Crouching in the darkness.

Tree-felling in the Amazon - an example of man's destruction of the environment. This can lead to the increase of disease by bringing man into closer contact with pathogens. Chagas disease is an example of this. Land clearance means that wild species now infest human dwellings and among these is the fly that carries the parasite Tryp. Crusii (discovered by Carlos Chagas in 1909). Through the fly's bite, it causes cardiovascular, digestive and nervous symptoms that can result in death. 50,000 people die each year from this. People can pass on the parasite through blood donation. The fly emerges at night and is hard to detect. Insecticides have very limited effect so the best approach is prevention, through education and fly control and the speedy diagnosis of infected individuals. In Colombia the disease is a major public health threat. Houses are infested with the flies and the only answer is demolition and the construction of new houses designed to discourage infestation. But migration of workers has already carried flies in luggage to other cities and the shanty towns which surround them. In North Argentina a new city grew up, already infested. Botanists, zoologists, architects and anthropologists can all help to overcome the spread of Chagas disease.