Prevalence and proportion of Plasmodium spp. triple mixed infections compared with double mixed infections: a systematic review and meta-analysis

BACKGROUND

Although mixed infection by two Plasmodium species has been recognized, mixed infection by three different Plasmodium species within one individual has not been clarified. This study sought to determine the pooled prevalence and proportion of triple mixed Plasmodium spp. infection compared with double mixed infection.

METHODS

Articles from PubMed, Scopus, and Web of Science were searched for cross-sectional studies of triple mixed infection by Plasmodium species and then were retrieved and extracted. The pooled proportion and prevalence of triple mixed infection by Plasmodium species were subjected to random-effects analysis. The secondary outcomes were differences in the pooled proportion between triple mixed infection and double mixed infection by Plasmodium species reported in the included studies.

RESULTS

Of 5621 identified studies, triple mixed infection data were available for 35 records, including 601 patients from 22 countries. The overall pooled prevalence of triple mixed infection was 4% (95% Confidence Interval (CI) 3-5%; I2 = 92.5%). The pooled proportion of triple mixed infection compared with double mixed infection was 12% (95% CI 9-18; I2 = 91%). Most of the included studies (29/35; 82.9%) presented a lower proportion of triple mixed infection than double mixed infection. Subgroup analysis demonstrated that the proportion of triple mixed infection was the highest in Oceania (23%; 95% CI 15-36%) and Europe (21%; 95% CI 5-86%), but the lowest in the USA (3%; 95% CI 2-4%). Moreover, the proportion of triple mixed infection was higher in residents (20%; 95% CI 14-29%) than in febrile patients (7%; 95% CI 4-13%), when compared with the proportion of double mixed infection. Subgroup analysis of the age groups demonstrated that, compared with the proportion of double mixed infection, triple mixed infection was lower in patients aged ≤ 5 years (OR = 0.27; 95% CI 0.13-0.56; I2 = 31%) and > 5 years (OR = 0.09; 95% CI 0.04-0.25, I2 = 78%).

CONCLUSIONS

The present study suggested that, in areas where triple mixed infection were endemic, PCR or molecular diagnosis for all residents in communities where malaria is submicroscopic can provide prevalence data and intervention measures, as well as prevent disease transmission and enhance malaria elimination efforts.

Low level of genetic diversity and high occurrence of vector-borne protozoa in water buffaloes in Thailand based on 18S ribosomal RNA and mitochondrial cytochrome b genes

Vector-borne pathogens (VBPs) pose a great risk to ruminant production through significant economic losses. Several previous studies in Thailand have mainly been focused on the health of dairy and beef cattle. Water buffaloes are one of the important ruminants in the country, but studies on their infection with VBPs remains limited. We conducted a molecular survey on blood samples from 456 buffaloes obtained from eight provinces across different geographical locations of Thailand. The PCR diagnostics indicated that 116 (25.4%) and 59 (12.9%) of these 456 samples were positive for piroplasm and Plasmodium spp., respectively, and were found in six and all eight regions, respectively, across Thailand. Co-infections of piroplasm and Plasmodium spp. were observed in 24 cases (5.26%). Babesia spp. was not detected in any of the 12 sequenced piroplasm-positive samples in the present study. Genetic comparisons and phylogenetic analyses of within and between parasite populations, based on the 18S ribosomal (r)RNA and cytochrome b (cytb) genes for T. orientalis and P. bubalis, respectively, revealed that T. orientalis shared a high similarity within its population and could be divided into four distinct haplotypes. Haplotypes 1 and 4 were placed in the same clade with the samples previously isolated from cattle in Korea, Japan, Australia, and the USA. Haplotypes 2, and 3 were novel and were placed in a separate clade not shared with the other isolates. We also confirmed our previous investigation that at least three cytb haplotypes of P. bubalis were distributed in the country with a relatively high degree of genetic polymorphisms within its population (based on cytb sequences). Type II P. bubalis was phylogenetically closely related to P. caprae in goats in Zambia and Thailand. This study improves our current understanding on the distribution, intra- and inter-population genetic diversity, and genetic relationship of piroplasms and Plasmodium spp. in water buffaloes.

Attraction of mosquitoes to primate odours and implications for zoonotic Plasmodium transmission

Vector-borne diseases often originate from wildlife and can spill over into the human population. One of the most important determinants of vector-borne disease transmission is the host preference of mosquitoes. Mosquitoes with a specialised host preference are guided by body odours to find their hosts in addition to carbon dioxide. Little is known about the role of mosquito host preference in the spillover of pathogenic agents from humans towards animals and vice versa. In the Republic of Congo, the attraction of mosquitoes to primate host odours was determined, as well as their possible role as malaria vectors, using odour-baited traps mimicking the potential hosts of mosquitoes. Most of the mosquito species caught showed a generalistic host preference. Anopheles obscurus was the most abundant Anopheles mosquito, with a generalistic host preference observed from the olfactory response and the detection of various Plasmodium parasites. Interestingly, Culex decens showed a much higher attraction towards chimpanzee odours than to human or cow odours. Human Plasmodium parasites were observed in both human and chimpanzee blood, although not in the Anopheles mosquitoes that were collected. Understanding the role of mosquito host preference for cross-species parasite transmission provides information that will help to determine the risk of spillover of vector-borne diseases.

