Detection of Plasmodium simium gametocytes in non-human primates from the Brazilian Atlantic Forest

BACKGROUND

Plasmodium species of non-human primates (NHP) are of great interest because they can naturally infect humans. Plasmodium simium, a parasite restricted to the Brazilian Atlantic Forest, was recently shown to cause a zoonotic outbreak in the state of Rio de Janeiro. The potential of NHP to act as reservoirs of Plasmodium infection presents a challenge for malaria elimination, as NHP will contribute to the persistence of the parasite. The aim of the current study was to identify and quantify gametocytes in NHP naturally-infected by P. simium.

METHODS

Whole blood samples from 35 NHP were used in quantitative reverse transcription PCR (RT-qPCR) assays targeting 18S rRNA, Pss25 and Pss48/45 malaria parasite transcripts. Absolute quantification was performed in positive samples for 18S rRNA and Pss25 targets. Linear regression was used to compare the quantification cycle (Cq) and the Spearman's rank correlation coefficient was used to assess the correlation between the copy numbers of 18S rRNA and Pss25 transcripts. The number of gametocytes/µL was calculated by applying a conversion factor of 4.17 Pss25 transcript copies per gametocyte.

RESULTS

Overall, 87.5% of the 26 samples, previously diagnosed as P. simium, were positive for 18S rRNA transcript amplification, of which 13 samples (62%) were positive for Pss25 transcript amplification and 7 samples (54%) were also positive for Pss48/45 transcript. A strong positive correlation was identified between the Cq of the 18S rRNA and Pss25 and between the Pss25 and Pss48/45 transcripts. The 18S rRNA and Pss25 transcripts had an average of 1665.88 and 3.07 copies/µL, respectively. A positive correlation was observed between the copy number of Pss25 and 18S rRNA transcripts. Almost all gametocyte carriers exhibited low numbers of gametocytes (< 1/µL), with only one howler monkey having 5.8 gametocytes/µL.

CONCLUSIONS

For the first time, a molecular detection of P. simium gametocytes in the blood of naturally-infected brown howler monkeys (Alouatta guariba clamitans) was reported here, providing evidence that they are likely to be infectious and transmit P. simium infection, and, therefore, may act as a reservoir of malaria infection for humans in the Brazilian Atlantic Forest.

The genome of the zoonotic malaria parasite Plasmodium simium reveals adaptations to host switching

BACKGROUND

Plasmodium simium, a malaria parasite of non-human primates (NHP), was recently shown to cause zoonotic infections in humans in Brazil. We sequenced the P. simium genome to investigate its evolutionary history and to identify any genetic adaptions that may underlie the ability of this parasite to switch between host species.

RESULTS

Phylogenetic analyses based on whole genome sequences of P. simium from humans and NHPs reveals that P. simium is monophyletic within the broader diversity of South American Plasmodium vivax, suggesting P. simium first infected NHPs as a result of a host switch of P. vivax from humans. The P. simium isolates show the closest relationship to Mexican P. vivax isolates. Analysis of erythrocyte invasion genes reveals differences between P. vivax and P. simium, including large deletions in the Duffy-binding protein 1 (DBP1) and reticulocyte-binding protein 2a genes of P. simium. Analysis of P. simium isolated from NHPs and humans revealed a deletion of 38 amino acids in DBP1 present in all human-derived isolates, whereas NHP isolates were multi-allelic.

CONCLUSIONS

Analysis of the P. simium genome confirmed a close phylogenetic relationship between P. simium and P. vivax, and suggests a very recent American origin for P. simium. The presence of the DBP1 deletion in all human-derived isolates tested suggests that this deletion, in combination with other genetic changes in P. simium, may facilitate the invasion of human red blood cells and may explain, at least in part, the basis of the recent zoonotic infections.

Ongoing host-shift speciation in Plasmodium simium

Plasmodium simium, a malaria parasite that infects platyrrhine monkeys and humans in the New World, is nearly identical to Plasmodium vivax. Recent genomic comparative analyses of these sister species have identified elevated divergence in a gene that may underlie P. simium adaptation to non-human primates during its gradual speciation process.

