Schistosomiasis in cattle

Total flavonoids of litchi Seed alleviates schistosomiasis liver fibrosis in mice by suppressing hepatic stellate cells activation and modulating the gut microbiomes

Infection with Schistosoma japonicum (S. japonicum) is an important zoonotic parasitic disease that causes liver fibrosis in both human and domestic animals. The activation of hepatic stellate cells (HSCs) is a crucial phase in the development of liver fibrosis, and inhibiting their activation can alleviate this progression. Total flavonoids of litchi seed (TFL) is a naturally extracted drug, and modern pharmacological studies have shown its anti-fibrotic and liver-protective effects. However, the role of TFL in schistosomiasis liver fibrosis is still unclear. This study investigated the therapeutic effects of TFL on liver fibrosis in S. japonicum infected mice and explored its potential mechanisms. Animal study results showed that TFL significantly reduced the levels of Interleukin-1β (IL-1β), Tumor Necrosis Factor-α (TNF-α), Interleukin-4 (IL-4), and Interleukin-6 (IL-6) in the serum of S. japonicum infected mice. TFL reduced the spleen index of mice and markedly improved the pathological changes in liver tissues induced by S. japonicum infection, decreasing the expression of alpha-smooth muscle actin (α-SMA), Collagen I and Collagen III protein in liver tissues. In vitro studies indicated that TFL also inhibited the activation of HCSs induced by Transforming Growth Factor-β1 (TGF-β1) and reduced the levels of α-SMA. Gut microbes metagenomics study revealed that the composition, abundance, and functions of the mice gut microbiomes changed significantly after S. japonicum infection, and TLF treatment reversed these changes. Therefore, our study indicated that TFL alleviated granulomatous lesions and improved S. japonicum induced liver fibrosis in mice by inhibiting the activation of HSCs and by improving the gut microbiomes.

Reaching the World Health Organization elimination targets for schistosomiasis: the importance of a One Health perspective

The past three years has seen the launch of a new World Health Organization (WHO) neglected tropical diseases (NTDs) roadmap, together with revised control and elimination guidelines. Across all, there is now a clear emphasis on the need to incorporate a One Health approach, recognizing the critical links between human and animal health and the environment. Schistosomiasis, caused by Schistosoma spp. trematodes, is a NTD of global medical and veterinary importance, with over 220 million people and untold millions of livestock currently infected. Its burden remains extremely high in certain regions, particularly within sub-Saharan Africa, despite over two decades of mass preventive chemotherapy (mass drug administration), predominantly to school-aged children. In Africa, in contrast to Asia, any zoonotic component of schistosomiasis transmission and its implications for disease control has, until recently, been largely ignored. Here, we review recent epidemiological, clinical, molecular, and modelling work across both Asia and Africa. We outline the evolutionary history and transmission dynamics of Schistosoma species, and emphasize the emerging risk raised by both wildlife reservoirs and viable hybridization between human and animal schistosomes. To achieve the 2030 WHO roadmap elimination targets, a truly multi-disciplinary One Health perspective must be implemented. This article is part of the theme issue 'Challenges and opportunities in the fight against neglected tropical diseases: a decade from the London Declaration on NTDs'.

Genetic profiles of Schistosoma haematobium parasites from Malian transmission hotspot areas

BACKGROUND

Although schistosomiasis is a public health issue in Mali, little is known about the parasite genetic profile. The purpose of this study was to analyze the genetic profile of the schistosomes of Schistosoma haematobium group in school-aged children in various sites in Mali.

METHODS

Urine samples were collected from 7 to 21 November 2021 and subjected to a filtration method for the presence S. haematobium eggs. The study took place in two schistosomiasis endemic villages (Fangouné Bamanan and Diakalèl), qualified as hotspots according to the World Health Organization (WHO) definition. Molecular genotyping on both Cox1 and ITS2/18S was used for eggs' taxonomic assignation.

RESULTS

A total of 970 miracidia were individually collected from 63 school-aged children and stored on Whatman FTA cards for molecular analysis. After genotyping 42.0% (353/840) and 58.0% (487/840) of miracidia revealed Schistosoma bovis and S. haematobium Cox1 profiles, respectively; 95.7 (885/925) and 4.3% (40/925) revealed S. haematobium and S. haematobium/S. curassoni profiles for ITS/18S genes, respectively. There was a significant difference in the Cox1 and ITS2/18S profile distribution according to the village (P < 0.0001). Overall, 45.6% (360/789) were hybrids, of which 72.0% (322/447) were from Diakalèl. Three hybrids' profiles (Sb/Sc_ShxSc with 2.3%; Sb/Sc_ShxSh with 40.5%; Sh_ShxSc with 2.8%) and one pure profile (Sh_ShxSh with 54.4%) were identified.

CONCLUSION

Our findings show, for the first time to our knowledge, high prevalence of hybrid schistosomes in Mali. More studies are needed on population genetics of schistosomes at the human and animal interface to evaluate the parasite's gene flow and its consequences on epidemiology of the disease as well as the transmission to humans.

Prevalence and associated risk factors of Schistosoma indicum infection in cattle of Assam, India

The hepato-intestinal schistosomosis, a chronic debilitating infection caused by Schistosoma indicum is one of the major helminthic problems which cause considerable reduction in production and productivity, and economic losses in Assam, India. Hence their accurate diagnosis by traditional and molecular methods is the key to its management. A total of 420 faecal samples and liver and intestinal mesenteries from different slaughter houses of Assam were collected and examined during March 2015 to February 2016 to record the prevalence of visceral schistosomosis. It was observed that prevalence rate of schistosomosis was found to be more in mesenteric and hepatic portal vein examination (12.38%) than the faecal examination (4.52%). The 28S RNA gene (28S) and mitochondrial cytochrome c oxidase subunit 1 (COI) gene of morphologically identified adult S. indicum was amplified with amplicon sizes 590 bp and 372 bp, respectively which could be used as molecular marker for diagnosis S. indicum infection. However, based on worm pair detection, the study showed an increasing incidence of schistosomosis from the month of May onward reached highest peak in July and gradually decline to lowest point in April, while coprological examination showed the highest peak in August and the lowest in March. The risk factors include age, breed and management systems of the cattle. Therefore, this study emphasizes on employing both conventional and molecular techniques to detect the various risk factors of S. indicum infection in cattle for successful control measures.

Modelling livestock test-and-treat: A novel One Health strategy to control schistosomiasis and mitigate drug resistance

Schistosomiasis, a neglected tropical disease, is a widespread chronic helminthiasis reported in 78 countries, predominantly those within sub-Saharan Africa, as well as Latin America, Asia, and most recently, even Europe. Species of the causative blood fluke infect not only humans but also animals, and hybrids between previously assumed human-specific and animal-specific schistosomes are being increasingly reported. Existing control programs across Africa focus on humans and rely heavily on mass drug administration of praziquantel, the sole drug available against schistosomiasis. Praziquantel is safe and highly efficacious but could become ineffective if resistance emerges. To reach the revised World Health Organization goal of elimination of schistosomiasis as a public health problem, and interruption of transmission within selected regions, by 2030, new consideration of the role of animal reservoirs in human transmission in general, and whether to also treat livestock with praziquantel in particular, has been raised. However, whilst there are no dedicated control programs targeting animals outside of Asia, there are emerging reports of the use and misuse of praziquantel in livestock across Africa. Therefore, to effectively treat livestock in Africa and to help mitigate against the potential evolution of praziquantel resistance, structured control strategies are required. Here, using a transmission modelling approach, we evaluate the potential effectiveness of a theoretical test-and-treat (TnT) strategy to control bovine schistosomiasis using a currently available point-of-care diagnostic test (developed for human use) to detect circulating cathodic antigen (POC-CCA). We show that implementing TnT at herd-level from 2022 to 2030 could be highly effective in suppressing infection in cattle and even, in lower prevalence settings, reaching nominal ‘elimination’ targets. We highlight the importance of enhancing the specificity of POC-CCA for use in livestock to avoid unnecessary treatments and discuss the outstanding challenges associated with implementing TnT as part of a holistic One Health approach to tackling human and animal schistosomiasis.

