It was long thought that bonobos might be immune to infection. But now it appears that they too, just like humans, can contract malaria – and become ill from it.
Malaria is a life-threatening disease and the biggest health problem in the world. The parasite still kills nearly half a million people worldwide every year. The disease is caused by the parasite Plasmodium falciparum that can be transmitted to humans by mosquitoes. Whether great apes also become seriously ill from it – and how deadly it is for them – we don’t really know. And that while this could well be important to control the disease in humans.
Symptoms
When someone contracts malaria, the symptoms often start out mild. Think of fever, headache and chills. However, a malaria infection can be fatal within 24 hours. As mentioned, how the disease unfolds in great apes is less known. “We don’t really have a good picture of the symptoms and the mortality rate yet,” says researcher Emily Wroblewski. “The number of infected animals in captivity showing symptoms of disease has remained limited. Sometimes they get a fever and other symptoms that indicate an infection, but sometimes they don’t. And in wild great apes this is even more difficult to bring to light.”
Twelve species
It is well known that chimpanzees and gorillas are not spared the disease. For example, scientists have found DNA from malaria parasites in the faeces. In fact, these African great apes harbor twelve different ones Plasmodiumspecies, seven of which are closely related to the human parasite that causes about 95 percent of human deaths (the aforementioned Plasmodium falciparum).
Escaped
However, the bonobo is the odd one out. In this way, this great ape managed to escape infection in all but two places. This is remarkable, because many malaria parasites occur in the areas where bonobos live. Does this mean that the bonobos here are somehow immune?
To compare
Because there apparently are both populations that do and do not get malaria, researchers decided in a new study comparing both groups. This difference gives researchers the chance to try to learn some basic facts about how malaria affects the health and mortality of great apes. So the team collected DNA extracted from feces from both infected populations – where 38 percent of bonobos had malaria parasites in their faeces – and uninfected bonobos living in ten other areas in the Democratic Republic of Congo.
Immune genes
The researchers found that bonobos living in areas where malaria infections are found are more likely to carry a particular variant of an immune gene (called Papa-B). This variant is very similar to a human variant (HLA-B*53). And that is striking. This is because HLA-B*53 mainly occurs in people who are better protected against malaria. It means these bonobos may have a similar defense mechanism. “There may be a selective advantage for those wearing this protective variant,” Wroblewski explains. “They are more likely to survive and reproduce a malaria infection, increasing the frequency of that variant.”
Sick
On the other hand, the researchers did not find the Papa-B immune gene in the so-called ‘immune’ group of bonobos. And that means these animals are probably far from protected against the disease. “It suggests that this group is more likely to die from infection or to reproduce less well,” says Wroblewski. “The differences between the bonobo populations are the first evidence – albeit indirect – that this wild ape can also contract and become ill with malaria.”
Threat
It means that malaria also affects the bonobo. Future studies will have to show how ill this great ape becomes from an infection. “It is important to understand this better because this is an endangered species,” Wroblewski underlines. “Diseases are therefore a major threat, as bonobos are increasingly under pressure from human activities.”
Moreover, the fact that the Papa-B immune gene discovered in the bonobo closely resembles the HLA-B*53 variant in humans is striking. “This is remarkable because these immune genes evolve very quickly as they try to keep up with rapidly evolving pathogens,” says Wroblewski. “Because of this, it’s actually very unusual to find a similar pattern between two close relatives.” The next step is to investigate how this specific immune gene variant protects – in both bonobos and humans. That could lead to improved treatment plans or even an effective vaccine.
