Visitors to the Brazilian Olympics and Paralympics are extremely unlikely to catch Zika, let alone infect their home countries, says a team of doctors from Yale. Even so, everybody going to the Games should practice safe sex or abstain for at least eight weeks, whether or not they think they caught the mosquito-borne disease. That's not only to prevent pregnancy and avoid the potential of birth defects caused by the virus: it's to prevent transmission of the disease through sex.
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The 2016 Olympic and Paralympic Games are expected to be attended by more than 10,500 athletes and as many as 500,000 visitors are expected in Brazil in August and September. Brazil is also where Zika - a viral disease that apparently originated in Africa – has become associated with a wave of severe, sometimes fatal, birth defects, including microcephaly. Many have called for the Games to be postponed or moved.
That's unnecessary, going by the Yale estimates published in "Low Risk for International Zika Virus Spread due to the 2016 Olympics in Brazil," in the Annals of Internal Medicine this week. The doctors' low estimates are based on the worst-case scenario: that visitors have exactly the same exposure potential as the local Brazilians, which of course, they do not.
First of all, many visitors will be spending much of their time in screened and air-conditioned accommodations, and all have been advised to wear long clothing and use mosquito repellent.
Secondly: true, mosquitoes are ubiquitous. That said, "In Brazil, the risk is concentrated in the poorest populations in the cities and in the favelas," lead author Dr. Joseph Lewnard of the Yale School of Public Health told Haaretz. Those are the areas most likely to have standing water, which is where the mosquitoes breed, he explains, and adds: "It's very unlikely for most of the people [visiting the Games] to be staying in such sorts of accommodation. So it's likely that the real incidence of disease will be even lower than we're estimating here."
Even assuming that all half-million visitors do stay in slum-like conditions, the Yale team estimates that an individual traveler's probability of getting Zika in Rio de Janeiro is between 6 to 80 total infections - yes, "including athletes, spectators, vendors and the media, everyone in total in Rio, because the Olympics are happening," Lewnard says.
Moreover, that low estimate includes asymptomatic infection, which is usually the case. Of the 6 to 80 likely to get Zika, only 1 to 16 are expected to show any signs of infection.
The word is condoms
Zika is transmitted by Aedes aegypti mosquitoes and also by Tiger mosquitoes (both of which exist in Israel). In horrible news, last Thursday Brazilian researchers warned that they found signs of Zika virus in a common mosquito - Culex quinquefasciatus. It is not known whether infected Culex can transmit the disease.
Theoretically the virus can become endemic anywhere carrying mosquitoes exist and indeed, it has been spreading, though cases reported in both Israel and Thailand seem to have been contracted elsewhere, meaning the disease isn't endemic yet. Israel is however on the list of countries with medium risk of the disease becoming entrenched.
Zika can also be spread by sex (in both directions: man to woman, woman to man). If people get infected by Zika in Brazil, go home, and then get bitten by any mosquito capable of harboring the disease (or have unprotected sex), they stand to contribute to its incidence in their home country. Recent evidence shows that Zika virus can remain active in semen for months after the symptoms fade.
The Yalies don't think visitors would have lesser natural immunity to Zika than local Brazilians (which would have skewed the estimates).
"We don’t have a very good idea where Zika has been historically in the world," Lewnard explains. The thinking is that it originated in Uganda, but in any case the disease had been considered a nonevent until the recent epidemic in the Americas, and ensuing rash of serious birth defects. "So there have been very few antibody studies that could answer the question about natural immunity to Zika," the doctor explains. The Brazil outbreak is considered to have happened on virgin soil, as it were.
The bottom line, given the uncertainties, is that absolutely everybody going to the Brazil Games should use condoms or abstain from sex for at least eight weeks after returning home, the Israeli Health Ministry and World Health Organization agree. That's because the disease is usually asymptomatic. You can't know if you have it or not. If the man is in a couple planning pregnancy, the period of safe-sex or abstinence should be six months - not only for the sake of preventing pregnancy and the possibility of zika-elated birth defects, but to prevent sexual transmission too.