Worldwide absence of canonical benzimidazole resistance-associated mutations within β-tubulin genes from Ascaris

BACKGROUND

The giant roundworm Ascaris is an intestinal nematode, causing ascariasis by infecting humans and pigs worldwide. Recent estimates suggest that Ascaris infects over half a billion people, with chronic infections leading to reduced growth and cognitive ability. Ascariasis affects innumerable pigs worldwide and is known to reduce production yields via decreased growth and condemnation of livers. The predominant anthelminthic drugs used to treat ascariasis are the benzimidazoles. Benzimidazoles interact with β-tubulins and block their function, and several benzimidazole resistance-associated mutations have been described in the β-tubulins of ruminant nematodes. Recent research on ascarids has shown that these canonical benzimidazole resistance-associated mutations are likely not present in the β-tubulins of Ascaris, Ascaridia or Parascaris, even in phenotypically resistant populations.

METHODS

To further determine the putative absence of key β-tubulin polymorphisms, we screened two β-tubulin isotypes of Ascaris, highly expressed in adult worms. Using adult and egg samples of Ascaris obtained from pigs and humans worldwide, we performed deep amplicon sequencing to look for canonical resistance-associated mutations in Ascaris β-tubulins. Subsequently, we examined these data in closer detail to study the population dynamics of Ascaris and genetic diversity within the two isotypes and tested whether genotypes appeared to partition across human and pig hosts.

RESULTS

In the 187 isolates, 69 genotypes were found, made up of eight haplotypes of β-tubulin isotype A and 20 haplotypes of isotype B. Single nucleotide polymorphisms were seen at 14 and 37 positions for β-tubulin isotype A and isotype B, respectively. No evidence of any canonical benzimidazole resistance-associated mutations was found in either human- or pig-derived Ascaris isolates. There was, however, a difference in the genetic diversity of each isotype and distribution of β-tubulin genotypes between human- and pig-derived Ascaris. Statistical tests of population differentiation show significant differences (p < 0.001) between pig- and human-derived worms; however, more diversity was seen between worms from different populations than worms from different hosts.

CONCLUSIONS

Our work suggests an absence of canonical β-tubulin mutations within Ascaris, but alternative modes of anthelminthic resistance may emerge necessitating continued genetic scrutiny alongside monitoring of drug efficacy.

Prospective pilot study on the relationship between seminal HIV-1 shedding and genital schistosomiasis in men receiving antiretroviral therapy along Lake Malawi

Male genital schistosomiasis (MGS) is hypothesized to increase seminal shedding of HIV-1. This prospective pilot study assessed seminal HIV-1 RNA shedding in men on long-term ART with and without a diagnosis of MGS. Study visits occurred at 0, 1, 3, 6 and 12 months. MGS was diagnosed by egg positivity on semen microscopy or PCR of seminal sediment. After optimization of the HIV-RNA assay, we examined 72 paired plasma and semen samples collected from 31 men (15 with and 16 without MGS) over 12 months. HIV-1 RNA was detected in 7/72 (9.7%) seminal samples and 25/72 (34.7%) plasma samples. When comparing sample pairs, 5/72 (6.9%) showed HIV-1 RNA detection only in the seminal sample. Overall, 3/31 (9.7%) participants, all with MGS, had detectable HIV-1 RNA in semen while plasma HIV-1 RNA was undetectable (< 22 copies/mL), with seminal levels ranging up to 400 copies/mL. Two participants showing HIV-1 RNA in seminal fluid from the MGS-negative group also had concomitant HIV-1 RNA detection in plasma. The findings suggest that MGS can be associated with low-level HIV-1 RNA shedding despite virologically suppressive ART. Further studies are warranted to confirm these observations and assess its implications.

Detection of male genital schistosomiasis (MGS) by real-time TaqMan® PCR analysis of semen from fishermen along the southern shoreline of Lake Malawi

Background

Male genital schistosomiasis (MGS) is an underappreciated complication of schistosomiasis, first described in 1911. However, its epidemiology, diagnostic testing and case management are not well understood in sub-Saharan Africa. To shed new light on MGS prevalence in Malawi, a longitudinal cohort study was conducted among adult fishermen along the southern shoreline of Lake Malawi using detection of schistosome DNA in participants' semen by real-time TaqMan® PCR analyses.

Methods

Upon recruitment of 376 participants, 210 submitted urine samples and 114 semen samples for parasitological tests. Thereafter, the available semen samples were subsequently analysed by real-time TaqMan® PCR. Praziquantel (PZQ) treatment was provided to all participants with follow-ups attempted at 1, 3, 6 and 12-months' intervals.

Results

At baseline, real-time PCR detected a higher MGS cohort prevalence of 26.6% (n = 64, Ct-value range: 18.9-37.4), compared to 10.4% by semen microscopy. In total, 21.9% of participants (n = 114) were detected with MGS either by semen microscopy and/or by real-time PCR. Subsequent analyses at 1-, 3-, 6- and 12-month follow-ups indicated variable detection dynamics.

Conclusions

This first application of a molecular method, to detect MGS in sub-Saharan Africa, highlights the need for development of such molecular diagnostic tests which should be affordable and locally accessible. Our investigation also notes the persistence of MGS over a calendar year despite praziquantel treatment.

ON LIVER FLUKE (FASCIOLA HEPATICA) IN CAPTIVE VICUÑAS (VICUGNA VICUGNA) AT KNOWSLEY SAFARI, PRESCOT, UNITED KINGDOM

Knowsley Safari (KS), Prescot, United Kingdom houses a variety of captive exotic ungulates. As part of their animal welfare plan, a prospective coprological survey was undertaken for liver fluke. In June 2021, 330 fecal samples, representative of 18 exotic ungulate species, were processed by sedimentation and filtration, with examination by coproscopy. Finding fascioliasis in all five vicuña alone, with fecal egg counts ranging from one to eight eggs per gram, anthelminthic treatment was attempted twice, with three coprological reviews. While the first anthelminthic treatment (oxyclozanide) was equivocal, the second anthelminthic treatment (triclabendazole) was proven effective upon two later follow-ups. An initial malacological survey of 16 freshwater sites in KS, first found Galba truncatula at two sites in June 2021, then upon more extensive searching subsequently within the vicuña's enclosure. It appears that F. hepatica was locally acquired, being the first report of fascioliasis within captive vicuñas in the United Kingdom. To develop a better fluke-management plan, regular coprological and malacological surveillance is justified, perhaps with molecular xenomonitoring of snails, alongside prompt administration of appropriate flukicide as required.

