Less than a year and a half since Ebola terrified the world, a new viral pandemic has emerged.
Zika fever, a mosquito-borne disease caused by the Zika virus, was first recorded in sub-Saharan Africa in the 1950s. Outbreaks—the biggest which was fewer than 200 cases—had been contained in equatorial Africa, Southeast Asia, and Micronesia until February 2014, when the virus reached French Polynesia. In May 2015, the first case was recorded in Brazil, and the virus then spread quickly through South and Central America. The outbreaks in the Americas have not only been much larger in size (an estimated 1.5 million people have contracted the disease in Brazil so far) but also more serious: while Zika fever is generally a rather mild, non life-threatening condition in adults, it has been associated with a sudden spike in newborn microencephaly (brain shrinkage) and a rare neurological condition causing a temporary paralysis, the Guillain-Barré syndrome.
Cases of Zika have now been recorded in 28 countries, including the US, where the Centers for Disease Control and Prevention have confirmed at least a dozen of cases. The World Health Organization (WHO) predicts that almost all countries in the Americas are at risk of the virus, which is currently spread by the Aedes aegypti mosquito.
Perhaps the most worrisome aspect of a possible epidemic is that we know so little about this virus. It’s partly due to a lack research on tropical, infectious diseases that typically affect the developing world and partly because a Zika epidemic of this size is unprecedented.
Quartz spoke with Professor Paul Roepe, director of the Georgetown University’s Center for Infectious Disease and Daniel Bausch, technical lead for the epidemic clinical management at the WHO to get a clearer understanding of what the Zika virus is and how to deal with it.
What is Zika fever?
Zika fever is an illness caused by the Zika virus, which is spread by the Aedes mosquito (the same vector responsible for spreading Dengue fever and Chikungunya). Zika fever occurs in about 20% of the people who are infected by the virus and is a typically mild illness lasting a few days to a week. Very rarely is Zika fever serious enough to cause hospitalization, and deaths are ever rarer.
Anyone can be infected with Zika virus. While 60-80% of Zika infections are asymptomatic (the incubation period lasts for three to 12 days), the most common symptoms are fever with muscle ache, a rash, and red eyes. Zika fever gets diagnosed through serum tests, and since there isn’t a commercially available test for it, misdiagnosis (for other types of fevers or viral infections) is relatively frequent.
Zika fever typically resolves on its own. As of now, there is no treatment for the virus; rest and hydration are recommended, and pain and fever medications can help. Several organizations are working on medications and vaccines, but there is no specific timeline in sight.
In very rare cases, Zika is suspected to cause brain shrinkage in the newborns of infected mothers, and to trigger Guillain-Barré syndrome, a neurological condition that can cause paralysis for up to two years.
Where did the virus come from?
The first case of Zika fever was identified in a rhesus macaque in the Zika forest, Uganda, in 1947. The first human case was found in 1954 in Nigeria. Subsequently, the virus was found primarily in areas of equatorial Africa and southeast Asia, where it is endemic, and in Micronesia and Polynesia.
The first case of Zika fever in Latin America was recorded in May 2015 in Brazil, and the virus has since spread quickly through Southern and Central America, causing the largest-recorded epidemic of Zika.
There are two primary ways Zika virus—and all other mosquito-borne diseases—travels:
- A mosquito carrying the virus catches a ride on a plane, or a ship;
- A person incubating the virus travels to another area of the world and is bitten by a mosquito, which starts spreading the virus.
Currently, the US Center for Disease Control has issued a Level 2 travel warning, asking to take “enhanced precautions” when travelling to 17 countries, and has confirmed at least a dozen Zika cases in the US.
Potentially, all areas of the world where Aedes mosquito is endemic are at risk. Zika virus can be spread by all Aedes mosquitos, though so far the Aedes aegypti, has been the most effective carrier. The areas where the virus is likely to spread next are the US southeastern states of Florida, the Gulf Coast region, and possibly Texas, where Aedes aegypti are endemic.
Why is everyone so worried?
Before the Brazil epidemic, no real concern related to Zika fever had emerged. However, in the past year, a 3,800% increase in microencephaly—brain shrinkage—in newborns of mothers infected with Zika has raised a high suspicion that there might in fact be a connection between Zika fever and brain shrinkage. Babies with microencephaly either don’t survive birth or are at risk of suffering lifelong developmental delays. So far, 46 children born with brain shrinkage have died in Brazil.
Zika is not the only virus suspected to cause microencephaly in fetuses. Measles does too, although the current evidence suggests a higher risk with Zika infections. While the data aren’t conclusive, we know that a Zika infection is linked to brain shrinkage only in rare cases. Most pregnant women who contract Zika fever do not give birth to children affected by microencephaly. So far, since the Zika epidemic started in Latin America, nearly 3,900 babies were born with brain shrinkage.
However, we don’t know yet how long after a woman is infected with the virus it is safe for her to get pregnant.
Is everyone but pregnant women safe?
No; Zika fever might also be linked to Guillain-Barré syndrome, a rare neurological condition in which the immune system attacks the patient’s nerves, often causing paralysis for up to a few months. The cause of the syndrome is unknown, but in about half the cases it is triggered by acute infections (viral or bacterial) like mononucleosis or the flu. A spike in cases in the areas affected by Zika (in El Salvador, where under 150 cases of Guillain-Barré syndrome are generally recorded in a year, almost 50 appeared in a month) suggests that the virus could trigger Guillain-Barré syndrome with higher frequency than other infections. While most patients recover in a few months to two years, in extremely rare cases Guillain-Barré syndrome can cause permanent paralysis, or be fatal. There is no particular demographic more at risk for Guillain-Barré syndrome.
Links between Zika fever, infant microencephaly and Guillain-Barré syndrome, while highly suspected, have not been definitively confirmed yet.
Can the Zika virus be transmitted directly from person to person?
So far, research suggests that the virus can not be transmitted through contact from person to person (except for its capacity to infect fetuses through the placenta). However, it should not be excluded. In 2009, one case of probable sexual transmission from a man to a woman was recorded.
What can people do to protect themselves against Zika fever?
The recommendation is the same generally given to people traveling to or living in tropical areas: be aware of mosquito bites. Wear mosquito repellent, long sleeves, and long trousers. The Aedes mosquito tends to bite during the day, so be especially vigilant when the sun is out. Pregnant women might consider avoiding travels to affected areas.
Several Latin American countries have issued unprecedented advice against pregnancy, up to two years. Elimination of Aedes mosquitoes through fumigation can also reduce the risk, though it’s not feasible to eliminate all mosquitoes. People might take extra precaution to avoid breeding Aedes mosquitoes: since they deposit eggs in clean water, it’s a good measure to avoid stagnant pools of water—for instance under plant pots, or in tires.