In February, the World Health Organization’s declaration of a global health emergency confirmed what doctors in Brazil had suspected for months: The mosquito-borne Zika virus had exploded in the South American country. Since 2015, physicians had seen an unprecedented spike in babies born with abnormally small skulls and severe neurological deficits.
Babies born with microcephaly may not develop normally, leaving them severely disabled. Microcephaly is rare — occurring in 6 out of 10,000 live births in the U.S. — but suddenly there were reports of thousands of women in Brazil giving birth to babies with the birth defect, other severe fetal abnormalities or Guillain-Barre syndrome, a nervous system disorder. And even babies who appeared to be healthy developed serious deficits later.
Zika has been around for decades. The virus was first reported in Uganda in 1947, and there were a couple of outbreaks in the Pacific islands, including French Polynesia in 2013, but it was seen as relatively harmless. Public health officials didn’t realize Zika caused birth defects until they had a sizable outbreak in which clear patterns began to emerge.
“It’s conceivable that this was happening at low levels all along,” says Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases in Maryland. “But it’s difficult to pick up these patterns in less-developed countries when there are so many other confounding variables.” Case in point: When epidemiologists looked back at data from the French Polynesian outbreak, they found an increased incidence of the same birth defects.
Since then, the virus has spread to 73 countries. It arrived in the continental United States early in 2016. And some parts of the U.S. are vulnerable to outbreaks: The Aedes aegypti and Aedes albopictus mosquitoes that spread the infection are alive and well in many Southern states. At the time of this writing, the U.S. reported 3,989 travel-associated cases and more than 30,000 locally acquired infections not only in Florida but also in Puerto Rico, American Samoa and the U.S. Virgin Islands.
However, aside from Puerto Rico, most regions in the U.S. lack the steamy tropical weather that has fueled the epidemic in Brazil. Those conditions incubate mosquito populations, and Brazil’s densely packed urban areas help to accelerate transmission. “There will be pockets in the U.S.,” and outbreaks are likely to be small and contained, says Denise Jamieson, chief of the Women’s Health and Fertility Branch of the Centers for Disease Control and Prevention in Atlanta. “Still, the lack of any treatment and the looming threat of infection highlight the need for effective vaccines.”
Three vaccine approaches have been shown to protect monkeys against Zika infection, and human trials began in July. However, it will take at least another year — and another outbreak — before researchers know if they work, says Fauci.
In the meantime, scientists are searching for ways to prevent Zika’s effects. At the University of Southern California, researchers have isolated the two proteins in the Zika virus that seem to be the culprits “that block normal fetal brain development,” says Jae Jung, the study’s lead author and a microbiologist at USC’s Keck School of Medicine. “Now that we know the pathway, this is a big step toward a targeted therapy.”
Who's At Risk:
Zika: A Timeline
1947: Scientists identify a new virus in rhesus monkeys in Uganda; first human cases detected in Uganda and Tanzania five years later.
2007: First large Zika outbreak in humans, on the Pacific island of Yap in Micronesia. An estimated 73 percent of residents become infected.
May 2015: Brazil confirms locally acquired Zika cases, the first time the disease has been found in South America.
October-November 2015: The virus spreads to the African island of Cabo Verde and at least six Central and South American countries.
November 2015: Brazilian officials declare a public health emergency after seeing an extreme uptick in microcephaly cases in newborns. Amniotic fluid from two pregnant women in Brazil tests positive for Zika, indicating the virus can be passed from the mother to the developing fetus.
Dec. 31, 2015: U.S. reports its first locally acquired Zika case in Puerto Rico. At press time, the island had 29,462 cases, according to the CDC.
January 2016: The CDC detects Zika in the brain tissue of babies born with microcephaly. Brazil reports 3,893 suspected cases of microcephaly, including 49 deaths. More than a half-dozen more countries report cases.
February 2016: The World Health Organization declares Zika a global public health emergency. President Barack Obama requests $1.9 billion in emergency funding to fight Zika. Congress refuses to approve the request.
April 2016: The CDC confirms Zika can cause microcephaly and issues a public health alert.
May 2016: Puerto Rico reports its first microcephaly case linked to Zika.
July 2016: Two human vaccine trials begin, one led by the U.S. National Institutes of Health and a second by U.S. company Inovio Pharmaceuticals and South Korean firm GeneOne.
July 29, 2016: Four cases of locally acquired Zika infection are reported in Miami-Dade and Broward counties in South Florida. Since then, there have been a total of 139 cases of local transmission in the state.
Aug. 1, 2016: The CDC issues a travel warning that pregnant women should avoid a specific neighborhood in Miami, one of the first times the agency has done this because of a disease outbreak in the continental U.S.
Aug. 12, 2016: U.S. government declares a public health emergency in Puerto Rico as a result of the Zika epidemic.
Sept. 6, 2016: WHO recommends practicing safe sex for six months to avoid transmission, based on findings that Zika can be detected in semen for several months.
Nov. 1, 2016: Stanford researchers report that Zika infection impairs male fertility in mice models.
As of November, there had been 30,000 cases of Zika virus infection, 3,268 pregnant women with evidence of Zika infection and 25 babies born with Zika-related birth defects in the U.S. and its territories.
[This article originally appeared in print as "A New Enemy Emerges"]