"Avoid visiting impoverished or overcrowded areas."
That phrase — initially included in the World Health Organization's statement of advice to visitors to Rio for the Olympic Games, has caused controversy in Brazil. Rio's mayor, among others, have condemned the recommendation, which some Brazilians feel unfairly stigmatizes poor residents and locks them out of tourist dollars during the Olympic games.
In Rio, "impoverished" areas refers to the urban neighborhoods known as "favelas."
From WHO's perspective, the point is that even though the cooler weather in August — that's Brazil's winter — will mean fewer mosquitoes that can spread the disease, visitors still face risks. But they can manage and minimize those risks, says Dr. Bruce Aylward, the interim director for the Outbreaks and Health Emergencies Cluster at WHO.
We asked WHO why "impoverished or overcrowded" areas were singled out. The Aedes aegypti mosquito that carries the Zika virus likes to breed in standing water that collects in discarded tires and flowerpots, says Aylward of WHO.
"And it is in these poorer or impoverished areas where you are more likely to find still water or standing water that has been collected. So again it's just looking at what factors drive the higher probability of getting bitten by mosquitoes."
He believes the probability will be higher in those poorer areas.
But Brazilian scientists say the link between poverty and Zika is not clear, especially in Rio de Janeiro. While the Zika virus only recently arrived to Brazil, scientists here have done a lot of studies on the dengue virus, which is transmitted by the same type of mosquito.
"Rio de Janeiro is a mosaic of poor neighborhoods and rich neighborhoods," says Cláudia Codeço, a biologist who specializes in mosquito-borne diseases at Brazil's largest research facility, the Oswaldo Cruz Foundation. "They are all mixed, so from the [mosquito's] perspective there's no boundary between one place and the other. So you are going to find them everywhere."
Codeço says research at the foundation has shown that because the Aedes aegypti mosquito prefers clean water, it is not especially drawn to an area where there is a lack of sanitation.
Besides, the mosquito has a limited range, but humans do not.
"Humans are the main long distance transmitters of dengue or Zika or chikungunya, in comparison to mosquitoes," she says.
That's because mosquitoes catch Zika from biting an already infected human. So an infected person could travel to any part of the city, then infect a mosquito in a different part of town, rich or poor.
And even though researchers and health officials often draw a link between poverty and the spread of mosquito-borne viruses, there aren't many studies to back up the claim. It likely depends on the specific city and the specific disease.
Last year, researchers at the University of Waterloo examined the link between dengue and poverty. They found 12 studies on the topic in English. And about half of those studies reported some link between measures of poverty and dengue. But the other half didn't. In some instances, the studies found actually the opposite of what was expected: higher incomes and higher education were linked with higher rates of infection.
"Taken together, the sample provides little in the way of conclusive evidence to support the assertion that dengue is a disease of poverty," the researchers wrote in journal Pathogens and Global Health.
That's good news for the favelas — Rio's shantytowns. Paulo Cesar Viera, known by his nickname Amendoim or Peanut, shared his perspectives with me during a tour of his favela, Rocinha.
He's 58 and has lived in Rocinha since he was a child.
"I feel proud," Viera says. "I am here since there is no water, no electricity no healthy, no sewage, no nothing. And now we have almost everything."
This vast community is home to tens of thousands of people. It's bustling and busy with shops and banks and schools. Viera is a community activist but also makes his living bringing tourists into the favela with the aim of showing them something different than the poverty and violence that is normally portrayed.
"People from other countries have totally bad information about us," he says. "It's important we take them to see the reality of favela."
And that's what he was hoping to do during the Olympics. Except he worries that the World Health Organization recommendation will keep people away.
But in fact, the research shows you have to take the same precautions to repel mosquitoes no matter what part of town you visit.
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