A retrospective study on Schistosoma spindale infection in domestic ruminants, Andhra Pradesh, India

The present study was undertaken to determine the prevalence of Schistosoma spindale infection in domestic ruminants in Krishna district, Andhra Pradesh by coprological and necropsy examination. Examination of 177 buffaloes, 283 sheep and 166 goats faecal samples (n = 626) revealed 2.25, 2.82 and 1.80% of S. spindale infection, respectively. Necropsy examination of 21 buffaloes, 185 sheep and 217 goats revealed 14.2, 1.08 and 3.68% of S. spindale infection, respectively. Overall, microscopic examination of faecal smears revealed 2.39% (n = 15) prevalence of S. spindale infection in ruminants in the study area, while 3.07% (n = 13) of ruminants were found to be positive for S. spindale during postmortem examination. Adult worms collected from the mesenteric veins were processed and identified as S. spindale. Grossly, the infected livers were found with petechial haemorrhages, cirrhotic changes and pinpoint granulomas in parenchymatous tissue. Histological sections of livers revealed microgranulomas with infiltration of mononuclears, eosinophils and fibroblast cells surrounding the Schistosome ova. The intestinal mucosa was thickened, edematous and haemorrhagic with copious mucous exudates. Cut section of infected intestines revealed severe inflammatory reactions in the mucosa and sub mucosa and granulomatous changes surrounding the Schistosoma eggs.

Transmission and diversity of Schistosoma haematobium and S. bovis and their freshwater intermediate snail hosts Bulinus globosus and B. nasutus in the Zanzibar Archipelago, United Republic of Tanzania

Background

The Zanzibar Archipelago (Pemba and Unguja islands) is targeted for the elimination of human urogenital schistosomiasis caused by infection with Schistosoma haematobium where the intermediate snail host is Bulinus globosus. Following multiple studies, it has remained unclear if B. nasutus (a snail species that occupies geographically distinct regions on the Archipelago) is involved in S. haematobium transmission on Zanzibar. Additionally, S. haematobium was thought to be the only Schistosoma species present on the Zanzibar Archipelago until the sympatric transmission of S. bovis, a parasite of ruminants, was recently identified. Here we re-assess the epidemiology of schistosomiasis on Pemba and Unguja together with the role and genetic diversity of the Bulinus spp. involved in transmission.

Methodology/Principal findings

Malacological and parasitological surveys were conducted between 2016 and 2019. In total, 11,116 Bulinus spp. snails were collected from 65 of 112 freshwater bodies surveyed. Bulinus species identification were determined using mitochondrial cox1 sequences for a representative subset of collected Bulinus (n = 504) and together with archived museum specimens (n = 6), 433 B. globosus and 77 B. nasutus were identified. Phylogenetic analysis of cox1 haplotypes revealed three distinct populations of B. globosus, two with an overlapping distribution on Pemba and one on Unguja. For B. nasutus, only a single clade with matching haplotypes was observed across the islands and included reference sequences from Kenya. Schistosoma haematobium cercariae (n = 158) were identified from 12 infected B. globosus and one B. nasutus collected between 2016 and 2019 in Pemba, and cercariae originating from 69 Bulinus spp. archived in museum collections. Schistosoma bovis cercariae (n = 21) were identified from seven additional B. globosus collected between 2016 and 2019 in Pemba. By analysing a partial mitochondrial cox1 region and the nuclear ITS (1–5.8S-2) rDNA region of Schistosoma cercariae, we identified 18 S. haematobium and three S. bovis haplotypes representing populations associated with mainland Africa and the Indian Ocean Islands (Zanzibar, Madagascar, Mauritius and Mafia).

Conclusions/Significance

The individual B. nasutus on Pemba infected with S. haematobium demonstrates that B. nasutus could also play a role in the local transmission of S. haematobium. We provide preliminary evidence that intraspecific variability of S. haematobium on Pemba may increase the transmission potential of S. haematobium locally due to the expanded intermediate host range, and that the presence of S. bovis complicates the environmental surveillance of schistosome infections.

Schistosomiasis is a snail-borne neglected tropical disease caused by parasitic blood flukes of the genus Schistosoma. Human urogenital schistosomiasis is targeted for elimination on the Zanzibar Archipelago, United Republic of Tanzania, with multiple interventions being implemented to curtail transmission of the parasite to humans on the islands since 2012. Environmental surveillance for schistosomiasis transmission by collecting intermediate host snails, checking snails for Schistosoma infection, and preserving collected snails and Schistosoma parasites offers the possibility for molecular analyses to investigate the evolutionary/genetic relationships of both snails and parasites. Schistosome transmission on Zanzibar was believed to involve a single schistosome species (Schistosoma haematobium) transmitted via a single intermediate host species (Bulinus globosus). However, our findings demonstrate the locally established presence of S. bovis, responsible for bovine intestinal schistosomiasis, and an extended intermediate host compatibility of S. haematobium with the snail B. nasutus on Pemba. Increased parasite diversity and intermediate host species compatibility may increase the transmission of Schistosoma species on Zanzibar and stretch resources for public health interventions with the need for Schistosoma species specific surveillance.

Schistosomiasis with a Focus on Africa

Schistosomiasis is a common neglected tropical disease of impoverished people and livestock in many developing countries in tropical Africa, the Middle East, Asia, and Latin America. Substantial progress has been made in controlling schistosomiasis in some African countries, but the disease still prevails in most parts of sub-Saharan Africa with an estimated 800 million people at risk of infection. Current control strategies rely primarily on treatment with praziquantel, as no vaccine is available; however, treatment alone does not prevent reinfection. There has been emphasis on the use of integrated approaches in the control and elimination of the disease in recent years with the development of health infrastructure and health education. However, there is a need to evaluate the present status of African schistosomiasis, primarily caused by Schistosoma mansoni and S. haematobium, and the factors affecting the disease as the basis for developing more effective control and elimination strategies in the future. This review provides an historical perspective of schistosomiasis in Africa and discusses the current status of control efforts in those countries where the disease is endemic.