DNA Methylation in Anopheles albimanus Modulates the Midgut Immune Response Against Plasmodium berghei

Epigenetic mechanisms such as DNA methylation and histone post-translational modifications are fundamental for the phenotypic plasticity of insects during their interaction with the environment. In response to environmental cues, the methylation pattern in DNA is dynamically remodeled to achieve an epigenetic control of gene expression. DNA methylation is the focus of study in insects for its evolutionarily conserved character; however, there is scant knowledge about the epigenetic regulation in vector mosquitoes, especially during their infection by parasites. The aim of the present study was to evaluate the participation of DNA methylation in the immune response of Anopheles albimanus to a Plasmodium infection. For this, we first investigated the presence of a fully functional DNA methylation system in A. albimanus by assessing its potential role in larval development. Subsequently, we evaluated the transcriptional response to Plasmodium berghei of two mosquito phenotypes with different degrees of susceptibility to the parasite, in a scenario where their global DNA methylation had been pharmacologically inhibited. Our study revealed that A. albimanus has a functional DNA methylation system that is essential to larval viability, and that is also responsive to feeding and parasite challenges. The pharmacological erasure of the methylome with azacytidine or decitabine abolished the divergent responses of both mosquito phenotypes, leading to a transcriptionally similar response upon parasite challenge. This response was more specific, and the infection load in both phenotypes was lowered. Our findings suggest that DNA methylation may constitute a key factor in vector competence, and a promising target for preventing malaria transmission.

Molecular Screening of Plasmodium (Haemosporidia: Plasmodiidae) Parasites from Reptiles in Brazil

Hemosporidians are a monophyletic group of protozoan parasites infecting all terrestrial vertebrate orders. Although Plasmodium is the most studied genus within the Haemosporidia, this research effort is heavily biased toward mammal and bird hosts. We screened 205 specimens of at least 18 reptile species from Brazil using a partial mitochondrial cytochrome b gene marker. Positive samples were sequenced and included in a phylogenetic assessment. Four positive PCR products matched others identified as Plasmodium using BLAST from 3 different host species, Ameiva ameiva, Tropidurus hispidus, and Hemidactylus mabouia. Recovery of similar haplotypes in the native T. hispidus and exotic H. mabouia (99.9%) indicate potential host-switching.

Howler monkeys are the reservoir of malarial parasites causing zoonotic infections in the Atlantic forest of Rio de Janeiro

BACKGROUND

Although malaria cases have substantially decreased in Southeast Brazil, a significant increase in the number of Plasmodium vivax-like autochthonous human cases has been reported in remote areas of the Atlantic Forest in the past few decades in Rio de Janeiro (RJ) state, including an outbreak during 2015-2016. The singular clinical and epidemiological aspects in several human cases, and collectively with molecular and genetic data, revealed that they were due to the non-human primate (NHP) parasite Plasmodium simium; however, the understanding of the autochthonous malarial epidemiology in Southeast Brazil can only be acquired by assessing the circulation of NHP Plasmodium in the foci and determining its hosts.

METHODOLOGY

A large sampling effort was carried out in the Atlantic forest of RJ and its bordering states (Minas Gerais, São Paulo, Espírito Santo) for collecting and examining free-living NHPs. Blood and/or viscera were analyzed for Plasmodium infections via molecular and microscopic techniques.

PRINCIPAL FINDINGS

In total, 146 NHPs of six species, from 30 counties in four states, were tested, of which majority were collected from RJ. Howler monkeys (Alouatta clamitans) were the only species found infected. In RJ, 26% of these monkeys tested positive, of which 17% were found to be infected with P. simium. Importantly, specific single nucleotide polymorphisms-the only available genetic markers that differentiate P. simium from P. vivax-were detected in all P. simium infected A. clamitans despite their geographical origin of malarial foci. Interestingly, 71% of P. simium infected NHPs were from the coastal slope of a mountain chain (Serra do Mar), where majority of the human cases were found. Plasmodium brasilianum/malariae was initially detected in 14% and 25% free-living howler monkeys in RJ and in the Espírito Santo (ES) state, respectively. Moreover, the malarial pigment was detected in the spleen fragments of 50% of a subsample comprising dead howler monkeys in both RJ and ES. All NHPs were negative for Plasmodium falciparum.

