High prevalence of asymptomatic Anaplasma spp. infection in school-aged children in southeastern Gabon.

OBJECTIVES: The objective of this study was to evaluate the detection rates of asymptomatic Anaplasma spp. and Ehrlichia spp. infections in children in southeastern Gabon. METHODS: We conducted a cross-sectional study among school-aged children in southeastern Gabon between May and June 2021. Blood samples were collected. Anaplasmataceae, Anaplasma spp., and Ehrlichia spp. were detected by microscopy and polymerase chain reaction. RESULTS: Of the 452 blood samples collected, 57.5% (n/N=260/452) of the samples were positive for Anaplasma spp. and/or Ehrlichia spp. by microscopy, 86.9% (n/N=393/452) of the samples were positive for both Anaplasmataceae and Anaplasma spp., and none of the samples were found positive for Ehrlichia spp. PCR was more sensitive and specific than microscopy for detection of Anaplasma spp.. CONCLUSIONS: In our study, a significant number of positive blood samples for Anaplasma spp. were found in school-aged children in southeastern Gabon. Further studies are needed to determine the prevalence of different species of Anaplasma, their pathogenicity, and their transmission patterns.

Staphylococcus aureus Host Spectrum Correlates with Methicillin Resistance in a Multi-Species Ecosystem.

Although antibiotic resistance is a major issue for both human and animal health, very few studies have investigated the role of the bacterial host spectrum in its dissemination within natural ecosystems. Here, we assessed the prevalence of methicillin resistance among Staphylococcus aureus (MRSA) isolates from humans, non-human primates (NHPs), micromammals and bats in a primatology center located in southeast Gabon, and evaluated the plausibility of four main predictions regarding the acquisition of antibiotic resistance in this ecosystem. MRSA strain prevalence was much higher in exposed species (i.e., humans and NHPs which receive antibiotic treatment) than in unexposed species (micromammals and bats), and in NHP species living in enclosures than those in captivity-supporting the assumption that antibiotic pressure is a risk factor in the acquisition of MRSA that is reinforced by the irregularity of drug treatment. In the two unexposed groups of species, resistance prevalence was high in the generalist strains that infect humans or NHPs, supporting the hypothesis that MRSA strains diffuse to wild species through interspecific transmission of a generalist strain. Strikingly, the generalist strains that were not found in humans showed a higher proportion of MRSA strains than specialist strains, suggesting that generalist strains present a greater potential for the acquisition of antibiotic resistance than specialist strains. The host spectrum is thus a major component of the issue of antibiotic resistance in ecosystems where humans apply strong antibiotic pressure.

Molecular Identification of Trypanosome Diversity in Domestic Animals Reveals the Presence of Trypanosoma brucei gambiense in Historical Foci of Human African Trypanosomiasis in Gabon.

Human African Trypanosomiasis (HAT) is an infectious disease caused by protozoan parasites belonging to the Trypanosoma genus. In sub-Saharan Africa, there is a significant threat as many people are at risk of infection. Despite this, HAT is classified as a neglected tropical disease. Over the last few years, several studies have reported the existence of a wide diversity of trypanosome species circulating in African animals. Thus, domestic and wild animals could be reservoirs of potentially dangerous trypanosomes for human populations. However, very little is known about the role of domestic animals in maintaining the transmission cycle of human trypanosomes in central Africa, especially in Gabon, where serious cases of infection are recorded each year, sometimes leading to hospitalization or death of patients. Komo-Mondah, located within Estuaries (Gabonese province), stays the most active HAT disease focus in Gabon, with a mean of 20 cases per year. In this study, we evaluated the diversity and prevalence of trypanosomes circulating in domestic animals using the Polymerase Chain Reaction (PCR) technique. We found that 19.34% (53/274) of the domestic animals we studied were infected with trypanosomes. The infection rates varied among taxa, with 23.21% (13/56) of dogs, 16.10% (19/118) of goats, and 21.00% (21/100) of sheep infected. In addition, we have observed a global mixed rate of infections of 20.75% (11/53) among infected individuals. Molecular analyses revealed that at least six Trypanosome species circulate in domestic animals in Gabon (T. congolense, T. simiae, T. simiae Tsavo, T. theileri, T. vivax, T. brucei (including T. brucei brucei, and T. brucei gambiense)). In conclusion, our study showed that domestic animals constitute important potential reservoirs for trypanosome parasites, including T. brucei gambiense, which is responsible for HAT.

Systematic Review on Diversity and Distribution of Anopheles Species in Gabon: A Fresh Look at the Potential Malaria Vectors and Perspectives.

