- Researchers have discovered presence of human malarial parasite in bonnet and rhesus monkeys in India, drawing attention to the rehabilitation monkeys involved in conflict with humans in urban areas.
- India has a vision of a malaria-free country by 2027 and eradication by 2030, in sync with the World Health Organisation’s goals for malaria eradication.
- Across India, monkeys causing disturbances in human settlements, are trapped and released in their “native” forest habitat. Such unnatural translocations could eventually lead to transmission of diseases within host species and in turn, to humans.
As India attempts to eliminate malaria over the next decade, researchers have for the first time unearthed presence of human malarial parasite Plasmodium falciparum in wild bonnet and rhesus monkeys in the country, drawing attention to the rehabilitation of “problem monkeys” that have rattled even its Parliament.
In trying to understand the different species of Plasmodium infecting Indian primates, study lead author Jyotsana Dixit was stumped when she discovered the genetic sequences of the P. falciparum parasite in faecal samples of bonnet (Macaca radiata) and rhesus macaques (M. mulatta) during tests.
The research team probed 349 faecal samples belonging to five different Indian primate species.
“Out of a total of 349 samples, 19 of 120 faecal samples of bonnet monkeys and one of 15 faecal samples of rhesus macaques showed the presence of P. falciparum. In addition, we also sourced blood and tissue samples of bonnet monkeys from Kerala forest department and Trichy zoo and found that two liver tissue samples tested positive for the presence of P. falciparum gene sequence,” Dixit told Mongabay-India.
Known for its “promiscuous” habits, P. falciparum seems to be “trying its luck” with these simians in India, which has a rich primate diversity with 15 species.
“What we have shown here is that P. falciparum is able to get inside the monkey but the question to be asked is whether it can infect the monkey or not. This parasite was not seen in monkeys in India before,” said Dixit of Indian Institute of Science, Bangalore.
Finding unexpected but not surprising
The finding was unexpected, said Dixit, but not surprising given such observations have been made before in other (non-human) primates such as those in Africa.
In India, the red-faced rhesus macaques are widely distributed in the north and bonnet monkeys range across southern India. Humans have a complex love-hate interaction with these primates, increasingly driven to human settlements to hunt for food as their habitats degrade.
Believed to be connected to the Hindu monkey god Hanuman, macaques are respected and fed in India. Notorious for raiding crops, monkeys also prompted the Himachal Pradesh government to a launch a sterilisation programme to “control the constantly increasing population of monkeys.”
In New Delhi, the national capital, for example, an advisory was shot off to members of the parliament ahead of the winter session to keep monkeys at bay.
“There is much interaction between humans and primates in India, which in turn provides ample opportunity for disease transmission. What complicates matters is the fact that when such ‘problem monkeys’ are captured and rehabilitated, they may end up spreading diseases in areas where there was no disease,” said Dixit.
India has a vision of a malaria-free country by 2027 and eradication by 2030 in sync with the Global Technical Strategy (GTS) for Malaria 2016-2030 of World Health Organisation. The agency says there are no reports of human-mosquito-human transmission of such “zoonotic” forms of malaria.
“But with increasing contact between humans and monkeys, it is crucial for us to consider zoonosis while we target malaria eradication by 2030,” Dixit added.
Indian macaques, primarily the bonnet, have been known to harbour at least three Plasmodium species including P. fragile, P.inui and P. cynomolgi. However, much of this work was done in the last century and since early 1980s there have been no studies on primate malaria in India.
Human malaria is caused by four different species of Plasmodium: P. falciparum, P. malariae, P. ovale and P. vivax. Humans occasionally become infected with Plasmodium species that normally infect animals, such as P. knowlesi.
In 2018, reports said several people in Malaysia became infected with P. knowlesi, a monkey malaria parasite. P. cynomolgi has been detected in several humans in the Nicobar Islands and recently in a patient in Malaysia.
“Our studies also confirmed the presence of P. fragile, P.inui and P. cynomolgi in M. radiata. This is also the first report of DNA sequence data obtained from Plasmodium species infecting wild populations of Indian macaques,” said Dixit.
Based on the genetic data, authors also found that Indian Plasmodium species (P. inui and P. cynomolgi and P. fragile) were genetically distinct from the Southeast Asian species. “There might be a possibility that these species belong to simian Plasmodium sub-species specific to India, however it requires further genetic data to confirm,” said Dixit.
Translocating urban monkeys could further spread disease
Parsing through the genetic analysis of population structures of bonnet macaques, the scientists could tell these monkeys were spread apart despite being known to live in matrilineal troops in which female offspring remain in their natal territory while male offspring disperse.
“Given their particular social structure we should have found one type of genetic composition at one place but the genes were quite mixed up. They were traveling all over the area. The main reason for this may be due to human-mediated transportation,” Dixit said.
Across India, monkeys that cause disturbances in human settlements, mainly from urban areas, are trapped and released in their “native” forest habitat. These urban monkeys are usually unable to survive in forests as they have been acclimatised to foraging in urban environments. Often these translocated monkeys then move to nearby human habitations to forage.
“In the case of primate specific malaria such unnatural translocations would facilitates the wider distribution of these pathogens in their host species which in turn would provide more opportunities for zoonoses,” the study stressed.
According to Pradipsinh K. Rathod, South Asia director of the International Center of Excellence for Malaria Research, researchers have always understood the potential importance of zoonosis and it’s not far-fetched to imagine human malaria parasite reservoirs beyond humans.
However, in malaria control strategies, human malaria in monkeys may not match worries about more immediate matters: hundreds of millions of humans in India are at risk for malaria and that feeds the ongoing transmission to other humans.
“Technically, human malaria parasites in monkey faeces is intriguing but it may or may not have anything to do with successful reverse blood-based transmission involving mosquitoes to humans. It could very well be a dead end in the monkeys,” Rathod said.
“In the end, biology is about change. There are lots of interesting questions and so deeper research on human malaria in Indian forest animals should continue,” said Rathod, adding that “when human malaria in India decreases by two orders of magnitude, residual infections in animals can become a significant worry.”
“… but even that may decrease, or even disappear, depending on the dynamics of infection”.
Dixit, J., Zachariah, A., Sajesh, P. K., Chandramohan, B., Shanmuganatham, V., & Karanth, K. P. (2018). Reinvestigating the status of malaria parasite (Plasmodium sp.) in Indian non-human primates. PLoS neglected tropical diseases, 12(12), e0006801.