CONCLUSIONS/SIGNIFICANCE

Our data indicate that howler monkeys act as the main reservoir for the Atlantic forest human malarial parasites in RJ and other sites in Southeast Brazil and reinforce its zoonotic characteristics.

Genetic characterisation of the erythrocyte-binding protein (PkβII) of Plasmodium knowlesi isolates from Malaysia

Plasmodium knowlesi contributes to the majority of human malaria incidences in Malaysia. Its uncontrollable passage among the natural monkey hosts can potentially lead to zoonotic outbreaks. The merozoite of this parasite invades host erythrocytes through interaction between its erythrocyte-binding proteins (EBPs) and their respective receptor on the erythrocytes. The regionII of P. knowlesi EBP, P. knowlesi beta (PkβII) protein is found to be mediating merozoite invasion into monkey erythrocytes by interacting with sialic acid receptors. Hence, the objective of this study was to investigate the genetic diversity, natural selection and haplotype grouping of PkβII of P. knowlesi isolates in Malaysia. Polymerase chain reaction amplifications of PkβII were performed on archived blood samples from Malaysia and 64 PkβII sequences were obtained. Sequence analysis revealed length polymorphism, and its amino acids at critical residues indicate the ability of PkβII to mediate P. knowlesi invasion into monkey erythrocytes. Low genetic diversity (π = 0.007) was observed in the PkβII of Malaysia Borneo compared to Peninsular Malaysia (π = 0.015). The PkβII was found to be under strong purifying selection to retain infectivity in monkeys and it plays a limited role in the zoonotic potential of P. knowlesi. Its haplotypes could be clustered into Peninsular Malaysia and Malaysia Borneo groups, indicating the existence of two distinct P. knowlesi parasites in Malaysia as reported in an earlier study.

Prevalence of Plasmodium parasites in non-human primates and mosquitoes in areas with different degrees of fragmentation in Colombia

BACKGROUND

Parasites from the genus Plasmodium, the aetiological agent of malaria in humans, can also infect non-human primates (NHP), increasing the potential risk of zoonotic transmission with its associated global public health concerns. In Colombia, there are no recent studies on Plasmodium spp. infecting free-ranging NHP. Thus, this study aimed to determine the diversity of Plasmodium species circulating in fragmented forests in central Colombia, both in Anopheles mosquitoes and in the four sympatric NHP in the region (Ateles hybridus, Cebus versicolor, Alouatta seniculus and Aotus griseimembra), in order to evaluate the risk of infection to humans associated with the presence of sylvatic hosts and vectors infected with Plasmodium spp.

METHODS

Overall, there were collected 166 fecal samples and 25 blood samples from NHP, and 442 individuals of Anopheles spp. DNA extraction, nested PCR using mitochondrial (cox3 gene) and ribosomal (18S rDNA) primers, electrophoresis and sequencing were conducted in order to identify Plasmodium spp. from the samples.

RESULTS

Plasmodium falciparum was detected in two fecal samples of Alouatta seniculus, while Plasmodium vivax/simium infected Ateles hybridus, Cebus versicolor and Alouatta seniculus. Co-infections with P. vivax/simium and Plasmodium malariae/brasilianum were found in three individuals. The highest prevalence from blood samples was found for Plasmodium malariae/brasilianum in two Alouatta seniculus while Plasmodium vivax/simium was most prevalent in fecal samples, infecting four individuals of Alouatta seniculus. Seven Anopheles species were identified in the study site: Anopheles (Anopheles) punctimacula, Anopheles (An.) malefactor, Anopheles (Nyssorhynchus) oswaldoi, Anopheles (Nys.) triannulatus, Anopheles (An.) neomaculipalpus, Anopheles (Nys.) braziliensis and Anopheles (Nys.) nuneztovari. Infection with P. vivax/simium was found in An. nuneztovari, An. neomaculipalpus, and An. triannulatus. Furthermore, An. oswaldoi and An. triannulatus were found infected with P. malariae/brasilianum. The effect of fragmentation and distance to the nearest town measured in five forests with different degrees of fragmentation was not statistically significant on the prevalence of Plasmodium in NHP, but forest fragmentation did have an effect on the Minimum Infection Rate (MIR) in Anopheles mosquitoes.

CONCLUSIONS

The presence of Plasmodium spp. in NHP and Anopheles spp. in fragmented forests in Colombia has important epidemiological implications in the human-NHP interface and the associated risk of malaria transmission.