Gabon is located in the malaria hyper-endemic zone, where data concerning malaria vector distribution remains fragmentary, making it difficult to implement an effective vector control strategy. Thus, it becomes crucial and urgent to undertake entomological surveys that will allow a better mapping of the Anopheles species present in Gabon. In this review, we examined different articles dealing with Anopheles in Gabon from ProQuest, Web of Science, PubMed, and Google scholar databases. After applying the eligibility criteria to 7543 articles collected from four databases, 42 studies were included that covered a 91-year period of study. The review revealed a wide diversity of Anopheles species in Gabon with a heterogeneous distribution. Indeed, our review revealed the presence of 41 Anopheles species, of which the most abundant were members of the Gambiae and Nili complexes and those of the Funestus and Moucheti groups. However, our review also revealed that the major and minor vectors of malaria in Gabon are present in both sylvatic, rural, and urban environments. The observation of human malaria vectors in sylvatic environments raises the question of the role that the sylvatic environment may play in maintaining malaria transmission in rural and urban areas. Ultimately, it appears that knowledge of biodiversity and spatial distribution of Anopheles mosquitoes is fragmentary in Gabon, suggesting that additional studies are necessary to complete and update these entomological data, which are useful for the implementation of vector control strategies.

Diversity of parasites in two captive chimpanzee populations in southern Gabon.

Captive chimpanzees living in confined environments like sanctuaries or primatology centers are frequently affected by gastrointestinal parasites. Some of these are likely to be transmitted to humans and may seriously affect public health. However little information is currently available on the gastrointestinal parasites of primates living in such environments. Here, we characterize the diversity and prevalence of gastrointestinal parasites in two populations of captive chimpanzees living in south-eastern Gabon. Our study reveals that at least nine parasite species infect the chimpanzees with high prevalence, including several helminths (Ascaris spp., Enterobius spp., Strongyloides spp., Trichuris spp., Hymenolepis spp., Mammomonogamus spp), three protozoa (Balantioides spp., Entamoeba spp. and Troglodytella spp) and several unidentified parasites. All the parasite taxa we identified had previously been identified in other primates, including humans. Age, sex and site type may influence infection rates and/or parasite diversity found in a particular host.

Author Correction: Genomes of all known members of a Plasmodium subgenus reveal paths to virulent human malaria.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Rodent malaria in Gabon: Diversity and host range.

Malaria parasites infect a wide range of vertebrate hosts, such as reptiles, birds and mammals (i.e., primates, ungulates, bats, and rodents). Four Plasmodium species and their subspecies infect African Muridae. Since their discoveries in the 1940s, these rodent Plasmodium species have served as biological models to explore many aspects of the biology of malaria agents and their interactions with their hosts. Despite that, surprisingly, little is known about their ecology, natural history and evolution. Most field studies on these parasites, performed from the 1940s to the early 1980s, showed that all rodent Plasmodium species infect only one main host species, the thicket rat. In the present study, we re-explored the diversity of Plasmodium parasites infecting rodent species living in peridomestic habitats in Gabon, Central Africa. Using molecular approaches, we found that at least two Plasmodium species (Plasmodium vinckei and Plasmodium yoelii) circulated among five rodent species (including the invasive species Mus musculus). This suggests that the host range of these parasites might be larger than previously considered. Our results also showed that the diversity of these parasites could be higher than currently recognized, with the discovery of a new phylogenetic lineage that could represent a new species of rodent Plasmodium.

Plasmodium vivax-like genome sequences shed new insights into Plasmodium vivax biology and evolution.

Although Plasmodium vivax is responsible for the majority of malaria infections outside Africa, little is known about its evolution and pathway to humans. Its closest genetic relative, P. vivax-like, was discovered in African great apes and is hypothesized to have given rise to P. vivax in humans. To unravel the evolutionary history and adaptation of P. vivax to different host environments, we generated using long- and short-read sequence technologies 2 new P. vivax-like reference genomes and 9 additional P. vivax-like genotypes. Analyses show that the genomes of P. vivax and P. vivax-like are highly similar and colinear within the core regions. Phylogenetic analyses clearly show that P. vivax-like parasites form a genetically distinct clade from P. vivax. Concerning the relative divergence dating, we show that the evolution of P. vivax in humans did not occur at the same time as the other agents of human malaria, thus suggesting that the transfer of Plasmodium parasites to humans happened several times independently over the history of the Homo genus. We further identify several key genes that exhibit signatures of positive selection exclusively in the human P. vivax parasites. Two of these genes have been identified to also be under positive selection in the other main human malaria agent, P. falciparum, thus suggesting their key role in the evolution of the ability of these parasites to infect humans or their anthropophilic vectors. Finally, we demonstrate that some gene families important for red blood cell (RBC) invasion (a key step of the life cycle of these parasites) have undergone lineage-specific evolution in the human parasite (e.g., reticulocyte-binding proteins [RBPs]).

