Strongyloides infections of humans and great apes in Dzanga-Sangha Protected Areas, Central African Republic and in degraded forest fragments in Bulindi, Uganda

Strongyloides in non-human primates: significance for public health control

Primates are an important source of infectious disease in humans. Strongyloidiasis affects an estimated 600 million people worldwide, with a global distribution and hotspots of infection in tropical and subtropical regions. Recently added to the list of neglected tropical diseases, global attention has been demanded in the drive for its control. Through a literature review of Strongyloides in humans and non-human primates (NHP), we analysed the most common identification methods and gaps in knowledge about this nematode genus. The rise of molecular-based methods for Strongyloides detection is evident in both humans and NHP and provides an opportunity to analyse all data available from primates. Dogs were also included as an important host species of Strongyloides and a potential bridge host between humans and NHP. This review highlights the lack of molecular data across all hosts-humans, NHP and dogs-with the latter highly underrepresented in the database. Despite the cosmopolitan nature of Strongyloides, there are still large gaps in our knowledge for certain species when considering transmission and pathogenicity. We suggest that a unified approach to Strongyloides detection be taken, with an optimized, repeatable molecular-based method to improve our understanding of this parasitic infection. This article is part of the Theo Murphy meeting issue 'Strongyloides: omics to worm-free populations'.

Genetic characterization of Strongyloides fuelleborni infecting free-roaming African vervets (Chlorocebus aethiops sabaeus) on the Caribbean island of St. Kitts

Human strongyloidiasis is an important neglected tropical disease primarily caused by the nematode Strongyloides stercoralis, and to a lesser extent Strongyloides fuelleborni which mainly infects non-human primates. Zoonotic sources of infection have important implications for control and prevention of morbidity and mortality caused by strongyloidiasis. Recent molecular evidence suggests that for S. fuelleborni, primate host specificity is variable among genotypes across the Old World, and consequently that these types likely vary in their capacity for human spillover infections. Populations of free-roaming vervet monkeys (Chlorocebus aethiops sabaeus), introduced to the Caribbean Island of Staint Kitts from Africa, live in close contact with humans, and concern has arisen regarding their potential to serve as reservoirs of zoonotic infections. In this study, we sought to determine the genotypes of S. fuelleborni infecting St. Kitts vervets to explore whether they are potential reservoirs for human-infecting S. fuelleborni types. Fecal specimens were collected from St. Kitts vervets and S. fuelleborni infections were confirmed microscopically and by PCR. Strongyloides fuelleborni genotypes were determined from positive fecal specimens using an Illumina amplicon sequencing-based genotyping approach targeting the mitochondrial cox1 locus and 18S rDNA hypervariable regions I and IV of Strongyloides species. Phylogenetic analysis of resultant genotypes supported that S. fuelleborni from St. Kitts vervets is of an exclusively African variety, falling within the same monophyletic group as an isolate which has been detected previously in a naturally infected human from Guinea-Bissau. This observation highlights that St. Kitts vervets may serve as potential reservoirs for zoonotic S. fuelleborni infection, which warrants further exploration.

Population genetics study of Strongyloides fuelleborni and phylogenetic considerations on primate-infecting species of Strongyloides based on their mitochondrial genome sequences

Strongyloides is a genus of parasitic nematodes of vertebrates comprising approximately 50 documented species, each with various host ranges. Among these, three species (S. stercoralis, S. fuelleborni, and S. cebus) are known to infect primate hosts. S. fuelleborni typically infects non-human primates in the Old World. To complement the existing information on the global genetic structure of this species, we conducted a genotyping study of S. fuelleborni samples collected from rhesus macaques in Myanmar, Japanese macaques in Japan, and some zoo-kept primates. This study identified a novel haplotype group in isolates from the Myanmar rhesus macaques. Subsequently, we obtained the complete or nearly complete mitochondrial genome sequences of S. fuelleborni, S. cebus (Strongyloides of New World monkeys), and S. vituli (Strongyloides of cattle). Phylogenetic analysis based on concatenated mitochondrial protein sequences of various Strongyloides species indicated a close relationship between S. fuelleborni, S. vituli and S. papillosus (Strongyloides in sheep and cattle). S. cebus is quite distantly related to both S. fuelleborni and S. stercoralis, which led to the hypothesis that the three primate Strongyloides species evolved independently as parasites of primates.

Molecular typing of Strongyloides stercoralis in Latin America, the clinical connection

This study analysed Strongyloides stercoralis genetic variability based on a 404 bp region of the cox1 gene from Latin-American samples in a clinical context including epidemiological, diagnosis and follow-up variables. A prospective, descriptive, observational study was conducted to evaluate clinical and parasitological evolution after ivermectin treatment of 41 patients infected with S. stercoralis. Reactivation of the disease was defined both by clinical symptoms appearance and/or direct larvae detection 30 days after treatment or later. We described 10 haplotypes organized in two clusters. Most frequent variants were also described in the Asian continent in human (HP24 and HP93) and canine (HP24) samples. Clinical presentation (intestinal, severe, cutaneous and asymptomatic), immunological status and eosinophil count were not associated with specific haplotypes or clusters. Nevertheless, presence of cluster 1 haplotypes during diagnosis increased the risk of reactivation with an odds ratio (OR) of 7.51 [confidence interval (CI) 95% 1.38–44.29, P = 0.026]. In contrast, reactivation probability was 83 times lower if cluster 2 (I152V mutation) was detected (OR = 0.17, CI 95% 0.02–0.80, P = 0.02). This is the first analysis of S. stercoralis cox1 diversity in the clinical context. Determination of clusters during the diagnosis could facilitate and improve the design of follow-up strategies to prevent severe reactivations of this chronic disease.