Ribozyme-mediated, multiplex CRISPR gene editing and CRISPR interference (CRISPRi) in rodent-infectious Plasmodium yoelii

Malaria remains a major global health issue, affecting millions and killing hundreds of thousands of people annually. Efforts to break the transmission cycle of the causal Plasmodium parasite, and to cure those that are afflicted, rely upon functional characterization of genes essential to the parasite's growth and development. These studies are often based upon manipulations of the parasite genome to disrupt or modify a gene of interest to understand its importance and function. However, these approaches can be limited by the availability of selectable markers and the time required to generate transgenic parasites. Moreover, there also is a risk of disrupting native gene regulatory elements with the introduction of exogenous sequences. To address these limitations, we have developed CRISPR-RGR, a Streptococcus pyogenes (Sp)Cas9-based gene editing system for Plasmodium that utilizes a ribozyme-guide-ribozyme (RGR) single guide RNA (sgRNA) expression strategy with RNA polymerase II promoters. Using rodent-infectious Plasmodium yoelii, we demonstrate that both gene disruptions and coding sequence insertions are efficiently generated, producing marker-free parasites with homology arms as short as 80-100 bp. Additionally, we find that the common practice of using one sgRNA can produce both unintended plasmid integration and desired locus replacement editing events, whereas the use of two sgRNAs results in only locus replacement editing. Lastly, we show that CRISPR-RGR can be used for CRISPR interference (CRISPRi) by binding catalytically dead SpCas9 (dSpCas9) to the region upstream of a gene of interest, resulting in a position-dependent, but strand-independent reduction in gene expression. This robust and flexible system facilitates efficient genetic characterizations of rodent-infectious Plasmodium species.

Genetic diversity of zoonotic malaria parasites from mosquito vector and vertebrate hosts

We explored and constructed haplotype network for simian malaria species: Plasmodium knowlesi, P. cynomolgi and P. inui aiming to understand the transmission dynamics between mosquitoes, humans and macaques. Mosquitoes were collected from villages in an area where zoonotic malaria is prevalent. PCR analysis confirmed Anopheles balabacensis as the main vector for macaque parasites, moreover nearly 60% of the mosquitoes harboured more than one Plasmodium species. Fragments of the A-type small subunit ribosomal RNA (SS rRNA) amplified from salivary gland sporozoites, and equivalent sequences obtained from GenBank were used to construct haplotype networks. The patterns were consistent with the presence of geographically distinct populations for P. inui and P. cynomolgi, and with three discrete P. knowlesi populations. This study provides a preliminary snapshot of the structure of these populations, that was insufficient to answer our aim. Thus, collection of parasites from their various hosts and over time, associated with a systematic analysis of a set of genetical loci is strongly advocated in order to obtain a clear picture of the parasite population and the flow between different hosts. This is important to devise measures that will minimise the risk of transmission to humans, because zoonotic malaria impedes malaria elimination.

Plasmodium ovale wallikeri in Western Lowland Gorillas and Humans, Central African Republic

Human malaria parasites have rarely been reported from free-ranging great apes. Our study confirms the presence of the human malaria parasite Plasmodium ovale wallikeri in western lowland gorillas and humans in Dzanga Sangha Protected Areas, Central African Republic, and discusses implications for malaria epidemiology.

Effects of host sex, body mass and infection by avian Plasmodium on the biting rate of two mosquito species with different feeding preferences

BACKGROUND

The transmission of mosquito-borne pathogens is strongly influenced by the contact rates between mosquitoes and susceptible hosts. The biting rates of mosquitoes depend on different factors including the mosquito species and host-related traits (i.e. odour, heat and behaviour). However, host characteristics potentially affecting intraspecific differences in the biting rate of mosquitoes are poorly known. Here, we assessed the impact of three host-related traits on the biting rate of two mosquito species with different feeding preferences: the ornithophilic Culex pipiens and the mammophilic Ochlerotatus (Aedes) caspius. Seventy-two jackdaws Corvus monedula and 101 house sparrows Passer domesticus were individually exposed to mosquito bites to test the effect of host sex, body mass and infection status by the avian malaria parasite Plasmodium on biting rates.

RESULTS

Ochlerotatus caspius showed significantly higher biting rates than Cx. pipiens on jackdaws, but non-significant differences were found on house sparrows. In addition, more Oc. caspius fed on female than on male jackdaws, while no differences were found for Cx. pipiens. The biting rate of mosquitoes on house sparrows increased through the year. The bird infection status and body mass of both avian hosts were not related to the biting rate of both mosquito species.

CONCLUSIONS

Host sex was the only host-related trait potentially affecting the biting rate of mosquitoes, although its effect may differ between mosquito and host species.

