A recent article posted in Mongabay News highlights a study posted in Emerging Infectious Diseases which suggests that deforestation and agricultural expansion are drivers for the increased prevalence of Plasmodium knowlesi malaria among humans in Malaysia.
Plasmodium knowlesi malaria is commonly referred to as ‘monkey malaria’ as it is traditionally known to use forest-dwelling macaques as natural reservoirs. The disease is transmitted via female Anopheles mosquitoes, the same mosquitoes that transmit the other four, better-understood strains of malaria which are known to infect humans. Plasmodium knowlesi malaria is zoonotic since the disease can be transmitted from animals to humans.
In the study, researchers from Malaysia, Australia, and the United Kingdom collected data on the number of P. knowlesi malaria cases reported and recorded the land use patterns within districts where those cases occurred. Researchers found that there were higher incidences of humans infected with monkey malaria within areas where deforestation was high. According to the Mongabay article, “the [research] team found that during the five-year period of study, 50 percent of the region’s villages lost more than 10 percent forest cover with a five kilometer (~3 miles) radius.” This forest loss had a strong correlation with the number of human malaria cases in the villages.
Deforestation has been linked with forest crowding, as more animals are forced into an ever decreasing amount of space. Increased contact between infected individuals could be responsible for the high rates of malaria transmission between macaques. Humans using previously-forested land for agriculture also increases the amount of shared land use between the three species. Thus, farmers who are moving closer to the edges of the forests are more susceptible to bites from mosquitoes infected with P. knowlesi.
The researchers offer these hypotheses for the prevalence of monkey malaria in deforested areas, but more research is required to identify the causes of this correlation. This is just one incident which highlights that conservation efforts for great apes can be extremely beneficial to humans in terms of preventing disease transmission. Other research has shown that wildlife diseases like HIV and Ebola can be transferred from great apes to humans through the consumption of bushmeat, an illegal activity which is threatening great ape populations. The overlap between conservation of primates and the study of disease interactions between great apes and humans will become increasingly relevant as globalization increases the transfer of diseases internationally.