Strongyloides genotyping: a review of methods and application in public health and population genetics

Strongyloidiasis represents a major medical and veterinary helminthic disease. Human infection is caused by Strongyloides stercoralis, Strongyloides fuelleborni fuelleborni and Strongyloides fuelleborni kellyi, with S.stercoralis accounting for the majority of cases. Strongyloides f. fuelleborni likely represents a zoonosis acquired from non-human primates (NHPs), while no animal reservoir for S. f. kellyi infection has been found. Whether S. stercoralis represents a zoonosis acquired from dogs and cats remains unanswered. Over the past two decades various tools have been applied to genotype Strongyloides spp. The most commonly sequenced markers have been the hyper-variable regions I and IV of the 18S rRNA gene and selected portions of the cytochrome c oxidase subunit I gene. These markers have been sequenced and compared in Strongyloides from multiple hosts and geographical regions. More recently, a machine learning algorithm multi-locus sequence typing approach has been applied using these markers, while others have applied whole genome sequencing. Genotyping of Strongyloides from dogs, cats, NHPs and humans has identified that S. stercoralis likely originated in dogs and adapted to human hosts. It has also been demonstrated that S. stercoralis is distinct from S. f. fuelleborni and S. f. kellyi. Two distinct genetic clades of S. stercoralis exist, one restricted to dogs and another infecting humans, NHPs, dogs and cats. Genotyping of S. f. fuelleborni has identified two separate clades, one associated with African isolates and another Indochinese peninsular clade. This review summarises the history and development of genotyping tools for Strongyloides spp. It describes the findings of major studies to date in the context of the epidemiology and evolutionary biology of these helminths, with a specific focus on human-infecting species.

Soil-transmitted helminth infections in free-ranging non-human primates from Cameroon and Gabon

BACKGROUND

Zoonotic diseases are a serious threat to both public health and animal conservation. Most non-human primates (NHP) are facing the threat of forest loss and fragmentation and are increasingly living in closer spatial proximity to humans. Humans are infected with soil-transmitted helminths (STH) at a high prevalence, and bidirectional infection with NHP has been observed. The aim of this study was to determine the prevalence, genetic diversity, distribution and presence of co-infections of STH in free-ranging gorillas, chimpanzees and other NHP species, and to determine the potential role of these NHP as reservoir hosts contributing to the environmental sustenance of zoonotic nematode infections in forested areas of Cameroon and Gabon.

METHODS

A total of 315 faecal samples from six species of NHPs were analysed. We performed PCR amplification, sequencing and maximum likelihood analysis of DNA fragments of the internal transcribed spacer 2 (ITS2) nuclear ribosomal DNA to detect the presence and determine the genetic diversity of Oesophagostomum spp., Necator spp. and Trichuris spp., and of targeted DNA fragments of the internal transcribed spacer 1 (ITS1) to detect the presence of Ascaris spp.

RESULTS

Necator spp. infections were most common in gorillas (35 of 65 individuals), but also present in chimpanzees (100 of 222 individuals) and in one of four samples from greater spot-nosed monkeys. These clustered with previously described type II and III Necator spp. Gorillas were also the most infected NHP with Oesophagostomum (51/65 individuals), followed by chimpanzees (157/222 individuals), mandrills (8/12 samples) and mangabeys (7/12 samples), with O. stephanostomum being the most prevalent species. Oesophagostomum bifurcum was detected in chimpanzees and a red-capped mangabey, and a non-classified Oesophagostomum species was detected in a mandrill and a red-capped mangabey. In addition, Ternidens deminutus was detected in samples from one chimpanzee and three greater spot-nosed monkeys. A significant relative overabundance of co-infections with Necator and Oesophagostomum was observed in chimpanzees and gorillas. Trichuris sp. was detected at low prevalence in a gorilla, a chimpanzee and a greater spot-nosed monkey. No Ascaris was observed in any of the samples analysed.

CONCLUSIONS

Our results on STH prevalence and genetic diversity in NHP from Cameroon and Gabon corroborate those obtained from other wild NHP populations in other African countries. Future research should focus on better identifying, at a molecular level, the species of Necator and Oesophagostomum infecting NHP and determining how human populations may be affected by increased proximity resulting from encroachment into sylvatic STH reservoir habitats.

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.

HTLV-I and Strongyloides in Australia: The worm lurking beneath

Strongyloidiasis and HTLV-I (human T-lymphotropic virus-1) are important infections that are endemic in many countries around the world with an estimated 370 million infected with Strongyloides stercoralis alone, and 5-10 million with HTVL-I. Co-infections with these pathogens are associated with significant morbidity and can be fatal. HTLV-I infects T-cells thus causing dysregulation of the immune system which has been linked to dissemination and hyperinfection of S. stercoralis leading to bacterial sepsis which can result in death. Both of these pathogens are endemic in Australia primarily in remote communities in Queensland, the Northern Territory, and Western Australia. Other cases in Australia have occurred in immigrants and refugees, returned travellers, and Australian Defence Force personnel. HTLV-I infection is lifelong with no known cure. Strongyloidiasis is a long-term chronic disease that can remain latent for decades, as shown by infections diagnosed in prisoners of war from World War II and the Vietnam War testing positive decades after they returned from these conflicts. This review aims to shed light on concomitant infections of HTLV-I with S. stercoralis primarily in Australia but in the global context as well.