Avian haemosporidians in the cattle egret (Bubulcus ibis) from central-western and southern Africa: High diversity and prevalence

We described the geographic distribution of 82 haemosporidian lineages (Plasmodium, Haemoproteus, and Leucocytozoon) in the cattle egret sampled in five countries in central-western and southern Africa. Seventy-three lineages have not previously been reported. We determined the prevalence of three haemosporidians in the samples. We investigated the influence of the internal environment of the host and environmental variables on the Plasmodium diversity and whether environmental variables may explain spatial variations in the prevalence of Plasmodium. We screened DNA from 509 blood samples from nestlings in 15 African colonies for infection by sequencing the cytochrome b gene of parasites. The molecular phylogenetic analysis was performed using Bayesian methods and including sequences from the MalAvi and GeneBank databases. We found 62 new Plasmodium lineages in a clade with MYCAME02, which is a lineage described in waterbirds and recently identified in birds of prey as Plasmodium paranucleophilum. Two Haemoproteus lineages identified in cattle egret formed a distinct group with Haemoproteus catharti and MYCAMH1 (Haemoproteus spp.). Seven Leucocytozoon lineages found in the cattle egret clustered with Leucocytozoon californicus. We found different Plasmodium diversities among the colonies sampled, demonstrating that the internal environment of the host is not the primary determinant of diversity. A linear mixed-effects multivariate model showed that precipitation was positively associated with Plasmodium diversity when controlling for the effects of temperature, colony composition (mixed and non-mixed species) and country. Moreover, a generalized mixed model showed that temperature was positively associated with the prevalence of Plasmodium when controlling for precipitation, elevation and country. We conclude that the cattle egret is a good model for future haemosporidian studies, as we found a significant number of new lineages in this host, which occupies regions with different climate characteristics where environmental variables exert an influence on the diversity and prevalence of Plasmodium.

Potential of Vitamin E Deficiency, Induced by Inhibition of α-Tocopherol Efflux, in Murine Malaria Infection

Although epidemiological and experimental studies have suggested beneficial effects of vitamin E deficiency on malaria infection, it has not been clinically applicable for the treatment of malaria owing to the significant content of vitamin E in our daily food. However, since α-tocopherol transfer protein (α-TTP) has been shown to be a determinant of vitamin E level in circulation, manipulation of α-tocopherol levels by α-TTP inhibition was considered as a potential therapeutic strategy for malaria. Knockout studies in mice indicated that inhibition of α-TTP confers resistance against malaria infections in murines, accompanied by oxidative stress-induced DNA damage in the parasite, arising from vitamin E deficiency. Combination therapy with chloroquine and α-TTP inhibition significantly improved the survival rates in murines with malaria. Thus, clinical application of α-tocopherol deficiency could be possible, provided that α-tocopherol concentration in circulation is reduced. Probucol, a recently found drug, induced α-tocopherol deficiency in circulation and was effective against murine malaria. Currently, treatment of malaria relies on the artemisinin-based combination therapy (ACT); however, when mice infected with malarial parasites were treated with probucol and dihydroartemisinin, the beneficial effect of ACT was pronounced. Protective effects of vitamin E deficiency might be extended to manage other parasites in future.

K. S, Chandramohan B, Shanmuganatham V, Karanth KP. Reinvestigating the status of malaria parasite (Plasmodium sp.) in Indian non-human primates

Many human parasites and pathogens have closely related counterparts among non-human primates. For example, non-human primates harbour several species of malaria causing parasites of the genus Plasmodium. Studies suggest that for a better understanding of the origin and evolution of human malaria parasites it is important to know the diversity and evolutionary relationships of these parasites in non-human primates. Much work has been undertaken on malaria parasites in wild great Apes of Africa as well as wild monkeys of Southeast Asia however studies are lacking from South Asia, particularly India. India is one of the major malaria prone regions in the world and exhibits high primate diversity which in turn provides ideal setting for both zoonoses and anthropozoonoses. In this study we report the molecular data for malaria parasites from wild populations of Indian non-human primates. We surveyed 349 fecal samples from five different Indian non-human primates, while 94 blood and tissue samples from one of the Indian non-human primate species (Macaca radiata) and one blood sample from M. mulatta. Our results confirm the presence of P. fragile, P. inui and P. cynomolgi in Macaca radiata. Additionally, we report for the first time the presence of human malarial parasite, P. falciparum, in M. mulatta and M. radiata. Additionally, our results indicate that M. radiata does not exhibit population structure probably due to human mediated translocation of problem monkeys. Human mediated transport of macaques adds an additional level of complexity to tacking malaria in human. This issue has implications for both the spread of primate as well as human specific malarias.