Biomphalaria pfeifferi (Gastropoda: Planorbidae) in Lake Malawi and Upper Shire River, Mangochi District, Malawi: Distribution, Genetic Diversity and Pre-Patent Schistosome Infections

In November 2017, Biomphalaria pfeifferi, the key intermediate host for Schistosoma mansoni in Africa, was first reported in Lake Malawi, Mangochi District. Two subsequent malacological surveys in 2018 and 2019 confirmed its lacustrine presence, as well as its presence along the Upper Shire River. These surveys provided sufficient specimens for analyses of the genetic structure and a transmission assessment for intestinal schistosomiasis. A total of 76 collected snails were characterized by a DNA sequence analysis of a 650 bp fragment of the mitochondrial cytochrome oxidase subunit 1 (cox1); by size fractionation of six fluorescently labelled microsatellite loci (Bgμl16, Bgμl, Bpf8, rg6, U-7, and rg9);by denaturing PAGE; and by detection of pre-patent Schistosoma infection by real-time PCR with a TaqMan® probe. Five closely related cox1 haplotypes were identified, all present within a single location, with only one haplotype common across all the other locations sampled. No allelic size variation was detected with the microsatellites and all loci were monomorphic. Overall, the pre-patent prevalence of Schistosoma spp. was 31%, with infected snails found at several sampling locations. In this part of Lake Malawi, Bi. pfeifferi exhibits low genetic diversity and is clearly being exposed to the miracidia of S. mansoni, which is likely facilitating the autochthonous transmission of this parasite.

Identification of key interactions of benzimidazole resistance-associated amino acid mutations in Ascaris β-tubulins by molecular docking simulations

Ascaris species are soil-transmitted helminths that infect humans and livestock mainly in low and middle-income countries. Benzimidazole (BZ) class drugs have predominated for many years in the treatment of Ascaris infections, but persistent use of BZs has already led to widespread resistance in other nematodes, and treatment failure is emerging for Ascaris. Benzimidazoles act by binding to β-tubulin proteins and destabilising microtubules. Three mutations in the β-tubulin protein family are associated with BZ resistance. Seven shared β-tubulin isotypes were identified in Ascaris lumbricoides and A. suum genomes. Benzimidazoles were predicted to bind to all β-tubulin isotypes using in silico docking, demonstrating that the selectivity of BZs to interact with one or two β-tubulin isotypes is likely the result of isotype expression levels affecting the frequency of interaction. Ascaris β-tubulin isotype A clusters with helminth β-tubulins previously shown to interact with BZ. Molecular dynamics simulations using β-tubulin isotype A highlighted the key role of amino acid E198 in BZ-β-tubulin interactions. Simulations indicated that mutations at amino acids E198A and F200Y alter binding of BZ, whereas there was no obvious effect of the F167Y mutation. In conclusion, the key interactions vital for BZ binding with β-tubulins have been identified and show how mutations can lead to resistance in nematodes.

Pathological Abnormalities Observed on Ultrasonography among Fishermen Associated with Male Genital Schistosomiasis (MGS) along the South Lake Malawi Shoreline in Mangochi District, Malawi

Schistosome eggs cause granulomata and pathological abnormalities, detectable with non-invasive radiological techniques such as ultrasonography which could be useful in male genital schistosomiasis (MGS). As part of our novel MGS study among fishermen along Lake Malawi, we describe pathologies observed on ultrasonography and praziquantel (PZQ) treatment over time. Fishermen aged 18+ years were recruited, submitted urine and semen for parasitological and molecular testing, and thereafter, transabdominal pelvic and scrotal ultrasonography, assessing pathologies in the prostate, seminal vesicles, epididymis and testes. Standard PZQ treatment and follow-up invitation at 1-, 3-, 6- and 12-months’ time-points were offered. A total of 130 recruited fishermen underwent ultrasonography at baseline (median age: 32.0 years); 27 (20.9%, n = 129) had S. haematobium eggs in urine (median: 1.0 egg/10 mL), 10 (12.3%, n = 81) in semen (defined as MGS, median: 2.9 eggs/mL ejaculate) and 16 (28.1%, n = 57) had a positive seminal Schistosoma real-time PCR. At baseline, 9 fishermen (6.9%, n = 130) had abnormalities, with 2 positive MGS having prostatic and testicular nodules. Fewer abnormalities were observed on follow-up. In conclusion, pathologies detected in male genitalia by ultrasonography can describe MGS morbidity in those with positive parasitological and molecular findings. Ultrasonography advances and accessibility in endemic areas can support monitoring of pathologies’ resolution after treatment.

In Silico Docking of Nematode β-Tubulins With Benzimidazoles Points to Gene Expression and Orthologue Variation as Factors in Anthelmintic Resistance

