Collaborator: London School of Hygiene and Tropical Medicine, Department of Health Sabah

Status: Completed

The MONKEYBAR Project was an initiative led by Dr Chris Drakeley from the London School of Hygiene and Tropical Medicine and was run in collaboration with institutions from Malaysia, The Philippines, Australia and the UK. The study was a multi-disciplinary, integrated research programme to investigate the disease ecology of Plasmodium knowlesi, a malaria parasite which is now considered the fifth malaria parasite infecting humans.

The project combines entomology and parasitology with clinical medicine, epidemiology, primatology, social science, and spatial science and was run in parallel in two sites: Sabah (Malaysia) and Palawan (Philippines). The MONKEYBAR Project had two intensive study sites in Sabah: Banggi Island and the Kudat District. The whole study area in Sabah also included the districts of Pitas and Ranau.

Plasmodium knowlesi (Pk) is a malaria parasite whose natural hosts are non-human primates, mainly the long-tailed and the pig-tailed macaque (Macaca fascicularis and M. nemestrina, respectively). It is transmitted by the bite of a vector, an anopheles mosquito of the Leucosphyrus group. Knowlesi malaria is not a new disease (identified in the 1930s) but became clear as a zoonotic disease in 2004. The increasing epidemiological evidence pointed Pk as an emerging public health problem, and some local governments in Southeast Asian countries were already routinely screening patients for Pk.

In Sabah, Pk has shown an increasing trend as the other malarias have been controlled. This type of malaria poses a risk of severity three-fold greater than that of P. falciparum. The transmission dynamics of Pk seem complex and similar to those of Yellow Fever, with a sylvatic cycle and an urban cycle. However, there are many aspects of the disease that are not known. For example:

  • What are the demographic groups at risk?
  • Are there any social practices involved with the spread of the disease?
  • What are the vectors responsible for transmission?
  • What aspects of the macaque ecology and behaviour are directly related to the transmission of Pk?
  • Are the environmental and land use changes involved, and how?
  • What are the interactions between the land use, the hosts, the vectors and the parasites?

The MONKEYBAR Project aimed to address those questions under the main hypothesis that deforestation and changes in environmental conditions, and human-macaque-vector contact are key drivers in increasing the risk of P. knowlesi infection in humans.

The core of the project was a Case-Control study, which is supported by four additional components: Entomology, Social Science, Land Use, and Primatology. The information gathered from all these components was used to prepare models of disease transmission. The Case-Control component recruited all malaria cases in Kudat and Kota Marudu hospitals; for each case, there were 3 controls from the same village. The Entomology component investigated anopheline diversity, identifying the Pk vectors and their distribution in time and space. The Social Science component worked with entire villages within the intensive study sites to identify disease perception through photovoice group discussions and identified human behaviour linked to the disease with time allocation studies and GPS tracking of random people in the area.

The Land Use component used a drone to map the study sites and classify land types; it also defines how the environment affects the distribution of people, mosquitoes and macaques, which may contribute to infection risk.

DGFC designed and led the Primatology component in Sabah under the authority of the Sabah Wildlife Department. Habitat loss can also change the behaviour and abundance of wildlife, affecting parasite transmission and distribution since they are influenced (among others) by host ranging patterns, density, intraspecific and interspecific contact rates, and host diet. Furthermore, as human population density continues to increase, speeding up the reduction and fragmentation of primate habitats, greater human-primate contact is inevitable, and even higher rates of parasite transmission are likely.

The objectives of the Primatology component were:

1) Determine the species and location of diurnal primates in the study area.

2) Determine the number of long-tailed macaque troops, the number of individuals per troop, and the location of each troop within the study site.

3) Determine troops/individuals infected with Pk (and other primate malarias) using non-invasive samples.

4) Determine the home range and movement patterns of the (infected) macaque troops.

5) Define factors which influence the proximity and interaction between humans and macaques

The Primatology component team in Sabah was managed by DGFC, led by our scientific advisor, and assisted by our primatologist and wildlife veterinarian. Fieldwork was carried out by a team of Sabahans, supervised by a Master student, while our molecular biologist conducted lab work.