Possible transmission of Strongyloides fuelleborni between working Southern pig-tailed macaques (Macaca nemestrina) and their owners in Southern Thailand: Molecular identification and diversity

Human strongyloidiasis is caused by Strongyloides stercoralis, S. fuelleborni fuelleborni and Strongyloides f. kellyi. Strongyloides fuelleborni is a soil-transmitted nematode parasite typically infecting non-human primates. The southern pig-tailed macaque (Macaca nemestrina) is distributed throughout the southern part of Thailand and could be a source of zoonotic transmission of this nematode. Here, we extracted DNA from Strongyloides speciescultured from the feces of southern pig-tailed macaques and their owners. Using PCR and sequencing of the extracted DNA, we compared the nucleotide sequences of these worms using portions of the 18S rDNA hypervariable region IV (HVR-IV) and the mitochondrial cytochrome c oxidase subunit 1 (cox1) gene. Sequences from the 18S rRNA gene were obtained from worms from 23 southern pig-tailed macaques and from one owner. These sequences were identical with each other and with all East and Southeast Asian S. fuelleborni sequences (from Japan, Thailand, and Lao PDR) in the GenBank database. A median-joining network of published cox1 sequences (n = 123), in combination with the present 24 new sequences, represented 107 haplotypes distributed among six clusters, which corresponded to geographical localities but did not relate to host species. The S. fuelleborni cox1 sequences from some southern pig-tailed macaques and the one infected owner shared the same cox1 haplotype. This is the first evidence of likely zoonotic transmission of S. fuelleborni from a reservoir host, M. nemestrina.

Status of Strongyloidiasis in Japan, 2000-2017

We reported 865 cases of soil-transmitted nematodiasis occurring in Japan during 2000-2017. The predominant nematode was Strongyloides stercoralis (n = 279, 32.3% of all cases), and other species included Ascaris lumbricoides (30.7%), Trichuris trichiura (23.1%), and Ancylostomidae spp. (13.9%). Strongyloides stercoralis was detected primarily in patients in Okinawa and Kagoshima prefectures, which are in the south of Japan and are endemic areas for this parasitic infection, and also in about half of the prefectures of all Japan. At least 15.5 cases of strongyloidiasis occurred on average each year. The period incidence rate of strongyloidiasis cases relative to the total population of Japan was 0.012 cases per 10⁵ person-years. The male-to-female ratio was 2.1. The average age was 75.1 ± 16.9 years, and 96.1% of patients were older than 50 years. Several reasons may explain why this previously non-endemic outside of Okinawa region, serious nematode disease is now found in much of Japan, including the increased number of transmigration and sightseeing trips in Japan, use of immunosuppressive drugs, and lack of awareness of the risks. Thus, information of strongyloidiasis and its risks must be disseminated to travelers, residents, and physicians to prevent this life-threatening parasite infection.

Autochthonous Human and Canine Strongyloides stercoralis Infection in Europe: Report of a Human Case in An Italian Teen and Systematic Review of the Literature

Autochthonous human and canine strongyloidiasis is reported in Europe but is unclear whether the transmission of infection still occurs. We report a previously unpublished human case in an Italian teen and perform a systematic review of literature on autochthonous human and canine strongyloidiasis in Europe to investigate the current dynamic of transmission. Overall, 109 papers published after 1987 were included and one previously unpublished Italian case was added. Eighty case reports were retrieved and 42 of them (52.5%) had severe strongyloidiasis. Most cases were diagnosed in Spain, Italy and France. The median age was 58, the most represented age group was 61-70 years, 11 patients were under 30, and 7 of them were diagnosed after 2000. Epidemiological studies on human strongyloidiasis showed prevalence ranging from 0.56% to 28%. Overall, agriculture work, mine work and walking barefoot were the most commonly reported risk factors for infection. Canine strongyloidiasis was reported mainly in Italy (68 cases), but a few cases occurred also in Iceland, Finland, England, Germany, France, Switzerland, Russia, Slovakia, Romania and Greece. Autochthonous strongyloidiasis is still reported in Europe and sporadic transmission still occurs. Health care professionals should be aware of this issue to identify infected subjects and avoid adverse outcomes, especially in immunosuppressed patients. Further investigations are needed to clarify the zoonotic transmission of this nematode.

Genomic studies on Strongyloides stercoralis in northern and western Thailand

Background

Strongyloidiasis is a soil borne helminthiasis, which in most cases is caused by Strongyloides stercoralis. Human infections with S. fuelleborni fuelleborni and S. fuelleborni kellyi also occur. Although up to 370 million people are currently estimated to be infected with S. stercoralis, this parasite is frequently overlooked. Strongyloides stercoralis is prevalent among humans in Thailand; however, S. fuelleborni fuelleborni has also been reported. Three recent genomic studies of individual S. stercoralis worms found genetically diverse populations of S. stercoralis, with comparably low heterozygosity in Cambodia and Myanmar, and less diverse populations with high heterozygosity in Japan and southern China that presumably reproduce asexually.