A Cas9 transgenic Plasmodium yoelii parasite for efficient gene editing

The RNA-guided endonuclease Cas9 has applied as an efficient gene-editing method in malaria parasite Plasmodium. However, the size (4.2 kb) of the commonly used Cas9 from Streptococcus pyogenes (SpCas9) limits its utility for genome editing in the parasites only introduced with cas9 plasmid. To establish the endogenous and constitutive expression of Cas9 protein in the rodent malaria parasite P. yoelii, we replaced the coding region of an endogenous gene sera1 with the intact SpCas9 coding sequence using the CRISPR/Cas9-mediated genome editing method, generating the cas9-knockin parasite (PyCas9ki) of the rodent malaria parasite P. yoelii. The resulted PyCas9ki parasite displays normal progression during the whole life cycle and possesses the Cas9 protein expression in asexual blood stage. By introducing the plasmid (pYCs) containing only sgRNA and homologous template elements, we successfully achieved both deletion and tagging modifications for different endogenous genes in the genome of PyCas9ki parasite. This cas9-knockin PyCas9ki parasite provides a new platform facilitating gene functions study in the rodent malaria parasite P. yoelii.

Adaptive Evolution of RH5 in Ape Plasmodium species of the Laverania Subgenus

Plasmodium falciparum, the major cause of malaria morbidity and mortality in humans, has been shown to have emerged after cross-species transmission of one of six host-specific parasites (subgenus Laverania) infecting wild chimpanzees (Pan troglodytes) and western gorillas (Gorilla gorilla). Binding of the parasite-encoded ligand RH5 to the host protein basigin is essential for erythrocyte invasion and has been implicated in host specificity. A recent study claimed to have found two amino acid changes in RH5 that "drove the host shift leading to the emergence of P. falciparum as a human pathogen." However, the ape Laverania data available at that time, which included only a single distantly related chimpanzee parasite sequence, were inadequate to justify any such conclusion. Here, we have investigated Laverania Rh5 gene evolution using sequences from all six ape parasite species. Searching for gene-wide episodic selection across the entire Laverania phylogeny, we found eight codons to be under positive selection, including three that correspond to contact residues known to form hydrogen bonds between P. falciparum RH5 and human basigin. One of these sites (residue 197) has changed subsequent to the transmission from apes to humans that gave rise to P. falciparum, suggesting a possible role in the adaptation of the gorilla parasite to the human host. We also found evidence that the patterns of nucleotide polymorphisms in P. falciparum are not typical of Laverania species and likely reflect the recent demographic history of the human parasite.IMPORTANCE A number of closely related, host-specific malaria parasites infecting wild chimpanzees and gorillas have recently been described. The most important cause of human malaria, Plasmodium falciparum, is now known to have resulted from a cross-species transmission of one of the gorilla parasites. Overcoming species-specific interactions between a parasite ligand, RH5, and its receptor on host cells, basigin, was likely an important step in the origin of the human parasite. We have investigated the evolution of the Rh5 gene and found evidence of adaptive changes during the diversification of the ape parasite species at sites that are known to form bonds with human basigin. One of these changes occurred at the origin of P. falciparum, implicating it as an important adaptation to the human host.

Phylogenetic analysis of simian Plasmodium spp. infecting Anopheles balabacensis Baisas in Sabah, Malaysia

BACKGROUND

Anopheles balabacensis of the Leucospyrus group has been confirmed as the primary knowlesi malaria vector in Sabah, Malaysian Borneo for some time now. Presently, knowlesi malaria is the only zoonotic simian malaria in Malaysia with a high prevalence recorded in the states of Sabah and Sarawak.

METHODOLOGY/PRINCIPAL FINDINGS

Anopheles spp. were sampled using human landing catch (HLC) method at Paradason village in Kudat district of Sabah. The collected Anopheles were identified morphologically and then subjected to total DNA extraction and polymerase chain reaction (PCR) to detect Plasmodium parasites in the mosquitoes. Identification of Plasmodium spp. was confirmed by sequencing the SSU rRNA gene with species specific primers. MEGA4 software was then used to analyse the SSU rRNA sequences and bulid the phylogenetic tree for inferring the relationship between simian malaria parasites in Sabah. PCR results showed that only 1.61% (23/1,425) of the screened An. balabacensis were infected with one or two of the five simian Plasmodium spp. found in Sabah, viz. Plasmodium coatneyi, P. inui, P. fieldi, P. cynomolgi and P. knowlesi. Sequence analysis of SSU rRNA of Plasmodium isolates showed high percentage of identity within the same Plasmodium sp. group. The phylogenetic tree based on the consensus sequences of P. knowlesi showed 99.7%-100.0% nucleotide identity among the isolates from An. balabacensis, human patients and a long-tailed macaque from the same locality.

CONCLUSIONS/SIGNIFICANCE

This is the first study showing high molecular identity between the P. knowlesi isolates from An. balabacensis, human patients and a long-tailed macaque in Sabah. The other common simian Plasmodium spp. found in long-tailed macaques and also detected in An. balabacensis were P. coatneyi, P. inui, P. fieldi and P. cynomolgi. The high percentage identity of nucleotide sequences between the P. knowlesi isolates from the long-tailed macaque, An. balabacensis and human patients suggests a close genetic relationship between the parasites from these hosts.

