An outbreak of the Zika virus that began in Brazil several months ago has now spread to 22 countries in the Western Hemisphere, the Pan American Health Organization said Tuesday. Cases have also been reported in European travelers arriving home from the Americas to Finland, Denmark, Germany, Britain, Portugal and Sweden.
Until recently, nearly all known cases of Zika — which may cause brain defects in the unborn — were confined to Asia and Africa. But starting in 2007, confirmed outbreaks began to emerge in a handful of island nations across the Pacific. Within the last year, Zika arrived in Brazil — possibly imported by people traveling to see the 2014 World Cup. Over the past year, an estimated 1.5 million Brazilians have been infected with the virus, which has since spread to nearly two-dozen other countries in South and North America, including the United States.
As of Tuesday, residents of Virginia and Arkansas have tested positive for the virus. For now, the U.S. Centers for Disease Control and Prevention (CDC) has advised Americans traveling abroad to “practice enhanced precautions."
Al Jazeera takes a brief look at the danger posed by the outbreak:
Virus may endanger the unborn
Although the CDC has urged caution, experts say that being infected with Zika is usually no reason to be alarmed. The World Health Organization (WHO) describes Zika symptoms as relatively short-lived: Those infected with the disease can expect to experience “fever, skin rashes, conjunctivitis, muscle and join paint, malaise, and headache” for two days to one week.
“About four out of five people that are infected with the virus don’t have symptoms, and for those that do have symptoms, it tends to be mild,” said Jimmy Whitworth, a professor at the London School of Hygiene and Tropical Medicine.
But the disease may carry greater risks for pregnant women. Around the same time that Zika arrived in Brazil, the country began experiencing a rise in the number of newborns born with microcephaly, a birth defect associated with unusually small head size and neurological disorders. In 2015, Brazil reported more than 3,500 cases of microcephaly — about 20 times their yearly average.
The posited link between Zika and birth defects remains unproven, but WHO’s Zika fact sheet says there is “an increasing body of evidence” to support the theory that a link exists. Medical researchers have established enough of a correlation for the CDC to advise that pregnant women delay travel to countries experiencing major Zika outbreaks.
In French Polynesia, an outbreak of Zika also occurred at the same time as 73 people developed Guillain-Barré syndrome and “other neurologic conditions,” according to the New England Journal of Medicine. Guillain-Barré syndrome is an autoimmune disorder that can cause paralysis and is fatal in some cases. As with microcephaly, the connection between Zika and Guillain-Barré syndrome is not yet proven.
“It looks like the virus does have a predilection for nervous tissue,” said Whitworth. “And so you’re getting this failure of development in the brains of unborn fetuses and you’re getting this ascending paralysis."
Transmitted by mosquitoes
A thorough survey of the available data from state health departments, conducted by Scientific American magazine, uncovered a little more than two dozen cases of Zika in the U.S. since the first recorded instance in 2007. There have been no confirmed cases in which a Zika carrier in the U.S. has transmitted the disease to anyone else stateside.
The primary mode of transmission for Zika is through mosquitoes, although there is some very thin evidence that it might also be sexually transmitted.
CDC recommends precautions
The current Zika epidemic evidently doesn’t warrant CDC’s most urgent warning level, “Avoid Nonessential Travel.” But the agency does advise that women who are pregnant should stay away from areas experiencing Zika outbreaks, and that women who are trying to get pregnant “should consult with their health care professional before traveling to those areas."
For all others traveling to Zika-stricken areas, basic precautions are in order to avoid mosquito bites: Wear long sleeves, use insect repellent and sleep in places that are sealed off from mosquitos.
Fortunately, “it looks like it is pretty difficult to transmit this infection from person to person,” said Whitworth.