Methods

We isolated individual Strongyloides spp. from different localities in northern and western Thailand and determined their nuclear small ribosomal subunit rDNA (18S rDNA, SSU), in particular the hypervariable regions I and IV (HVR-I and HVR-IV), mitochondrial cytochrome c oxidase subunit 1 (cox1) and for a subset whole genome sequences. These sequences were then compared with each other and with published sequences from different geographical locations.

Results

All 237 worms isolated from 16 different human hosts were S. stercoralis, no S. fuelleborni was found. All worms had the common S. stercoralis SSU HVR IV haplotype A. Two different SSU HVR I haplotypes (I and II), both previously described in S. stercoralis, were found. No animal heterozygous for the two haplotypes was identified. Among the twelve cox1 haplotypes found, five had not been previously described. Based upon the mitochondrial cox1 and the nuclear whole genome sequences, S. stercoralis in Thailand was phylogenetically intermixed with the samples from other Southeast Asian countries and did not form its own branch. The genomic heterozygosity was even slightly lower than in the samples from the neighboring countries.

Conclusions

In our sample from humans, all Strongyloides spp. were S. stercoralis. The S. stercoralis from northern and western Thailand appear to be part of a diverse, intermixing continental Southeast Asian population. No obvious indication for genetic sub-structuring of S. stercoralis within Thailand or within the Southeast Asian peninsula was detected.

From the feces to the genome: a guideline for the isolation and preservation of Strongyloides stercoralis in the field for genetic and genomic analysis of individual worms

Strongyloidiasis is a soil-borne helminthiasis, which, in spite of the up to 370 million people currently estimated to be infected with its causing agent, the nematode Strongyloides stercoralis, is frequently overlooked. Recent molecular taxonomic studies conducted in Southeast Asia and Australia, showed that dogs can carry the same genotypes of S. stercoralis that also infect humans, in addition to a presumably dog-specific Strongyloides species. This suggests a potential for zoonotic transmission of S. stercoralis from dogs to humans. Although natural S. stercoralis infections have not been reported in any host other than humans, non-human primates and dogs, other as yet unidentified animal reservoirs cannot be excluded. Molecular studies also showed that humans carry rather different genotypes of S. stercoralis. As a result, their taxonomic status and the question of whether they differ in their pathogenic potential remains open. It would therefore be very important to obtain molecular genetic/genomic information about S. stercoralis populations from around the world. One way of achieving this (with little additional sampling effort) would be that people encountering S. stercoralis in the process of their diagnostic work preserve some specimens for molecular analysis. Here we provide a guideline for the isolation, preservation, genotyping at the nuclear 18S rDNA and the mitochondrial cox1 loci, and for whole genome sequencing of single S. stercoralis worms. Since in many cases the full analysis is not possible or desired at the place and time where S. stercoralis are found, we emphasize when and how samples can be preserved, stored and shipped for later analysis. We hope this will benefit and encourage researchers conducting field studies or diagnostics to collect and preserve S. stercoralis for molecular genetic/genomic analyses and either analyze them themselves or make them available to others for further analysis.

Assessment of the global paradigms of genetic variability in Strongyloides stercoralis infrapopulations determined by mitochondrial DNA sequences

Microevolutionary data of Strongyloides stercoralis infrapopulations are regarded as a requirement for determining the global genetic structure and transmission paradigms of this neglected tropical nematode among the neighboring countries of the world. English databases were searched from 2010 to 2019, analyzing a total of 10 publications. The cytochrome c oxidase subunit 1 sequences of S. stercoralis isolated from Asian and African continents were subjected to calculate the diversity indices and genetic differentiation. A parsimonious haplotype network indicated a star-like trait a total of 106 (Homo sapiens) and 48 haplotypes (Canid) being grouped into four distinct geographical haplogroups. A significant genetic diversity was identified in human-derived S. stercoralis (Haplotype diversity: 0.78) and those with dog (Hd: 0.86) origins. Cladistic phylogenetic tree indicated the Japanese, Thailandish, and Myanmarese clades have a sister relationship with the Laotian clade. The statistically significant Fst values indicated that human S. stercoralis populations of Japanese-Thailandish, Japanese-Myanmarese, and Japanese-Laotian origins were genetically differentiated (Fst: 0.48430 to 0.54903). We conclude that a high gene migration of human strongyloidiasis is being unequivocally shared between the Laotion-Myanmarese and Laotion-Thailandish population pairs. The current findings enhance our knowledge to assess the transmission dynamics and the evolutionary patterns of S. stercoralis in various geographical regions of the globe; also it will serve as a basis for public health policy to control human strongyloidiasis particularly in immunocompromised individuals. Besides, the infected canids and other environmental reservoirs for zoonotic transmission of S. stercoralis to humans should be de-wormed along with their owners.