The detection of Schistosoma bovis in livestock on Pemba Island, Zanzibar: A preliminary study

Schistosoma bovis is a parasitic trematode of ungulates transmitted by freshwater snails in Sub-Saharan Africa causing bovine intestinal schistosomiasis that leads to chronic morbidity and significant agricultural economic losses. The recently reported occurrence of Bulinus globosus infected with S. bovis for the first time on Pemba Island (Zanzibar, United Republic of Tanzania) is a cause of concern for livestock/wildlife health and complicates the surveillance of Schistosoma haematobium. To confirm that local cattle are infected with S. bovis, fresh faecal samples were collected from six adult cows surrounding two schistosomiasis transmission sites in Kinyasini, Pemba Island. Schistosome eggs were concentrated, egg hatching stimulated and miracidia were individually captured and identified by analysis of the partial mitochondrial cytochrome c oxidase subunit 1 (cox1) and the partial nuclear internal transcribed spacer region (ITS1+5.8S+ITS2). Two S. bovis miracidia were collected from one faecal sample with two cox1 haplotypes, one matching cox1 data obtained from S. bovis cercariae, collected previously at the same site in Pemba, the other matching S. bovis cox1 data originating from coastal Tanzania. The findings conclude that S. bovis transmission has been established on Pemba Island and is likely to have been imported through livestock trade with East Africa. Increasing the sensitivity of non-invasive diagnostics for bovine schistosomiasis, together with wider sampling, will enable a better assessment on the epidemiology of S. bovis on Pemba Island.

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The bovine schistosome Schistosoma bovis is detected for the first time from cattle in Zanzibar.

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Local transmission of S. bovis is confirmed on Pemba Island.

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Bovine schistosomes complicate the xenomonitoring and surveillance of human urogenital schistosomiasis.

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Bovine schistosomiasis could lead to chronic morbidity of cattle and agricultural economic losses.

Development of a Molecular Snail Xenomonitoring Assay to Detect Schistosoma haematobium and Schistosoma bovis Infections in their Bulinus Snail Hosts

Schistosomiasis, a neglected tropical disease of medical and veterinary importance, transmitted through specific freshwater snail intermediate hosts, is targeted for elimination in several endemic regions in sub-Saharan Africa. Multi-disciplinary methods are required for both human and environmental diagnostics to certify schistosomiasis elimination when eventually reached. Molecular xenomonitoring protocols, a DNA-based detection method for screening disease vectors, have been developed and trialed for parasites transmitted by hematophagous insects, such as filarial worms and trypanosomes, yet few have been extensively trialed or proven reliable for the intermediate host snails transmitting schistosomes. Here, previously published universal and Schistosoma-specific internal transcribed spacer (ITS) rDNA primers were adapted into a triplex PCR primer assay that allowed for simple, robust, and rapid detection of Schistosoma haematobium and Schistosoma bovis in Bulinus snails. We showed this two-step protocol could sensitively detect DNA of a single larval schistosome from experimentally infected snails and demonstrate its functionality for detecting S. haematobium infections in wild-caught snails from Zanzibar. Such surveillance tools are a necessity for succeeding in and certifying the 2030 control and elimination goals set by the World Health Organization.

Cattle as natural host for Schistosoma haematobium (Bilharz, 1852) Weinland, 1858 x Schistosoma bovis Sonsino, 1876 interactions, with new cercarial emergence and genetic patterns

Schistosomiasis remains a parasitic infection which poses serious public health consequences around the world, particularly on the African continent where cases of introgression/hybridization between human and cattle schistosomiasis are being discovered on a more frequent basis in humans, specifically between Schistosoma haematobium and S. bovis. The aim of this paper is to analyze the occurrence of S. bovis in cattle and its relationship with S. haematobium in an area where cattle and humans share the same site in Benin (West Africa). We used the chronobiology of cercarial emergence as an ecological parameter and both molecular biology (COI mtDNA and ITS rDNA) of the larvae and morphology of the eggs as taxonomic parameters. The results showed a chronobiological polymorphism in the cercarial emergence rhythm. They showed for the first time the presence of S. bovis in Benin, the presence of introgressive hybridization between S. bovis and S. haematobium in domestic cattle, and the presence of atypical chronobiological patterns in schistosomes from cattle, with typical S. haematobium shedding pattern, double-peak patterns, and nocturnal patterns. Our results showed that the chronobiological life-history trait is useful for the detection of new hosts and also may reveal the possible presence of introgressive hybridization in schistosomes. Our results, for the first time, place cattle as reservoir host for S. haematobium and S. bovis x S. haematobium. The consequences of these results on the epidemiology of the disease, the transmission to humans, and the control of the disease are very important.

Accuracy of the sedimentation and filtration methods for the diagnosis of schistosomiasis in cattle

Infection with blood flukes of the genus Schistosoma causes considerable human and animal morbidity, mortality and economic loss to the livestock industry. Current diagnostic tools have limitations. In this study, we compared the sedimentation and filtration methods for the diagnosis of schistosomiasis in livestock. A total of 196 faecal samples from cattle in Côte d'Ivoire were subjected to sedimentation and filtration for the diagnosis of schistosomiasis and other intestinal parasite infections. Schistosoma eggs or miracidia were discovered in 32 samples: 15 by filtration only, seven by sedimentation only, six concurrently by both methods and four by observing miracidia swimming on the sedimentation slide. The sensitivity of sedimentation and filtration was 41% and 66%, respectively. Cases with no Schistosoma eggs identified in the sediment but miracidia swimming on the slide indicate that eggs had hatched before microscopy. More accurate diagnostic are required for livestock schistosomiasis, in order to better understand the epidemiology and inform control and elimination efforts in livestock and human populations.

Whole-genome sequence of the bovine blood fluke Schistosoma bovis supports interspecific hybridization with S. haematobium

Mesenteric infection by the parasitic blood fluke Schistosoma bovis is a common veterinary problem in Africa and the Middle East and occasionally in the Mediterranean Region. The species also has the ability to form interspecific hybrids with the human parasite S. haematobium with natural hybridisation observed in West Africa, presenting possible zoonotic transmission. Additionally, this exchange of alleles between species may dramatically influence disease dynamics and parasite evolution. We have generated a 374 Mb assembly of the S. bovis genome using Illumina and PacBio-based technologies. Despite infecting different hosts and organs, the genome sequences of S. bovis and S. haematobium appeared strikingly similar with 97% sequence identity. The two species share 98% of protein-coding genes, with an average sequence identity of 97.3% at the amino acid level. Genome comparison identified large continuous parts of the genome (up to several 100 kb) showing almost 100% sequence identity between S. bovis and S. haematobium. It is unlikely that this is a result of genome conservation and provides further evidence of natural interspecific hybridization between S. bovis and S. haematobium. Our results suggest that foreign DNA obtained by interspecific hybridization was maintained in the population through multiple meiosis cycles and that hybrids were sexually reproductive, producing viable offspring. The S. bovis genome assembly forms a highly valuable resource for studying schistosome evolution and exploring genetic regions that are associated with species-specific phenotypic traits.

In this article we detail the assembly and functional annotation of the Schistosoma bovis genome. S. bovis is a parasitic flatworm that primarily infects bovines, with important economic consequences in affected countries. However, it is also a close relative of the human carcinogenic parasite Schistosoma haematobium which is a serious health issue in many endemic countries in Sub-Saharan Africa. The close relationship and overlapping geographical distribution of S. bovis and S. haematobium allows these to hybridise in the wild increasing their genetic diversity and presenting the risk of zoonotic transmission, i.e. the transmission from animals to humans. The hybridization between human and ruminant schistosomes is of particular interest as interspecific hybridization may have dramatic impacts on transmission rates, disease dynamics, control interventions and parasite evolution. By whole-genome sequencing and comparative genomics we present evidence that fertile hybrids are indeed present in the wild, presenting the potential risk of transmission from animal reservoirs to humans.