The efficacy of benzimidazole anthelmintics can vary depending on the target parasite, with Ascaris nematodes being highly responsive, and whipworms being less responsive. Anthelmintic resistance has become widespread, particularly in strongyle nematodes such as Haemonchus contortus in ruminants, and resistance has recently been detected in hookworms of humans and dogs. Past work has shown that there are multiple β-tubulin isotypes in helminths, yet only a few of these contribute to benzimidazole interactions and resistance. The β-tubulin isotypes of ascarids and soil-transmitted helminths were identified by mining available genome data, and phylogenetic analysis showed that the ascarids share a similar repertoire of seven β-tubulin isotypes. Strongyles also have a consistent pattern of four β-tubulin isotypes. In contrast, the whipworms only have two isotypes, with one of these clustering more basally and distinct from any other group. Key β-tubulin isotypes selected based on previous studies were the focus of in silico molecular docking simulations to look at the interactions with benzimidazoles. These showed that all β-tubulins had similar interactions with benzimidazoles and maintained the key bond with residue E198 in all species, indicating similar mechanisms of action. However, the interaction was stronger and more consistent in the strongyles and whipworms than it was in the ascarids. Alteration of β-tubulin isotypes with the common resistance-associated mutations originally identified in H. contortus resulted in similar interaction modeling for all species. In conclusion, ascarids, strongyles, and whipworms all have their own unique repertoire of β-tubulins, which could explain why benzimidazole resistance and susceptibility varies between these groups of parasites. These data complement recent work that has highlighted the roles of essential residues in benzimidazole drug binding and shows that there is a separation between strongyle parasites that frequently develop resistance and ascarid parasites, which have been much less prone to developing resistance.

Male Genital Schistosomiasis Along the Shoreline of Lake Malawi: Baseline Prevalence and Associated Knowledge, Attitudes and Practices Among Local Fishermen in Mangochi District, Malawi

Male genital schistosomiasis (MGS) is an often-overlooked chronic consequence of urogenital schistosomiasis (UGS) associated with Schistosoma haematobium eggs and associated pathologies in the genital system of afflicted men. Despite the first formal description of MGS in 1911 by Madden, its epidemiology, diagnostic testing and case management of today are not well-described. However, since several interactions between MGS and the Human Immunodeficiency Virus (HIV) are known, there is renewed public health interest in MGS across sub-Saharan Africa (SSA). To shed new light upon MGS in Malawi, a longitudinal cohort study was set up among fishermen along the southern shoreline of Lake Malawi in Mangochi District, Malawi, to document its prevalence and assess mens' knowledge, attitudes and practices (KAP). After providing informed written consent, fishermen (n = 376) aged 18+ years (median age: 30 years, range: 18-70 years) were recruited and submitted urine and semen for point-of-care (POC) field and laboratory diagnostic parasitological tests. Individual questionnaires were administered to assess their KAP, with praziquantel (PZQ) treatment provided to all participants. Baseline prevalence of MGS (S. haematobium eggs in semen) was 10.4% (n = 114, median: 5.0 eggs per ml, range: 0.1-30.0) while for UGS (S. haematobium eggs in urine) was 17.1% (n = 210, median: 2.3 eggs per 10 ml, range: 0.1-186.0) and 3.8% were positive by POC circulating cathodic antigen (POC-CCA), indicative of a Schistosoma mansoni infection. Just under 10% of participants reported having experienced symptoms associated with MGS, namely genital or coital pain, or haemospermia. A total of 61.7% reported previous difficulties in accessing PZQ therapy, with 34.8% having received PZQ therapy before. There was a significant correlation between MGS infection and the frequency of fishing in a week (rho = -0.25, n = 100, p = 0.01). In conclusion, MGS is prevalent among local fishermen yet knowledge of the disease is poor. We therefore call for improved availability and accessibility to MGS diagnostics, PZQ treatment within ongoing control interventions. This will improve the lives and reproductive health of men, their partners and communities in this shoreline environment of Lake Malawi.

Piloting an integrated approach for estimation of environmental risk of Schistosoma haematobium infections in pre-school-aged children and their mothers at Barombi Kotto, Cameroon

Within schistosomiasis control, assessing environmental risk of currently non-treated demographic groups e.g. pre-school-aged children (PSAC) and their mothers is important. We conducted a pilot micro-epidemiological assessment at the crater lake of Barombi Kotto, Cameroon with GPS tracking and infection data from 12 PSAC-mother pairs (n = 24) overlaid against environmental sampling inclusive of snail, parasite and water-use information. Several high-risk locations or 'hotspots' with elevated water contact, increased intermediate snail host densities and detectable schistosome environmental DNA (eDNA) were identified. Exposure between PSAC and mother pairs was temporally and spatially associated, suggesting interventions which can benefit both groups simultaneously might be feasible. When attempting to interrupt parasite transmission in future, overlaid maps of snail, parasite and water contact data can guide fine-scale spatial targeting of environmental interventions.

An outbreak of intestinal schistosomiasis, alongside increasing urogenital schistosomiasis prevalence, in primary school children on the shoreline of Lake Malawi, Mangochi District, Malawi

BACKGROUND

Intestinal schistosomiasis was not considered endemic in Lake Malawi until November 2017 when populations of Biomphalaria pfeifferi were first reported; in May 2018, emergence of intestinal schistosomiasis was confirmed. This emergence was in spite of ongoing control of urogenital schistosomiasis by preventive chemotherapy. Our current study sought to ascertain whether intestinal schistosomiasis is transitioning from emergence to outbreak, to judge if stepped-up control interventions are needed.

METHODS

During late-May 2019, three cross-sectional surveys of primary school children for schistosomiasis were conducted using a combination of rapid diagnostic tests, parasitological examinations and applied morbidity-markers; 1) schistosomiasis dynamics were assessed at Samama (n = 80) and Mchoka (n = 80) schools, where Schistosoma mansoni was first reported, 2) occurrence of S. mansoni was investigated at two non-sampled schools, Mangochi Orphan Education and Training (MOET) (n = 60) and Koche (n = 60) schools, where B. pfeifferi was nearby, and 3) rapid mapping of schistosomiasis, and B. pfeifferi, conducted across a further 8 shoreline schools (n = 240). After data collection, univariate analyses and Chi-square testing were performed, followed by binary logistic regression using generalized linear models, to investigate epidemiological associations.