A global genotyping survey of Strongyloides stercoralis and Strongyloides fuelleborni using deep amplicon sequencing

Strongyloidiasis is a neglected tropical disease caused by the human infective nematodes Strongyloides stercoralis, Strongyloides fuelleborni fuelleborni and Strongyloides fuelleborni kellyi. Previous large-scale studies exploring the genetic diversity of this important genus have focused on Southeast Asia, with a small number of isolates from the USA, Switzerland, Australia and several African countries having been genotyped. Consequently, little is known about the global distribution of geographic sub-variants of these nematodes and the genetic diversity that exists within the genus Strongyloides generally. We extracted DNA from human, dog and primate feces containing Strongyloides, collected from several countries representing all inhabited continents. Using a genotyping assay adapted for deep amplicon sequencing on the Illumina MiSeq platform, we sequenced the hyper-variable I and hyper-variable IV regions of the Strongyloides 18S rRNA gene and a fragment of the mitochondrial cytochrome c oxidase subunit 1 (cox1) gene from these specimens. We report several novel findings including unique S. stercoralis and S. fuelleborni genotypes, and the first identifications of a previously unknown S. fuelleborni infecting humans within Australia. We expand on an existing Strongyloides genotyping scheme to accommodate S. fuelleborni and these novel genotypes. In doing so, we compare our data to all 18S and cox1 sequences of S. fuelleborni and S. stercoralis available in GenBank (to our knowledge), that overlap with the sequences generated using our approach. As this analysis represents more than 1,000 sequences collected from diverse hosts and locations, representing all inhabited continents, it allows a truly global understanding of the population genetic structure of the Strongyloides species infecting humans, non-human primates, and domestic dogs.

Strongyloidiasis is a neglected tropical disease caused by the human infective worms (nematodes) Strongyloides stercoralis, Strongyloides fuelleborni fuelleborni and Strongyloides fuelleborni kellyi. Little is known about the genetic diversity of these nematodes and the possibility of geographically isolated genetic types is a particularly interesting research question, given the unique life cycle of these worms which includes both sexual and asexual stages. We extracted DNA from human, dog and primate feces containing Strongyloides, collected from several countries representing all inhabited continents. Using next-generation sequencing, we analyzed three Strongyloides DNA fragments from these specimens; two fragments of the 18S gene and one from the cytochrome c oxidase subunit 1 (cox1) gene. Using this approach, we discovered some unique S. stercoralis and S. fuelleborni genotypes, and identified a previously unknown S. fuelleborni infecting humans within Australia. We compared our data to all 18S and cox1 sequences of S. fuelleborni and S. stercoralis available in public databases and identified several patterns relating to the global distribution of certain genotypes. This knowledge could allow us to infer the origin of human Strongyloides infections in the future, and assess the role certain animals (non-human primates and dogs) might play in the transmission of Strongyloides to humans.

Advances in the Molecular and Cellular Biology of Strongyloides spp

Purpose of Review

This paper constitutes an update of recent studies on the general biology, molecular genetics, and cellular biology of Strongyloides spp. and related parasitic nematodes.

Recent Findings

Increasingly, human strongyloidiasis is considered the most neglected of neglected tropical diseases. Despite this, the last 5 years has seen remarkable advances in the molecular biology of Strongyloides spp. Genome sequences for S. stercoralis, S. ratti, S. venezuelensis, S. papillosus, and the related parasite Parastrongyloides trichosuri were created, annotated, and analyzed. These genomic resources, along with a practical transgenesis platform for Strongyloides spp., aided a major achievement, the advent of targeted mutagenesis via CRISPR/Cas9 in S. stercoralis and S. ratti. The genome sequences have also enabled significant molecular epidemiologic and phylogenetic findings on human strongyloidiasis, including the first genetic evidence of zoonotic transmission of S. stercoralis between dogs and humans. Studies of molecular signaling pathways identified the nuclear receptor Ss-DAF-12 as one that can be manipulated in the parasite by exogenous application of its steroid ligands. The chemotherapeutic implications of this were unscored by a study in which a Ss-DAF-12 ligand suppressed autoinfection by S. stercoralis in a new murine model of human strongyloidiasis.

Summary

Seminal advances in genomics of Strongyloides spp. have transformed research into strongyloidiasis, facilitating fundamental phylogenetic and epidemiologic studies and aiding the deployment of CRISPR/Cas9 gene disruption and editing as functional genomic tools in Strongyloides spp. Studies of Ss-DAF-12 signaling in S. stercoralis demonstrated the potential of this pathway as a novel chemotherapeutic target in parasitic nematodes.

Detection of classic and cryptic Strongyloides genotypes by deep amplicon sequencing: A preliminary survey of dog and human specimens collected from remote Australian communities

Strongyloidiasis is caused by the human infective nematodes Strongyloides stercoralis, Strongyloides fuelleborni subsp. fuelleborni and Strongyloides fuelleborni subsp. kellyi. The zoonotic potential of S. stercoralis and the potential role of dogs in the maintenance of strongyloidiasis transmission has been a topic of interest and discussion for many years. In Australia, strongyloidiasis is prevalent in remote socioeconomically disadvantaged communities in the north of the continent. Being an isolated continent that has been separated from other regions for a long geological period, description of diversity of Australian Strongyloides genotypes adds to our understanding of the genetic diversity within the genus. Using PCR and amplicon sequencing (Illumina sequencing technology), we sequenced the Strongyloides SSU rDNA hyper-variable I and hyper-variable IV regions using Strongyloides-specific primers, and a fragment of the mtDNA cox1 gene using primers that are broadly specific for Strongyloides sp. and hookworms. These loci were amplified from DNA extracted from Australian human and dog faeces, and one human sputum sample. Using this approach, we confirm for the first time that potentially zoonotic S. stercoralis populations are present in Australia, suggesting that dogs represent a potential reservoir of human strongyloidiasis in remote Australian communities.