Investigations on the distribution of Schistosoma turkestanicum Skrjabin, 1913 (Trematoda: Schistosomatidae) infection of red deer in Hungary and a combined method for the detection of S. turkestanicum eggs in droppings

Additional geographical distribution of the Central European populations of Schistosoma turkestanicum and the detectability of their eggs in droppings were investigated in red deer samples, because this rare species had previously been shown only in a single Hungarian habitat. Samples from visceral organs, intestinal contents, and droppings on the ground from 11 hunting areas of Hungary were investigated to find a new presence of this fluke. Close to the first site of detection in the Gemenc forest another habitat along the southern border of the country was found where the parasite lives in red deer. Therefore, it is possible that the worm also occurs in neighbouring Serbia or Croatia. Schistosoma turkestanicum causes a low-intensity infection in red deer and this host sheds low amounts of eggs, therefore the eggs are difficult to detect. Droppings were cleared by sedimentation, filtered by sieve screening and then the eggs were flotated using solutions with an increasing density of 1200 g/L, 1300 g/L, 1350 g/L, and 1400 g/L while they were being stained red with acid fuchsin. Eggs in fresh faeces can be most efficiently separated from plant fibres using a flotation solution of 1350 g/L density, but in some cases eggs in old dung can be detected using a solution of a specific gravity lower or higher than that. By combining the advantages of the three concentration processes, eggs of S. turkestanicum, which are more recognisable by the red stain, can be found in samples in which they are present at a density lower than 1/g.

Urogenital schistosomiasis and hybridization between Schistosoma haematobium and Schistosoma bovis in adults living in Richard-Toll, Senegal

Since the construction of the Diama Dam (1985), the epidemiology of schistosomiasis along the Senegal River Basin (SRB) has been extremely dynamic with outbreaks of both intestinal and urogenital schistosomiasis. In the early 2000s, technicians reported cases of suspected urogenital schistosomiasis in adults from the local hospital in Richard-Toll, Lower SRB. The genetic analysis of schistosome miracidia isolated from 11 patients in 2012 from two neighbourhoods (Campement and Gaya) of Richard-Toll confirmed infection with Schistosoma haematobium but also S. haematobium/S. bovis hybrids. Thirty-seven per cent of the miracidia were S. bovis/S. haematobium hybrids and 63% were pure S. haematobium. The data are discussed in relation to the ongoing dynamic epidemiology of the schistosomes in Senegal and the need to treat non-target individuals.

Occurrence of Schistosoma bovis on Pemba Island, Zanzibar: implications for urogenital schistosomiasis transmission monitoring

The causative agent of urogenital schistosomiasis, Schistosoma haematobium, was thought to be the only schistosome species transmitted through Bulinus snails on Unguja and Pemba Island (Zanzibar, United Republic of Tanzania). For insights into the environmental risk of S. haematobium transmission on Pemba Island, malacological surveys collecting Bulinus globosus and B. nasutus, two closely related potential intermediate hosts of S. haematobium were conducted across the island in November 2016. Of 1317 B. globosus/B. nasutus collected, seven B. globosus, identified through sequencing a DNA region of the mitochondrial cytochrome oxidase subunit 1 (cox1), were observed with patent infections assumed to be S. haematobium. However, when the collected cercariae were identified through sequencing a region of the cox1 and the nuclear internal transcribed spacer (ITS1 + 2), schistosomes from five of these B. globosus collected from a single locality were in fact S. bovis. The identified presence of S. bovis raises concerns for animal health on Pemba, and complicates future transmission monitoring of S. haematobium. These results show the pertinence for not only sensitive, but also species-specific markers to be used when identifying cercariae during transmission monitoring, and also provide the first molecular confirmation for B. globosus transmitting S. bovis in East Africa.

Schistosome Vaccines for Domestic Animals

Schistosomiasis is recognized as a tropical disease of considerable public health importance, but domestic livestock infections due to Schistosoma japonicum, S. bovis, S. mattheei and S. curassoni are often overlooked causes of significant animal morbidity and mortality in Asia and Africa. In addition, whereas schistosomiasis japonica is recognized as an important zoonosis in China and the Philippines, reports of viable schistosome hybrids between animal livestock species and S. haematobium point to an underappreciated zoonotic component of transmission in Africa as well. Anti-schistosome vaccines for animal use have long been advocated as part of the solution to schistosomiasis control, benefitting humans and animals and improving the local economy, features aligning with the One Health concept synergizing human and animal health. We review the history of animal vaccines for schistosomiasis from the early days of irradiated larvae and then consider the recombinant DNA technology revolution and its impact in developing schistosome vaccines that followed. We evaluate the major candidates tested in livestock, including the glutathione S-transferases, paramyosin and triose-phosphate isomerase, and summarize some of the future challenges that need to be overcome to design and deliver effective anti-schistosome vaccines that will complement current control options to achieve and sustain future elimination goals.

Kinases: Molecular Stage Directors for Schistosome Development and Differentiation

Understanding schistosome biology is still a challenging mission. The reproductive biology of this parasitic trematode is closely associated with the pathologic consequences of schistosomiasis, the devastating infectious disease caused by members of the family Schistosomatidae worldwide. Recent studies of signaling mechanisms confirmed the prominent roles of protein kinases (PKs) in directing schistosome biology, and first evidence was obtained for an additional contribution of kinases with substrates different from proteins (non-PKs). This review provides an overview of the Schistosoma mansoni kinome in the context of male-female interaction and summarizes recent studies of kinases controlling development and differentiation. Due to their importance for schistosome biology, kinases represent Achilles' heels and are therefore of high value also for translational research.

A review of bovine fasciolosis and other trematode infections in Nigeria

Trematode infections cause serious economic losses to livestock worldwide. Global production losses due to fasciolosis alone exceed US$3 billion annually. Many trematode infections are also zoonotic and thus a public health concern. The World Health Organization has estimated that about 56 million people worldwide are infected by at least one zoonotic trematode species, and up to 750 million people are at risk of infection. Fasciolosis caused by the fluke Fasciola gigantica is endemic in Nigeria and is one of the most common causes of liver condemnation in abattoirs. Total cattle losses from Fasciola infection in Nigeria have been estimated to cost £32.5 million. Other trematode infections of cattle, including paramphistomosis, dicrocoeliasis and schistosomiasis, have all been reported in various parts of Nigeria, with varying prevalence. Most publications on trematode infections are limited to Nigerian local and national journals, with very few international reports. This paper therefore summarized the current data on distribution, control and zoonotic trematode infections in Nigeria and other African countries. We also identified research gaps and made recommendations for future research and areas for funding for policy/planning.

