A mosquito-borne virus that has rapidly spread across 21 countries and territories of the Americas since May 2015 will likely continue to stretch across more countries, the World Health Organization said.
The first cases of the latest Zika virus outbreak were reported in Brazil in May 2015, according to WHO.
The virus' "rapid spread" is exacerbated by two conditions, according to WHO: a lack of immunity because the Americas had not been previously exposed to the virus and the prevalence of the Aedes mosquitoes -- the main carrier of Zika -- in all of the region, save Canada and continental Chile.
The Pan American Health Organization, which serves as WHO's Regional Office for the Americas, said it anticipated the Zika virus would "continue to spread and will likely reach all countries and territories of the region where Aedes mosquitoes are found."
Transmission of the virus by Aedes mosquitoes is well documented, health officials said, although researchers continued to investigate other possible transmission routes.
Earlier this month, doctors in Hawaii noted a child born with a health defect which caused its head to be unusually small apparently contracted Zika virus before birth through his mother. She had been diagnosed with Zika in Brazil, according to the Hawaii State Department of Health.
Scientists have also found evidence Zika may be transmitted through sexual contact, but more information is needed to confirm the link, WHO said.
The virus is also occasionally transmitted through blood. Precautions have already been put in place to ensure safe blood donations and transfusions, according to WHO.
Mosquito populations should be reduced and controlled by eliminating breeding sites. Containers that can hold even small amounts of water where mosquitoes can breed, such as buckets, flower pots or tires, should be emptied, cleaned or covered to prevent mosquitoes from breeding in them. This will also help to control dengue and chikungunya, which are also transmitted by Aedes mosquitoes. Other measures include using larvicide to treat standing waters.
All people living in or visiting areas with Aedes mosquitoes should protect themselves from mosquito bites by using insect repellent; wearing clothes (preferably light-colored) that cover as much of the body as possible; using physical barriers such as screens, closed doors and windows; and sleeping under mosquito nets, especially during the day when Aedes mosquitoes are most active.
Pregnant women should be especially careful to avoid mosquito bites. Although Zika typically causes only mild symptoms, outbreaks in Brazil have coincided with a marked increase in microcephaly—or unusually small head size—in newborns. Women planning to travel to areas where Zika is circulating should consult a healthcare provider before traveling and upon return. Women who believe they have been exposed to Zika virus should consult with their healthcare provider for close monitoring of their pregnancy. Any decision to defer pregnancy is an individual one between a woman, her partner and her healthcare provider.