A Review of Strongyloides spp. Environmental Sources Worldwide

Strongyloides spp. are parasitic nematodes that are transmitted through the environment and are capable of causing disease. These nematodes affect an estimated 3–300 million humans worldwide. Identifying the environmental reservoirs of Strongyloides spp. is essential for the development of appropriate control strategies. This systematic literature review examined all published studies that identified Strongyloidesstercoralis, Strongyloidesfuelleborni, Strongyloidesfuellebornikellyi, and Strongyloides spp. from an environmental source. Most studies detected the nematode from dog and primate fecal samples. Other environmental sources identified were ruminants, cats, rodents, insects, water, soil, as well as fruit and vegetables. Most studies used microscopy-based identification techniques; however, several employed molecular-based techniques, which have become increasingly popular for the detection of Strongyloides spp. A limitation identified was a lack of studies that comprehensively screened all potential environmental samples in a region. Future research should undertake this holistic screening process to identify which environmental reservoirs pose the greatest significance to human health. Potential controls can be identified through the identification of environmental sources. Understanding where Strongyloides spp. is commonly found within the environment of endemic areas will inform environmental control strategies to reduce this neglected disease.

Characterization of a non-sexual population of Strongyloides stercoralis with hybrid 18S rDNA haplotypes in Guangxi, Southern China

Strongyloidiasis is a much-neglected but sometimes fatal soil born helminthiasis. The causing agent, the small intestinal parasitic nematode Strongyloides stercoralis can reproduce sexually through the indirect/heterogonic life cycle, or asexually through the auto-infective or the direct/homogonic life cycles. Usually, among the progeny of the parasitic females both, parthenogenetic parasitic (females only) and sexual free-living (females and males) individuals, are present simultaneously. We isolated S. stercoralis from people living in a village with a high incidence of parasitic helminths, in particular liver flukes (Clonorchis sinensis) and hookworms, in the southern Chinese province Guangxi. We determined nuclear and mitochondrial DNA sequences of individual S. stercoralis isolated from this village and from close by hospitals and we compared these S. stercoralis among themselves and with selected published S. stercoralis from other geographic locations. For comparison, we also analyzed the hookworms present in the same location. We found that, compared to earlier studies of S. stercoralis populations in South East Asia, all S. stercoralis sampled in our study area were very closely related, suggesting a recent common source of infection for all patients. In contrast, the hookworms from the same location, while all belonging to the species Necator americanus, showed rather extensive genetic diversity even within host individuals. Different from earlier studies conducted in other geographic locations, almost all S. stercoralis in this study appeared heterozygous for different sequence variants of the 18S rDNA hypervariable regions (HVR) I and IV. In contrast to earlier investigations, except for three males, all S. stercoralis we isolated in this study were infective larvae, suggesting that the sampled population reproduces predominantly, if not exclusively through the clonal life cycles. Consistently, whole genome sequencing of individual worms revealed higher heterozygosity than reported earlier for likely sexual populations of S. stercoralis. Elevated heterozygosity is frequently associated with asexual clonal reproduction.

First molecular identification of Strongyloides fuelleborni in long-tailed macaques in Thailand and Lao People's Democratic Republic reveals considerable genetic diversity

Strongyloides fuelleborni is a soil-transmitted nematode parasite of non-human primates. The worm is prevalent also in human populations in Africa and South-East Asia. In this study, we amplified and sequenced a portion of the 18S ribosomal RNA gene (rRNA) and of the mitochondrial cytochrome c oxidase subunit 1 (cox1) gene of Strongyloides adult males recovered from faecal samples from long-tailed macaques (Macaca fascicularis) in Thailand and Lao PDR. The prevalence in Thailand was 31.1% (55/177) and in Lao PDR it was 62.1% (41/66), with an overall prevalence of 39.5% (96/243). All 18S rRNA sequences that we obtained (n = 96) showed 100% identity with published S. fuelleborni sequences. The 96 cox1 sequences that we obtained represented 32 new haplotypes. When included with the 17 previously known haplotypes from S. fuelleborni, the cox1 sequences fell into four clusters, which had clear geographical structure. This is the first molecular confirmation of S. fuelleborni in long-tailed macaques in Thailand and Lao PDR. Clearly, awareness needs to be raised of the zoonotic potential of S. fuelleborni. A monitoring programme should be organized, taking into account the role of reservoir hosts (i.e. monkeys) in the natural background of human strongyloidiasis caused by S. fuelleborni.

Strongyloides stercoralis: detection of parasite-derived DNA in serum samples obtained from immunosuppressed patients

Strongyloidiasis is an important neglected disease, which is life threatening in immunocompromised patients. This study aimed to evaluate the frequency of Strongyloides stercoralis infection among immunosuppressed subjects living in endemic communities by conventional PCR of the 18S rRNA and Cox1 genes to detect cell-free DNA in the patients' serum samples. Fresh stool and serum samples were obtained from participants. The stool samples were examined using parasitological methods. Total DNA was extracted from the serum samples and S. stercoralis larvae isolated from patient fecal samples. Conventional PCR to amplify a 101 bp fragment of the 18S rRNA gene was carried out for all extracted DNA, and then positive samples were further evaluated for a 121 bp fragment of the Cox1 gene. The PCR products of selected samples were sequenced and BLAST analysis was performed. Out of 120 patients, 57 and 63 cases had autoimmune disorders and cancer, respectively. The 101 bp fragments of the 18S rRNA were successfully amplified in 36 out of 120 (30%) serum samples. The PCR products of five samples were sequenced and compared with reference sequences in GenBank, which showed 97% identity and 90% coverage. In conclusion, to the best of our knowledge, this is the first molecular study for the detection of S. stercoralis cell-free DNA in human serum samples. These results provide useful insights for future studies and show that serum is an alternative specimen and may be useful in molecular diagnosis of diseases, particularly in immunosuppressive patients.