Schistosoma bovis-host interplay: Proteomics for knowing and acting

Schistosoma bovis is a parasite of ruminants that causes significant economic losses to farmers throughout Africa, Southwestern Asia and the Mediterranean. Additionally, recent studies have reported its zoonotic potential through the formation of S. bovis×Schistosoma haematobium hybrids. As observed in the Schistosoma species infecting humans, it is assumed that S. bovis has also evolved host regulatory molecules that ensure its long-term survival in the bloodstream of its host. Since these molecules could be potential targets for the development of new drugs and anti-schistosome vaccines, their identification and functional characterization were undertaken. With this aim in mind, the molecular interface between S. bovis and its vertebrate host was subjected to a series of proteomic studies, which started with the analysis of the proteomes of the S. bovis moieties exposed to the host, namely, the excretory/secretory products and the tegument surface. Thus, a wealth of novel molecular information of S. bovis was obtained, which in turn allowed the identification of several parasite proteins with fibrinolytic and anticoagulant activities that could be used by S. bovis to regulate the host defensive systems. Following on, the host interface was investigated by studying the proteome of the host vascular endothelium surface at two points along the infection: in the lung vessels during the schistosomula migration and in the portal vein after the parasites have reached adulthood and sexual maturity. These studies have provided original data regarding the proteomes of the endothelial cell surface of pulmonary vasculature and portal vein in S. bovis-infected animals, and have shown significant changes in these proteomes associated with infection. This review compiles current information and the analyses of all the proteomic data from S. bovis and the S. bovis-host interface, including the molecular and functional characterization of S. bovis proteins that were found to participate in the regulation of the host coagulation and fibrinolysis systems.

Derivatives of biarylalkyl carboxylic acid induce pleiotropic phenotypes in adult Schistosoma mansoni in vitro

Schistosomes and other parasitic platyhelminths cause infectious diseases of worldwide significance for humans and animals. Despite their medical and economic importance, vaccines are not available and the number of drugs is alarmingly limited. For most platyhelminths including schistosomes, Praziquantel (PZQ) is the commonly used drug. With respect to its regular application in mass treatment programs, however, there is increasing concern about resistance development.Previous studies demonstrated that inhibitors used to treat non-parasitic human diseases may be useful to be tested for their effects on parasites. To this end, we focused on biarylalkyl carboxylic acids (BACAs) as basis, which had been shown before to be interesting candidates in the context of finding alternative approaches to treat diabetes mellitus. We tested 32 chemically modified derivatives of these substances (biarylalkyl carboxylic acid derivatives (BACADs)) for their effects on adult Schistosoma mansoni in vitro. Treatment with 18 BACADs resulted in egg production-associated phenotypes and reduced pairing stability. In addition, 12 of these derivatives affected vitality and/or caused severe tegument damage, gut dilatation, or other forms of tissue disintegration which led to the death of worms. In most cases (10/12), one derivative caused more than one phenotype at a time. In vitro experiments in the presence of serum albumin (SA) and alpha-acidic glycoprotein (AGP) indicated a varying influence of these blood components on the effects of two selected derivatives. The variety of observed phenotypes suggested that different targets were hit. The results demonstrated that BACADs are interesting substances with respect to their anti-schistosomal effects.

The combination of the aliphatic diamine AA0029 in ADAD vaccination system with a recombinant fatty acid binding protein could be a good alternative for the animal schistosomiasis control

Fatty acid binding proteins (FABP) from Fasciola hepatica have demonstrated immune cross-protection against schistosomes. The present study was conducted to develop a new formulation of the recombinant FABP rFh15 with the synthetic immunomodulator AA0029 in the adjuvant adaptation (ADAD) vaccination system and to evaluate its ability to induce immune response and protection against the challenge with Schistosoma bovis cercariae. Immunization of BALB/c mice showed high levels of TNFα, IFNγ, interleukin (IL)-2, IL-6, and IL-4 in splenocyte supernatant culture and also high levels of serum specific anti-rFh15 IgG, IgG1, IgG2a IgE and IgM antibodies suggesting a mixed Th1/Th2 immune response. Using this approach, high levels of protection against experimental challenge with S. bovis cercariae were observed in the mouse and hamster models. A marked reduction up to 64% in worm burden, as well as in the number of eggs retained in liver (66%) and intestine (77%) and hepatic lesions (42%), was achieved in vaccinated BALB/c mice. Golden hamsters vaccinated and challenged in similar conditions had reductions in recovered worms (83%), liver eggs (90%), intestine eggs (96%), liver lesions (56%) and worm fecundity (48-80%). These data suggest that formulation of rFh15 in the ADAD vaccination system using the AA0029 immunomodulator could be a good option to drive an effective immunological response against schistosomiasis.

Isolation, enrichment and primary characterisation of vitelline cells from Schistosoma mansoni obtained by the organ isolation method

In the emerging era of post-genomic research on schistosomes, new methods are required to functionally analyse genes of interest in more detail. Among other tools, schistosome cell lines are needed to overcome present research constraints. Based on a recently established organ isolation protocol for adult Schistosoma mansoni, we report here on the successful enrichment of vitellarium tissue and isolation of vitelline cells. Morphological analyses performed by bright field, fluorescence, scanning and transmission electron microscopy showed typical features of S1 to S4 stage vitelline cells. In addition, molecular analyses using reverse transcription-PCR confirmed the identity of vitelline cells. Cytological and physiological studies included staining experiments with viability dyes and a neutral lipid stain, as well as calcium (Ca2+) imaging. Together they demonstrated cell viability, the possibility to define the differentiation stage of individual vitelline cells, and the suitability to investigate Ca(2+)-associated processes herein. Finally, fluorescence-activated cell sorting was shown to be a convenient way to separate and enrich S1 to S4 stage vitelline cells. In summary, these results demonstrate the expedience of the organ isolation protocol to obtain vitellarium tissue. Importantly, the protocol allows vitelline cells representing defined differentiation stages to be purified, which can be cultured in vitro and used to investigate diverse aspects of schistosome reproductive biology in the post-genomic era.

Re-positioning protein-kinase inhibitors against schistosomiasis

For decades, Praziquantel (PZQ) is the drug of choice against one of the most afflicting helminthic diseases worldwide, schistosomiasis. With respect to the fear of upcoming PZQ resistance, efforts are needed to find new chemotherapeutic options. Protein kinases (PKs) are essential molecules in signaling processes and indispensable to life. Aberrant PK functions take distinctive roles in human diseases and represent targets in chemotherapies. In schistosomes, conserved PKs were found to possess similar pivotal roles contributing not only to reproduction processes, but also to the pathology of schistosomiasis, which is closely associated to egg production. Exploiting the similarity of PKs of humans and schistosomes, PK inhibitors designed to treat human diseases may serve as lead compounds for new drugs against schistosomiasis.

Targeting kinases in Plasmodium and Schistosoma: Same goals, different challenges

With respect to parasite-induced infectious diseases of worldwide importance, members of the genera Plasmodium and Schistosoma are top pathogens. Nearly half a billion people suffer from malaria caused by Plasmodium spp. and schistosomiasis (bilharzia) induced by Schistosoma spp. Resistance against essentially all drugs used for malaria treatment has been reported. For schistosomiasis justified fear of upcoming resistance is discussed against the background of only one widely used drug for treatment. Research of the recent decade has demonstrated that essential steps of the biology of these and other parasites are controlled by kinases, which represent attractive targets for new-generation antiparasitic compounds. This article is part of a Special Issue entitled: Inhibitors of Protein Kinases.

Serum albumin and α-1 acid glycoprotein impede the killing of Schistosoma mansoni by the tyrosine kinase inhibitor Imatinib

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The Abl tyrosine-kinase inhibitor Imatinib is toxic to S. mansoni in vitro but not in vivo in rodents.

