Workers in Campinas have embarked on a huge operation to eradicate mosquitos, which spread the disease, before the Portuguese and Nigerian teams arrive.
Some 32,384 people have been infected by dengue this year in the southeastern city about one hour from Sao Paulo. At least three people have died.
"It's a record epidemic. It's bigger than the 11,500 cases registered in all of 2007," said Andrea Von Zuben, who coordinates the Campinas dengue control program.
Dengue is a viral infection carried by the aedes aegypti mosquito.
The fever is like chronic influenza with severe headaches, muscle and joint pain, vomiting and a rash.
Severe cases can be deadly. Three people have died of dengue this year in Campinas, women aged 27, 69 and 81. Three other deaths are being investigated to see if they were caused by the disease.
There is no cure for dengue, so prevention is the best medicine.
The World Health Organization recommends people in infected areas prevent mosquito bites with window screens, insect repellant and mosquito coils.
It also suggests covering up exposed skin -- advice that may cramp Portuguese captain Ronaldo's bare-chested style, a topic of much commentary after his pectoral-flexing goal celebration at this year's Champions League final.
Brazil has been hit harder by dengue than any other country so far this century, with seven million cases reported between 2000 and 2013.
Von Zuben said the Campinas outbreak was being driven by a heatwave at the beginning of the year, the prevalence of a particularly virulent dengue strain and poor sanitation that leaves pools of standing water where mosquitos breed.
But she said the areas where the Nigerian and Portuguese squads will be are a mosquito-control priority for health officials.
"We put larvicides and anti-mosquito poisons at the airport, in the training centers and in the hotels, so the teams will run a much smaller risk than the local population," she told AFP.
- Team doctors 'concerned' -
The authorities have been in touch with the teams' doctors, who were "concerned," Von Zuben said.
She said her staff had recommended insect repellant.
"We've been guaranteed that the situation has been identified and is under control. There shouldn't be any reason for alarm," said the Portuguese Football Federation (FPF).
In early May, when Portuguese coach Paulo Bento visited the training center, city officials told him three mosquito-control operations would be carried out before the team arrives on June 11.
The army has helped sanitation workers clean up 83,000 tonnes of rubbish and dozens of buildings have been sealed off and sprayed.
Campinas is not the only city facing the dengue threat.
Medical journal The Lancet Infectious Diseases recently said World Cup host cities Natal, Fortaleza and Recife in the northeast were also at risk.
Of course, infectious diseases are a two-way street.
Campinas has also launched a program to give citizens free vaccinations before World Cup fans descend on the city from Africa and Europe, where "polio and measles are still persistent," it said.
Priority will be given to taxi and bus drivers, employees at restaurants and tourist attractions, and the staff of six major hotels.