Malaria is one of the world's most important human pathogens. Malaria is an infection caused by the protozoan parasite Plasmodium and spread by mosquitos. Globally, 250 million human cases and over 600,00 deaths were recorded in 2022, according to the World Health Organization.
Control of malaria is a major public health priority for many developing nations. Interventions such as controlling mosquito populations, improving diagnostic testing, and supplying effective preventatives and treatments can reduce or even eliminate malaria over time.
However, a different form of malaria, Plasmodium knowlesi, has been spreading across south-east Asia in humans since the early 2000s. While this parasite's normal host is macaque monkeys, its mosquito vector has been brought closer to humans by deforestation, leading to thousands of cases. In 2022, all malarial deaths in Thailand and Malaysia were due to this zoonotic form of malaria.
The presence of a wildlife reservoir and the outdoor-biting behaviour of this particular mosquito vector mean that while treatment can clear a person of the disease, future disease transmission is not prevented. As such, elimination, which is the usual goal in malaria control, is probably not possible for zoonotic malaria. With the WHO recently updating their definition of elimination to include 'negligible' transmission of zoonotic malaria, this is a heavy blow for countries like Malaysia, where classical human malaria is now controlled after years of dedicated effort.
Like many zoonotic diseases, responding to the threat of zoonotic malaria will need a new approach. Increasing public awareness, innovative practices to reduce mosquito bites at urban-forest edges, early diagnosis and treatment of cases, and tracking the genetic features of zoonotic malaria to see if human-to-human transmission develops are all recommended polices. With infections strongly associated with deforestation and forest boundaries, a truly One Health approach must also integrate sustainable land management policies if control is to be achieved.
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