RESULTS

In total, 520 children from 12 lakeshore primary schools were examined, mean prevalence of S. mansoni by 'positive' urine circulating cathodic antigen (CCA)-dipsticks was 31.5% (95% confidence interval [CI]: 27.5-35.5). Upon comparisons of infection prevalence in May 2018, significant increases at Samama (relative risk [RR] = 1.7, 95% CI: 1.4-2.2) and Mchoka (RR = 2.7, 95% CI: 1.7-4.3) schools were observed. Intestinal schistosomiasis was confirmed at MOET (18.3%) and Koche (35.0%) schools, and in all rapid mapping schools, ranging from 10.0 to 56.7%. Several populations of B. pfeifferi were confirmed, with two new eastern shoreline locations noted. Mean prevalence of urogenital schistosomiasis was 24.0% (95% CI: 20.3-27.7).

CONCLUSIONS

We notify that intestinal schistosomiasis, once considered non-endemic in Lake Malawi, is now transitioning from emergence to outbreak. Once control interventions can resume after coronavirus disease 2019 (COVID-19) suspensions, we recommend stepped-up preventive chemotherapy, with increased community-access to treatments, alongside renewed efforts in appropriate environmental control.

Intestinal Schistosomiasis and Giardiasis Co-Infection in Sub-Saharan Africa: Can a One Health Approach Improve Control of Each Waterborne Parasite Simultaneously?

Both intestinal schistosomiasis and giardiasis are co-endemic throughout many areas of sub-Saharan Africa, significantly impacting the health of millions of children in endemic areas. While giardiasis is not considered a neglected tropical disease (NTD), intestinal schistosomiasis is formally grouped under the NTD umbrella and receives significant advocacy and financial support for large-scale control. Although there are differences in the epidemiology between these two diseases, there are also key similarities that might be exploited within potential integrated control strategies permitting tandem interventions. In this review, we highlight these similarities and discuss opportunities for integrated control of giardiasis in low and middle-income countries where intestinal schistosomiasis is co-endemic. By applying new, advanced methods of disease surveillance, and by improving the provision of water, sanitation and hygiene (WASH) initiatives, (co)infection with intestinal schistosomiasis and/or giardiasis could not only be more effectively controlled but also better understood. In this light, we appraise the suitability of a One Health approach targeting both intestinal schistosomiasis and giardiasis, for if adopted more broadly, transmission of both diseases could be reduced to gain improvements in health and wellbeing.

Case Report: Highlighting Male Genital Schistosomiasis (MGS) in Fishermen from the Southwestern Shoreline of Lake Malawi, Mangochi District

Urogenital schistosomiasis causes morbidity within the genitalia but is underreported and infrequently examined in men. To draw attention to male genital schistosomiasis (MGS), a longitudinal cohort study was conducted among fishermen along the southwestern shoreline of Lake Malawi. A case series of five participants is presented inclusive of questionnaire interviews, parasitological examinations, ultrasonography, and provision of a standard dose (40 mg/kg) of praziquantel (PZQ) treatment at baseline, 1-, 3-, 6-, and 12-month follow-up time points. Eggs of Schistosoma haematobium were observed in urine or semen across all time points; parasitological diagnostics were bolstered by real-time PCR for Schistosoma DNA in semen and by portable ultrasonography to document putative MGS-associated morbidity. We highlight the importance of developing standard diagnostic tests for MGS and increasing the accessibility of PZQ treatment to men, especially those in at-risk endemic areas.

Schistosome Interactions within the Schistosoma haematobium Group, Malawi

Molecular analysis of atypical schistosome eggs retrieved from children in Malawi revealed genetic interactions occurring between human (Schistosoma haematobium) and livestock (S. mattheei and S. bovis) schistosome species. Detection of hybrid schistosomes adds a notable new perspective to the epidemiology and control of urogenital schistosomiasis in central Africa.

Schistosoma mansoni Infection as a Predictor of Low Aerobic Capacity in Ugandan Children

Using the 20-meter shuttle run test (20mSRT) as a morbidity metric, we assessed whether Schistosoma mansoni infection was associated with decreased aerobic capacity in Ugandan children across a range of altitudes, either at low (∼600 m) or high (∼1,000 m) altitudes. A total of 305 children were recruited from six schools within the Buliisa District, Lake Albert, Uganda. A subset (n = 96) of these had been previously assessed and treated for schistosomiasis ± malaria 2 weeks prior. Fitness scores on the 20mSRT were translated into VO2max using a standardized equation. Unadjusted and multivariable-adjusted analyses were performed using VO2max as the primary outcome. Analysis of fitness scores from 304 children, inclusive of the subset follow-up cohort, revealed a median VO2max of 45.4 mL kg-1 min-1 (interquartile range: 42.9-48.0 mL kg-1 min-1). Children residing at high altitudes demonstrated increased aerobic capacities (46.3 versus 44.8 mL kg-1 min-1, P = 0.031). The prevalence of stunting, wasting, S. mansoni egg patent infection, malaria, giardiasis, anemia, and fecal occult blood were 36.7%, 16.1%, 44.3%, 65.2%, 21.4%, 50.6%, and 41.2%, respectively. Median VO2max was elevated in those previously treated, compared with those newly recruited (46.3 versus 44 mL kg-1 min-1, P < 0.001). Multivariable-adjusted analysis revealed a strong negative association between S. mansoni egg patent infection and VO2max at low altitude (beta coefficient: -3.96, 95% CI: -6.56 to -137, P = 0.004). This is the first study to document a negative association between S. mansoni infection and aerobic capacity at low altitudes using the 20mSRT.

Non-invasive surveillance of Plasmodium infection by real-time PCR analysis of ethanol preserved faeces from Ugandan school children with intestinal schistosomiasis

Background

As part of ongoing co-surveillance of intestinal schistosomiasis and malaria in Ugandan school children, a non-invasive detection method for amplification of Plasmodium DNA using real-time (rt)PCR analysis of ethanol preserved faeces (EPF) was assessed. For diagnostic tabulations, results were compared to rtPCR analysis of dried blood spots (DBS) and field-based point-of-care (POC) rapid diagnostic tests (RDTs).

Methods

A total of 247 school children from 5 primary schools along the shoreline of Lake Albert were examined with matched EPF and DBS obtained. Mean prevalence and prevalence by school was calculated by detection of Plasmodium DNA by rtPCR using a 18S rDNA Taqman^® probe. Diagnostic sensitivity, specificity, positive and negative predictive values were tabulated and compared against RDTs.

