Due to its devastating effects on humans, the conversation surrounding malaria infections is often focused on the public health threat—rightfully so, as close to 50% of the world’s population live in areas endemic to malaria with over 200 million cases annually and almost half a million deaths. However, the fact that malaria parasites can infect a huge array of animal species is not only important from an agricultural and economic standpoint but also could provide valuable insight into the evolution of the parasite, revealing some of its potential weakness that can be exploited therapeutically.
Studying how our closest evolutionary relatives become infected with malaria has provided a host of information about parasite transmission and even recently uncovered a parasite strain that can infect both humans and primates (Plasmodium knowlesi). Interestingly, although widespread among wild chimpanzees and gorillas, malaria parasites have not been detected in bonobos, a chimp cousin. This idea didn’t sit well with many researchers, so a team of investigators led by scientists at the Perelman School of Medicine within the University of Pennsylvania conducted a more extensive biological survey, increasing both the number and places they sampled wild bonobo populations for potential malaria infections. Amazingly, the research team found evidence of a new malaria species in bonobos, limited to one small area of their range.
Findings from the new study were released today in Nature Communications, in an article entitled “Wild Bonobos Host Geographically Restricted Malaria Parasites Including a Putative New Laverania Species.”
“Not finding any evidence of malaria in wild bonobos just didn't make sense, given that captive bonobos are susceptible to this infection,” explained senior study investigator Beatrice Hahn, M.D., professor of microbiology at Penn. “We look for biological loopholes to potentially exploit the life history of these pathogens to understand better how they cross over to humans.”
Dr. Hahn's lab studies ape relatives of human pathogens such as human immunodeficiency virus (HIV) and malaria to gain a greater insight into the microbes that cause these diseases in humans. African nonhuman primates are highly endangered and require noninvasive sampling methods to gain insight into their health. To address this, Dr. Hahn's and her colleagues perfected a sensitive assay that allows them to obtain genetic information of malaria parasites from ape fecal matter gathered from the forest floor.
The research team found that bonobos are, in fact, susceptible to a wide variety of malaria parasites, including a previously unknown Laverania species that is specific to bonobos. (Laverania parasites are close relatives of the human malaria parasite Plasmodium falciparum.) Wild bonobos are found in the forests of central Africa, south of the Congo River in the Democratic Republic of Congo (DRC). However, natural infection was only detected in the easternmost part of the bonobo range.
“Testing 1556 faecal samples from 11 field sites, we identify high prevalence Laverania infections in the Tshuapa-Lomami-Lualaba (TL2) area, but not at other locations across the Congo,” the authors wrote. “TL2 bonobos harbor P. gaboni, formerly only found in chimpanzees, as well as a potential new species, Plasmodium lomamiensis sp. nov. Rare co-infections with non-Laverania parasites were also observed. Phylogenetic relationships among Laverania species are consistent with co-divergence with their gorilla, chimpanzee and bonobo hosts, suggesting a timescale for their evolution.”
Until recently, there were six known ape Laverania species that exhibited strict host specificity (association with a single host species) in wild populations—three in chimpanzees and three in western gorillas. In 2010, Dr. Hahn and her colleagues discovered that gorillas were the origin of the human malaria parasite P. falciparum, the most lethal of the malaria parasites that infect people.
“It seems likely that these parasites co-evolved with African apes, suggesting that the ancestors of bonobos were infected, and implying that most wild-living communities of bonobos have somehow lost their malaria parasites,” remarked study co-author Paul Sharp, Ph.D., an evolutionary biologist from the University of Edinburgh.
The research team tried to narrow down the reasons for the absence of Plasmodium from most bonobo field sites. However, neither parasite seasonality nor bonobo population structure could explain what they observed.
“For now, the geographic restriction of bonobo Plasmodium infection remains a mystery,” noted co-lead study investigator Weimin Liu, Ph.D., a senior research investigator in Dr. Hahn's laboratory.
“We have yet to identify the causes,” added co-lead study investigator Scott Sherrill-Mix, Ph.D., a postdoctoral fellow in Dr. Hahn’s lab. “We looked at what plants bonobos eat and what types of bacteria make up their gut microbiome, but these could not explain the absence of Plasmodium from most of the bonobo sites. From this, we suspect that factors that influence parasite transmission are involved.”
As scientists consider how malaria can be eliminated from the human population, Dr. Hahn noted that it is important to understand more about these ape parasites, what factors affect their distribution and host specificity, and whether there are circumstances under which any of them could again jump into humans.