The World Health Organization has declared the outbreak of Zika virus a "public health emergency of international concern."
The announcement follows a Feb. 1 emergency meeting convened to address concerns about the mosquito-borne virus, which appears to have triggered a devastating surge in birth defects in Brazil. Zika is now spreading like wildfire through Central and South America, Mexico, the Caribbean and surrounding areas.
This is only the fourth time the WHO has invoked its highest alert level, placing the current Zika outbreak in the ranks of the global H1N1 flu epidemic of 2009, the 2014 polio resurgence in Pakistan and Syria and the West African Ebola outbreak of 2014-2015.
Until a few years ago, Zika was relatively obscure. Only Africa, Southeast Asia and islands of the South Pacific had confirmed cases of the virus until 2014. That year, the World Health Organization received the first reports of Zika on the American continents, where it spread rapidly through Latin America, hitting Brazil in May 2015.
Zika is transmitted by mosquitoes of the Aedes species, the same that carry dengue and chikungunya. (A mosquito bites a person infected with the virus, and then delivers it to the next person it bites.) The virus can cause rash, headache, fever, conjunctivitis and joint pain in adults, but it's usually asymptomatic, making it hard to track the number of people infected. Rarely, Zika can cause neurological damage. There is no vaccine or cure.
The global emergency began to unfold toward the end of 2015. In what it called "an unprecedented situation in world scientific research" (via Google translation), Brazil's health ministry announced it had linked a rise in newborn microcephaly, a rare condition characterized by abnormally small head size and, usually, an underdeveloped brain, with the country's Zika outbreak, which began in 2015.
The year before the outbreak, Brazil had 147 reported cases of microcephaly. Between October 2015 and the end of January 2016, that number was 4,180, with 49 potentially related infant deaths.
Suspecting the spike in newborn brain damage could be related to the Zika outbreak, investigators in Brazil began questioning mothers of affected babies and discovered most of them had experienced Zika-like symptoms early in their pregnancies. In November, researchers strengthened the link when they found the virus in the amniotic fluid of two women whose fetuses were diagnosed with microcephaly via ultrasound, as well as in the brain tissue of a newborn who died from the birth defect.
The findings in Brazil have been groundbreaking. They mark the first suggestion of any association between maternal contraction of Zika virus and the birth defect. According to the Mayo Clinic, some known causes of newborn microcephaly include genetic abnormalities, maternal malnutrition, and fetal conditions like inadequate oxygen to the brain, exposure to toxic substances, including alcohol, and infection with a virus like rubella or chickenpox.
Some experts believe the number of confirmed Zika-related microcephaly cases will be fewer than the government's currently suspected count, but it will likely still represent a dramatic increase over pre-Zika levels. As of Jan. 23, testing had confirmed Zika-related microcephaly in 270 infants and ruled it out in 462. Investigators still have 3,500 possible cases to address.
In addition to microcephaly, Brazil has noted an increase in cases of Guillain-Barre syndrome, a neurological disease that can cause paralysis.
As science tries to catch up to the escalating emergency, little is certain. Health officials are quick to note that the link between Zika and microcephaly is tentative, but on Jan. 28, WHO director general Margaret Chan reported that while a "causal relationship between Zika virus infection and birth malformations and neurological syndromes has not yet been established, [it] is strongly suspected."
On Feb. 1, the Colombian government joined Brazil in urging women to hold off on getting pregnant. More than 2,000 pregnant Colombians have tested positive for the virus so far, but the country reports no corresponding increase in microcephaly births.
Reuters reports El Salvador has also recommended women postpone pregnancy, with a suggested waiting period of two years.
The increasingly desperate situation should benefit from Zika's designation as a global health emergency. The WHO can now prioritize research and coordinated efforts to combat the virus, including development of a vaccine. In the meantime, the CDC has Level 2 travel advisories in place for Zika-affected areas in Central and South America, Mexico, Samoa, Cape Verde and the Caribbean. Level 2 is "Practice Enhanced Precautions," with the CDC recommending travelers take extra measures to prevent mosquito bites.
It recommends pregnant women postpone travel to any of the Zika-affected areas.
The CDC on Jan. 28 reported 31 confirmed cases in the U.S., all travel-related. On Feb. 2, the Dallas County health authorities reported the first sexually transmitted case of Zika infection. The person infected had not traveled abroad and is not pregnant.
Editor's Note: This story was updated to reflect current cases and research since it first published under the title "As Zika Spreads, Brazil Advises Women to Rethink Pregnancy Plans" on Jan. 13, 2016.