Despite heavy mosquito-control efforts, some athletes came home from Rio with mosquito-borne illnesses, new study shows. (Luca Bruno/Associated Press)

Some athletes who competed at the 2016 Olympics in Rio de Janeiro brought home medals. Others, however, brought home less desirable souvenirs: mosquito-borne illnesses.

According to a new study conducted by the University of Utah and the United States Olympic Committee, 32 athletes contracted either West Nile, dengue fever or chikungunya, all viruses that are transmitted by mosquitoes, during their stays in Rio last summer. Not on the list of illnesses was Zika, a mosquito-borne virus connected to birth defects that made international headlines ahead of the Games.

“Everyone was concentrating on Zika and ignoring that there could be other infections caused by mosquito bites,” Utah infectious disease specialist Dr. Krow Ampofo, who worked on the study, said in a press statement. “We did not expect to find so many [athletes] with these other infections.”

The study collected blood samples from 457 athletes before and after the Rio Games looking for new antibodies in their samples that would suggest they had been fighting off a new disease. Of the 32 athletes whose before and after tests differed, 27 showed antibodies that suggested they contracted West Nile, three had chikungunya antibodies, and two had antibodies for dengue. None of the athletes showed severe health problems, while only a handful showed any symptoms at all, mostly body aches and rashes, according to the study.

The initial numbers may not sound alarming, but public health officials see the results as cause for concern because the athletes who tested positive may have contracted the illnesses in areas of the city that had undergone extensive mosquito control.

“If you think about it, the athletes are likely the least affected,” Amir Attaran, a public health professor at the University of Ottawa, told NPR this weekend. Attaran was one of more than 100 health professionals who called on the Olympics to be moved or postponed due to Zika threats.

“[The athletes] and their support crew stayed in the Olympic Village — and that’s as good as mosquito control got,” Attaran continued. “So, if you’re picking up in this study 32 cases of some mosquito-borne illness among the most coddled group during the Olympics, what does that tell you about the rest?”

The good news related to the study is that no athletes showed evidence that they had been infected with Zika, which is what originally prompted Utah to launch the monitoring program.

“We were thrilled that there were no cases of Zika,” lead investigator Dr. Carrie Byington said.

Others who worked on the study, however, see the results as a good reminder to remain vigilant regarding other more common, mosquito-born threats.

“We all had our Hollywood sunglasses on, and they blinded us to other possibilities,” Marc Couturier, a medical director at ARUP Laboratories, which conducted the testing, said. “We can’t forget that West Nile virus has been around for a while, and is still here.”

While rarely deadly, the West Nile virus is one of the most commonly spread mosquito-borne illness. Outbreaks have been linked to several areas of the world, including North and South America. Most of those infected show no symptoms, while some might develop a rash or fever. Only 1 out of 150 cases develop into a serious, possible fatal illness, however, according to the Centers for Disease Control and Prevention.

Chikungunya, meanwhile, which only recently made landfall in the Americas, also rarely develops into a serious illness, but is often associated with fever and joint pain. Dengue fever, on the other hand, is one of the leading causes of illness and death in the tropics and subtropics, according to the CDC. While symptoms can present as mild, they can also become severe, causing persistent vomiting, bleeding gums and difficulty breathing.

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