Lurking in the dark: Cryptic Strongyloides in a Bornean slow loris

Within host communities, related species are more likely to share common parasitic agents, and as a result, morphological similarities have led researchers to conclude that parasites infecting closely related hosts within a community represent a single species. However, genetic diversity within parasite genera and host range remain poorly investigated in most systems. Strongyloides is a genus of soil-transmitted nematode that has been reported from several primate species in Africa and Asia, and has been estimated to infect hundreds of millions of people worldwide, although no precise estimates are available. Here we describe a case of infection with a cryptic species of Strongyloides in a Bornean (Philippine) slow loris (Nycticebus menagensis) living within a diverse community of several primate species in the Lower Kinabatangan Wildlife Sanctuary, Malaysian Borneo. Fresh fecal samples were collected from five primate species and nematode larvae cultured from these samples were selected for phylogenetic analyses. Sequences obtained for most larvae were identified as S. fuelleborni, grouping into three different clusters and showing no aggregation within specific hosts or geographic location. In contrast, a set of parasite sequences obtained from a slow loris clustered closely with S. stercoralis into a different group, being genetically distinct to sequences reported from other primate hosts, humans included. Our results suggest that although S. fuelleborni infects all haplorrhines sampled in this primate community, a different species might be infecting the slow loris, the only strepsirrhine in Borneo and one of the least studied primates in the region. Although more data are needed to support this conclusion, we propose that Strongyloides species in primates might be more diverse than previously thought, with potential implications for ecological and evolutionary host-parasite associations, as well as epidemiological dynamics.

Zoonotic Enterobacterial Pathogens Detected in Wild Chimpanzees

Infectious diseases including those acquired through direct or indirect contact with people and livestock threaten the survival of wild great apes. Few studies have reported enterobacterial pathogens in chimpanzees. We used multiplex PCR to screen faeces of chimpanzees sharing a landscape with villagers and livestock in Bulindi, Uganda for Salmonella spp., enterohemorrhagic Escherichia coli (E. coli) and Shigella spp./enteroinvasive E. coli. All three potentially zoonotic pathogens were detected. Individual prevalence ranged between 7 and 20%, with most infections observed in mature male chimpanzees. These preliminary findings suggest detailed investigation of enterobacterial infections in people, primates and livestock in this ecosystem is warranted.

Gastrointestinal protists and helminths of habituated agile mangabeys (Cercocebus agilis) at Bai Hokou, Central African Republic

Infectious diseases including those caused by parasites can be a major threat to the conservation of endangered species. There is thus a great need for studies describing parasite infections of these species in the wild. Here we present data on parasite diversity in an agile mangabey (Cercocebus agilis) group in Bai Hokou, Dzanga-Sangha Protected Areas (DSPA), Central African Republic. We coproscopically analyzed 140 mangabey fecal samples by concentration techniques (flotation and sedimentation). Agile mangabeys hosted a broad diversity of protistan parasites/commensals, namely amoebas (Entamoeba spp., Iodamoeba buetschlli), a Buxtonella-like ciliate and several parasitic helminths: strongylid and spirurid nematodes, Primasubulura sp., Enterobius sp., and Trichuris sp. Importantly, some of the detected parasite taxa might be of potential zoonotic importance, such as Entamoeba spp. and the helminths Enterobius sp., Trichuris sp., and strongylid nematodes. Detailed morphological examination of ciliate cysts found in mangabeys and comparison with cysts of Balantioides coli from domestic pigs showed no distinguishing structures, although significant differences in cyst size were recorded. Scanning or transmission electron microscopy combined with molecular taxonomy methods are needed to properly identify these ciliates. Further studies using molecular epidemiology are warranted to better understand cross-species transmission and the zoonotic potential of parasites in sympatric non-human primates and humans cohabiting DSPA.

Different but overlapping populations of Strongyloides stercoralis in dogs and humans-Dogs as a possible source for zoonotic strongyloidiasis

Strongyloidiasis is a much-neglected soil born helminthiasis caused by the nematode Strongyloides stercoralis. Human derived S. stercoralis can be maintained in dogs in the laboratory and this parasite has been reported to also occur in dogs in the wild. Some authors have considered strongyloidiasis a zoonotic disease while others have argued that the two hosts carry host specialized populations of S. stercoralis and that dogs play a minor role, if any, as a reservoir for zoonotic S. stercoralis infections of humans. We isolated S. stercoralis from humans and their dogs in rural villages in northern Cambodia, a region with a high incidence of strongyloidiasis, and compared the worms derived from these two host species using nuclear and mitochondrial DNA sequence polymorphisms. We found that in dogs there exist two populations of S. stercoralis, which are clearly separated from each other genetically based on the nuclear 18S rDNA, the mitochondrial cox1 locus and whole genome sequence. One population, to which the majority of the worms belong, appears to be restricted to dogs. The other population is indistinguishable from the population of S. stercoralis isolated from humans. Consistent with earlier studies, we found multiple sequence variants of the hypervariable region I of the 18 S rDNA in S. stercoralis from humans. However, comparison of mitochondrial sequences and whole genome analysis suggest that these different 18S variants do not represent multiple genetically isolated subpopulations among the worms isolated from humans. We also investigated the mode of reproduction of the free-living generations of laboratory and wild isolates of S. stercoralis. Contrary to earlier literature on S. stercoralis but similar to other species of Strongyloides, we found clear evidence of sexual reproduction. Overall, our results show that dogs carry two populations, possibly different species of Strongyloides. One population appears to be dog specific but the other one is shared with humans. This argues for the strong potential of dogs as reservoirs for zoonotic transmission of S. stercoralis to humans and suggests that in order to reduce the exposure of humans to infective S. stercoralis larvae, dogs should be treated for the infection along with their owners.