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Blood components like serum albumin and alpha-1 acid glycoprotein (AGP) negated Imatinib’s toxicity in vitro.

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Erythromycin partially restored the toxicity of Imatinib in vitro.

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High levels of AGP upon infection make rodents poor models for examining some small molecule inhibitors.

In the search for new drugs and drug targets to treat the flatworm disease schistosomiasis, protein kinases (PKs) have come under particular scrutiny because of their essential roles in developmental and physiological processes in schistosome parasites. In this context the application of the anti-cancer Abl tyrosine kinase (TK) inhibitor Imatinib (Gleevec/Glivec; STI-571) to adult Schistosoma mansoni in vitro has indicated negative effects on diverse physiological processes including survival.

Motivated by these in vitro findings, we performed in vivo experiments in rodent models of S. mansoni infection. Unexpectedly, Imatinib had no effect on worm burden or egg-production. We found that the blood components serum albumin (SA) and alpha-1 acid glycoprotein (AGP or orosomucoid) negated Imatinib’s deleterious effects on adult S. mansoni and schistosomula (post-infective larvae) in vitro. This negative effect was partially reversed by erythromycin. AGP synthesis can increase as a consequence of inflammatory processes or infection; in addition upon infection AGP levels are 6–8 times higher in mice compared to humans. Therefore, mice and probably other rodents are poor infection models for measuring the effects of Imatinib in vivo. Accordingly, we suggest the routine evaluation of the ability of AGP and SA to block in vitro anti-schistosomal effects of small molecules like Imatinib prior to laborious and expensive animal experiments.

Imatinib treatment causes substantial transcriptional changes in adult Schistosoma mansoni in vitro exhibiting pleiotropic effects

BACKGROUND

Schistosome parasites cause schistosomiasis, one of the most important infectious diseases worldwide. For decades Praziquantel (PZQ) is the only drug widely used for controlling schistosomiasis. The absence of a vaccine and fear of PZQ resistance have motivated the search for alternatives. Studies on protein kinases (PKs) demonstrated their importance for diverse physiological processes in schistosomes. Among others two Abl tyrosine kinases, SmAbl1 and SmAbl2, were identified in Schistosoma mansoni and shown to be transcribed in the gonads and the gastrodermis. SmAbl1 activity was blocked by Imatinib, a known Abl-TK inhibitor used in human cancer therapy (Gleevec/Glivec). Imatinib exhibited dramatic effects on the morphology and physiology of adult schistosomes in vitro causing the death of the parasites.

METHODOLOGY/PRINCIPAL FINDINGS

Here we show modeling data supporting the targeting of SmAbl1/2 by Imatinib. A biochemical assay confirmed that SmAbl2 activity is also inhibited by Imatinib. Microarray analyses and qRT-PCR experiments were done to unravel transcriptional processes influenced by Imatinib in adult schistosomes in vitro demonstrating a wide influence on worm physiology. Surface-, muscle-, gut and gonad-associated processes were affected as evidenced by the differential transcription of e.g. the gynecophoral canal protein gene GCP, paramyosin, titin, hemoglobinase, and cathepsins. Furthermore, transcript levels of VAL-7 and egg formation-associated genes such as tyrosinase 1, p14, and fs800-like were affected as well as those of signaling genes including a ribosomal protein S6 kinase and a glutamate receptor. Finally, a comparative in silico analysis of the obtained microarray data sets and previous data analyzing the effect of a TGFβR1 inhibitor on transcription provided first evidence for an association of TGFβ and Abl kinase signaling. Among others GCP and egg formation-associated genes were identified as common targets.

CONCLUSIONS/SIGNIFICANCE

The data affirm broad negative effects of Imatinib on worm physiology substantiating the role of PKs as interesting targets.

The Schistosoma japonicum self-cure phenomenon in water buffaloes: potential impact on the control and elimination of schistosomiasis in China

Schistosomiasis japonica, caused by Schistosoma japonicum, is an important zoonotic disease in China, the Philippines and small pockets of Indonesia. In addition to infecting people, S. japonicum can infect over 40 species of wild and domestic animals which have varying impacts on human infection. It is now generally accepted that bovines, particularly water buffaloes, are the major reservoir for human infection in China as they are naturally infected with schistosomes and deposit more eggs into the environment than humans or any other animal host. This complicates control efforts and the economic burden associated with schistosomiasis morbidity and mortality has taken its toll on both human and livestock populations. Over the last 50years, the schistosomiasis control program in China has made great strides in reducing prevalence and morbidity, and the Chinese authorities now aim to eliminate the disease nationwide in the next decade. Current Chinese control strategies place particular importance on interventions targeting bovines including: praziquantel treatment, barrier farming to prevent grazing in transmission areas, their replacement with mechanized tractors and possible bovine vaccination. A number of studies have shown that in the period following S. japonicum infection, the worm burden drops sharply in water buffaloes and some other animal hosts such as pigs. This is due to a self-cure phenomenon whereby there is parasite clearance by both immune and non-immune factors. Here we review studies investigating the self-cure effect, paying particular attention to S. japonicum infection in water buffaloes, and discuss its potential impact on the future schistosomiasis control and elimination efforts in China. Further understanding of the mechanism of self-cure in water buffaloes could be important for future schistosome vaccine design and delivery.

Diagnosis of cattle diseases endemic to sub-Saharan Africa: evaluating a low cost decision support tool in use by veterinary personnel

BACKGROUND

Diagnosis is key to control and prevention of livestock diseases. In areas of sub-Saharan Africa where private practitioners rarely replace Government veterinary services reduced in effectiveness by structural adjustment programmes, those who remain lack resources for diagnosis and might benefit from decision support.

METHODOLOGY/PRINCIPAL FINDINGS

We evaluated whether a low-cost diagnostic decision support tool would lead to changes in clinical diagnostic practice by fifteen veterinary and animal health officers undertaking primary animal healthcare in Uganda. The eight diseases covered by the tool included 98% of all bovine diagnoses made before or after its introduction. It may therefore inform proportional morbidity in the area; breed, age and geographic location effects were consistent with current epidemiological understanding. Trypanosomosis, theileriosis, anaplasmosis, and parasitic gastroenteritis were the most common conditions among 713 bovine clinical cases diagnosed prior to introduction of the tool. Thereafter, in 747 bovine clinical cases estimated proportional morbidity of fasciolosis doubled, while theileriosis and parasitic gastroenteritis were diagnosed less commonly and the average number of clinical signs increased from 3.5 to 4.9 per case, with 28% of cases reporting six or more signs compared to 3% beforehand. Anaemia/pallor, weakness and staring coat contributed most to this increase, approximately doubling in number and were recorded in over half of all cases. Finally, although lack of a gold standard hindered objective assessment of whether the tool improved the reliability of diagnosis, informative concordance and misclassification matrices yielded useful insights into its role in the diagnostic process.

CONCLUSIONS/SIGNIFICANCE

The diagnostic decision support tool covered the majority of diagnoses made before or after its introduction, leading to a significant increase in the number of clinical signs recorded, suggesting this as a key beneficial consequence of its use. It may also inform approximate proportional morbidity and represent a useful epidemiological tool in poorly resourced areas.

