The Zika virus is a flavivirus transmitted primarily through the bite of an infected Aedes species mosquito. While many people infected with Zika experience mild or no symptoms, the virus poses a severe threat during pregnancy, where it can cause serious birth defects, including microcephaly. Since there is currently no vaccine or specific antiviral treatment, the only effective defense relies entirely on proactive prevention measures to break the cycle of transmission.
Personal Defense Against Mosquito Bites
Protection against Aedes mosquitoes, which are most active during the daytime, is the primary defense. Individuals should apply an Environmental Protection Agency (EPA)-registered insect repellent directly to exposed skin. The most effective active ingredients include DEET, picaridin, Oil of Lemon Eucalyptus (OLE) or its synthetic version PMD, and IR3535.
When using repellent, follow the product label instructions precisely, especially when applying to children, avoiding their hands, eyes, and mouth. If using sunscreen, apply it first and allow it to dry before applying the repellent, as combination products are generally not recommended. Wearing long-sleeved shirts and long pants also acts as a physical barrier against bites, and light-colored clothing is less attractive to mosquitoes.
For an added layer of protection, clothing and gear such as boots, pants, and tents can be treated with permethrin, an insecticide that repels and kills mosquitoes. Permethrin is intended for fabric only and should never be applied directly to the skin. When sleeping in non-screened or unscreened areas, using a permethrin-treated bed net, tucked under the mattress, can prevent nighttime bites.
Eliminating Mosquito Breeding Grounds
Controlling the local environment by eliminating the habitats where Aedes mosquitoes breed is essential. These mosquitoes are known as “container breeders” because they lay their eggs in small collections of standing water, which can be as small as a bottle cap. Regularly inspecting and managing your immediate surroundings to remove stagnant water is a highly effective strategy.
The core principle of environmental control is known as “Tip ‘n Toss,” which involves routinely emptying and discarding water-holding containers. This should be done at least once or twice a week for items such as:
- Flowerpots
- Birdbaths
- Pet water bowls
- Unused buckets
- Pool covers
Any items that can hold water and are no longer needed, such as old tires or discarded appliances, should be thrown away or recycled.
For water sources that cannot be easily emptied, such as certain rain barrels, ornamental ponds, or septic tanks, they should be covered tightly with a lid or wire mesh to prevent mosquitoes from accessing the water. Alternatively, a larvicide product, such as a mosquito dunk containing Bacillus thuringiensis israelensis (Bti), can be used to treat larger, unavoidable water bodies, killing the mosquito larvae without harming other animals. Furthermore, ensuring all windows and door screens are intact and properly sealed prevents adult mosquitoes from entering indoor spaces where they can feed and lay eggs.
Preventing Sexual Transmission
Zika virus is unique among arboviruses because it can be sexually transmitted, as it persists in bodily fluids, particularly semen, longer than in the blood. To prevent this route of transmission, consistent and correct use of barrier methods is necessary. Condoms, including male and female types, must be used for all types of sexual activity, including vaginal, anal, and oral sex.
For men with confirmed Zika infection or recent exposure, the virus can remain in semen for an extended period. Current health authority guidance recommends that males returning from an area with risk of Zika should use condoms or abstain from sex for at least three months after the last possible exposure or the start of symptoms. For women with confirmed infection or exposure, the recommended period for practicing safer sex or abstinence is at least two months.
Special Precautions for Travelers and Expectant Parents
Travelers should check the Centers for Disease Control and Prevention (CDC) travel advisories, which identify areas with active Zika transmission. Pregnant women should avoid travel to any area with a risk of Zika virus infection to prevent serious harm to the fetus. If travel to a risk area is unavoidable, strict adherence to mosquito bite prevention measures is necessary throughout the trip. Upon returning from an area with Zika risk, all travelers should continue to take mosquito bite precautions for three weeks.
Couples planning a pregnancy must exercise caution. Women should wait at least two months after the last possible exposure or symptom onset before attempting to conceive, while men should wait at least three months. If a male partner has traveled to a Zika-affected area and the female partner is pregnant, the couple should consistently use condoms or abstain from sex for the entire duration of the pregnancy.