The Zika virus is a viral illness transmitted primarily through the bite of an infected Aedes species mosquito. While many infected individuals show no symptoms or only experience mild illness, the virus gained global attention due to its link to severe congenital effects. Infection during pregnancy can lead to congenital Zika syndrome, which includes neurological defects like microcephaly. Because there is currently no vaccine to prevent the infection and no specific treatment exists, prevention is the only effective defense against the virus.
Personal Measures Against Mosquito Bites
Protecting oneself from mosquito bites is the most immediate way to prevent Zika infection. The Centers for Disease Control and Prevention (CDC) recommends using Environmental Protection Agency (EPA)-registered insect repellents.
These products contain active ingredients such as DEET, Picaridin, IR3535, and oil of lemon eucalyptus (OLE), all proven safe and effective when used according to label instructions, even for pregnant women. Repellents containing 20% to 50% DEET are highly effective and can provide protection for several hours. Picaridin and IR3535 are other excellent choices that are often better tolerated on the skin.
The Aedes mosquitoes that transmit Zika are aggressive daytime biters, which means protection measures must be used throughout the day. In addition to applying repellent to exposed skin, clothing and gear can be treated with permethrin, an insecticide that repels and kills mosquitoes. Permethrin should never be applied directly to the skin, but it is highly effective when used to treat items like boots, pants, socks, and bed nets. Wearing long-sleeved shirts and long pants reduces exposed skin.
Controlling Mosquito Breeding Sources
The Aedes mosquito species breed in small amounts of standing water, preferring man-made containers found near human dwellings. This makes source reduction—the removal or destruction of these larval habitats—a foundational component of mosquito control.
Homeowners should regularly empty, cover, or dispose of items that collect water, such as old tires, buckets, flower pots, bird baths, and clogged gutters. Since the mosquito life cycle from egg to adult takes about seven to ten days, eliminating standing water at least once a week can interrupt the cycle. For containers that must hold water, such as rain barrels, they should be tightly covered or treated with a biological larvicide like Bacillus thuringiensis israelensis (BTI).
Inside the home, maintaining intact window and door screens prevents mosquitoes from entering the living space. Using air conditioning, when available, also reduces the presence of mosquitoes indoors. These environmental controls are essential because the Aedes mosquitoes that transmit Zika have a limited flight range.
Preventing Transmission Through Sexual Contact
Zika virus can be transmitted through sexual contact. This transmission can occur even if the infected person has no symptoms or after their symptoms have resolved. The virus persists longer in semen than in other bodily fluids, increasing the risk of sexual transmission from men.
The use of barrier methods, specifically condoms, is advised for all types of sexual activity to prevent transmission. Abstinence is another method couples can use to completely eliminate the risk. For men who have traveled to an area with Zika but remained asymptomatic, safer sex practices are recommended for at least eight weeks after returning.
If a male partner develops symptoms of Zika, the recommended period for using condoms or abstaining is extended to at least six months from the onset of symptoms. This longer duration is a precautionary measure.
Situational Guidance for High-Risk Groups
Pregnant individuals face the most serious risk, as the virus can be passed to the fetus, potentially causing severe birth defects known as congenital Zika syndrome. Pregnant women are advised to avoid non-essential travel to areas with active Zika transmission.
If travel to an area with risk is unavoidable, or for pregnant individuals residing in such areas, strict adherence to mosquito bite prevention is mandatory throughout the entire pregnancy. This includes using EPA-registered repellents and protective clothing. Their male partners should practice safer sex or abstain for the duration of the pregnancy.
Travelers returning from areas with ongoing Zika transmission should take precautions to prevent local spread of the virus. Individuals should continue to prevent mosquito bites for at least three weeks after returning home. This prevents an infected person from being bitten by a local mosquito, which could then spread the virus to others in a new area. Women planning pregnancy are advised to wait at least two months after travel before trying to conceive, while men should wait at least three months.