Cloning and characterization of a plasminogen-binding surface-associated enolase from Schistosoma bovis

Schistosoma bovis is a ruminant parasite able to survive prolonged periods in the vasculature of its host without either being cleared by the host defensive systems or inducing thrombotic or coagulation disturbances. This suggests that the parasite modulates both the immune and haemostatic host responses. Previous studies have shown that host plasminogen binds to the surface of S. bovis adult worms, and that a tegument extract from S. bovis fixes and activates host plasminogen, generating plasmin, which in turn could both inhibit blood clotting and dissolve clots. Enolase has been identified among the tegumental proteins that bind plasminogen. The aim of the present study is to determine the physiological role of the enolase found in the tegument of S. bovis adult worms as regards plasminogen-binding and activation, and to confirm its surface exposure on the parasite. The study included the cloning and sequencing of S. bovis enolase cDNA, collection of the corresponding recombinant protein and evaluation of its plasminogen-binding and activation activity, and an exploration of the expression and localization of native enolase in adult worms and lung schistosomulae. Here we show that S. bovis male adult worms express enolase on their tegumental surface and that this protein binds host plasminogen and increases its activation in the presence of host tissue plasminogen activator (t-PA). This suggests that the surface-associated enolase found here is a physiological receptor of plasminogen that plays a role in the activation of the host fibrinolytic system, most probably to avoid blood clot formation on the worm's surface.

Rapid diagnostic multiplex PCR (RD-PCR) to discriminate Schistosoma haematobium and S. bovis

Schistosoma haematobium and S. bovis are widespread schistosome species causing human and cattle schistosomiasis, respectively, in Africa. The sympatric occurrence of these two species and their ability to infect the same Bulinus intermediate snail hosts necessitates precise methods of identification of the larval stages. A rapid diagnostic 'mulitplex' one-step polymerase chain reaction protocol (RD-PCR) was developed using cytochrome oxidase subunit 1 (COX1) mitochondrial DNA (mtDNA) to discriminate between S. haematobium and S. bovis. A single forward primer and two species-specific reverse primers were used to produce a polymerase chain reaction (PCR) fragment of 306 bp and 543 bp for S. bovis and S. haematobium, respectively. Serial dilutions were carried out on various lifecycle stages and species combinations to test the sensitivity and specificity of the primers. This RD-PCR proved highly sensitive, detecting a single larval stage and as little as 0.78 ng of genomic DNA (gDNA) from an adult schistosome, providing a cost-effective, rapid and robust molecular tool for high-throughput screening of S. haematobium and S. bovis populations. In areas where human and cattle schistosomiasis overlap and are transmitted in close proximity, this mitochondrial assay will be a valuable identification tool for epidemiological studies, especially when used in conjunction with other nuclear diagnostic markers.

Proteomic analysis of the tegument and excretory-secretory products of adult Schistosoma bovis worms

Schistosoma bovis is a ruminant pathogen that is poorly known at a molecular level. With an aim of identifying the parasite proteins involved in host-parasite interplay, we studied two protein extracts that contain, respectively, the proteins excreted/secreted by the adult worm (ES) and the tegumental proteins exposed to the host (TG). The 2-DE, 2-D immunoblot and MS were employed to separate and identify the antigenic proteins and the most abundant non-antigenic proteins in each extract. There were some 400 and 600 spots detected in the ES and the TG extracts, respectively. Ninety-six spots were subjected to MS analysis and 64 of them were identified. Overall, we identified 18 S. bovis proteins located at the host-parasite interface, 16 of which have not been identified previously in this parasite, and one of which -lysozyme- has never been reported in a Schistosoma species. Of the proteins identified, at least 4 can counteract host defence mechanisms. The other proteins are also likely to play some role in the host-parasite relationships. Therefore, studies in grater depth on all these proteins will provide a better understanding of how this parasite interacts with its host and new strategies for anti-schistosome drug or vaccine design.

Carbohydrate profiling and protein identification of tegumental and excreted/secreted glycoproteins of adult Schistosoma bovis worms

Schistosoma bovis is a parasite of wild and domestic ruminants that is broadly distributed throughout many tropical and temperate regions of the old world. S. bovis causes severe health problems and significant economic losses in livestock, but in contrast to human schistosomes, S. bovis has been little investigated at a molecular level. Since schistosome glycans and glycoproteins can play important roles in the host-parasite interplay, the aims of the present work were: (i) to characterize the glycans expressed by adult S. bovis worms on their excreted/secreted (ES) and tegumental (TG) glycoproteins and (ii) to identify their carrier protein backbones by mass spectrometry. Using a panel of lectins and monoclonal and polyclonal anti-glycan antibodies, we observed: (i) the absence of sialic acid in S. bovis; (ii) the presence of complex-type N-glycans and LDN antennae on ES glycoproteins; (iii) the presence of glycans containing the Fucalpha1-2Galbeta motif in many TG glycoproteins, and (iv) the presence of glycans containing the Fucalpha1-3GlcNAc motif on many ES and TG glycoproteins but, simultaneously, the absence of the F-LDN(-F) glycans from both the ES and TG glycoproteins. Interestingly, we also found the Lewis(X) and Lewis(Y) antigens co-expressed on several TG isoforms of ATP:guanidino kinase and glyceraldehyde-3-phosphate dehydrogenase. Finally, by ELISA we observed the presence of antibodies against Lewis(X), Lewis(Y) and F-LDN(-F) in the sera of sheep experimentally infected with S. bovis.

Vaccines against the zoonotic trematodesSchistosoma japonicum,Fasciola hepaticaandFasciola gigantica

Schistosoma japonicum,Fasciola hepaticaandF. giganticaare digenetic trematodes and, therefore, possess similar life cycles. While schistosomiasis japonica has for a long time been recognised as a major disease of both humans and animals, infection with fasciolids has only been considered of relevance to animals. However, a number of recent reports indicate that fasciolosis is becoming a serious public health problem, especially in South America, Egypt and Iran (sporadic cases are also on the increase throughout Europe). Vaccines targeted at animals could play an important role in controlling these three diseases in animals and, by blocking transmission of infection, have a concurrent beneficial effect on disease in humans. Approaches towards identifying and producing vaccines against these parasites are similar and are discussed in this reveiw.

Schistosoma bovis: plasminogen binding in adults and the identification of plasminogen-binding proteins from the worm tegument

Schistosoma bovis is a ruminant haematic parasite that lives for years in the mesenteric vessels of the host. The aim of this work was to investigate the ability of adult S. bovis worms to interact with plasminogen, a central component in the host fibrinolytic system. Confocal microscopy analysis revealed that plasminogen bound to the tegument surface of the male-but not female-S. bovis worms and that this binding was strongly dependent on lysine residues. It was also observed that a protein extract of the worm tegument (TG) had the capacity to generate plasmin and to enhance the plasmin generation by the tissue-type plasminogen activator. Proteomic analysis of the TG extract identified 10 plasminogen-binding proteins, among which the major ones were enolase, glyceraldehyde-3-phosphate dehydrogenase and actin. This study represents the first report about the binding of plasminogen to Schistosoma sp. proteins.