Genomes of all known members of a Plasmodium subgenus reveal paths to virulent human malaria.

Plasmodium falciparum, the most virulent agent of human malaria, shares a recent common ancestor with the gorilla parasite Plasmodium praefalciparum. Little is known about the other gorilla- and chimpanzee-infecting species in the same (Laverania) subgenus as P. falciparum, but none of them are capable of establishing repeated infection and transmission in humans. To elucidate underlying mechanisms and the evolutionary history of this subgenus, we have generated multiple genomes from all known Laverania species. The completeness of our dataset allows us to conclude that interspecific gene transfers, as well as convergent evolution, were important in the evolution of these species. Striking copy number and structural variations were observed within gene families and one, stevor, shows a host-specific sequence pattern. The complete genome sequence of the closest ancestor of P. falciparum enables us to estimate the timing of the beginning of speciation to be 40,000-60,000 years ago followed by a population bottleneck around 4,000-6,000 years ago. Our data allow us also to search in detail for the features of P. falciparum that made it the only member of the Laverania able to infect and spread in humans.

The host specificity of ape malaria parasites can be broken in confined environments.

Recent studies have revealed a large diversity of Plasmodium spp. among African great apes. Some of these species are related to Plasmodium falciparum, the most virulent agent of human malaria (subgenus Laverania), and others to Plasmodium ovale, Plasmodium malariae and Plasmodium vivax (subgenus Plasmodium), three other human malaria agents. Laverania parasites exhibit strict host specificity in their natural environment. Plasmodium reichenowi, Plasmodium billcollinsi, Plasmodium billbrayi and Plasmodium gaboni infect only chimpanzees, while Plasmodium praefalciparum, Plasmodium blacklocki and Plasmodium adleri are restricted to gorillas and Plasmodium falciparum is pandemic in humans. This host specificity may be due to genetic and/or environmental factors. Infrastructures hosting captive primates, such as sanctuaries and health centres, usually concentrate different primate species, thus favouring pathogen exchanges. Using molecular tools, we analysed blood samples from captive non-human primates living in Gabon to evaluate the risk of Plasmodium spp. transfers between host species. We also included blood samples from workers taking care of primates to assess whether primate-human parasite transfers occurred. We detected four transfers of Plasmodium from gorillas towards chimpanzees, one from chimpanzees to gorillas, three from humans towards chimpanzees and one from humans to mandrills. No simian Plasmodium was found in the blood samples from humans working with primates. These findings demonstrate that the genetic barrier that determines the apparent host specificity of Laverania is not completely impermeable and that parasite exchanges between gorillas and chimpanzees are possible in confined environments.

Ape malaria transmission and potential for ape-to-human transfers in Africa.

Recent studies have highlighted the large diversity of malaria parasites infecting African great apes (subgenus Laverania) and their strong host specificity. Although the existence of genetic incompatibilities preventing the cross-species transfer may explain host specificity, the existence of vectors with a high preference for a determined host represents another possibility. To test this hypothesis, we undertook a 15-mo-long longitudinal entomological survey in two forest regions of Gabon, where wild apes live, at different heights under the canopy. More than 2,400 anopheline mosquitoes belonging to 18 species were collected. Among them, only three species of Anopheles were found infected with ape Plasmodium: Anopheles vinckei, Anopheles moucheti, and Anopheles marshallii Their role in transmission was confirmed by the detection of the parasites in their salivary glands. Among these species, An. vinckei showed significantly the highest prevalence of infection and was shown to be able to transmit parasites of both chimpanzees and gorillas. Transmission was also shown to be conditioned by seasonal factors and by the heights of capture under the canopy. Moreover, human landing catches of sylvan Anopheles demonstrated the propensity of these three vector species to feed on humans when available. Our results suggest therefore that the strong host specificity observed in the Laveranias is not linked to a specific association between the vertebrate host and the vector species and highlight the potential role of these vectors as bridge between apes and humans.

Haemosporidian Parasites of Antelopes and Other Vertebrates from Gabon, Central Africa.

Re-examination, using molecular tools, of the diversity of haemosporidian parasites (among which the agents of human malaria are the best known) has generally led to rearrangements of traditional classifications. In this study, we explored the diversity of haemosporidian parasites infecting vertebrate species (particularly mammals, birds and reptiles) living in the forests of Gabon (Central Africa), by analyzing a collection of 492 bushmeat samples. We found that samples from five mammalian species (four duiker and one pangolin species), one bird and one turtle species were infected by haemosporidian parasites. In duikers (from which most of the infected specimens were obtained), we demonstrated the existence of at least two distinct parasite lineages related to Polychromophilus species (i.e., bat haemosporidian parasites) and to sauropsid Plasmodium (from birds and lizards). Molecular screening of sylvatic mosquitoes captured during a longitudinal survey revealed the presence of these haemosporidian parasite lineages also in several Anopheles species, suggesting a potential role in their transmission. Our results show that, differently from what was previously thought, several independent clades of haemosporidian parasites (family Plasmodiidae) infect mammals and are transmitted by anopheline mosquitoes.

