Laurie Garrett :
(From previous issue)
Virus hunter Edward Hayes of the Barcelona Centre for International Health Research writes that, “There is to date no solid evidence of nonprimate reservoirs of [Zika],” though rodents can be infected experimentally. He concludes that any sylvatic cycle would have to involve monkeys and apes – which are plentiful in places like the vast Amazon, but rarely seen in the large urban centers of the Americas. Nikos Vasilakis of the University of Texas Medical Branch in Galveston has shown through his work that dengue and yellow fever – both viruses native to the Old World – have established firm sylvatic cycles in South America, infecting monkeys and a range of wild mosquito species, and occasionally spilling over into urban areas to infect and sicken people. So, given evidence that other mosquito-carried viral diseases that are new to the Americas have found permanent homes there, including in New World animals and birds, how likely is it that Zika will become a permanent feature of the public health landscape and ecologies of the Western Hemisphere? I polled several prominent arbovirus experts in the United States, Canada, Brazil, and Mexico, and asked them how likely a sylvatic scenario might be for Zika.
Maurício Lacerda Nogueira of the São José do Rio Preto medical school in Brazil told me that virtually zero funding is available for the study of disease ecology in Latin America, and none of the research that is urgently needed is supported by the region’s governments. Nogueira’s U.S. colleagues say the funding situation is equally bad in the country, and funding cycles are so distant that scientists would have to wait until 2017 to get money to chase mosquitoes and animals in the Everglades, or capture and test wild mosquitoes all over the country.
The Zika blood test is quite poor, researchers bemoan, and even when using sophisticated laboratory technology it is extremely difficult to find the virus in infected people, much less insects, birds, and animals. Lyle Peterson and his team at the CDC have developed an improved RT-PCR test – nerd-speak for a DNA-based screening method – but even within the United States only a handful of public health labs know how to use it, he told a special Jan. 28 Zika meeting at the WHO.
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.
But Zika has been circulating in South America since last April or May, and explosive spread in Brazil has been underway since October. The correlation (if not causation) between Zika, pregnancy, and microcephaly has been noted by Brazilian health authorities since November, as have a worrying number of cases of paralytic Guillain-Barré syndrome. Yet the WHO has done little publicly throughout November and December, save releasing a few press statements. This week, the New York Times and Newsweek, among others, asked whether the WHO was asleep at the wheel.
My conclusion is that public health leaders and politicians had better brace for a very long haul on Zika. The virus will hide, infecting a range of insects, perhaps monkeys, even birds. And it will return in seasonal cycles, as have other mosquito-carried viruses, such as yellow fever, West Nile virus, chikungunya, and dengue. Because so many “foreign” viruses carried by mosquitoes are now spreading across the Western Hemisphere at the same time, there will be misdiagnosis, mystery, and perhaps acute illnesses due to co-infections. Until we have an effective vaccine and have executed mammoth immunization campaigns in all of the nations of the Americas, Zika will haunt us, sicken some of us, and endanger our babies.
(Laurie Garrett is senior fellow for global health at the Council on Foreign Relations and a Pulitzer Prize winning science writer). (Concluded)
