SciDev.Net

Two international teams of scientists have decoded the DNA of two important malaria parasites, Plasmodium vivax and Plasmodium knowlesi.

Their studies were published in Nature last week (8 October).

Arnab Pain, project manager at the UK-based  Wellcome Trust Sanger Institute and lead author of the P. knowlesi study, told SciDev.Net they hope the sequences will "feed into drug or vaccine development, whether in determining essential genes to target with drugs or in defining less variable genes to target with vaccine candidates".

P. knowlesi is emerging as a potentially life-threatening cause of human malaria. Originally identified in monkeys, the number of cases has been grossly underestimated due to its misdiagnosis as the benign P. malariae (see Fatal malaria strain 'mistaken for more benign form').

Pain says the scale of misdiagnosis, particularly in South-East Asia, has only begun to be recognised. 

He explains the genome sequence of P. knowlesi displays 'molecular mimicry', a tactic used by the parasite to avoid detection by interfering with the immune recognition processes. Understanding this phenomenon is crucial to curb the survival and propagation of the parasite in the body.

P. vivax has been neglected because it is rarely fatal. But up to 40 per cent of global malaria cases are caused by P. vivax, so it is "hugely significant", says Jane Carlton, a parasitologist at the New York University Langone Medical Center who led the P. vivax research.

She told SciDev.Net the parasite is restricted to a certain type of red blood cell not found in Africans, therefore it is not as widespread as deadlier strains of malaria like P. falciparum.

But, she adds, the parasite can remain dormant in the liver for years after an initial infection before resurfacing.

Currently, only one drug can be used against this dormant stage — and it cannot be taken by pregnant women or people with certain blood deficiencies.

"You can treat P. vivax parasites in the blood, but they will still hibernate in the liver. [To eradicate malaria], we're really going to have to develop more drugs against this particular dormant stage," says Carlton.

She told SciDev.Net, "One genome is never enough. We are sequencing six more strains of P. vivax. Then we can really start to look at the genetic variation within the species and gain insight into some of the genes involved in drug resistance or virulence."

Link to Carlton article in Nature

Link to Pain article in Nature