Genetic diversity of Plasmodium falciparum isolates from Baka Pygmies and their Bantu neighbours in the north of Gabon.

BACKGROUND: There have been many reports on the population genetic structure of Plasmodium falciparum from different endemic regions especially sub-Saharan Africa. However, few studies have been performed on neglected populations, such as the Pygmy populations. In this study, the population genetic structure of P. falciparum was investigated in the Baka Pygmies of Gabon and compared to that observed in neighboring villages composed mostly of Bantu farmers. METHODS: A total of 342 blood samples were collected from 170 Baka Pygmies and 172 Bantus in the north of Gabon (Woleu Ntem Province). Plasmodium infections were characterized by sequencing a portion of the parasite cytochrome b gene. Population genetic structure of P. falciparum in the different villages was analysed using microsatellite markers and genes coding for antigenic proteins (MSP1, MSP2, GLURP, and EBA-175). RESULTS: Overall, prevalence of P. falciparum was around 57 % and no significant difference of prevalence was observed between Pygmies and Bantus. No significant differences of population genetic structure of P. falciparum was found between Pygmy and Bantu people except for one antigen-coding gene, glurp, for which genetic data suggested the existence of a potentially disruptive selection acting on this gene in the two types of populations. The genetic structure of P. falciparum followed a pattern of isolation by distance at the scale of the study. CONCLUSION: The prevalence and genetic diversity of P. falciparum observed in Baka demonstrates a significant transmission of the parasite in this population, and some exchanges of parasites with Bantu neighbours. Despite that, some antigen-coding genes seem to have had a particular evolutionary trajectory in certain Pygmy populations due to specific local human and/or mosquito characteristics.

No evidence for ape Plasmodium infections in humans in Gabon.

African great apes are naturally infected by a multitude of Plasmodium species most of them recently discovered, among which several are closely related to human malaria agents. However, it is still unknown whether these animals can serve as source of infections for humans living in their vicinity. To evaluate this possibility, we analysed the nature of Plasmodium infections from a bank of 4281 human blood samples collected in 210 villages of Gabon, Central Africa. Among them, 2255 were detected positive to Plasmodium using molecular methods (Plasmodium Cytochrome b amplification). A high throughput sequencing technology (454 GS-FLX Titanium technology, Roche) was then used to identify the Plasmodium species present within each positive sample. Overall, we identified with confidence only three species infecting humans in Gabon: P. falciparum, P. malariae and P. ovale. None of the species known to infect non-human primates in Central Africa was found. Our study shows that ape Plasmodium parasites of the subgenus Laverania do not constitute a frequent source of infection for humans. It also suggests that some strong host genetic barriers must exist to prevent the cross species transmission of ape Plasmodium in a context of ever increasing contacts between humans and wildlife.

Diversity of malaria parasites in great apes in Gabon.

BACKGROUND: Until 2009, the Laverania subgenus counted only two representatives: Plasmodium falciparum and Plasmodium reichenowi. The recent development of non-invasive methods allowed re-exploration of plasmodial diversity in African apes. Although a large number of great ape populations have now been studied regarding Plasmodium infections in Africa, there are still vast areas of their distribution that remained unexplored. Gabon constitutes an important part of the range of western central African great ape subspecies (Pan troglodytes troglodytes and Gorilla gorilla gorilla), but has not been studied so far. In the present study, the diversity of Plasmodium species circulating in great apes in Gabon was analysed. METHODS: The analysis of 1,261 faecal samples from 791 chimpanzees and 470 gorillas collected from 24 sites all over Gabon was performed. Plasmodium infections were characterized by amplification and sequencing of a portion of the Plasmodium cytochrome b gene. RESULTS: The analysis of the 1,261 samples revealed that at least six Plasmodium species circulate in great apes in Gabon (Plasmodium praefalciparum, Plasmodium gorA (syn Plasmodium adleri), Plasmodium gorB (syn Plasmodium blacklocki) in gorillas and Plasmodium gaboni, P. reichenowi and Plasmodium billcollinsi in chimpanzees). No new phylogenetic lineages were discovered. The average infection rate was 21.3% for gorillas and 15.4% for chimpanzees. A logistic regression showed that the probability of infection was significantly dependent on the freshness of the droppings but not of the host species or of the average pluviometry of the months of collection.