Elements

How Zika Virus Can Spread

By Carolyn Kormann

http://www.newyorker.com/tech/elements/how-zika-virus-can-spread

When Andrew Haddow was a boy, in the nineteen-eighties, his father told him bedtime stories about his grandfather, a Scottish scientist named Alexander John Haddow, who studied rare viruses in the jungle outside Entebbe, Uganda. As Haddow got older, he began reading his grandfather’s papers. One of them was about the discovery, in 1947, of a virus in the blood of a rhesus monkey that lived in the Zika Forest. This virus—which, like dengue fever and yellow fever, is transmitted to humans mostly by mosquitoes—remained virtually unknown for the next sixty years, but it interested Haddow. In 2012, Haddow, now a medical entomologist, published a paper on the genetic lineage of the Zika virus. Haddow identified two points of origin—one African, the other Asian—and showed that a recent outbreak on the island of Yap, in the Federated States of Micronesia, had been caused by the latter strain. His paper also warned that Zika might spread.

Today, in much of Latin America, Haddow’s prediction has become a frightening reality. The World Health Organization estimates that the virus could infect as many as four million people in the coming months; on Monday, it declared the outbreak a “Public Health Emergency of International Concern,” a designation that has rarely been applied in the past, and is intended to coördinate international funds and expertise. Fortunately, the majority of people who catch Zika (perhaps eighty per cent) will experience no symptoms. But what no one, including Haddow, foresaw was the apparent, though still unproven, link between the virus and microcephaly, a condition that causes babies to be born with abnormally small heads and, in most cases, irreversible brain damage. In Brazil, where the virus was first reported in May, health officials have implicated Zika in thirty-seven hundred new cases of microcephaly. (Fewer than a hundred and fifty cases surfaced in 2014.) Some epidemiologists have said that the virus’s invisibility makes it more dangerous; a pregnant woman might not know that she has contracted it.

Although mosquitoes are responsible for the great majority of transmissions, Haddow helped to discover that the virus can also be sexually communicated. In 2009, during a field study in Senegal, he met another medical entomologist, Kevin Kobylinski, who was conducting malaria research. They went out for beers, and Kobylinski described a mysterious illness—rash, extreme fatigue, joint pain, blood in his semen—that had plagued both him and a colleague, Brian Foy, after a trip to the country the previous year. Foy’s wife, who had not been to Senegal, had also become ill, nine days after his return to the United States. Haddow immediately suspected Zika. Kobylinski sent him blood samples, which proved that the diagnosis was correct. In 2011, they co-authored a paper in the journal Emerging Infectious Diseases suggesting, based on circumstantial evidence, that Foy had unwittingly infected his wife with Zika. Foy also proposed that sexual transmissions might have contributed to the outbreak on Yap, which touched seventy-three per cent of the island’s population.

Meanwhile, Zika had been travelling east. In 2013 and 2014, French Polynesia experienced a large outbreak. The virus had hopscotched across the South Pacific—the Cook Islands, New Caledonia, Easter Island. In each place, local mosquitoes likely fed on the Zika-infected blood of travellers. Then, in August of 2014, according to Didier Musso, a French scientist based in Tahiti, teams from those South Pacific island groups competed in a canoe race, the Va’a World Sprint Championship, which was held in Rio de Janeiro.

Now the virus has spread to more than twenty countries in the Americas. It’s coming our way. So far, thirty-six Americans, including four pregnant women and five New Yorkers, are reported to have contracted the disease, all while travelling outside the country. Air-conditioning, screened windows, and modern plumbing will most likely prevent Zika from spreading too readily here. The same cannot be said of Brazil, or Colombia, or El Salvador. It’s the rainy season in much of Latin America, and the mosquito population in cities is at its festering peak. Brazil has deployed two hundred thousand troops to reduce the numbers of bugs, an effort that promises to be about as effective as using a colander to remove salt from the sea. Colombia’s national health institute reported that twenty-one hundred pregnant women have contracted the Zika virus. In El Salvador, the government recently announced that women should not get pregnant until 2018—despite the fact that abortion is illegal there and contraceptives are difficult to find.