A low cost decision support tool for the diagnosis of endemic bovine infectious diseases in the mixed crop-livestock production system of sub-Saharan Africa

Diagnosis and treatment of endemic infectious disease is crucial for productivity of cattle in rural sub-Saharan Africa, but shortages of trained veterinary professionals necessitate support for less well-trained cadres of animal health worker. A Delphi survey of veterinary experts provided quantitative information on key clinical signs associated with eight endemic bovine diseases, then heuristics and dendrogram analysis identified a reduced sign set to be incorporated in a diagnostic decision support tool implemented as a simple colour-banded card. One hundred and seventy disease-sign questionnaire returns were obtained from 32 veterinary research scientists and 14 veterinary practitioners. Preliminary validation of the decision support tool for 16 prototypical cases resulted in 'correct' diagnosis over 90% of the time. The card potentially serves as a training aid and aide-mémoire, and could improve the diagnostic competence of animal healthcare providers.

Prospects for development of a transmission blocking vaccine against Schistosoma japonicum

Despite intensive long-term control programmes, schistosomiasis japonica remains a serious public health problem in China and the Philippines. The termination of mass praziquantel-treatment has seen a dramatic recent rebound in both its prevalence and associated morbidity. Schistosomiasis japonica is a zoonosis but, despite complicating control efforts, this feature provides a practical method for attacking Schistosoma japonicum through development and deployment of a transmission blocking veterinary vaccine. A recently completed bovine drug intervention trial and mathematical modelling of the transmission of S. japonicum underpin the concept that such a vaccine, targeting water buffalo, would have major implications for future integrated schistosomiasis control in China. A major block to success is the low ceiling efficacy achieved with current vaccine molecules. To solve this challenge, an antigen discovery pipeline needs to be established for identification of new vaccine targets that induce greater potency than the current anti-S. japonicum candidate vaccines. Excretory-secretory products and molecules exposed on epithelial surfaces (including receptors) which interact directly with the host immune system warrant especial attention. Extensive schistosome genomics programmes currently underway coupled with new advances in proteomics and microarray technology provide an unparalleled opportunity to identify new molecules exploitable as vaccine targets. These will then need to be produced in quantity and rigorously tested first in the laboratory and then the field. If a transmission blocking veterinary vaccine developed for bovines can be put into practice in combination with other control strategies such as human chemotherapy, elimination of S. japonicum from China may be achievable.

Trematodes and snails: an intimate association

Trematode parasites share an intimate relationship with their gastropod intermediate hosts, which act as the vehicle for their development and transmission. They represent an enormous economic and medical burden in developing countries, stimulating much study of snail–trematode interactions. Laboratory-maintained snail–trematode systems and in vitro cell cultures are being used to investigate the molecular dialogue between host and parasite. These dynamic and finely balanced antagonistic relationships, in which parasites strongly influence the physiology of the host, are highly specific and may occasionally demonstrate co-speciation. We consider the mechanisms and responses deployed by trematodes and snails that result in compatibility or rejection of the parasite, and the macroevolutionary implications that they may effect. Although for gastropods the fossil record gives some insight into evolutionary history, elucidation of trematode evolution must rely largely upon molecular approaches, and for both, such techniques have provided fresh and often surprising evidence of their origins and dispersal over time. Co-evolution of snails and trematodes is becoming increasingly apparent at both cellular and population levels; the implications of which are only beginning to be understood for disease control. Untangling the complex interactions of trematodes and snails promise fresh opportunities for intervention to relieve the burden of parasitic disease.

On the longevity of Schistosoma curassoni

It is demonstrated that Schistosoma curassoni, a parasite of sheep, cattle and goats in parts of West Africa, will live for at least 8 years 5 months in a sheep. The sheep was exposed to 500 cercariae of S. curassoni liberated from infected Bulinus wrighti. The sheep died of natural causes, and at post-mortem 28 pairs of adult S. curassoni were removed from the mesenteric and rectal veins. All female worms were gravid, and eggs were hatched from faeces to produce miracidia. The development of immune responses of the host had apparently little or no effect on the viability of the eggs. Histological studies of the liver, small and large intestines revealed mild pathological symptoms. The longevity of S. curassoni is the first record of longevity of schistosomes to be based on worm counts.

The relationship between faecal egg counts, worm burden and tissue egg counts in early Schistosoma mattheei infections in cattle

The relationships between schistosome faecal egg counts (EPG), total tissue egg counts (TEC) and adult female worm burdens (FW) recorded at post-mortem examination of 30 Friesian calves from three different field trials were analysed. The calves in study 1 (n=14) had been exposed to natural Schistosoma mattheei infections for 2 months, those of study 2 (n=9) for between 4 and 12 months, and those in study 3 (n=7) for 8 months. No clinical schistosomiasis was observed in any of the groups, and at perfusion, EPG's varied from 5 to 210, TEC's from 28,800 to 2,439,400 and FW's from 11 to 1218. There was as much variation in EPG, TEC and FW between calves with the same duration of exposure as between calves with different duration of exposure. There were very similar significant positive relationships between log transformed FW and log transformed EPG in all three groups (P<0.007, R2>0.46, slopes 0.957-1.015). There were also significant positive relationships between log transformed FW and log transformed TEC in all three groups (P<0.034, R2>0.45) and between log transformed TEC and log transformed EPG in all three groups (P<0.025, R2>0.48). All three studies had a linear relationship between log transformed FW and log transformed EPG with a slope value close to 1 (P>0.845 for different from one). This indicates that there was no evidence of density dependence in the three studies for the relationship between FW and EPG. In contrast, there was no consistent relationship (in terms of slope) between either log transformed TEC and log transformed FW in the three studies (after correcting for differential duration of exposure), or log transformed TEC and log transformed EPG. For all three sets of comparisons the predictability of one parameter based on another was poor for a single sample.

Recent studies on the reproductive biology of the schistosomes and their relevance to speciation in the Digenea

The members of the family Schistosomatidae, dioecious Digenea, are discussed with regard to their distribution, intermediate and definitive host-parasite relationships. The biological species concept is considered together with the difficulties of its application to Schistosoma spp. and the Digenea. The correlation between pairing of adult schistosomes, physical and sexual development and the maintenance of reproductive potential is emphasised. Development of the female reproductive system does not depend upon species-specific pairing. In some combinations, e.g., Schistosoma haematobium/Schistosoma intercalatum and Schistosoma bovis/Schistosoma curassoni, a specific mate choice system apparently does not exist, whereas it does in other combinations, e.g., Schistosoma mansoni/Schistosoma intercalatum. In mixed infections change of mate may occur and when the opportunity arises heterospecific pairs of worms will change partners to conspecific pairs. Interspecific pairing in adult schistosomes will lead to either hybridisation or parthenogenesis. Yet the majority of schistosomes that inhabit the same definitive host maintain their genetic identity: specific mate recognition, site selection within the host and heterologous immunity have been suggested as isolating mechanisms. Experimental intraspecific crosses have enabled evaluation of the degree to which some populations separated and became reproductively isolated through pre-mating isolating mechanisms, indicative of incipient speciation, e.g., the Lower Guinea and Zaire strains of S. intercalatum. The occurrence and significance of parthenogenesis in schistosomes and other species of Digenea are discussed. The consequences of interspecific mating interactions in schistosomes with regard to parasite epidemiology, interspecific competition and genetic heterogeneity are debated. Geographical isolation and host specificity represent important pre-zygotic isolating mechanisms. It is suggested that site selection within the host and heterologous immunity may both reduce interspecific genetic interchange when digenean parasites utilise the same definitive host.