Scientists complete the genome sequences of malaria parasites

An international team of scientists has sequenced the genomes of the final two species of malaria parasites. The findings have important implications for malaria eradication worldwide and will help researchers to develop new drugs and a vaccine.

The results of the study have been published today in the highly prestigious journal Nature.

The research was led by a team from the Wellcome Trust Sanger Institute in the United Kingdom and involved collaborators from QIMR Berghofer Medical Research Institute, and the Menzies School of Health Research.

Malaria is caused by one of five different species of Plasmodium parasites, which are spread to humans by the female Anopheles mosquito. The genomes of three of the species are relatively well studied, especially Plasmodium falciparum, the most common malaria parasite.

However, very little was known about Plasmodium malariae and Plasmodium ovale, which are believed to cause up to five per cent of malaria cases, or an estimated 10 million cases, worldwide each year. These species can remain dormant in humans for years.

By comparing these new genomes with those of the three malaria parasites already sequenced, the researchers identified genes that could be involved in human infection and in adapting to the human host. They found that up to 40 per cent of the Plasmodium malariae and Plasmodium ovale genomes contained genes that probably allowed the parasites to evade the human immune system.

Professor James McCarthy from QIMR Berghofer said the findings would enable better surveillance and diagnosis of malaria.

“Although these two species of parasites are rarer and less lethal than Plasmodium falciparum, they are likely to be much more difficult to eliminate,” Professor McCarthy said.

“It’s crucial that we develop better tools to diagnose these parasites, as well as drugs and vaccines to control them.

“Having these genomes sequenced should help with the development of a vaccine and improved diagnostic tools, and should also help to ensure that drugs work against the parasites.”

Professor Ric Price from the Menzies School of Health Research said the study had significantly added to the available body of knowledge on malaria.

“It is very difficult to study these parasites because they can’t be grown in the lab,” Professor Price said.

“In this study we isolated the parasites from blood samples directly from malaria patients and determined these final Plasmodium genome sequences.

“This will help us understand the evolution of the Plasmodium species, and how these parasites can survive undetected in patients’ blood for long periods of time.”

Plasmodium ovale actually consists of two distinct species, Plasmodium ovale wallikeri and Plasmodium ovale curtisi. The authors showed that the split between these species was ancient and occurred long before the much more virulent Plasmodium falciparum emerged.

The researchers also sequenced Plasmodium parasites taken from chimpanzees living in a sanctuary in Gabon. They compared these to the human samples, and to existing data from other Plasmodium parasite infections in chimpanzees, which offered insights into how malaria parasites have adapted to different host species.

The study’s lead author, Dr Thomas Dan Otto from the Sanger Institute, said the study provided long-awaited reference genomes for the malaria research community.

“The parasites are present in malaria zones worldwide yet researchers have limited knowledge about their biology,” Dr Otto said.

“The genomes of these more neglected species will enable the development of tools to study malaria transmission and spread, which will be essential to achieve the goal of complete malaria eradication.”

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