Want to get sick? Just cut down more forest

A recent essay is underscoring what a lot of environmental scientists have long suspected: deforestation often begets more human diseases.

Why?  Well, there are lots of reasons:

1.  Mosquitoes -- notorious vectors of diseases such as malaria and dengue fever -- love deforested areas.  One study found roughly 300 times as many malaria-carrying mosquitoes in deforested areas of Peru than in areas with intact rainforest.

2.  Deforested areas are much more rife with cutaneous leishmaniasis -- a debilitating disease that causes massive scarring of the skin.  The reason: the sandflies flies that carry the disease normally live in the forest canopy, and when the trees are felled the flies come into contact with those felling the forests.

Cutaneous leishmaniasis

3.  Areas that have been deforested have more people and more roads.  More people means more hosts and reservoirs for human diseases.  And more roads mean that diseases can enter an area more easily.  In Africa, for instance, AIDS has been shown to follow major trucking routes, as some truck drivers avail themselves of prostitutes who carry the disease.

4.  Deforested areas are typically hotter than those that retain forest.  This happens for two reasons.  First, the land surface is exposed to more direct solar radiation.  Second, the evaporative cooling effect of the forest is largely lost.  Many diseases and disease vectors like such hot conditions.

5.  Newly deforested areas expose humans to new pathogens.  Hunters, for instance, can encounter new diseases when they hunt in new areas or eat weak or sickened animals.  Ebola, AIDS, hantavirus, yellow fever, cutaneous leishmaniasis, leptospirosis, and malaria are just a few of the known examples of severe pathogens that can be transmitted to those in frontier areas.

Ebola... a grim prognosis for most victims.

And remember, in the frenetically globalized world in which we now live, a disease that pops up in a remote location can quickly become a global pandemic.

The bottom line: felling the world's rainforests doesn't just bring giant risks for biodiversity and ecosystem health.  It can actually imperil all of us.