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About 600 million people are estimated to be infected with Strongyloides stercoralis, the species that causes most of the human strongyloidiasis cases. S. stercoralis can also infect non-human primates (NHPs), dogs and cats, rendering these animals putative sources for zoonotic human S. stercoralis infection. S. fuelleborni is normally found in old world NHPs but occasionally also infects humans, mainly in Africa. Dogs in southeast Asia carry at least two types of Strongyloides, only one of which appears to be shared with humans (\"dog only\" and \"human and dog\" types). For S. stercoralis with molecular taxonomic information, there is a strong sampling bias towards southeast and east Asia and Australia. In order to extend the geographic range of sampling, we collected human and dog derived Strongyloides spp. and hookworms from two locations in Bangladesh and subjected them to molecular taxonomic and genomic analysis based on nuclear and mitochondrial sequences. All hookworms found were Necator americanus. Contrary to earlier studies in Asia, we noticed a rather high incidence of S. fuelleborni in humans. Also in this study, we found the two types of S. stercoralis and no indication for genetic isolation from the southeast Asian populations. However, we found one genomically \"dog only\" type S. stercoralis in a human sample and we found two worms in a dog sample that had a nuclear genome of the \"dog only\" but a mitochondrial genome of the \"human and dog\" type. S. fuelleborni may play a more prominent role as a human parasite in certain places in Asia than previously thought. The introgression of a mitochondria haplotype into the \"dog only\" population suggests that rare interbreeding between the two S. stercoralis types does occur and that exchange of genetic properties, for example a drug resistance, between the two types is conceivable.

This paper reviews the occurrence and impact of threadworms, Strongyloides spp., in companion animals and large livestock, the potential zoonotic implications and future research. Strongyloides spp. infect a range of domestic animal species worldwide and clinical disease is most often encountered in young animals. Dogs are infected with Strongyloides stercoralis while cats are infected with different species according to geographical location (Strongyloides felis, Strongyloides tumefaciens, Strongyloides planiceps and perhaps S. stercoralis). In contrast to the other species, lactogenic transmission is not a primary means of infection in dogs, and S. stercoralis is the only species considered zoonotic. Strongyloides papillosus in calves has been linked to heavy fatalities under conditions of high stocking density. Strongyloides westeri and Strongyloides ransomi of horses and pigs, respectively, cause only sporadic clinical disease. In conclusion, these infections are generally of low relative importance in livestock and equines, most likely due to extensive use of macrocyclic lactone anthelmintics and/or improved hygiene. Future prevalence studies need to include molecular typing of Strongyloides species in relation to different hosts. More research is urgently needed on the potential zoonotic capacity of Strongyloides from dogs and cats based on molecular typing, information on risk factors and mapping of transmission routes.

The majority of the 30–100 million people infected with Strongyloides stercoralis, a soil transmitted intestinal nematode, have subclinical (or asymptomatic) infections. These infections are commonly chronic and longstanding because of the autoinfective process associated with its unique life cycle. A change in immune status can increase parasite numbers, leading to hyperinfection syndrome, dissemination, and death if unrecognized. Corticosteroid use and HTLV-1 infection are most commonly associated with the hyperinfection syndrome. Strongyloides adult parasites reside in the small intestine and induce immune responses both local and systemic that remain poorly characterized. Definitive diagnosis of S. stercoralis infection is based on stool examinations for larvae, but newer diagnostics – including new immunoassays and molecular tests – will assume primacy in the next few years. Although good treatment options exist for infection and control of this infection might be possible, S. stercoralis remains largely neglected.