Gastrointestinal parasite infections and self-medication in wild chimpanzees surviving in degraded forest fragments within an agricultural landscape mosaic in Uganda

Monitoring health in wild great apes is integral to their conservation and is especially important where they share habitats with humans, given the potential for zoonotic pathogen exchange. We studied the intestinal parasites of wild chimpanzees (Pan troglodytes schweinfurthii) inhabiting degraded forest fragments amid farmland and villages in Bulindi, Uganda. We first identified protozoan and helminth parasites infecting this population. Sixteen taxa were demonstrated microscopically (9 protozoa, 5 nematodes, 1 cestode, and 1 trematode). DNA sequence analysis enabled more precise identification of larval nematodes (e.g. Oesophagostomum stephanostomum, O. bifurcum, Strongyloides fuelleborni, Necator sp. Type II) and tapeworm proglottids (genus Bertiella). To better understand the ecology of infections, we used multidimensional scaling analysis to reveal general patterns of association among parasites, climate, and whole leaf swallowing-a prevalent self-medicative behaviour at Bulindi linked to control of nodular worms (Oesophagostomum spp.). Prevalence of parasites varied with climate in diverse ways. For example, Oesophagostomum sp. was detected in faeces at higher frequencies with increasing rainfall but was most clearly associated with periods of low temperature. Certain parasites occurred together within chimpanzee hosts more or less frequently than expected by chance. For example, the commensal ciliate Troglodytella abrassarti was negatively associated with Balantidium coli and Oesophagostomum sp., possibly because the latter taxa make the large intestine less suitable for T. abrassarti. Whole leaves in faeces showed independent associations with the prevalence of Oesophagostomum sp., Strongyloides sp., and hookworm by microscopic examination, and with egestion of adult O. stephanostomum by macroscopic inspection. All parasites identified to species or genus have been reported in wild chimpanzees inhabiting less-disturbed environments than Bulindi. Nevertheless, several disease-causing taxa infecting these chimpanzees are potentially transmissible between apes and humans (e.g. rhabditoid and strongyle nematodes), underscoring the importance of identifying and reducing risks of pathogen exchange in shared landscapes.

A possible origin population of pathogenic intestinal nematodes, Strongyloides stercoralis, unveiled by molecular phylogeny

Humans and dogs are the two major hosts of Strongyloides stercoralis, an intestinal parasitic nematode. To better understand the phylogenetic relationships among S. stercoralis isolates infecting humans and dogs and to assess the zoonotic potential of this parasite, we analyzed mitochondrial Cox1, nuclear 18S rDNA, 28S rDNA, and a major sperm protein domain-containing protein genes. Overall, our analyses indicated the presence of two distinct lineages of S. stercoralis (referred to as type A and type B). While type A parasites were isolated both from humans and dogs in different countries, type B parasites were found exclusively in dogs, indicating that the type B has not adapted to infect humans. These epidemiological data, together with the close phylogenetic relationship of S. stercoralis with S. procyonis, a Strongyloides parasite of raccoons, possibly indicates that S. stercoralis originally evolved as a canid parasite, and later spread into humans. The inability to infect humans might be an ancestral character of this species and the type B might be surmised to be an origin population from which human-infecting strains are derived.

First molecular identification and genetic diversity of Strongyloides stercoralis and Strongyloides fuelleborni in human communities having contact with long-tailed macaques in Thailand

The parasitic nematodes, Strongyloides stercoralis and Strongyloides fuelleborni, can infect humans and non-human primates. We amplified and sequenced a portion of the 18S ribosomal RNA gene (rRNA) and of the mitochondrial cytochrome c oxidase subunit 1 (cox1) gene of Strongyloides from humans in the study area in Thailand, where people have frequent contact with long-tailed macaques. Fresh stool samples were obtained from 213 people and were examined using the agar plate culture method. The overall prevalence of Strongyloides infection was 8.92% (19/213). From a total of 19 worms (one per infected person), 18 adult males had 18S rRNA sequences identical with that of S. stercoralis and one adult female had a sequence almost identical with that of S. fuelleborni. A median-joining network of cox1 sequences revealed nine new haplotypes from S. stercoralis, and an overall haplotype diversity (Hd) of 0.9309. The single haplotype of S. fuelleborni was also new and contributed to an overall haplotype diversity for that species of 0.9842. This is the first molecular identification of S. stercoralis and S. fuelleborni in a human community having contact with long-tailed macaques in Thailand. It is also the first report of S. fuelleborni infecting a human in Thailand.