The United States and 31 other counties on Friday learn their opponents for the opening rounds of the 2014 FIFA World Cup[1] in Brazil next June and July. The football teams and their fans will also find out in which of the 12 tournament venues, scattered across South America's largest nation, their matches will be played.


Three of the host cities -- Fortaleza, Natal and Salvador -- all in Brazil's northeast, will be near peak dengue[2] season then.


Brazil is a hot spot for the rising tropical disease, a mosquito-transmitted virus that lacks a vaccine or treatment. The nation's 573 dengue deaths in 2013 through Nov. 20 is nearly double the [3] 2012 toll. Most people recover without complications, but the most severe form of dengue kills one of four victims[4] .


"There's been a persistent increase of dengue through a good part of world, especially South America," said John Brownstein, a pediatrician and researcher at Children's Hospital Boston.


The number of global cases of dengue has grown to an estimated 390 million a year[5] , according to a study co-authored by Brownstein in April.


Urbanization, transportation and climate change all may contribute to its surge -- and may increase risks during next summer's World Cup. But experts said they hope the added spotlight will help raise awareness and action against a disease overshadowed by malaria.


"Brazil is in a strong position to lead international action against dengue," said Simon Hay, an infectious disease expert at the University of Oxford, who warned of the risks in a commentary[6] in the journal Nature on Saturday.


In preparation for two major international sporting events -- Brazil also will host the 2016 Summer Olympics -- the country is building multiple stadiums and developing many of its cities. Hay noted that the World Cup tournament is expected to sell more than 3 million tickets.



Aedes aegypti, the mosquitoes that are dengue's primary carriers, "love human environments," said Cory Morin, a postdoctoral research associate in geography and development at The University of Arizona. "The more the area is urbanized, the better it is for that mosquito."


Just as the assembly of thousands of football fans could fuel transmission, urbanization means more people for mosquitoes to bite. It also means more tires, toys, planters, impervious concrete and construction sites to collect water and provide perfect breeding grounds.


"If they do a lot of landscaping, they could integrate more mosquito habitat in areas close to stadiums," said Shannon LaDeau of the Cary Institute of Ecosystem Studies in Millbrook, N.Y. She suggested that gardens and the garbage that comes with massive crowds could breed problems in Brazil. "If you've got rain and garbage, you will have mosquito habitat."


"Maybe this attention from the World Cup will be a great motivator to make more permanent changes," LaDeau added. "I sure hope whatever development happens doesn't add to Brazil's problems."


Oxford's Hay recommended that Brazilian authorities implement "aggressive" mosquito control prior to dengue season and the tournament. That includes clearing “rubbish” and other places where water collects and deploying insecticides once they detect adult mosquitos. For World Cup travelers, Hay suggested choosing accommodations with screened windows, doors and air conditioning, as well as using insect repellent and wearing clothing that covers the arms and legs. He and other experts emphasized the importance of educating the public and promoting personal protection.


"You've got people coming in from places where they may not have seen the real problems caused by mosquito-borne disease," said Brownstein. "They may not be sensitized to the risk."


A quick glance at DengueMap[7] could help a traveler see the extent of the current risk. Bright red spots indicate the presence of the disease.


Brownstein has helped to build maps for infectious diseases, including this visual tool, which mines official databases, newspapers, social media and other sources to provide timely estimates[8] of dengue risk throughout the world. He noted that his team will be keeping a close eye on Brazil -- and countries connected via transportation routes -- during the soccer tournement.


Another worry is World Cup fans carrying the virus back home. Most cases of dengue that have popped up in the U.S. have been imported by travelers returning from tropical trips. Dengue can take about a week from the time a mosquito bites to show its characteristic high fever, severe pain behind the eyes and joint aches. While most cases resolve within a few days, a small percentage can turn into dengue hemorrhagic fever, a life-threatening condition.


More than 40 percent of the world [9] is already at risk.


Developed nations have faired far better against dengue than the rest of the world, thanks in large part to air conditioning, access to health care, storm water systems and well-sealed homes. Still, experts warned that countries like the U.S. are not immune. While imported dengue cases rarely turn into outbreaks, there is some evidence that dengue could reestablish a foothold in Florida[10] and Texas[11] after a hiatus of several decades.


Climate change, some experts said, may be among factors making parts of the U.S. more welcome to the Aedes aegypti mosquito, which usually dwells in tropical regions. The invasive Aedes aegypti made its debut in northern California[12] this summer.


The Asian tiger mosquito[13] , another invasive species increasingly common around the U.S., has also shown the ability to transmit dengue. The Asian tiger, too, seems to be expanding its range north with the warming climate.


Arizona's Morin is the lead author on a study published this week on the complex role of climate change in dengue[14] .


Warmer temperatures, Morin explained, can speed key steps involved in the spread of the disease: growth of the mosquito population, replication of virus inside the mosquito and the time between a mosquito taking a blood meal and being able to transfer the virus to another person.


High heat and low humidity, however, can be bad news for mosquitoes, said Morin. The interplay between climate change, temperature and precipitation is complicated[15] .


Overall, Morin said, climate change may have less of an effect on Brazil than on the U.S. "Brazil already has ideal temperatures," he said. "But southern Florida may be on just on the edge of the transmission threshold, so a littler warmer could make a bigger difference."


Brazilians have staged multiple protests[16] against the government for spending of billions of dollars to host the World Cup and Summer Olympics. Many citizens believe that money should be spent alleviating poverty and improving the nation's health care system and public infrastructure -- investments that could be critical in combatting dengue.


Hay told HuffPost that neither the Brazilian government nor FIFA, the organization that governs the World Cup, have responded to his journal commentary. He said he hopes the article will stimulate discussion.


"Brazil is just one of over 100 countries fighting an ever increasing dengue burden," added Hay. "Bringing this issue to the forefront, in the context of the World Cup, presents a good opportunity to call for a more coordinated more international response to this growing global tropical disease."