7 March 2013 | EN
Farmers and plantation workers increasingly contract lesser-known malaria
[KUALA LUMPUR] Scientists in Malaysia have reported an increase in malaria cases in Borneo caused by the Plasmodium knowlesi parasite, threatening the region's hopes for malaria elimination.
P. knowlesi is a strand of parasite found in macaques, which are native to the forests of Sabah, in northern Borneo. The parasite causes severe malaria in humans. It is transmitted via the forest-dwelling Anopheles leucosphyrus mosquito.
Research has indicated that while cases of the more common malaria strands, such as Plasmodium falciparum and Plasmodium vivax, have seen a huge decline, P. knowlesi cases have increased dramatically since the early 2000s.
State health records indicate that P. falciparum notifications peaked at 33,153 in 1994 and decreased to just 605 in 2011. P. vivax notifications peaked at 15,857 in 1995 and decreased to 628 in 2011.
In 1992, P. knowlesi only accounted for one per cent of reported malaria infections. In 2011 that figure had jumped to 35 per cent.
Timothy William, one of the study's authors and a researcher at the Queen Elizabeth Hospital, Sabah, says there is currently no conclusive evidence for the reasons behind the P. knowlesi increase.
"We suspect that deforestation may have something to do with it as most of the cases were recorded in rural areas," he says. "Our studies showed that more than 70 per cent of P. knowlesi patients were male and from the 25-45 age group. Many of these were farmers or plantation workers, which are moving further into the macaques territory increasing chances of contracting [the disease]."
William adds that there have also been cases reported outside Borneo, including eight in Peninsular Malaysia and five in the Philippines.
The WHO has recommended that each country affected should formulate a comprehensive strategy to control the disease.
"Rapid diagnosis, appropriate and timely treatment, personal protection, surveillance and health information targeted at risk populations and health staff, as well as operational research, are vital for successful elimination," says Timothy O' Leary, public information officer at the WHO's Western Pacific Regional Office.
P. malariae is closely related to P. falciparum and P. Vivax but is considered to be "benign malaria": it is milder and relatively easy to treat. Because of its similarity to P. knowlesi, notifications of both strains are considered as a single group.
The WHO estimates that in 2010 there were 660,000 malaria related deaths, mostly affecting African children, and around 219 million malaria cases worldwide.
This article has been produced by SciDev.Net's South-East Asia & Pacific desk.
PLOS Neglected Tropical Diseases doi:10.1371/journal.pntd.0002026 (2013)
Balbir Singh ( Universiti Malaysia Sarawak | Malaysia )
12 March 2013
The natural hosts of Plasmodium knowlesi are long-tailed and pig-tailed macaques which are found throughout Southeast Asia. P. knowlesi infections have been confirmed in these macaques in Sarawak (Malaysian Borneo), Singapore, Peninsular Malaysia, Philippines and Thailand. Human knowlesi malaria cases reported in the literature, with numbers reported in brackets, are as follows: Sarawak (801), Sabah (665), Peninsular Malaysia (96), Myanmar (37), Thailand (36), Vietnam (35), Philippines (7), Singapore (6), Indonesia (2) and Cambodia (2). Knowlesi malaria cases have therefore been reported in all the countries in Southeast Asia, except Laos. These are just the cases that have been detected by molecular detection methods, since it is virtually impossible to differentiate P. knowlesi from P. malariae. Whether there has been a genuine increase in knowlesi malaria cases or whether this is due to increased awareness, coupled with utilisation of molecular detection methods instead of microscopy, is open to debate.
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