The Facts so Far on Zika Virus

The Zika virus outbreak has global public health officials aptly concerned. Every day, it seems, there are new breaking news items. It can seem a bit difficult to keep up with the latest information and recommendations for avoiding Zika virus; here is some of the latest of what we know.

  • Zika virus is spread by mosquitoes, and not by person-to-person contact, though a small number of cases of sexual transmission have been documented. The outbreak began in Brazil last May and has moved into more than 20 countries in Latin America.
  • The continental U.S. has not yet seen any cases of local transmission of Zika virus via mosquito, according to the Department of Health and Human Services. Puerto Rico is particularly vulnerable to an outbreak, however. The Annals of Internal Medicine published a report of a traveler who returned to the U.S. after acquiring Zika in Costa Rica, which is less than 1,300 miles from Puerto Rico.
  • Zika is not new to the U.S. Even as early as 2007, when the mosquito-borne disease had its first large outbreak in the Pacific island nation of Micronesia, the virus directly touched the U.S., sickening one American traveler. Since then more than two dozen domestic cases have been reported, all from travelers who contracted Zika abroad. None were domestically acquired, according to the U.S. Centers for Disease Control and Prevention.
  • Until more is known about the risk of sexual transmission, all men and women returning from an area where Zika is circulating—especially pregnant women and their partners—should practice safe sex, including through the correct and consistent use of condoms. Zika virus can persist in semen for as long as two months after symptom onset, according to a letter in Emerging Infectious Diseases reported by the CDC.
  • The World Health Organization has recommended that pregnant women delay travel to regions with active Zika transmission, based on the latest evidence that Zika virus infection during pregnancy may be linked to microcephaly in newborns, a condition that causes brain damage and unusually small craniums.
  • All travelers going to an area where Zika infection is occurring should do everything possible to prevent mosquito bites during the trip, including using DEET insect repellent, covering as much of the body as possible with clothing, keeping screens, doors and windows closed, sleeping under mosquito nets (especially during the day when the mosquitoes that transmit the virus are most active)and  eliminating mosquito breeding sites (empty or cover containers holding even small amounts of water).
  • On January 25, the WHO predicted that Zika would spread throughout the Americas because the mosquitoes that transmit it are everywhere except in Chile and Canada. Despite the WHO having declared the spread of Zika virus an international public health emergency, the main worry is the virus’s link to microcephaly in infants. As serious as that is, Zika is typically mild—causing a week of flu-like aches and rash. But the virus has also been linked to the autoimmune disease Guillain–Barré syndrome, which can cause paralysis.
  • Scientists in Brazil are working on a genetically-modified Aedes aegypti mosquito to combat the spread of Zika. Male mosquitoes would pass a deadly gene to their offspring that would kill them prior to adulthood.
  • Scientific American has constructed a map showing where all of the imported cases of Zika have landed. The states with the darkest shades of purple have the most cases.
  • As of early February, the states with the most cases were New York (7), Texas (6) and California (6). Other states with even fewer cases where the virus has made an appearance include Florida, Massachusetts, New Jersey, Maryland, Pennsylvania, Virginia, Minnesota, Arizona, Illinois, Oregon and Alaska.

The data clearly suggests that the virus is hardly running rampant through the U.S. at this point in time. Still, if you're planning to travel abroad, do follow the precautions outlined above.

U.S. States with Known Cases of Zika Virus

Graphic by Amanda Montanez courtesy of Scientific American

Ann. Int. Med., Published online Feb. 10, 2016, doi:10.7326/L16-0075,

WHO, Information for travellers visiting Zika affected countries, Feb. 2016,

CDC, 2016, Vol. 22, No. 5,

Scientific American, February 2016,

NEJM, February 2016, Physician’s First Watch

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