There, I said it. Normally I pride myself on being non-alarmist, but this is a moment to issue some very loud warnings. This is a moment that we will look back on as one that could have changed the course of things: if only they had moved the Olympics. Why is this so critical? Zika virus. I am formally adding my voice to those saying that sending hundreds of thousands of visitors from all over the world to the active epidemic zone is a terrible, terrible idea.
Elison W. holds his baby brother Jose, who was born with microcephaly following Zika infection of their mother [Image: Felipe Dana/Associated Press]
Zika virus infection causes fever, joint pain, headache, fatigue and occasionally a rash in infected patients, but is rarely fatal. The infectious disease community is deeply concerned about Zika for another reason, however: it is now indisputable that neurological birth defects (microcephaly) in newborns are associated with Zika infection of their mothers during pregnancy. The current recommendations indicate that pregnant women should not attend the Olympics in Brazil. This makes perfect sense; however, it is a woefully inadequate measure. I am not saying that those who travel to Rio de Janeiro are themselves at risk for severe illness or death. I am saying they are at risk of infection, and an infected person, whether or not they are overtly sick, becomes an excellent delivery vehicle for Zika. Given the number of international visitors predicted to arrive in Brazil, these vehicles will then drive all over the world, delivering Zika virus to wherever they go next. Will they recover without infecting anyone else? Hopefully, but not necessarily.
How likely is this scenario? After all, the Games will be held in Rio’s winter, making bites by Zika’s mosquito vector less likely. “Less likely” is a very relative term. The average winter temperature in Rio de Janeiro is about 70° (21°C), which is hardly cold enough to eliminate the possibility of mosquito bites. There is plenty of evidence from other viruses spread by the same mosquito that infection rates will likely slow down, but certainly not disappear. It stands to reason, then, that some of these international visitors will become infected with Zika.
If they return home, how likely are they to spread it to others? To answer this, we have to look at how it is spread. Zika is primarily spread by one of several mosquito species (Aedes aegypti, Aedes albopictus, Aedes africanus, Aedes luteocephalus, and Aedes opok), but can also be spread by sexual contact and blood transfusion. It is generally agreed that Zika emerging as an exclusive sexually-transmitted pathogen is unlikely; however, any place where any of the aforementioned mosquitoes live represents a possible site for a future outbreak. Looking at a distribution map of Aedes aegypti alone indicates that local transmission is possible in many parts of the world where it does not currently occur, most notably India, northern Australia, the southeastern United States, and coastal China. This could result in small numbers of cases in the US and Australia. To truly have an extensive epidemic, a high population density in urban areas would be required. The potential for satellite epidemics in India and China is therefore extremely high. When one looks at the distribution of Aedes albopictus, Japan also represents a high epidemic risk. It is further worth noting that we are not yet exhaustively sure of the list of mosquitoes capable of spreading Zika. More places could be at risk than we currently realize.
Aedes aegypti Distribution (VizDataGobal)
But how likely is any of this? On a global scale, travelers to the Olympic Games represent a small number of people. What are the odds they bring it back to their home countries, where it can infect the most vulnerable? Should we be this worried about a coming generation of children with severe birth defects that will leave them mentally challenged, lower their life expectancy, and rob them of their eyesight, their hearing, or both? As a scientist, a mother, and a human being, I would argue that the odds are irrelevant. Every case in the Western hemisphere right now is somehow linked back to a single Zika-infected traveler who was bitten while visiting Latin America. All it takes is one patient, one mosquito, under the right set of circumstances. It is not worth the risk.