Results

By rtPCR of EPF and DBS, 158 (63.9%; 95% CI 57.8–69.7) and 198 (80.1%, 95% CI 74.7–84.6) children were positive for Plasmodium spp. By RDT, 138 (55.8%; 95% CI 49.6–61.9) and 45 (18.2%; 95% CI 13.9–23.5) children were positive for Plasmodium falciparum, and with non-P. falciparum co-infections, respectively. Using RDT results as a convenient field-based reference, the sensitivity of rtPCR of EPF and DBS was 73.1% (95% CI 65.2–79.8) and 94.2% (95% CI 88.9–97.0) while specificity was 47.7% (95% CI 38.5–57.0) and 37.6% (95% CI 29.0–46.9), respectively. With one exception, school prevalence estimated by analysis of EPF was higher than that by RDT. Positive and negative predictive values were compared and discussed.

Conclusions

In this high transmission setting, EPF sampling with rtPCR analysis has satisfactory diagnostic performance in estimation of mean prevalence and prevalence by school upon direct comparison with POC-RDTs. Although analysis of EPF was judged inferior to that of DBS, it permits an alternative non-invasive sampling regime that could be implemented alongside general monitoring and surveillance for other faecal parasites. EPF analysis may also have future value in passive surveillance of low transmission settings.

Biomphalaria pfeifferi Snails and Intestinal Schistosomiasis, Lake Malawi, Africa, 2017-2018

Two surveys conducted in 2017 and 2018 demonstrated Biomphalaria pfeifferi snails in Lake Malawi in Africa. Epidemiologic examination of 175 local children at 3 primary schools confirmed emergence of intestinal schistosomiasis. These findings highlight autochthonous transmission of Schistosoma mansoni flukes in Lake Malawi and the need to revise international travel advice.

X-ray structure of Fasciola hepatica Sigma class glutathione transferase 1 reveals a disulfide bond to support stability in gastro-intestinal environment

Sigma class GST (Prostaglandin D synthase), FhGST-S1, is present in the excretory–secretory products (ES) of the liver fluke parasite Fasciola hepatica as cargo of extracellular vesicles (EVs) released by the parasite. FhGST-S1 has a well characterised role in the modulation of the immune response; a key fluke intercession that allows for establishment and development within their hosts. We have resolved the three-dimensional structure of FhGST-S1 in complex with its co-factor glutathione, in complex with a glutathione-cysteine adduct, and in a glutathione disulfide complex in order to initiate a research pipeline to mechanistically understand how FhGST-S1 functions within the host environment and to rationally design selective inhibitors. The overall fold of FhGST-S1 shows high structural similarity to other Sigma class GSTs. However, a unique interdomain disulfide bond was found in the FhGST-S1 which could stabilise the structure within the host gastro-intestinal environment. The position of the two domains of the protein with respect to each other is seen to be crucial in the formation of the active site cleft of the enzyme. The interdomain disulfide bond raises the possibility of oxidative regulation of the active site of this GST protein.

Molecular characterisation and taxon assemblage typing of giardiasis in primary school children living close to the shoreline of Lake Albert, Uganda

As part of an epidemiological survey for gastrointestinal parasites in school children across five primary schools on the shoreline of Lake Albert, the prevalence of giardiasis was 87.0% (n = 254) as determined by real-time PCR analysis of faecal samples with a genus-specific Giardia 18S rDNA probe. Faecal samples were further characterised with taxon assemblage-specific triose phosphate isomerase (TPI) Taqman® probes and by sequence characterisation of the β-giardin gene. While less sensitive than the 18S rDNA assay, general prevalence by TPI probes was 52.4%, with prevalence by taxon assemblage of 8.3% (assemblage A), 35.8% (assemblage B) and 8.3% co-infection (A & B assemblages). While assemblage B was dominant across the sample, proportions of assemblages A and B, and co-infections thereof, varied by school and by age of child; mixed infections were particularly common at Runga school (OR = 6.9 [95% CI; 2.5, 19.3]) and in children aged 6 and under (OR = 2.7 [95% CI; 1.0, 7.3]). Infection with assemblage B was associated with underweight children (OR = 2.0 [95% CI; 1.0, 3.9]). The presence of each assemblage was also confirmed by sequence analysis of the β-giardin gene finding sub-assemblage AII and further genetic diversity within assemblage B. To better explore the local epidemiology of giardiasis and its impact on child health, additional sampling of school children with assemblage typing would be worthwhile.

Urogenital schistosomiasis and soil-transmitted helminthiasis (STH) in Cameroon: An epidemiological update at Barombi Mbo and Barombi Kotto crater lakes assessing prospects for intensified control interventions

BACKGROUND

The crater lakes of Barombi Mbo and Barombi Kotto are well-known transmission foci of schistosomiasis and soil-transmitted helminthiasis having had several important control initiatives previously. To collect contemporary epidemiological information, a cross-sectional survey was undertaken inclusive of: signs and symptoms of disease, individual treatment histories, local water, sanitation and hygiene (WASH)-related factors and malacological surveillance, with molecular characterisation of specimens.

METHODS

At each lake, a community cross-sectional survey was undertaken using a combination of stool and urine parasitological sampling, and interview with pro-forma questionnaires. A total of 338 children and adults participated. Material from snail and parasite species were characterised by DNA methods.

