people and wildlife;
  • Apply pesticides in a way that avoids contact with people—avoiding daytime spraying when people are outside, and using targeted, rather than broadcast, spraying whenever possible;
  • Provide advance notice of planned spraying, so families can close windows, clean off play equipment before use, etc.

If you’re in an area treated with pesticides:

When pesticide is applied widely, residents—particularly pregnant women and children—should take precautions to avoid exposure to the pesticide. For example, avoid breathing pesticide spray in the air or touching items that have pesticide residue on them.

Some things you can do to protect yourself and your family:

  • Talk to your local county health department about its mosquito control plans, and ask to be notified in advance if your neighborhood will be treated;
  • Learn about when and where pesticides will be sprayed;
  • Stay indoors or away from the area during pesticide applications;
  • Shut all windows and doors, and turn off air conditioning to minimize pesticide flow into the house;
  • Take children's toys inside, and wash down any items left outside before children play with them again;
  • Wipe down outdoor furniture, food grills and other items before using them again; and,
  • Keep pets indoors and bring pet items like food bowls and toys inside.

What about the pesticide Naled?

Mosquitos that can carry Zika virus may already be resistant to many of the less toxic pesticides. So the CDC and others have moved towards Naled (sold under the brand name Dibrom®), which is an organophosphate pesticide used primarily for adult mosquito control (see Safety Data Sheet for more information).

Organophosphate pesticides like Naled are neurotoxic. When inhaled, they may cause acute illness. Signs may include runny nose, coughing, wheezing, and difficulty breathing or shortness of breath. Skin contact can cause swelling at the sight of contact and involuntary muscle contractions. Getting organophosphate pesticides in the eyes can cause stinging, tearing, and blurred vision. Within minutes or hours of these types of exposures, the pesticide can cause systemic effects, including nausea, vomiting, diarrhea, sweating, muscle weakness or twitching, and slurred speech. (see Safety Data Sheet for more information).

At doses far below those that trigger acute poisoning, organophosphate pesticides have been linked to long-term neurodevelopmental abnormalities in children exposed prenatally, making it especially important that pregnant women, infants and young children take extra precautions to avoid exposures (see Project TENDR scientific statement on OP's).  

Naled can break down in the environment to dichlorvos, which is also a toxic pesticide and is classified as a possible human carcinogen by the World Health Organization, based on evidence from experimental animal studies (IARC 1991).

The U.S. EPA has a very good webpage specifically on Naled for Mosquito Control with more information.

If you think you, or a family member including a pet, has had a reaction to mosquito spray, talk to your doctor/veterinarian and report it to your regional Poison Control Center at 1-800-222-1222.