KUCHING: Zoonotic malaria remains a serious threat, accounting for over 80 per cent of overall malaria cases in Sarawak.
Director of the Universiti Malaysia Sarawak (UNIMAS) Malaria Research Centre, Dr Paul Cliff Simon Civis, said that this type of malaria is caused by the Plasmodium knowlesi parasite, while the remaining cases are due to imported human malaria brought back to Sarawak by individuals returning from countries where malaria is endemic, caused by Plasmodium falciparum or Plasmodium vivax.
Paul explained that the consistently high number of zoonotic malaria cases can be attributed to agricultural activities such as farming, and forest-related activities like logging or hunting.
“Most of these cases are reported in the Kapit division,” he said in an interview with New Sarawak Tribune recently, coinciding with the national-level Malaria Day celebrations.
He noted individuals usually contract zoonotic malaria during these activities when bitten by infected Anopheles mosquitoes that have previously fed on infected monkeys.
According to him, unlike urban-dwelling Aedes mosquitoes, Anopheles mosquitoes are forest dwellers, attracted to both monkeys and humans for blood feeding.
Paul highlighted that no cases of indigenous human malaria, which is primarily transmitted between humans through infected Anopheles mosquitoes and caused by Plasmodium falciparum or Plasmodium vivax, have been reported in Malaysia for the past four years.
This success, he said, is due to the Ministry of Health’s (MOH) effective malaria elimination programme.
A review of secondary data on all diagnosed and reported malaria cases submitted to the MOH indicated that between 2013 and 2017, Malaysia experienced 16,500 malaria cases.
Sabah and Sarawak contributed 43.3 per cent and 34.4 per cent of the cases, respectively. The majority of patients were male, accounting for 82.1 per cent of the cases. In Sabah and Sarawak, the highest number of cases occurred in the 30 to 39 years age group (21.6 per cent).
The Sabah Bumiputera and Sarawak Bumiputera races accounted for the highest number of malaria cases in these regions, at 43.7 per cent and 35.1 per cent, respectively. Plasmodium knowlesi emerged as the most common parasites in Sabah and Sarawak (77.1 per cent).
The overall average incidence rate, mortality rate, and case fatality rates for malaria in Malaysia from 2013 to 2017 were 0.106/1000, 0.030/100,000, and 0.27 per cent, respectively.
Sarawak reported the highest average incidence rate at 0.420/1000 population, followed by Sabah with 0.383/1000.
The shift in malaria epidemiology from indigenous to zoonotic presents new challenges for control and elimination efforts.
“Its unique transmission pathway, involving wild monkeys as reservoir hosts, complicates matters,” he added.
This situation necessitates different control strategies and surveillance systems compared to indigenous human malaria.
Environmental factors, such as the presence of suitable mosquito breeding habitats, significantly impact the risk of zoonotic malaria incidence.
“Mosquitoes need stagnant water to breed, with factors like temperature, humidity, and rainfall affecting the availability of breeding sites,” said the parasitologist.
He also emphasised the role of deforestation and land-use changes for agriculture or economic development in altering mosquito populations and creating new habitats for them.
Paul further highlighted the importance of suitable animal reservoir hosts, such as wild long-tailed and pig-tailed macaques, in zoonotic malaria transmission.
“Human encroachment into forested areas or changes in land-use patterns can increase contact between humans and animals, raising the risk of disease transmission,” he warned.
Despite these challenges, zoonotic malaria is currently treatable with anti-malaria drugs like artemisinin-based combination therapy (ACT), and no reports of drug resistance have emerged.
However, the recently developed Oxford-AstraZeneca malaria vaccine is not effective against zoonotic malaria caused by Plasmodium knowlesi, as it only targets human malaria caused by Plasmodium falciparum.
To effectively control zoonotic malaria infections, Paul emphasised the need for a multi-pronged approach.
“This includes vector control, early diagnosis and treatment, and addressing social and environmental determinants of malaria transmission,” he asserted.
Health education about zoonotic malaria risks and the importance of preventive measures is also crucial in reducing cases.
“Effective awareness programmes for at-risk individuals can inform them of malaria’s signs and symptoms, and stress the importance of seeking prompt medical attention if symptoms arise,” he concluded.
The theme of the World Malaria Day celebration this year is ‘Time to deliver zero malaria: invest, innovate, implement’. The occasion is celebrated each year on April 25 in recognition of the global efforts in controlling malaria.