RESULTS

Egg-patent prevalence of urogenital schistosomiasis was 8.7% at Barombi Mbo (all light-intensity infections) and 40.1% at Barombi Kotto (21.2% heavy-intensity infections). Intestinal schistosomiasis was absent. At Barombi Kotto, significantly more women reported signs and symptoms associated with female genital schistosomiasis. While there had been extensive recent improvement in WASH-related infrastructure at Barombi Mbo, water contact risk scores were higher among schistosomiasis-infected participants (P < 0.001) and at Barombi Kotto in general (P < 0.001). Across both lakes, mean prevalence of STH was very low (6.3%) evidencing an impressive decrease of 79.0% over the last decade; neither Strongyloides stercoralis nor Ascaris lumbricoides were found. A total of 29 freshwater sampling sites were inspected for snails, 13 in Barombi Mbo and 16 in Barombi Kotto; water chemistry differed significantly (P < 0.0001) between lakes for both mean pH (7.9 v. 9.6) and mean conductivity (64.3 μS v. 202.1 μS) respectively. Only two Bulinus camerunensis found on the central island of Barombi Kotto were observed to shed schistosome cercariae, but schistosome DNA was later detected in Bulinus sampled from both lakes as well as in Indoplanorbis exustus, an invasive species from Asia.

CONCLUSIONS

STH is currently at very low levels while urogenital schistosomiasis is of greatest concern at Barombi Kotto. This assessment highlights a unique opportunity for further study of the epidemiological dynamics at these crater lakes, to evaluate future intensified interventions both in terms of gaining and sustaining control at Barombi Kotto or in moving towards local interruption of transmission of both diseases at Barombi Mbo.

Intestinal schistosomiasis in Uganda at high altitude (>1400 m): malacological and epidemiological surveys on Mount Elgon and in Fort Portal crater lakes reveal extra preventive chemotherapy needs

Background

Intestinal schistosomiasis is of public health importance in Uganda but communities living above 1400 m are not targeted for control as natural transmission is thought unlikely. To assess altitudinal boundaries and at-risk populations, conjoint malacological and epidemiological surveys were undertaken on Mount Elgon (1139 m–3937 m), in Fort Portal crater lakes and in the Rwenzori Mountains (1123 m–4050 m).

Methods

Seventy freshwater habitats [Mount Elgon (37), Fort Portal crater lakes (23), Rwenzori Mountains (8) and Lake Albert (2)] were inspected for Biomphalaria species. Water temperature, pH and conductivity were recorded. A parasitological examination of 756 schoolchildren [Mount Elgon (300), Fort Portal crater lakes (456)] by faecal microscopy of duplicate Kato-Katz smears from two consecutive stool samples was bolstered by antigen (urine-CCA dipstick) and antibody (SEA-ELISA) diagnostic assays.

Results

Biomphalaria spp. was found up to 1951 m on Mount Elgon and 1567 m in the Fort Portal crater lakes. Although no snail from Mount Elgon shed cercariae, molecular analysis judged 7.1% of snails sampled at altitudes above 1400 m as having DNA of Schistosoma mansoni; in Fort Portal crater lakes three snails shed schistosome cercariae. Prevalence of intestinal schistosomiasis as measured in schoolchildren by Kato-Katz (Mount Elgon = 5.3% v. Fort Portal crater lakes = 10.7%), CCA urine-dipsticks (18.3% v. 34.4%) and SEA-ELISA (42.3% v. 63.7%) showed negative associations with increasing altitude with some evidence of infection up to 2000 m.

Conclusions

Contrary to expectations, these surveys clearly show that natural transmission of intestinal schistosomiasis occurs above 1400 m, possibly extending up to 2000 m. Using spatial epidemiological predictions, this now places some extra six million people at-risk, denoting an expansion of preventive chemotherapy needs in Uganda.

Electronic supplementary material

The online version of this article (doi:10.1186/s40249-017-0248-8) contains supplementary material, which is available to authorized users.

Stage-specific Proteomes from Onchocerca ochengi, Sister Species of the Human River Blindness Parasite, Uncover Adaptations to a Nodular Lifestyle

Despite 40 years of control efforts, onchocerciasis (river blindness) remains one of the most important neglected tropical diseases, with 17 million people affected. The etiological agent, Onchocerca volvulus, is a filarial nematode with a complex lifecycle involving several distinct stages in the definitive host and blackfly vector. The challenges of obtaining sufficient material have prevented high-throughput studies and the development of novel strategies for disease control and diagnosis. Here, we utilize the closest relative of O. volvulus, the bovine parasite Onchocerca ochengi, to compare stage-specific proteomes and host-parasite interactions within the secretome. We identified a total of 4260 unique O. ochengi proteins from adult males and females, infective larvae, intrauterine microfilariae, and fluid from intradermal nodules. In addition, 135 proteins were detected from the obligate Wolbachia symbiont. Observed protein families that were enriched in all whole body extracts relative to the complete search database included immunoglobulin-domain proteins, whereas redox and detoxification enzymes and proteins involved in intracellular transport displayed stage-specific overrepresentation. Unexpectedly, the larval stages exhibited enrichment for several mitochondrial-related protein families, including members of peptidase family M16 and proteins which mediate mitochondrial fission and fusion. Quantification of proteins across the lifecycle using the Hi-3 approach supported these qualitative analyses. In nodule fluid, we identified 94 O. ochengi secreted proteins, including homologs of transforming growth factor-β and a second member of a novel 6-ShK toxin domain family, which was originally described from a model filarial nematode (Litomosoides sigmodontis). Strikingly, the 498 bovine proteins identified in nodule fluid were strongly dominated by antimicrobial proteins, especially cathelicidins. This first high-throughput analysis of an Onchocerca spp. proteome across the lifecycle highlights its profound complexity and emphasizes the extremely close relationship between O. ochengi and O. volvulus The insights presented here provide new candidates for vaccine development, drug targeting and diagnostic biomarkers.

