In Malaysia, a rare form of malaria caused by the parasite Plasmodium knowlesi has leapfrogged other sources of the disease to cause 68 percent of the country’s malaria cases in 2013. While causality has not yet been proven, Dr. Balbir Singh, Director of the Malaria Research Center at Universiti Malaysia Sarawak, believes that deforestation is putting macaque monkeys (which are common hosts of the parasite) in closer contact with humans, resulting in an increase in cross-species transmission.
According to a 2013 study published in Science, Malaysia lost around 14 percent of its forests between 2000 and 2012. This was chiefly due to to logging and the transformation of forests into palm oil plantations. These activities put humans and macaques in closer proximity to one another, and human infections with P. knowlesi are reportedly concentrated at these interfaces.
Dr. Singh says. “This is a form of malaria that was once rarely seen in people, but today, in some remote areas of the country, all of the indigenous malaria cases we are seeing are caused by the P. knowlesi parasite. If the number of cases continue to increase, human-to-human transmission by mosquitoes becomes possible. In fact, this may already have happened, which would allow P. knowlesi malaria to spread more easily throughout Southeast Asia.” This shift from macaque-to-human to human-to-human transmission is a great cause for concern.
While not considered the most deadly of the Plasmodium species – that dubious honor is reserved for P. falciparum – P. knowlesi is notable for the speed at which it replicates: just 24 hours. In contrast, P. falciparum replicates in 48 hours, and P. malariae in 72 hours. This makes it very hard for doctors to test and diagnose patients before the disease has taken hold. It also allows the disease to spread more rapidly. To make matters worse, the mosquito vectors for P. knowlesi are active outdoors. This makes Malaysia’s current methods for combating other mosquito-borne diseases such as dengue ineffective, as they are transmitted by mosquitoes that prefer dark interiors. It’s clear, however, that a rapid response is needed on many levels, and slowing the rate of deforestation might not be such a bad idea either!