COVID-19 is just one of many infectious diseases that have been transmitted from wildlife to humans. Another zoonosis is a type of malaria parasite, Plasmodium knowlesi. It is found in different species of macaques and can be transmitted through the bite of certain Anopheles mosquitoes. By studying the ecology and behavior of these mosquitoes, we can understand how different environmental conditions can present an increased risk of transmitting zoonotic malaria to humans.
Long-tailed macaques (Macaca fascicularis) (Photo credit: Theo Jones)
The COVID-19 pandemic has once again brought the importance of preserving ecosystems into focus. Habitat changes are one of the main causes of so-called “spillover” events, for example deforestation and urbanization reduce the habitats of many wild species and increase the possibility of human contact. Malaysian Borneo is an area that is changing rapidly with the conversion of forests into agricultural land Knowledge of Plasmodium Malaria infections in humans. This was shown by a study by Dr. Kimberly Fornace from the London School of Hygiene and Tropical Medicine.
Dr. Fornace used hospital records from P. knowledge Infections and environmental variables derived from satellite remote sensing data to establish a positive association between P. knowledge Incidence in humans and the current forest cover and historical forest loss in the surrounding areas. Knowledge of Plasmodium has the potential to cause serious illness and death in humans, and most studies so far have focused on the mosquito ecology associated with human infections. However, in this blog we describe a study that shows the transmission and maintenance of infections within the reservoir host, a population of long-tailed macaques (Macaca fascicularis), carried out at the Danau Girang Field Center (DGFC) in Borneo, Malaysia, in collaboration with the University of Glasgow and Universiti Malaysia Sabah.
The field side
DGFC is located in the Lower Kinabatangan Wildlife Sanctuary (LKWS), a seven-hour drive and 40-minute boat ride from Sabah’s capital, Kota Kinabalu. This study area was chosen because the LKWS is home to hundreds of macaques, allowing study of mosquito vectors that macaques bite in the absence of humans. Here we were able to find out about the frequency and diversity of potential vector species as well as about the malaria infections in mosquitoes and in the stool of macaques in order to get a clearer picture of the malaria transmission from macaques to macaques.
We used commercial mosquito magnet traps positioned at the base of trees used by long-tailed macaques as roosts along the Kinabatangan River to catch mosquitoes that feed near long-tailed macaques. We worked with Amaziasizamoria Jumial (Maz), a primatologist and Masters student at Universiti Malaysia Sabah, who used a thermal imaging camera to scan the river banks to locate trees where macaques wanted to sleep overnight. We waded through the mud, setting one trap each night at the foot of a sleeping area and another on a control tree of the same type and structure, but free of monkeys. The following morning we returned before sunrise (before the monkeys were awake) and Maz used her thermal imaging camera to estimate the number of macaques sleeping from the boat. We then collected the mosquito traps and macaque stool from the sleeping area to be examined in the laboratory for malaria infections.
The after-dawn field work was accompanied by gibbons, proboscis monkeys crashing from tree to tree, macaques scurrying across the riverbanks and hornbills soaring overhead. We often disturbed large saltwater crocodiles resting on the mud, and one morning a herd of pygmy elephants crossed the river in the dark in front of us. On our return from the site, we held back when two adults helped a newborn cross by protecting it from the strong current.
The mosquito magnetic traps were a reliable method of sampling malaria vectors that host hunters sought near where macaques roost. the P. knowledge vector, Anopheles balabacensis, was caught in small quantities, but significantly more were caught in roosting places of long-tailed macaques than in control places where no macaques were present, indicating a tendency to feed on this host species. A high Plasmodium Prevalence was found in macaque populations by screening stool samples, but none P. knowledge was ascertained. Besides, no P. knowledge was found in mosquitos, but two A. balabacensis would have Plasmodium Inui Infections, so P. inui possibly circulating with high prevalence in macaques in LKWS. Currently natural transmission of P. inui was not detected in people in Sabah, but due to the infections found here and in A. balabacensis trapped around human settlements in previous studies, it provokes an awareness of its potential for future encroachment on humans.
A key finding from this study is that the Mosquito Magnet Independence Trap successfully captures vectors of primate malaria that feed on long-tailed macaques and therefore can be a valuable monitoring tool for monitoring infections that are circulating in wild ape populations. no P. knowledge were found in mosquitos or in macaque stool samples, which could mean that this type of malaria is not found in all macaque communities. Some people suggest killing macaques to remove the malaria reservoir host altogether, however the heterogeneity in infections suggests that this method could be inefficient and highly unethical.
To reduce the risk of future outbreaks, after identifying vectors that pose a risk of infection in the area, the next steps would be to take mosquito control measures such as spraying insecticides or applying repellants.
For decades, many were unaware of the interrelationship between biodiversity, land use and emerging infectious diseases. COVID-19 has highlighted the need to study the role of biodiversity in the transmission of pathogens and to take a more vigilant stance towards potential zoonoses. Countries should also have adequate monitoring, preparedness and response plans in place. Natural infections of Plasmodium cynomolgi have been detected in humans in Malaysia, but this has not yet been reported P. inui. However, these malaria species are most common in macaques and mosquito vectors in Malaysia. Since human infection with these species is likely to cause a more harmless disease than P. knowledge Because of its slower rate of replication, infection can go undetected in humans. Hence, in the future, monitoring of human infections and vectors in the vicinity of human settlements will be required to prevent spread of. easy to recognize P. inui or P. cynomolgi in people.