However, very little was known about Plasmodium malariae
and Plasmodium ovale
which are believed to cause up to 5% of malaria worldwide,
corresponding to approximately 10 million cases annually. These species
can remain hidden in the host for years.
‘The genomes of the two least common species of human malaria parasites are revealed by scientists. This will enable improved surveillance and diagnosis of these rarer parasites.’
The genomes of the two least common species of human malaria parasites are revealed in Nature
by a team of scientists from the Wellcome Trust Sanger Institute and
their international collaborators. These sequences will enable improved
surveillance and diagnosis of these rarer parasites that still cause
more than 10 million malaria cases every year.
The research has important implications for malaria eradication worldwide, and casts light on a malaria vaccine target.
The researchers determined the genome sequences of these Plasmodium
parasite species. By comparing these new genomes with those of the
malaria parasites already sequenced, the researchers were able to
identify genes that could be involved in human infection and in adapting
to the human host. They found that up to 40% of the P. malariae
and P. ovale
genomes contain genes that are probably involved in evading an immune response.
The study revealed that P. malariae
contains two new families of genes that are similar in shape to a vital gene in P. falciparum
, known as RH5. This gene is essential for the P. falciparum
parasite to invade human red blood cells and is one of the top targets for malaria vaccine design. It is likely that the novel P. malariae
genes are also involved in binding to host cell receptors.
Gavin Rutledge, first author on the paper from the Wellcome Trust
Sanger Institute, said: "It is really hard to study these parasites
because we can't grow them in the lab. Here, we isolated the parasites
from blood samples of malaria patients and determined these final
Plasmodium genome sequences. This will help us understand the evolution
of the Plasmodium species, and maybe even give us an idea which routes
to drug resistance these parasites may possess."
Professor James McCarthy from QIMR Berghofer Medical Research
Institute, said: "Although they are less lethal than Plasmodium
falciparum, the rarer malaria species are likely to be much more
difficult to eliminate. Better tools to diagnose these parasites, as
well as drugs and vaccines to control them will be essential. These new
genomes should now make it possible to develop improved diagnostic
tools for these Plasmodium species, to ensure that drugs work against
them and to assist vaccine development."
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 P. falciparum
emerged. The researchers also sequenced Plasmodium
parasites taken from chimpanzees living in a sanctuary in Gabon. They
compared these with the human samples, and existing data from other
Plasmodium parasites that also infected chimpanzees, offering insights
into how malaria parasites have adapted to different host species.
The new genetic information is already available for other
scientists in the malaria research community to use via the Sanger
Institute GeneDB database or the European Nucleotide Archive at the
European Bioinformatics Institute.
Dr. Thomas Dan Otto, lead author from the Sanger Institute, said:
"This study provides 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. 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."