When we mess with our environment, we often create unforeseen consequences that come to bite us in the butt later. A new study by the Center for Disease Control (CDC) shows that it is likely that deforestation is a contributing factor to the spread of a malaria parasite (Plasmodium knowlesi) usually found in macaques to humans in Malaysia.
It might not seem obvious at first why cutting down trees would increase the transmission of a form of monkey malaria to humans, but when looking at what environmental disturbance was responsible, the researchers discovered that it had an impact:
Here's a map showing where malaria can be found around the world. Note that the Eastern U.S. used to be afflicted:
“That’s when we started looking at deforestation,” said the new study’s lead author, Kimberly Fornace, a research fellow at the London School of Hygiene and Tropical Medicine. She said she and her colleagues had an idea that “forest clearing and development are actually causing people and mosquitoes and macaques to be in much closer contact than before.”
By comparing data from health clinics between 2008 and 2012 with satellite photos showing the progression of deforestation in the surrounding areas, the study authors were able to decipher patterns of infection that correlate with forest cover.
They found that areas with a high historical rate of deforestation — in other words, the amount of deforestation that had occurred in the years leading up to an incidence of human malaria — were associated with higher rates of infection. However, they also found that areas that still had more than 65 percent of their forest cover were also tied to high infection rates.
The explanation has to do with a phenomenon known as the edge effect, which is when ecosystems experience high degrees of environmental change right at the edges of a habitat. These effects tend to be most pronounced in areas where humans have left certain parts of the ecosystem standing, but have sliced them into fragments through activities such as logging and clearing.
It is at those edges, where humans and macaques are most likely to be in close proximity, that is most critical for the transmission of the parasite.
The destruction of the monkeys' habitat is also likely to have an impact, crowding them into smaller areas and forcing them out of the forest to find food.
So add this to the list of reasons (as if we needed more!) why deforestation must be stopped. Not only is it bad for biodiversity and the climate, but it could also cause new diseases to spread to humans (as well as other animals).