Early hepatic and peritoneal changes and immune response in goats vaccinated with a recombinant glutathione transferase sigma class and challenged with Fasciola hepatica

Changes and local immune response were evaluated in the peritoneal cell populations, duodenal lamina propria and liver from goats immunized with recombinant glutathione transferase sigma class (rFhGST-S1) during early stages of infection with Fasciola hepatica. Group 1 (n=7) was unimmunized and uninfected; group 2 (n=10) was immunized with adjuvant Quil A and infected; group 3 (n=10) was immunised with rFhGST-S1 and infected. Three goats from each group were killed at 7-9 days post-infection (dpi) to evaluate early changes and immune response. The remaining goats were killed at 15 weeks post-infection (wpi). rFhGST-S1 vaccination induced variable response: three goats showed low fluke burden at 15 wpi and two goats showed low hepatic damage at early infection stages. This response was associated to a severe infiltrate of eosinophils in peritoneal fluid and hepatic necrotic foci, high iNOS expression in peritoneal cells and abundant infiltrate of eosinophils surrounding hepatic migrating flukes. T lymphocyte subsets were found in the vicinity of necrotic areas but they were absent in the vicinity of migrating larvae. No significant variation for T cell subsets, except for CD4 and γδ T lymphocytes, that were higher in the Quil A group compared to the rFhGST-S1 group. Expression of IL4 and IFN-γ in the hepatic inflammatory infiltrates was very occasional.

Bovine fasciolosis at increasing altitudes: parasitological and malacological sampling on the slopes of Mount Elgon, Uganda

BACKGROUND

To clarify the extent and putative transmission zone of bovine fasciolosis on the slopes of Mount Elgon, Uganda, conjoint parasitological and malacological surveys, inclusive of inspection of animals at slaughter, were undertaken at increasing altitudes.

RESULTS

A total of 239 cattle were sampled across eight locations ranging in elevation from 1112-2072 m. Faecal material was examined for presence of Fasciola eggs and sera were tested by ELISA for antibodies against Fasciola antigens. Bolstering this, 38 cattle at slaughter from 2 abattoir sites at 1150 m and 1947 m were inspected; in addition, wild buffalo stool (n=10) opportunistically picked within Mount Elgon National Park (MENP) at 3640 m was examined. By faecal egg detection, prevalence of Fasciola gigantica at low (<1500 m) and high (>1500 m) altitude sites was 43.7% (95% CI 35.4-52.2) and 1.1% (95% CI 0.0-6.0), respectively, while by ELISA was much higher, low altitude--77.9% (95% CI 69.7-85.4) and high altitude--64.5% (95% CI 51.3-76.3). The decline in prevalence with increasing altitude was corroborated by abattoir sampling. Thirty seven aquatic habitats, ranging from 1139-3937 m in altitude were inspected for freshwater snails, 12 of which were within MENP. At lower altitudes, Lymnaea (Radix) natalensis was common, and often abundant, but at higher altitudes became much rarer ceasing to be found above 1800 m. On the other hand, Lymnaea (Galba) truncatula was found only at altitudes above 3000 m and within MENP alone. The snail identifications were confirmed by DNA analysis of the ribosomal 18S gene.

CONCLUSIONS

Active infections of F. gigantica in cattle are common in lower altitude settings but appear to diminish with increasing elevation. This is likely due to a growing paucity of intermediate hosts, specifically populations of L. natalensis for which a natural boundary of 1800 m appeared. Although F. hepatica was not encountered, the presence of several populations of L. truncatula at elevations over 3000 m point towards a potential transmission zone within MENP should this parasite be introduced.

The Sigma class glutathione transferase from the liver fluke Fasciola hepatica

Background

Liver fluke infection of livestock causes economic losses of over US$ 3 billion worldwide per annum. The disease is increasing in livestock worldwide and is a re-emerging human disease. There are currently no commercial vaccines, and only one drug with significant efficacy against adult worms and juveniles. A liver fluke vaccine is deemed essential as short-lived chemotherapy, which is prone to resistance, is an unsustainable option in both developed and developing countries. Protein superfamilies have provided a number of leading liver fluke vaccine candidates. A new form of glutathione transferase (GST) family, Sigma class GST, closely related to a leading Schistosome vaccine candidate (Sm28), has previously been revealed by proteomics in the liver fluke but not functionally characterised.

Methodology/Principal Findings

In this manuscript we show that a purified recombinant form of the F. hepatica Sigma class GST possesses prostaglandin synthase activity and influences activity of host immune cells. Immunocytochemistry and western blotting have shown the protein is present near the surface of the fluke and expressed in eggs and newly excysted juveniles, and present in the excretory/secretory fraction of adults. We have assessed the potential to use F. hepatica Sigma class GST as a vaccine in a goat-based vaccine trial. No significant reduction of worm burden was found but we show significant reduction in the pathology normally associated with liver fluke infection.

Conclusions/Significance

We have shown that F. hepatica Sigma class GST has likely multi-functional roles in the host-parasite interaction from general detoxification and bile acid sequestration to PGD synthase activity.

Combating neglected parasitic diseases is of paramount importance to improve the health of human populations and/or their domestic animals. Uncovering key roles in host-parasite interactions may support the vaccine potential portfolio of a parasite protein. Fasciola hepatica causes global disease in humans and their livestock but no commercial vaccines are available. Members of the Sigma class glutathione transferase (GST) family have long been highlighted as vaccine candidates towards parasitic flatworms. To this end, a Sigma class GST is currently undergoing phase II clinical trials to protect against infection from the schistosomes. In this study we characterise the protein from F. hepatica following four work pathways that 1) confirm its designation as a Sigma class GST using substrate profiling, 2) assess prostaglandin synthase activity and its effect on host immune cells, 3) localise the Sigma GST within adult fluke and between ontogenic stages and 4) measure its potential as a vaccine candidate. The work presented here shows F. hepatica Sigma class GST to have key host-parasite roles and we suggest, warrants further investigation for inclusion into vaccine formulations.

