RIO DE JANEIRO (Reuters) - As Rio de Janeiro prepares to welcome hundreds of thousands of visitors for upcoming Carnival festivities and the Olympic Games in August, the city is scrambling to expel one unwelcome new arrival: the Zika virus.
It will be an uphill battle.
Zika is causing a widening health scare across tropical and subtropical regions of the Americas, where it has spread to over 20 countries.
In Brazil, where the virus is believed to have arrived in the hemisphere before spreading via mosquitoes, it has been linked to a brain defect in nearly 4,000 newborns.
But even as authorities knock on doors to warn people about the virus and spray tourist sites and mosquito hotbeds with insecticide, public health officials see no easy solution because the area is rife with the insects that transmit Zika and there is no vaccine.
"We are losing the battle in a big way," Marcelo Castro, Brazil's health minister, told reporters after meeting with President Dilma Rousseff late on Monday.
Castro announced plans to deploy 220,000 troops in February to distribute educational pamphlets and help scour cities for mosquito breeding grounds.
The illness is minor for most people except pregnant women and others affected by complications that scientists still struggle to understand. Zika has become more widespread as the Aedes aegypti mosquito that transmits the virus by biting an infected person has migrated around the globe.
Early on Tuesday, just over a week before Rio kicks off annual Carnival celebrations, the city deployed workers to spray insecticide at the parade grounds where the marquee festivities occur.
More than 3,000 municipal health agents are deployed across Rio targeting mosquito hotbeds. Carnival and Olympic venues will be inspected daily during the big events.
Governments and health agencies, including the World Health Organization and the U.S. Centers for Disease Control and Prevention, have cautioned pregnant women to consult physicians before they travel to affected countries.
U.S. health officials are stepping up efforts to study the link between Zika infections and birth defects in infants amid predictions for widespread circulation of the virus within the United States during warmer months.
But travel agents and hotel operators in Brazil say that, while they are receiving a lot of questions about the precautions the government is taking, the Zika scare has yet to lead to many cancellations from would-be visitors.
Government sources told Reuters on Tuesday it is preparing an international campaign through social media and travel agencies to inform potential visitors about the virus, and what Brazil is doing to fight it, in a bid to avoid any impact on the Olympics.
Warm-up festivities for Carnival in recent days have lured thousands to street marches and block parties, even if the smell of insect repellent now rivals that of the beer, sweat and urine more commonly associated with the revelry.
The virus is expected to continue spreading apace because the Aedes aegypti mosquito is notoriously adaptive.
The insect thrives in puddles, nooks and crannies common in Rio and other tropical cities peppered with chaotic and unplanned neighbourhoods, where rainwater, open sewers and litter offer ample habitat.
"It is the perfect set-up for proliferation," said Isaac Bogoch, a tropical infectious disease specialist at Toronto General Hospital, who published a scientific paper predicting Zika's rapid spread. "It can keep spreading until we find a way to contain the virus or keep the mosquitoes from transmitting it."
Zika was first identified in Uganda in 1947 and has caused limited outbreaks ever since, most recently on Pacific islands in the last decade. Officials believe it may have arrived in Brazil with a traveller when the country hosted the 2014 World Cup.
So little is known about Zika that the believed association with microcephaly, the brain defect in babies born to women thought to have carried the virus, was not hypothesised until the Pacific outbreak.
The link was only empirically tested when scientists began collecting amniotic samples from mothers of affected children in northeast Brazil last year.
Now, laboratories are rushing to produce a test that can identify the virus quickly in suspected patients and, more significantly, develop a vaccine, a process that scientists say will take years.
Meanwhile, doctors and public health administrators say the challenge is to get citizens engaged in the struggle against the mosquito.
Not only does poor development and gaping inequality across Latin America provide ripe terrain for urban infestations, some residents are dismissive or downright hostile towards a public sector that often fails to provide basic health, sanitation, education and other public services.
In Rio, health agents sometimes cannot even enter neighbourhoods because of crime and security risks.
"A lot of people don't want to hear anything the city or state has to say," said Hermano de Castro, director of the National School of Public Health at the Oswaldo Cruz Foundation, a health institute run by Brazil's government. "It's hard to get people involved when health workers are considered outsiders."
Previous efforts to target Aedes aegypti have failed. The mosquito is known to carry other tropical maladies, including yellow fever, dengue and chikungunya.
Although authorities have sought to educate locals about the dangers of stagnant water, dengue has worsened in recent years. Last year, Rio registered 10 times as many cases as in 2014, including at least 22 deaths.
The outbreaks come at a time when Rio's state government, strapped for cash because of plummeting royalties from offshore oil fields, has been forced to shutter hospitals and research laboratories.
"We can't even control dengue and now we have Zika to battle," said Daniel Becker, a prominent paediatrician in Rio who, like many doctors, fears the microcephaly scare might lead to a dangerous surge in clandestine abortions in Brazil, where terminating pregnancies is illegal.
Reporting by Paulo Prada; Editing by Kieran Murray and James Dalgleish