Chronic Plasmodium brasilianum infections in wild Peruvian tamarins

There is an increased interest in potential zoonotic malarias. To date, Plasmodium malariae that infects humans remains indistinguishable from Plasmodium brasilianum, which is widespread among New World primates. Distributed throughout tropical Central and South America, the Callitrichidae are small arboreal primates in which detection of natural Plasmodium infection has been extremely rare. Most prior screening efforts have been limited to small samples, the use of low-probability detection methods, or both. Rarely have screening efforts implemented a longitudinal sampling design. Through an annual mark-recapture program of two sympatric callitrichids, the emperor (Saguinus imperator) and saddleback (Saguinus fuscicollis) tamarins, whole blood samples were screened for Plasmodium by microscopy and nested PCR of the cytochrome b gene across four consecutive years (2012-2015). Following the first field season, approximately 50% of the samples collected each subsequent year were from recaptured individuals. In particular, out of 245 samples from 129 individuals, 11 samples from 6 individuals were positive for Plasmodium, and all but one of these infections was found in S. imperator. Importantly, the cytochrome b sequences were 100% identical to former isolates of P. malariae from humans and P. brasilianum from Saimiri sp. Chronic infections were detected as evidenced by repeated infections (7) from two individuals across the 4-year study period. Furthermore, 4 of the 5 infected emperor tamarins were part of a single group spanning the entire study period. Overall, the low prevalence reported here is consistent with previous findings. This study identifies two new natural hosts for P. brasilianum and provides evidence in support of chronic infections in wildlife populations. Given that callitrichids are often found in mixed-species associations with other primates and can be resilient to human-disturbed environments, they could contribute to the maintenance of P. malariae populations if future work provides entomological and epidemiological evidence indicating human zoonotic infections.

Identification of Plasmodium spp. in Neotropical primates of Maranhense Amazon in Northeast Brazil

In the Brazilian Amazon region, malaria caused by Plasmodium malariae is considered to be a zoonosis because of cross-transfer of the parasite between humans and Neotropical primates. To contribute information on this issue, we investigated occurrences of natural infection with Plasmodium sp. among Neotropical primates in the Maranhense Amazon (Amazon region of the state of Maranhão), in the northeastern region of Brazil. Blood samples were collected from 161 Neotropical primates of six species that were caught in an environmental reserve (Sítio Aguahy) and from captive primates (CETAS-Wildlife Screening Center, municipality of São Luís), in Maranhão. Plasmodium sp. was diagnosed based on light microscopy, PCR, qPCR and LAMP for amplification of the 18S rRNA gene. Serum samples were also assayed by means of indirect immunofluorescence for IgG antibodies against P. malariae/P. brasilianum, P. falciparum and P. berghei. Parasites were detected through light microscopy on five slides from captive primates (four Sapajus spp. and one Callithrix jacchus). In the molecular tests, 34.16% (55/161) and 29.81% (48/161) of the animals sampled were positive in the qPCR and PCR assays, respectively. In the PCR, 47/48 animals were positive for P. malariae/P. brasilianum; of these, eight were free-living primates and 39 from CETAS, São Luís. One sample showed a band in the genus-specific reaction, but not in the second PCR reaction. Anti-P. malariae/P. brasilianum IgG antibodies were detected in four serum samples from Sapajus spp. in captivity. In this study, circulation of P. malariae/P. brasilianum in Neotropical primates was confirmed, with low levels of parasitemia and low levels of antibodies. The importance of these animals as reservoirs of human malaria in the region studied is still unknown. This scenario has an impact on control and elimination of malaria in this region.

Lys48 ubiquitination during the intraerythrocytic cycle of the rodent malaria parasite, Plasmodium chabaudi

Ubiquitination tags proteins for different functions within the cell. One of the most abundant and studied ubiquitin modification is the Lys48 polyubiquitin chain that modifies proteins for their destruction by proteasome. In Plasmodium is proposed that post-translational regulation is fundamental for parasite development during its complex life-cycle; thus, the objective of this work was to analyze the ubiquitination during Plasmodium chabaudi intraerythrocytic stages. Ubiquitinated proteins were detected during intraerythrocytic stages of Plasmodium chabaudi by immunofluorescent microscopy, bidimensional electrophoresis (2-DE) combined with immunoblotting and mass spectrometry. All the studied stages presented protein ubiquitination and Lys48 polyubiquitination with more abundance during the schizont stage. Three ubiquitinated proteins were identified for rings, five for trophozoites and twenty for schizonts. Only proteins detected with a specific anti- Lys48 polyubiquitin antibody were selected for Mass Spectrometry analysis and two of these identified proteins were selected in order to detect the specific amino acid residues where ubiquitin is placed. Ubiquitinated proteins during the ring and trophozoite stages were related with the invasion process and in schizont proteins were related with nucleic acid metabolism, glycolysis and protein biosynthesis. Most of the ubiquitin detection was during the schizont stage and the Lys48 polyubiquitination during this stage was related to proteins that are expected to be abundant during the trophozoite stage. The evidence that these Lys48 polyubiquitinated proteins are tagged for destruction by the proteasome complex suggests that this type of post-translational modification is important in the regulation of protein abundance during the life-cycle and may also contribute to the parasite cell-cycle progression.