Strongyloides stercoralis infection is a neglected condition that places people who are immunocompromised at risk of hyperinfection and death. Ivermectin is the drug of choice for the treatment of S stercoralis infection, but there is no definitive evidence on the optimal dose. This trial aimed to assess whether multiple doses of ivermectin were superior to a single dose for the treatment of non-disseminated strongyloidiasis. Our study was designed as a multicentre, open-label, phase 3, randomised controlled superiority trial. Participants were enrolled in four centres in Italy, three in Spain, and two in the UK, and recruiting sites were predominantly hospitals. Eligible patients were older than 5 years, weighed more than 15 kg, were residents in an area not endemic for S stercoralis, and either were positive for S stercoralis in faecal tests and on serology (any titre) or had a positive serological test with high titres, irrespective of the result of faecal tests. Patients were randomly assigned (1:1) using a computer-generated, blinded allocation sequence (with randomly mixed block sizes of six, eight, and ten participants) to receive either one dose of ivermectin 200 μg/kg or four doses of ivermectin 200 μg/kg (given on days 1, 2, 15, and 16). The primary endpoint was the proportion of participants with clearance of S stercoralis infection at 12 months, which was assessed in all randomly assigned participants who were not lost to follow-up (modified full-analysis set) and in participants in the modified full-analysis set who did not deviate from the assigned treatment regimen (per-protocol set). All participants were included in the safety analysis. The trial was registered with ClinicalTrials.gov, NCT01570504, and is now closed for recruitment. Of the 351 patients assessed for eligibility, 309 recruited between March 26, 2013, and May 3, 2017, were randomly assigned to one dose (n=155) or four doses (n=154) of ivermectin. At 12 months in the modified full-analysis set, 86% (95% CI 79 to 91; 102 of 118 participants) had responded to treatment in the single-dose group compared with 85% (77 to 90; 96 of 113 participants) in the four-dose group (risk difference 1·48%, 95% CI −7·55 to 10·52; p=0·75); similar results were observed in the per-protocol set. Adverse events were generally of mild intensity and more frequent in the multiple-dose than in the single-dose group. The trial was terminated early due to futility. Multiple doses of ivermectin did not show higher efficacy and was tolerated less than a single dose. A single dose should therefore be preferred for the treatment of non-disseminated strongyloidiasis. There was no funding source for this study.

Strongyloides spp. are common parasites of vertebrates and two species, S. ratti and S. venezuelensis, parasitize rats; there are no known species that naturally infect mice. Strongyloides ratti and S. venezuelensis overlap in their geographical range and in these regions co-infections appear to be common. These species have been widely used as tractable laboratory systems in rats as well as mice. The core biology of these two species is similar, but there are clear differences in aspects of their within-host biology as well as in their free-living generation. Phylogenetic evidence suggests that S. ratti and S. venezuelensis are the result of two independent evolutionary transitions to parasitism of rats, which therefore presents an ideal opportunity to begin to investigate the basis of host specificity in Strongyloides spp.

IntroductionStrongyloidiasis can persist and cause hyperinfection years after acquisition when host immunity is impaired. European Crohn's and Colitis Organisation guidelines1 on opportunisitc infections recommend that Inflammatory Bowel Disease (IBD) patients returning from endemic areas be screened. However, prevalence of intestinal helminths in migrant IBD patients is unknown. We investigated the sero-prevalence of Strongyloidiasis and factors associated with infection.MethodsMigrant patients attending IBD clinic over a 10-month period, with a diagnosis of Crohn's disease (CD) or Ulcerative colitis (UC), were tested for Strongyloides serology. Eosinophil count and inflammatory markers were measured. Ethnicity was used as a proxy for migrant status. Sero-positive patients were followed-up with a Strongyloides charcoal culture before treatment with Ivermectin. Repeat eosinophil count and inflammatory markers were performed 3months later. T test and chi 2 analysis (p<0.05) were performed using SPSS for Windows.Results97 migrant patients (54 CD vs 43 UC) were tested. 13/97 patients were sero-positive. In both groups, over 70% of patients were from Asia. Mean eosinophil counts (109/l) were not different between the two groups (0.29 vs 0.22, p>0.05). No significant change was seen in eosinophil count or in inflammatory markers post treatment. In the sero-positive group 23% had past and current eosinophilia, but this was not statistically different from sero-negative patients. 9/13 reportable charcoal stool cultures were negative. No patients with Strongyloides were taking steroids, compared to 23% of sero-negative patients. In both groups, >40% were on two or more immunosuppressants.ConclusionThere is a high sero-prevalence of Strongyloides in migrant IBD patients. Patients from Asia demonstrated the highest prevalence. Eosinophilia and raised inflammatory markers were not predictive of positive serology, most likely due to the high rate of immunosuppression. We cannot confirm all sero-positive patients were infected; published data2 supports the specificity of Strongyloides serology for current infection. We recommend ECCO guidelines and current British Society of Gastroenterology guidelines are adapted to include targetting IBD patients who originate from endemic areas and serological testing be first line. Follow-up of patients is required to assess the impact of treatment on IBD activity.Competing interestsNone declared.References1. Rahier JF, et al. J Crohn's Colitis 2009; 3:47-91.2. Loutfy MR, et al. Am J Trop Med Hyg 2002; 66:749-52.

