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Until the last few years, Zika was an obscure virus, confined to equatorial Africa and Asia, and known only to specialists in tropical medicine. It was discovered in 1947, when scientists studying yellow fever in the Zika Forest of Uganda stumbled on a previously unknown virus in a feverish rhesus monkey. In 1958, it was shown that Zika is primarily spread by the bite of the Aedes mosquito. (Zika can also be sexually transmitted.)
The current Zika pandemic began in 2007, when the virus mysteriously appeared in Yap, a remote island in the Pacific Ocean. By 2013, Zika had spread to French Polynesia, an archipelago 5,000 miles away. Over the following year, it spread throughout much of Polynesia, including Easter Island. In early 2015, doctors identified Zika as the cause of an outbreak in the Brazilian state of Bahia. Zika might have arrived in Brazil during the 2014 World Cup, or during the 2014 world championships of Polynesian outrigger canoe racing, which took place in Rio de Janeiro. As many as 1.5 million Brazilians have been infected with Zika.
Human infection with Zika virus
The vast majority of people with Zika virus are not very sick. In fact, most have no symptoms at all. In the outbreak on Yap, 77% of those with antibodies against Zika in their blood samples (indicating infection with the virus) were never ill.
In those who do get symptoms, the most common finding is an itchy red rash. Fever, headache, joint and muscle pains, and inflamed eyes are also frequent. People typically recover in 2 to 7 days, and death is rare.
If infection with Zika virus is usually mild, why all the fuss? Unfortunately, the virus has two uncommon but severe complications that make it a menace to public health. The Zika outbreak in French Polynesia was associated with a twenty-fold increased risk of Guillain-Barré syndrome. This is an autoimmune disease, often triggered by infections, in which the immune system attacks the myelin lining of nerve cells, resulting in widespread weakness and paralysis. Weakness and paralysis spread from the legs upward. Two-thirds of patients lose the ability to walk, and 25% need to be put on a mechanical ventilator because of weakness of the respiratory muscles. Although most people make a partial or full recovery, 20% are still unable to walk at 6 months after diagnosis.
The other condition linked to Zika virus is microcephaly, a birth defect in which a developing baby’s brain fails to grow to its usual size. Almost 4,000 Brazilian infants with microcephaly have been born since the start of the Zika epidemic, which is about 20 times the expected number. In Paraiba, one of the areas hardest hit by Zika, officials reported microcephaly in one out of every 100 newborns, a rate which is 100 times higher than usual. Hearing and vision problems have also been reported in newborns exposed to Zika in the womb.
Protecting yourself against Zika and other mosquito-borne viruses
Zika infection is not harmful in the overwhelming majority of people. Although the association with Guillain-Barré syndrome is troubling, this is still a rare complication. Epidemics of Zika virus seem to increase the rate of Guillain-Barré syndrome from one out of 100,000 people per year to one out of 5,000 people per year.
As there is currently no vaccine or treatment for Zika, the Centers for Disease Control recommend that pregnant women consider postponing travel to countries where active Zika transmission is ongoing (updated travel advisories may be found here).
Pregnant women going to countries with Zika activity are recommended to protect themselves against mosquito bites by
- wearing long-sleeved shirts and long pants
- staying in lodgings with screened-in windows and air conditioning
- consider using an insecticide-treated mosquito net when napping, as Aedes mosquitoes often bite in the daytime
- using permethrin-treated clothing and gear (permethrin is probably safe in pregnancy, although data on first-trimester exposure are scanty)
- using EPA–registered insect repellents; according to the CDC, insect repellents containing DEET, picaridin, and IR3535 are safe for pregnant women when used as directed
- using protection against mosquitoes throughout the day, and both outdoors and indoors, as Aedes mosquitoes are often found inside.
An American Zika outbreak would likely be on a much smaller scale than the one that happened in Brazil. Greater access to window screens, air conditioners, and insecticide spraying in the United States should limit human contact with Aedes mosquitoes.
If there is local transmission of Zika (or dengue or chikungunya, which are also spread by Aedes mosquitoes), in addition to the measures listed above, you should take the following steps to control mosquitoes:
- Get rid of rain barrels, bird baths, tires, tins, and other sources of standing water. Mosquitoes like to breed in stagnant water.
- Dump out any water that collects in your garbage cans, and turn pails upside down so they don’t collect water.
- Inside your home, change water in flower vases every other day, and dump out excess water from flower pot plates. Aedes mosquitoes will breed in your house, if given the chance.
- Don’t buy a bug zapper. Studies have shown that these do not reduce mosquito bites, and may actually increase mosquito populations by killing off beneficial insects that prey on mosquitoes. And don’t bother with an ultrasound device, as they don’t work either.