Brazilians fight dengue with bacteria | Science| In-depth reporting on science and technology | DW | 02.01.2013
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Brazilians fight dengue with bacteria

Dengue epidemics continue to break out in South America. Last year, more than 100,000 people contracted dengue fever in Rio de Janeiro alone. In its fight against the deadly virus, the city is employing unique methods.

The endless battle against Rio de Janeiro's mosquitoes takes Luciano do Campos Lobo to dark courtyards in Rio de Janeiro's cramped favelas and to its luxurious villas, hidden away behind imposing iron gates and walls. Armed with a clipboard, Luciano knocks on doors and stomps around abandoned parks, on the lookout for eggs, larvae and mosquitoes.

Today, Luciano is fighting to make himself heard over the din of the many taxis and busses speeding along the busy road. As he yells into a crackling intercom, a little old lady teeters past, dragging a manicured poodle on a leash behind her. She eyes Luciano's black beard and heavy boots and gives a disappointed sniff as she disappears into the gleaming white tower block.

The enemy in ponds and puddles

Dengue inspector going about his work in Rio de Janeiro (Photo: Naomi Conrad, 2012, Brazil)

Luciano Do Campos Lobo works as a mosquito inspector

The security guard greets him more enthusiastically. Every three months, Luciano, who works for Rio de Janeiro's Department of Health and Civil Defense, inspects the building's underground garage - flashing his torch behind pillars and under the residents' Mercedes cars. It takes him 15 minutes to inspect the garage, pour chemicals into a small puddle and sign off on a security guard's log book.

Luciano is one of 3,000 mosquito inspectors that the Ministry of Health sends out every day to patrol Rio de Janeiro's ponds and puddles: potential breeding grounds for a dangerous army of mosquitoes.

"The only thing the mosquito needs is a very small amount of water," Betina Durovni explains. A dripping pipe or abandoned pond can endanger an entire neighborhood she says. Durovni, a medical doctor by training, is the second in command in Rio de Janeiro's Department of Health. Every two to three years, dengue epidemics sweep through the city. "This is an urban area with a tropical climate - it's very difficult to control," she says, gesturing out of her window on the eighth floor of Rio de Janeiro's Health Ministry.

View over Copacabana beach (Copyright: DW/Naomi Conrad 2012)

Dengue cases explode in the summer months

With Rio de Janeiro's hot and humid summer months approaching, Durovni says the risk of infections is set to rise again. Dengue is so dangerous because it sees victims go from being healthy to very ill, particularly quickly. The World Health Organization says serious dengue (previously known as dengue haemorrhagic fever) is a leading cause of death amongst children in Latin American and Asian countries. The symptoms include headache, fever, throbbing pain behind the eyes and muscle pain, followed by dehydration. Death can follow shortly thereafter if there is no adequate medical care.

'We have avoided many deaths'

The city has opened some 30 new health clinics in the last couple of years, says Durovni. They have also tried to heighten awareness through the use of social media. So far the strategy has been successful, according to Durovni. In the outbreak at the end of 2011, there were some 111,000 dengue cases with 30 of them being fatal. In 2008, there were 157 fatal cases.

"We know that we avoided many, many deaths in the last outbreak," Durvoni says. But, she adds, more deaths and further outbreaks are expected. Scientists are currently testing a first vaccine but the results have so far been disappointing, according to a recent report in the "New York Times."

That is why the Brazilian government is trying another approach in the fight against dengue - namely, bacteria.

Mosquitoes fed with human blood

Luciano Moreira's laboratory is situated in a huge park in Rio de Janeiro's noisy port area, hidden away behind the thick walls of the Oswald Cruz Foundation, Latin America's most important medical research institute.

It's hot and humid in Moreira's lab, 27 degrees Celsius and 60 percent humidity. Perfect breeding conditions, Moreira says. Moreira’s mosquitoes only survive on a diet of human blood, he says.

City Centre Rio de Janeiro (Photo: DW/Naomi Conrad 2012)

Rio de Janeiro's densely populated housing areas are at risk

The biology professor has been experimenting with mosquitoes for 16 years. He is part of an international team of scientists experimenting with Wobachia bacteria. It took them four years to manage to inject mosquito eggs with these tiny parasites. Each insect reacts differently to the parasite, which can be found all over the world, Moreira says. "They're everywhere in the food chain, like fruit flies," he says in response to whether such meddling with the food chain may have any effect on human beings. "They're even in bananas," he adds.

In mosquitoes the bacteria prevents the transmission of dengue. "When we collect saliva from mosquitoes 14 days after they were infected, we don't find any virus there."

The fight continues

The project, which comprises Australian, Brazilian and Vietnamese scientists, is co-financed by the Brazilian government. In Australia, first colonies of treated mosquitoes were released into the wild. Soon, Moreira says, his team will release mosquitoes into isolated areas in a controlled experiment.

But, he stresses, his mosquitoes are unlikely to win the battle against dengue single-handedly. He hopes that there will be a vaccine eventually. "We have to continue doing what we have been doing. We have to use insecticides and educate people to get rid of all the breeding containers at home."

After all, it's nearly impossible to prevent mosquito bites, Moreira remarks as a tiny mosquito flutters past his hand. He bats it away, looking irritated. Then he shrugs. His mosquitoes, after all, don't transmit dengue.

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