The deadly Zika virus may have arrived in Brazil in 2013, one year before previously believed and two years before cases of the disease were initially reported, according to a new study.
Scientists from Oxford University in Britain and the Evandro Chagas Institute in Brazil looked at genetic profiles of seven Brazilian Zika cases, one of which was from an adult patient who died and another from a newborn with microcephaly. They say that the mosquito-borne virus may have been spread to the country between May and December 2013 through international travel from French Polynesia, which saw an outbreak of the disease from 2013 to 2014.
While Brazilian health officials reported a large number of illnesses that consisted of fevers and rashes in late 2014, it wasn't until May 2015 that these patients were diagnosed with Zika. The virus has since spread to another 33 countries across the Americas and has also been linked to microcephaly, a birth defect that leads to small heads and brain damage in infants, as well as eye abnormalities in infants and Guillain-Barre Syndrome, a neurological disorder that can result in temporary paralyses.
The research team involved in the study noted that Brazil saw an increase in air travel passengers coming into the country from late 2012 to 2015, mostly because of popular sports events, which leads them to believe that Zika came in during the 2013 Confederations Cup. One of the participants in the soccer tournament was a team from Tahiti, which experienced a Zika epidemic that year.
The Brazilian government currently estimates that Zika has affected as many as 1.5 million people in the country, and it has already confirmed almost 1,000 microcephaly cases. A vaccine has yet to be developed for Zika, and neither Zika nor microcephaly have a treatment as of now.
"This is the first study combining genetic and epidemiological data on the Zika virus in Brazil, so it is a good baseline for future research," said Nuno Faria, study co-author from Oxford University.
Faria added that it is "very plausible" that Zika spread through co-infection with a virus like dengue, which has existed in Brazil for years, or previous exposure to dengue.
Scott Weaver, director of the Institute for Human Infections and Immunity and scientific director of the Galveston National Laboratory in Texas, said that it is extremely possible that Zika managed to stay under the radar of health officials for at least a year, as its symptoms are similar to those of dengue and another mosquito-borne virus called chikungunya.
Such symptoms tend to be mild and include a fever, rash, joint pain and pink eye, and about 80 percent of people with Zika have no symptoms. Weaver added that even if dengue is suspected, doctors rarely run tests for it unless patients start hemorrhaging. It has also been very difficult to test Zika due to a lack of commercially available tests.
The new study provides a better way for scientists to understand how Zika has evolved, though definite proof has yet to be provided of the virus's arrival in Brazil in 2013. Karin Nielsen of the David Geffen School of Medicine at the University of California, Los Angeles believes that researchers would be better able to prove that Zika arrived by re-examining blood samples from 2013 and testing them for the virus.
Faria's team has an opportunity to do so, as it plans to visit the country in May and use a portable new technology to profile 1,000 genomes. "It's going to be targeting genetic surveillance," Faria said.
The study was published in the March 24 issue of the journal Science.
