Thursday September 23 2010
Gorillas can host a similar malaria parasite to humans
“Malaria first passed to humans from gorillas thousands of years ago,” the Daily Mail reported. The newspaper said that the new discovery that gorillas can also host the human malaria parasite raises hopes of a vaccine for the disease.
The story comes from research that analysed the genetics of malarial parasites in the faeces of chimpanzees and gorillas living wild in central Africa. It found that a parasite present in the western gorilla species was nearly identical in its genetic make-up to Plasmodium falciparum, the most common and most harmful malaria parasite that infects humans. This suggests that the two parasites had a common ancestor.
This novel study may provide clues about the nature of malarial parasites and better ways to control malaria. However, it is debatable whether it will lead to the development of a vaccine in the near future, as newspapers have suggested. The best way to avoid malaria infection is to use simple but effective prevention measures such as antimalarial tablets and mosquito nets when visiting areas where malaria is prevalent.
Where did the story come from?
The study was carried out by several research institutes in the Democratic Republic of the Congo, the US, France and the UK. It was funded by a number of organisations, including the US National Institutes of Health. The study was published in the peer-reviewed journal Nature.
Generally, the media reported the study fairly, although the BBC’s claim that malaria was originally “caught from gorillas” is an over-simplification, and the Daily Mail’s headline that malaria “first passed to humans thousands of years ago” is not substantiated by this research. TheMail’s claim that the findings raise hopes of a vaccine for malaria is overly optimistic.
What kind of research was this?
The researchers point out that malaria is a blood infection caused by mosquito-borne parasites. The most prevalent and lethal malaria parasite that infects humans, Plasmodium falciparum, causes more than 1 million deaths annually. This laboratory study aimed to identify the types of Plasmodium parasites found in wild-living apes, and to examine their genetic make-up to see whether it could provide clues to the origin of the human parasite Plasmodium falciparum.
The researchers say that the origin of the human malaria parasite remains controversial, and many scientists think that in the past it diverged from a chimpanzee parasite. Recently, other closely related Plasmodium strains have been detected in other apes, indicating that the parasite found in humans could have developed through cross-species transmission. However, previous research has only looked at a small number of apes, many of which were captive and living in close quarters to humans. The researchers are also critical of the methods that previous studies used to analyse the parasites’ genetic make-up.
In this laboratory study, faecal samples were collected from apes living in the wild in central Africa. These samples were screened for the presence of genetic material from parasites related to Plasmodium falciparum. Using DNA sequencing, the researchers set out to compare the genetic make-up of any malarial parasites found and to investigate how they were related to the human Plasmodium falciparum parasite.
What did the research involve?
The researchers used nearly 3,000 faecal samples from wild apes living in central Africa, which had been collected for the study of other infections. The samples, which came from chimpanzees, western and eastern gorillas and bonobos (pygmy chimpanzees), were screened for the presence of any Plasmodium parasites using genetic techniques.
Researchers then looked at the genetic make-up of the parasites that were present and used complex statistical methods to draw a genetic “family tree” to show how closely the parasites were related and how they might have evolved from common ancestors. They also looked at the DNA from parasite samples taken from 80 chimpanzees and 55 gorillas, using existing information about the DNA sequence of human Plasmodium parasites to guide these analyses.
What were the basic results?
The researchers found that malaria parasites were widespread in chimpanzees and western gorillas, of which an estimated 32-48% were infected. However, none of the eastern gorillas and bonobos tested were infected with malaria parasites.
The researchers found at least nine different Plasmodium species in the apes, and some apes were infected with more than one species. Their genetic analysis of the parasites found that the human Plasmodium falciparum parasite was nearly identical to one of three species of Plasmodium found in western gorillas. More distant relations to the malarial parasites were found in other apes.
How did the researchers interpret the results?
The researchers concluded that both chimpanzees and western gorillas are naturally infected with at least nine different types of malaria parasites and are, therefore, a “substantial reservoir” of these parasites. They say that their results show that the human malarial parasite is of gorilla origin and not of chimpanzee or ancient human origin, as originally thought.
They say that all known human strains of malaria may have resulted from a single cross-species transmission event, although it is still unclear when this really happened. Further research, including screening of humans living near wild apes, is needed to find out more about potential cross-species transmission. The researchers believe this will inform efforts to eradicate the disease.
This study suggests that the closest relative of the Plasmodium falciparum parasite, which causes human malaria, is a malarial parasite in western gorillas, and that a common ancestor may have been passed from gorillas to humans in the past.
Further research is needed into whether cross-species transmission between gorillas and humans is currently occurring. The findings of such studies may have implications for future research on the best way to eradicate the disease.
While this avenue of research may eventually have some application in the treatment of malaria, prevention remains a vitally important strategy in the fight against this disease. Relatively simple steps, such as taking anti-malarial tablets and using mosquito nets and insecticide, can help prevent infection. Anyone visiting regions where there is a risk of malaria should read up on malaria prevention.