Proteomic profiling and protein identification by MALDI-TOF mass spectrometry in unsequenced parasitic nematodes

Lack of genomic sequence data and the relatively high cost of tandem mass spectrometry have hampered proteomic investigations into helminths, such as resolving the mechanism underpinning globally reported anthelmintic resistance. Whilst detailed mechanisms of resistance remain unknown for the majority of drug-parasite interactions, gene mutations and changes in gene and protein expression are proposed key aspects of resistance. Comparative proteomic analysis of drug-resistant and -susceptible nematodes may reveal protein profiles reflecting drug-related phenotypes. Using the gastro-intestinal nematode, Haemonchus contortus as case study, we report the application of freely available expressed sequence tag (EST) datasets to support proteomic studies in unsequenced nematodes. EST datasets were translated to theoretical protein sequences to generate a searchable database. In conjunction with matrix-assisted laser desorption ionisation time-of-flight mass spectrometry (MALDI-TOF-MS), Peptide Mass Fingerprint (PMF) searching of databases enabled a cost-effective protein identification strategy. The effectiveness of this approach was verified in comparison with MS/MS de novo sequencing with searching of the same EST protein database and subsequent searches of the NCBInr protein database using the Basic Local Alignment Search Tool (BLAST) to provide protein annotation. Of 100 proteins from 2-DE gel spots, 62 were identified by MALDI-TOF-MS and PMF searching of the EST database. Twenty randomly selected spots were analysed by electrospray MS/MS and MASCOT Ion Searches of the same database. The resulting sequences were subjected to BLAST searches of the NCBI protein database to provide annotation of the proteins and confirm concordance in protein identity from both approaches. Further confirmation of protein identifications from the MS/MS data were obtained by de novo sequencing of peptides, followed by FASTS algorithm searches of the EST putative protein database. This study demonstrates the cost-effective use of available EST databases and inexpensive, accessible MALDI-TOF MS in conjunction with PMF for reliable protein identification in unsequenced organisms.

Proteomic analyses of Caenorhabditis elegans dauer larvae and long-lived daf-2 mutants implicates a shared detoxification system in longevity assurance

The insulin/insulin-like growth factor-1 (IGF-1) signaling system is a public regulator of aging in the model animals Caenorhabditis elegans, Drosophila melanogaster, and Mus musculus. For the first time, proteomic analyses of the environmentally resistant and 'nonaging' C. elegans dauer stage and long-lived daf-2 mutants has provided a unique insight into the protein changes which mediate survival against endogenously produced toxins. These changes support a diversion of energy consumption away from anabolic processes toward enhanced cellular maintenance and detoxification processes as previously described by the 'Green Theory of Aging'. Important components of this enhanced longevity system identified in this proteomics study include the alpha-crystallin family of small heat shock proteins, anti-ROS defense systems and cellular phase II detoxification (in daf-2 only). Among those proteins involved in phase II cellular detoxification that were significantly upregulated was a Pi-class glutathione transferase (GST) CE00302. Targeting this GST with RNAi revealed compensatory regulation within the Pi-class GSTs. Furthermore, a recombinant form of the GST protein was found to detoxify and/or bind short-chain aldehydic natural toxic products of lipid peroxidation and long-chained fatty-acids at physiologically relevant concentrations, which may indicate a role in longevity.

Glutathione transferase (GST) as a candidate molecular-based biomarker for soil toxin exposure in the earthworm Lumbricus rubellus

The earthworm Lumbricus rubellus (Hoffmeister, 1843) is a terrestrial pollution sentinel. Enzyme activity and transcription of phase II detoxification superfamily glutathione transferases (GST) is known to respond in earthworms after soil toxin exposure, suggesting GST as a candidate molecular-based pollution biomarker. This study combined sub-proteomics, bioinformatics and biochemical assay to characterise the L. rubellus GST complement as pre-requisite to initialise assessment of the applicability of GST as a biomarker. L. rubellus possesses a range of GSTs related to known classes, with evidence of tissue-specific synthesis. Two affinity-purified GSTs dominating GST protein synthesis (Sigma and Pi class) were cloned, expressed and characterised for enzyme activity with various substrates. Electrospray ionisation mass spectrometry (ESI-MS) and tandem mass spectrometry (MS/MS) following SDS-PAGE were superior in retaining subunit stability relative to two-dimensional gel electrophoresis (2-DE). This study provides greater understanding of Phase II detoxification GST superfamily status of an important environmental pollution sentinel organism.

Comparative Proteomics of Excretory-Secretory Proteins Released by the Liver Fluke Fasciola hepatica in Sheep Host Bile and during in Vitro Culture ex Host

Livestock infection by the parasitic fluke Fasciola hepatica causes major economic losses worldwide. The excretory-secretory (ES) products produced by F. hepatica are key players in understanding the host-parasite interaction and offer targets for chemo- and immunotherapy. For the first time, subproteomics has been used to compare ES products produced by adult F. hepatica in vivo, within ovine host bile, with classical ex host in vitro ES methods. Only cathepsin L proteases from F. hepatica were identified in our ovine host bile preparations. Several host proteins were also identified including albumin and enolase with host trypsin inhibitor complex identified as a potential biomarker for F. hepatica infection. Time course in vitro analysis confirmed cathepsin L proteases as the major constituents of the in vitro ES proteome. In addition, detoxification proteins (glutathione transferase and fatty acid-binding protein), actin, and the glycolytic enzymes enolase and glyceraldehyde-3-phosphate dehydrogenase were all identified in vitro. Western blotting of in vitro and in vivo ES proteins showed only cathepsin L proteases were recognized by serum pooled from F. hepatica-infected animals. Other liver fluke proteins released during in vitro culture may be released into the host bile environment via natural shedding of the adult fluke tegument. These proteins may not have been detected during our in vivo analysis because of an increased bile turnover rate and may not be recognized by pooled liver fluke infection sera as they are only produced in adults. This study highlights the difficulties identifying authentic ES proteins ex host, and further confirms the potential of the cathepsin L proteases as therapy candidates.

Binding of hematin by a new class of glutathione transferase from the blood-feeding parasitic nematode Haemonchus contortus

The phase II detoxification system glutathione transferase (GST) is associated with the establishment of parasitic nematode infections within the gastrointestinal environment of the mammalian host. We report the functional analysis of a GST from an important worldwide parasitic nematode of small ruminants, Haemonchus contortus. This GST shows limited activity with a range of classical GST substrates but effectively binds hematin. The high-affinity binding site for hematin was not present in the GST showing the most identity, CE07055 from the free-living nematode Caenorhabditis elegans. This finding suggests that the high-affinity binding of hematin may represent a parasite adaptation to blood or tissue feeding from the host.