Study: Sabah farmers at higher risk of catching monkey malaria

KOTA KINABALU: Adult male farmers are more than twice as likely to contract Plasmodium knowlesi (P. knowlesi) – a malaria parasite usually found only in monkeys – than other people in their communities, according to a report.

The study was conducted by the London School of Hygiene & Tropical Medicine, Menzies School of Health Research, Darwin, and the Sabah Health Department.

The research team found that farmers in Sabah who work in plantations, clear vegetation and take part in forestry work are the most at risk.

P. knowlesi is a zoonotic malaria parasite which is common in forest-dwelling macaque monkeys and transmitted between hosts by mosquitoes. It has a rapid growth rate in the blood that can lead to a high level of parasites in a short time and can cause severe and fatal disease.

Recent deforestation in the Sabah region has brought humans into closer contact with the forest.

P. knowlesi is now the most common form of human malaria in many areas of Malaysia, and has also been reported across South-East Asia.

In 2014, the Health Ministry reported that 2,584 out of the country’s 3,923 malaria cases derived from P. knowlesi, and that proportion is known to have risen further.

The researchers conducted a large case control study of more than 1,000 people in the Sabah districts of Kudat and Kota Marudu. Individuals with P. knowlesi were compared with those with other types of human malaria and a control group without malaria.

Detailed questionnaires recorded information on daily activities, residence and the frequency with which participants saw monkeys.

Men are four times more likely to have P. knowlesi infection than women, and although male farmers are more likely to contract monkey malaria, they are not at higher risk of contracting other types of malaria.

Indoor work such as shopkeeping, traditional female household duties, and studying are associated with a lower risk of P. knowlesi malaria in these communities.

The findings suggest that humans working on the fringes of the forest are at risk of contracting P. knowlesi, as well as in the forest itself when they carry out activities such as hunting.

A number of cases in women and children were also found which, along with the characteristics of mosquito and macaque populations, need further investigation.