Non-human primate and human malaria: past, present and future

BACKGROUND

Studies of the malaria parasites infecting various non-human primates (NHPs) have increased our understanding of the origin, biology and pathogenesis of human Plasmodium parasites.This review considers the major discoveries concerning NHP malaria parasites, highlights their relationships with human malaria and considers the impact that this may have on attempts to eradicate the disease.

RESULTS

The first description of NHP malaria parasites dates back to the early 20th century. Subsequently, experimental and fortuitous findings indicating that some NHP malaria parasites can be transmitted to humans have raised concerns about the possible impact of a zoonotic malaria reservoir on efforts to control human malaria.Advances in molecular techniques over the last 15 years have contributed greatly to our knowledge of the existence and geographical distribution of numerous Plasmodium species infecting NHPs, and extended our understanding of their close phylogenetic relationships with human malaria parasites. The clinical application of such techniques has also made it possible to document ongoing spillovers of NHP malaria parasites (Plasmodium knowlesi, P. cynomolgi, P. simium, P. brasilianum) in humans living in or near the forests of Asia and South America, thus confirming that zoonotic malaria can undermine efforts to eradicate human malaria.

CONCLUSIONS

Increasing molecular research supports the prophetic intuition of the pioneers of modern malariology who saw zoonotic malaria as a potential obstacle to the full success of malaria eradication programmes. It is, therefore, important to continue surveillance and research based on one-health approaches in order to improve our understanding of the complex interactions between NHPs, mosquito vectors and humans during a period of ongoing changes in the climate and the use of land, monitor the evolution of zoonotic malaria, identify the populations most at risk and implement appropriate preventive strategies.

Plasmodium simium: population genomics reveals the origin of a reverse zoonosis

The population history of Plasmodium simium, which causes malaria in sylvatic Neotropical monkeys and humans along the Atlantic Coast of Brazil, remains disputed. Genetically diverse P. vivax populations from various sources, including the lineages that founded the species P. simium, are thought to have arrived in the Americas in separate migratory waves. However, here we find a minimal genome-level differentiation between P. simium and present-day New World P. vivax isolates, consistent with their common geographic origin and subsequent divergence on this continent. The meagre genetic diversity in P. simium samples from humans and monkeys implies a recent transfer from humans to non-human primates - a unique example of malaria as a reverse zoonosis of public health significance. Likely genomic signatures of P. simium adaptation to new hosts include the deletion of >40% of a key erythrocyte invasion ligand, PvRBP2a, which may have favored more efficient simian host cell infection.

Plasmodium infection in Kerteszia cruzii (Diptera: Culicidae) in the Atlantic tropical rain forest, southeastern Brazil

In Southeastern Brazil, Kerteszia cruzii (former Anopheles cruzii), a bromeliad mosquito species, is considered an efficient human Plasmodium spp. vector. In this region, recent studies showed asymptomatic or sub-patent Plasmodium falciparum infection. In areas of the Atlantic coast in Rio de Janeiro, Plasmodium simium infection was recently reported in both human and howler monkey. Considering that (1) few malaria cases are reported each year in areas across the tropical Atlantic rain forest in southeastern Brazil; (2) malaria elimination in Atlantic forest is challenged by circulation of P. falciparum and P. simium in humans; (3) the complexity of malaria epidemiology in this region; and (4) the public health importance of Kerteszia cruzii as a sylvatic vector; the major goal of this study is to evaluate Plasmodium infection in Ke. cruzii. Mosquito sampling collections were conducted in Esteiro do Morro and Sítio Itapuan, in Cananeia municipality, and Tapiraí municipality in Ribeira Valley, southeastern São Paulo state, Brazil. Influence of climate and landscape factors in Plasmodium infection in Ke. cruzii was addressed. Among the 1719 mosquitoes tested, 3 females collected in Sítio Itapuan and three from Tapiraí were found infected with either P. vivax or P. simium. Results of statistical analyses did not demonstrate association between Plasmodium infection in mosquito and the landscape. Mosquito infection was found in two landscape clusters, with Plasmodium detected in forest fringe mosquitoes. This finding shows that Ke. cruzii can facilitate transmission among human and non-human primates. Plasmodium falciparum was not identified in the samples analyzed. Spatiotemporal variation in local malaria incidence, low prevalence of Plasmodium, variations in humidity and temperature can explain the absence of mosquitoes infected with P. falciparum in the study.