There are enormous gaps in our understanding of Zika, the scientists tell me, and it is unlikely funding will materialize before the virus has taken up residence all over the hemisphere. Virtually nothing definitive is known about the interactions between Zika and New World animals. Scott Weaver of the University of Texas Medical Branch, in a lengthy correspondence over email, told me he thinks it’s highly unlikely Zika will be spread by Culex and notes that the Aedes mosquitoes are so efficient in spreading the virus that the Culex issue may not be very important. Kansas State University expert Stephen Higgs says that it is very difficult to predict what will happen when a new virus enters a complex insect and animal ecology or to know which mosquito species will play a role in transmission: There have been surprises. He notes that in 2007 Zika was spread by albopictus, or “tiger mosquitoes,” in Gabon, which was a complete surprise at the time. West Nile virus has now been found in some 60 different mosquito species in North America, he says — also a complete surprise.
When G.W.A. Dick of the National Institute for Medical Research in London discovered Zika in 1947 in Uganda, he used captive rhesus monkeys to see if the yellow fever virus infected primates, tying the animals to trees and waiting for them to be bit by mosquitoes. The animals were bit, but the virus inserted by the mosquitoes into their blood was something never previously seen. Dick named it “Zika” after the local forest area. Today, despite startling advances in metagenomics research and virus analysis, Dick’s 1947 experimental method is not much improved. It is difficult to hunt down infected animals, snare wild forest mosquitoes, and analyze them in a laboratory.
At the U.S. National Institutes of Health, David Morens is leading new Zika research initiatives. He tells me that Zika has found new life cycles in each new ecology it has entered and will likely do so across the Western Hemisphere. “But what would they be? We can only speculate at this point,” he said. In the spirit of speculation, Morens added, “Regarding birds, while it can’t be ruled out, the Western Hemisphere is a new area for this virus, with different species and ecologic niches. It wouldn’t be my greatest fear, but it has to be considered a possibility.”
Overall, the scientists I was in touch with who work in this field told me two things: First, not enough is known about Zika (especially in the New World) to definitively answer the question; and second, other similar viruses (dengue, yellow fever, and chikungunya) have become endemic and sylvatic in the Americas, so, why not Zika, too?
I asked Claudio Maierovitch, the director of Communicable Diseases Surveillance for Brazil’s Ministry of Health, at a WHO press conference Thursday about the possibility. “Most things about the Zika virus are not known yet, and that is a big question,” Maierovitch said, noting that most of Brazil’s work is at the cellular level, infecting insect and human cells. Bruce Aylward, who runs the WHO’s epidemic response unit, added, “It would be a mistake to say [that what is now known about Zika] explains what we see now,” in the Americas.