Saturday, 13 March 2010

Fever in the Forest

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.

4 comments:

Steven said...

I have been told by several people that:
The mosquitos carrying dengue are only active during daylight, sepecically dawn and dusk.

They live on or near the ground and adults are safe if wearing socks and long trousers.

A Google search shows conflicting results. There are lots of warnings about dusk and dawn but confusion about whether the danger period is dawn to dusk or vice versa.

The low flying dengue mozzie sounds like folklore to me. I reckon that feet are the easiest target. I cannot find anything authoritative.

So can anyone give any specific advice?

Mynah Bird said...

Interesting post. Dengue has been a lot in news in Kerala, where due to open sources of natural water & poor drainage, the erdaication or the control of mosquitos is a huge problem.

But I am more curious about the prevalence of the viral RNA in rodents, marsupials etc.Does the disease manifest in these animals or does it lay dormant? Is the RNA similar to that found in humans or is it a variant?

Bec said...

So what do you make of the item in the UK news stating that there is a plan to release sterile male mosquitos as a way to wipe out diseases spread by mosquitos?

Anonymous said...

Very good! I would like to learn more about this! By the way, nice collections of posters!