Malaria transmission in Cambodia: Are plantations a hotspot?

Thesis

Background: Malaria is a leading cause of morbidity in Cambodia with an estimated 55,000 cases in 2014. Malaria prevalence is highest in forested rural areas, where a large proportion of the population live and work. Plantations are hypothesised to be “hotspots” for malaria transmission due to their proximity to forests and the vectors therein.

Methods: An analysis of malaria incidence data collected on plantations and in surrounding local villages in north-eastern Cambodia, as well as epidemiological analysis of risk factors for malaria prevalence on plantations. A deterministic compartmental model was developed to simulate malaria transmission dynamics on plantations.

Findings and conclusions: Malaria incidence in both villages and plantations follows a seasonal pattern with a peak in cases toward the end of the wet season in October to November. There was no statistical difference in incidence between settings. Mondulkiri province has a second peak at the start of the wet season which may be attributed to the type of work conducted on the plantations at that time or population migration. Permanent non-vector permeable housing in the wet season (OR 0.30; 95% CI: 0.11–0.86, p <0.05) and use of bed nets in the dry season (OR 0.15; 95% CI: 0.03–0.62, p <0.001) were the only factors found to have a significantly reduced odds of malaria prevalence. The plantation malaria model demonstrates that importation of cases by migrant workers is currently not a factor in malaria transmission on plantations. Plantation workers with immunity and asymptomatic malaria act as a reservoir enhancing malaria transmission and need to be targeted in elimination efforts. The malaria model also shows that as the plantations approach elimination, the transmission pattern will shift from a stable endemic to unstable epidemic pattern due to declining immunity which is likely to result in more clinical and severe malaria.

Authors: Mendelsohn, S

• DOI: 10.5287/ora-xkjyxroo1
• Type of award: MSc
• Level of award: Masters
• Awarding institution: University of Oxford
• Language: English
• Keywords: rubber plantation; malaria transmission; migrant workers; plantation; malaria modelling; Malaria; south east Asia; hotspot; Cambodia
• Subjects: Mathematical Modelling; Epidemiology