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Zika disease is caused by infection with the Zika virus, transmitted most often by the bite of an infected mosquito. The two mosquito species most likely involved in U.S. transmission are Aedes aegypti (the yellow fever mosquito) and Aedes albopictus (the Asian tiger mosquito). These "container mosquitoes" are also responsible for transmitting chikungunya and dengue viruses to humans.

Transmission and Symptoms

Most people infected with Zika do not get sick. Those who do become ill may develop fever, rash, joint pain, and conjunctivitis. Death from Zika infection is extremely rare, though pregnant women face elevated risks — the virus has been linked to birth defects. Beyond mosquito bites, transmission occurs through sexual contact, from mother to child, and blood transfusions.

Imported vs. Local Cases

• Imported cases occur when a person contracts the disease while traveling abroad and returns home infected
• Local transmission means the virus is circulating in U.S. mosquitoes and humans are infected locally

Check CDC's up-to-date map of areas with local Zika transmission.

Vector Biology — "Container Mosquitoes"

Container mosquitoes deposit their eggs on the sides of water-holding containers, just above the water line. Eggs can remain dormant until flooding triggers hatching. Adult container mosquitoes don't fly much more than 500 feet from their aquatic habitat — anyone being bitten at home should check nearby containers.

Common container types: tires, potted plant saucers, tree holes, bottles, cups, pet dishes, flower vases, bird baths, tarps, cisterns, trash cans, buckets, and clogged roof gutters.

Risk Reduction

• Conduct weekly removal of discardable water-holding items
• Clean small containers weekly by dumping water and scrubbing the inside wall to remove eggs (April through November)
• Use insect screening or larvicides (Bacillus thuringiensis israelensis/Bti, or methoprene) on larger water bodies like rain barrels
• Wear EPA-approved mosquito repellents

Ineffective products include: mosquito repellent bracelets, patches, bug zappers, consumption of vitamins, and ultrasonic devices.

Resources

• National Pest Alert — Zika Virus (PDF)
• CDC Interim Guidance for District and School Administrators — Zika Virus
• Zika Virus Information for Pregnant Women — CDC
• CDC Travel Information — Zika Virus