Now and again through the evening calm comes the sound of a powerful petrol motor, and soon afterwards the streets are filled with a thick grey cloud. This is insecticide, and they are fumigating against the mosquito Aedes aegypti. Aedes is one of the banes of mankind, in many ways, but the worry here is Dengue fever.
Dengue is a virus, and causes fever, joint pains and, even sometimes hemorrhage and death. It is incredibly common in tropical regions around the world, with about 50 million cases a year. You can´t catch it by shaking hands, or sneezing or eating the wrong foods, it has to be transmitted blood to blood, which in practice means the bite of a female mosquito of the Aedes genus. Hence the attempt to eradicate this little pest.
But does this really have anything to do with the Mata Atlantica? It´s not just the mosquito bite that causes a disease, there has to have been someone infectious to infect the insect. Or something infectious. Some animals act as reservoirs for human diseases, the sylvan equivalent of typhoid Mary. Yellow fever, for example, is notorious for infecting primate populations, so lumberjacks clearing forest are often particularly at risk.
In the Americas at least, that was thought not to be the case with Dengue, not least because it is not native here. It was brought over with slaves from Africa and immigrants from Asia, and so is not adapted for local wildlife. However, recent research in French Guyana, the French colony north of Brazil, found viral RNA in quite a few animals, including rodents, marsupials and bats. Several of these, such as the mouse opossum Marmosa murina are found in the Mata Atlantica and the presence of virus in their systems suggests that it is adapting. This is bad news for attempts to eradicate the disease.