New research conducted in Malaysia has drawn a link between deforestation and a rise in a specific strain of malaria often carried by macaques, a link the study’s lead author says could hold true for Cambodia as well.
The results of the study, published in Emerging Infectious Diseases last week, found that deforestation in two districts of Malaysia was linked to “a steep rise of [plasmodium] knowlesi malaria”. The strain went from accounting for just 2 per cent of malaria cases in the districts studied to accounting for 62 per cent over nine years.
The P knowlesi strain, first identified only a few decades ago, is usually carried by macaque monkeys, which appear to increasingly transfer the disease to humans as settlements push deeper into previously undisturbed forests, the study found. Two human cases were reported in 2011 in Cambodia’s Pailin province, which has high deforestation rates.
Dr Kimberly Fornace, the study’s lead author and a fellow at the London School of Hygiene and Tropical Medicine, said that “in Cambodia, deforestation is strongly associated with human malaria . . . It has to do with the fact that mosquitoes are forest-breeding”.
As for P knowlesi specifically, Fornace said, “the conclusion [in Malaysia] is applicable to Cambodia”, given that parasite-carrying macaques and deforestation both exist in the Kingdom’s forests.
Explaining the findings, Fornace said there is a “strong statistical link with macaques seeing people” and the increase in infections. Deforestation, she continued, creates gaps in forest cover that lead to a “high spatial overlap” between human and macaque populations, and cause P knowlesi infections to become increasingly common.
Very little research exists on P knowlesi in Cambodia, and data on the macaque population is also lacking. The authors who reported the P knowlesi cases in Pailin concluded that “further wide-scale studies are required to assess the prevalence and distribution of P knowlesi malaria cases”.
Dr Rabindra Romauld Abeyasinghe, the World Health Organization’s regional coordinator for its malaria, vectorborne and parasitic diseases unit, said the disease remains relatively uncommon in humans, but acknowledged that “when people enter forests, the disease may be transmitted to humans”, and that studies have found serious and even fatal human cases.
The WHO in Cambodia and a spokesman for the Ministry of Health referred questions to Dr Huy Rekol of the National Malaria Centre, but multiple attempts to contact him were unsuccessful.