Three Divergent Subpopulations of the Malaria Parasite Plasmodium knowlesi

Multilocus microsatellite genotyping of Plasmodium knowlesi isolates previously indicated 2 divergent parasite subpopulations in humans on the island of Borneo, each associated with a different macaque reservoir host species. Geographic divergence was also apparent, and independent sequence data have indicated particularly deep divergence between parasites from mainland Southeast Asia and Borneo. To resolve the overall population structure, multilocus microsatellite genotyping was conducted on a new sample of 182 P. knowlesi infections (obtained from 134 humans and 48 wild macaques) from diverse areas of Malaysia, first analyzed separately and then in combination with previous data. All analyses confirmed 2 divergent clusters of human cases in Malaysian Borneo, associated with long-tailed macaques and pig-tailed macaques, and a third cluster in humans and most macaques in peninsular Malaysia. High levels of pairwise divergence between each of these sympatric and allopatric subpopulations have implications for the epidemiology and control of this zoonotic species.

New potential Plasmodium brasilianum hosts: tamarin and marmoset monkeys (family Callitrichidae)

BACKGROUND

Non-human primates (NHPs) as a source for Plasmodium infections in humans are a challenge for malaria elimination. In Brazil, two species of Plasmodium have been described infecting NHPs, Plasmodium brasilianum and Plasmodium simium. Both species are infective to man. Plasmodium brasilianum resembles morphologically, genetically and immunologically the human quartan Plasmodium malariae. Plasmodium brasilianum naturally infects species of non-human primates from all New World monkey families from a large geographic area. In the family Callitrichidae only the genus Saguinus has been described infected so far. The present study describes the natural infection of P. brasilianum in tamarins and marmosets of the genera Callithrix, Mico and Leontopithecus in the Atlantic forest.

METHODS

One hundred and twenty-two NHPs of the family Callitrichidae housed in the Primate Centre of Rio de Janeiro (CPRJ) were sampled in June 2015, and January and July 2016. The CPRJ is located in the Atlantic forest in the Guapimirim municipality, in the Rio de Janeiro state, where human autochthonous cases of malaria have been reported. The samples were screened for the presence of Plasmodium using optical microscopy and nested PCR for detection of 18S small subunit rRNA gene. The amplicon was sequenced to confirm the molecular diagnosis.

RESULTS

The frequency of Plasmodium infections detected by nested PCR in New World monkeys of the family Callitrichidae was 6.6%. For the first time, Callitrichidae primates of genera Callithrix, Mico and Leontopithecus were found naturally infected with P. brasilianum. Infection was confirmed by sequencing a small fragment of 18S rRNA gene, although no parasites were detected in blood smears.

CONCLUSIONS

The reported P. brasilianum infection in NHP species maintained in captivity suggests that infection can be favoured by the presence of vectors and the proximity between known (and unknown) hosts of malaria. Thus, the list of potential malaria reservoirs needs to be further explored.

Molecular Detection of Plasmodium malariae/Plasmodium brasilianum in Non-Human Primates in Captivity in Costa Rica

One hundred and fifty-two blood samples of non-human primates of thirteen rescue centers in Costa Rica were analyzed to determine the presence of species of Plasmodium using thick blood smears, semi-nested multiplex polymerase chain reaction (SnM-PCR) for species differentiation, cloning and sequencing for confirmation. Using thick blood smears, two samples were determined to contain the Plasmodium malariae parasite, with SnM-PCR, a total of five (3.3%) samples were positive to P. malariae, cloning and sequencing confirmed both smear samples as P. malariae. One sample amplified a larger and conserved region of 18S rDNA for the genus Plasmodium and sequencing confirmed the results obtained microscopically and through SnM-PCR tests. Sequencing and construction of a phylogenetic tree of this sample revealed that the P. malariae/P. brasilianum parasite (GenBank KU999995) found in a howler monkey (Alouatta palliata) is identical to that recently reported in humans in Costa Rica. The SnM-PCR detected P. malariae/P. brasilianum parasite in different non-human primate species in captivity and in various regions of the southern Atlantic and Pacific coast of Costa Rica. The similarity of the sequences of parasites found in humans and a monkey suggests that monkeys may be acting as reservoirs of P.malariae/P. brasilianum, for which reason it is important, to include them in control and eradication programs.