Human strongyloidiasis is a serious disease mostly attributable to Strongyloides stercoralis and to a lesser extent Strongyloides fuelleborni, a parasite mainly of non-human primates. The role of animals as reservoirs of human-infecting Strongyloides is ill-defined, and whether dogs are a source of human infection is debated. Published multi-locus sequence typing (MLST) studies attempt to elucidate relationships between Strongyloides genotypes, hosts, and distributions, but typically examine relatively few worms, making it difficult to identify population-level trends. Combining MLST data from multiple studies is often impractical because they examine different combinations of loci, eliminating phylogeny as a means of examining these data collectively unless hundreds of specimens are excluded. A recently-described machine learning approach that facilitates clustering of MLST data may offer a solution, even for datasets that include specimens sequenced at different combinations of loci. By clustering various MLST datasets as one using this procedure, we sought to uncover associations among genotype, geography, and hosts that remained elusive when examining datasets individually. Multiple datasets comprising hundreds of S. stercoralis and S. fuelleborni individuals were combined and clustered. Our results suggest that the commonly proposed ‘two lineage’ population structure of S. stercoralis (where lineage A infects humans and dogs, lineage B only dogs) is an over-simplification. Instead, S. stercoralis seemingly represents a species complex, including two distinct populations over-represented in dogs, and other populations vastly more common in humans. A distinction between African and Asian S. fuelleborni is also supported here, emphasizing the need for further resolving these taxonomic relationships through modern investigations.

Taisei Kikuchi, Mark Viney, Matthew Berriman and colleagues report the genome sequences of six species of nematodes from the Strongyloides clade of nematodes, including human and animal pathogens, facultative parasites and a free-living species. They find that expansions of the astacin and SCP/TAPS gene families are associated with parasitism in these species. Soil-transmitted nematodes, including the Strongyloides genus, cause one of the most prevalent neglected tropical diseases. Here we compare the genomes of four Strongyloides species, including the human pathogen Strongyloides stercoralis , and their close relatives that are facultatively parasitic ( Parastrongyloides trichosuri ) and free-living ( Rhabditophanes sp. KR3021). A significant paralogous expansion of key gene families—families encoding astacin-like and SCP/TAPS proteins—is associated with the evolution of parasitism in this clade. Exploiting the unique Strongyloides life cycle, we compare the transcriptomes of the parasitic and free-living stages and find that these same gene families are upregulated in the parasitic stages, underscoring their role in nematode parasitism.

The human pathogenic nematode Strongyloides stercoralis infects approximately 30–100 million people worldwide. Analysis of the adaptive immune response to S. stercoralis beyond descriptive studies is challenging, as no murine model for the complete infection cycle is available. However, the combined employment of different models each capable of modelling some features of S. stercoralis life cycle and pathology has advanced our understanding of the immunological mechanisms involved in host defence. Here we review: (i) studies using S. stercoralis third stage larvae implanted in diffusion chambers in the subcutaneous tissue of mice that allow analysis of the immune response to the human pathogenic Strongyloides species; (ii) studies using Strongyloides ratti and Strongyloides venezuelensis that infect mice and rats to extend the analysis to the parasites intestinal life stage and (iii) studies using S. stercoralis infected gerbils to analyse the hyperinfection syndrome, a severe complication of human strongyloidiasis that is not induced by rodent specific Strongyloides spp. We provide an overview of the information accumulated so far showing that Strongyloides spp. elicits a classical Th2 response that culminates in different, site specific, effector functions leading to either entrapment and killing of larvae in the tissues or expulsion of parasitic adults from the intestine.

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.