The World Health Organization has warned that the mosquito-borne Zika virus, which has been linked to abnormal births, is likely to spread to all countries in the Americas, except Canada and Chile.
The warning comes amid evidence of a possible link between Zika and an increase in the number of babies born with abnormally small heads in Brazil, at the same time as evidence accumulates that the virus is advancing throughout the region.
The WHO also seconded an earlier warning from the US Centers for Disease Control to pregnant women to avoid areas where the virus has been found. Both organizations also called on women in those places to take special precautions.
"Pregnant women should be especially careful to avoid mosquito bites," the WHO said in a statement on Sunday. "Women who believe they have been exposed to the Zika virus should consult with their healthcare provider for close monitoring of their pregnancy."
Meanwhile, the authorities in five countries in the region — El Salvador, Colombia, Honduras, Jamaica and Ecuador — have urged women to delay plans to have children.
"We would like to suggest that women of fertile age take measures to plan their pregnancies and avoid getting pregnant in the next year and a half," El Salvador's deputy minister of health, Eduardo Espinoza, told reporters last week.
The Colombian health authorities have circulated a recommendation that "all couples in national territory" should avoid pregnancies until July. They also advised pregnant women living above 2,200 meters (7,217 feet) not to travel to lower-lying areas, where the mosquitoes thrive.
The symptoms of the illness are similar to those of dengue fever, which is also carried by the Aedes aegypti mosquito. They include fever and a rash, as well as joint and muscle pain. The Centers for Disease Control, however, has said that approximately 80 percent of the people that get infected with Zika are asymptomatic.
The sudden emergence of concern over Zika began in November when the Brazilian health ministry announced it was investigating whether the virus was behind a sharp increase in cases of babies born with microcephaly, a condition that means they have abnormally small heads and underdeveloped brains.
Now Brazilian researchers are also investigating possible links between the virus and Guillan-Barré syndrome, in which the body's immune system attacks parts of the central nervous system.
The Zika virus was first identified in 1947 and was apparently confined to Africa, Southeast Asia, and the Pacific islands until the first cases in the American continent were registered in Brazil in May 2015.
According to the WHO the virus has now been detected in 21 countries in the continent. The organization said that it has advanced particularly fast both because the mosquito is widespread, and because local populations have yet to develop any immunity to the disease.
Mexico's authorities have so far confirmed 15 Zika cases, but refrained from issuing any general warnings.
"We don't have an epidemiological alert yet in Mexico, but considering the rapid spread of the virus and the fact that we already have cases shows that we must be on alert," Carmen Robles, former deputy director of La Raza Medical Center in Mexico City, told VICE News. "The best we can do is prevent, just like what we've done in the past with dengue."
The only reported cases so far in the US have involved people who have returned from other countries where the virus is present.
As the virus and the associated fear about its consequences extends, the race is on to develop a vaccine.
"We've got no drugs and we've got no vaccines. It's a case of deja vu because that's exactly what we were saying with Ebola," Trudie Lang, a professor of global health at the University of Oxford, told Reuters. "It's really important to develop a vaccine as quickly as possible."
Saana Ihamäki__ contributed to this report.
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