Immunity to schistosomiasis in animals: an update

A Mathematical Model of the Transmission Dynamics of Bovine Schistosomiasis with Contaminated Environment

Schistosomiasis, a vector-borne chronically debilitating infectious disease, is a serious public health concern for humans and animals in the affected tropical and sub-tropical regions. We formulate and theoretically analyze a deterministic mathematical model with snail and bovine hosts. The basic reproduction number [Formula: see text] is computed and used to investigate the local stability of the model's steady states. Global stability of the endemic equilibrium is carried out by constructing a suitable Lyapunov function. Sensitivity analysis shows that the basic reproduction number is most sensitive to the model parameters related to the contaminated environment, namely: shedding rate of cercariae by snails, cercariae to miracidia survival probability, snails-miracidia effective contact rate and natural death rate of miracidia and cercariae. Numerical results show that when no intervention measures are implemented, there is an increase of the infected classes, and a rapid decline of the number of susceptible and exposed bovines and snails. Effects of the variation of some of the key sensitive model parameters on the schistosomiasis dynamics as well as on the initial disease transmission threshold parameter [Formula: see text] are graphically depicted.

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.

Molecular epidemiology and pathology of spirorchiid infection in green sea turtles (Chelonia mydas)

Spirorchiid blood fluke infections affect endangered turtle populations globally, and are reported as a common cause of mortality in Queensland green sea turtles. Both the flukes and their ova are pathogenic and can contribute to the stranding or death of their host. Of particular interest are ova-associated brain lesions, which have been associated with host neurological deficits. Accurate estimations of disease frequency and the relative effect of infection relating to different spirorchiid species are made difficult by challenges in morphological identification of adults of some genera, and a lack of species-level identifying features for ova. A new specifically designed molecular assay was used to detect and identify cryptic spirorchiids and their ova in Queensland green sea turtle tissues collected from 2011 to 2014 in order to investigate epidemiology, tissue tropisms and pathology. Eight spirorchiid genotypes were detected in 14 distinct tissues, including multiple tissues for each. We found no evidence of a characteristic pathway of the eggs to the exterior; instead the results suggest that a high proportion of eggs become lost in dead-end tissues. The most common lesions observed were granulomas affecting most organs with varying severity, followed by arteritis and thrombi in the great vessels. The number of spirorchiid types detected increased with the presence and severity of granulomatous lesions. However, compared with other organs the brain showed relatively low levels of spirorchiid diversity. An inverse relationship between host age and spirorchiid diversity was evident for the liver and kidneys, but no such relationship was evident for other organs. Molecular data in this study, the first of its kind, provides the first species-level examination of spirorchiid ova and associated pathology, and paves the way for the future development of targeted ante-mortem diagnosis of spirorchiidiasis.

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First species-level molecular study of spirorchiidiasis.

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Eight genotypes detected across fourteen tissue types.

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Species investigated in terms of tissue tropisms and pathology.

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Granulomas and arteritis/thrombosis most common lesions.

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Number of species present correlated with presence and severity of lesions.

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.

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.

A Fasciola hepatica-derived fatty acid binding protein induces protection against schistosomiasis caused by Schistosoma bovis using the adjuvant adaptation (ADAD) vaccination system

Several efforts have been made to identify anti-schistosomiasis vaccine candidates and new vaccination systems. The fatty acid binding protein (FAPB) has been shown to induce a high level of protection in trematode infection. The adjuvant adaptation (ADAD) vaccination system was used in this study, including recombinant FABP, a natural immunomodulator and saponins. Mice immunised with the ADAD system were able to up-regulate proinflammatory cytokines (IL-1 and IL-6) and induce high IgG2a levels. Moreover, there was a significant reduction in worm burden, egg liver and hepatic lesion in vaccinated mice in two independent experiments involving Schistosoma bovis infected mice. The foregoing data shows that ADAD system using FABP provide a good alternative for triggering an effective immune response against animal schistosomiasis.

Trematode infections in cattle in Arumeru District, Tanzania are associated with irrigation

BACKGROUND

The relationship between the environment and infection of cattle with trematodes was studied at Arumeru District, Arusha Region, northern Tanzania. Randomly selected villages were grouped into three cattle management strata, (i) zero-grazing (ZZ) (ii) communal grazing without irrigation (ZC) and (iii) communal grazing with irrigation (ZCI).

METHODS

Faecal samples were collected from 241 cattle, and processed using the Flukefinder method. Snail intermediate hosts were collected with a snail scoop from the water bodies in the study villages and identified morphologically.

RESULTS

The overall prevalence of F. gigantica, paramphistomes and S. bovis were 33%, 37% and 2% respectively. Prevalence for F. gigantica, paramphistomes, and S. bovis for each stratum were, zero-grazing (ZZ) (29.7%, 36.0% and 0%), communal grazing without irrigation (ZC) (6.3%, 15.0% and 3.8%) and communal grazing with irrigation (ZCI) (57.7%, 56.7% and 1.0%) respectively. The differences between strata were significant for F. gigantica (p < 0.001) and paramphistomes (p < 0.05) but not for S. bovis. Irrigation could account for the high prevalence of F. gigantica and paramphistomes in the ZCI stratum as compared to the ZZ and ZC strata. The higher prevalences of F. gigantica and paramphistomes in the ZZ stratum compared with the ZC stratum were unexpected and attributed to the practice of farmers in some ZZ stratum villages buying fodder for their cattle obtained from pastures in ZCI villages.

CONCLUSION

Trematode infections in cattle are prevalent in Arumeru District. Fasciola gigantica and paramphistomes are associated with grazing in areas with irrigation of crops. Zero-grazing of cattle does not necessarily prevent the risk of infection.

The Worm Turns

A reductionist approach to the study of infection does not lend itself to an appraisal of the interactions that occur between 2 or more organisms that infect a host simultaneously. In reality, hosts are subject to multiple simultaneous influences from multiple pathogens along the spectrum from symbiotic microflora to virulent pathogen. In this review, we draw from our own work on Fasciola hepatica and that of others studying helminth co-infection to give examples of how such interactions can influence not only the outcome of infection but also its diagnosis and control. The new tools of systems biology, including both the “omics” approaches and mathematical biology, have significant promise in unraveling the as yet largely unexplored complexities of co-infection.

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.

Molecular and functional characterization of a Schistosoma bovis annexin: fibrinolytic and anticoagulant activity

Annexins belong to an evolutionarily conserved multigene family of proteins expressed throughout the animal and plant kingdoms. Although they are soluble cytosolic proteins that lack signal sequences, they have also been detected in extracellular fluids and have been associated with cell surface membranes, where they could be involved in anti-haemostatic and anti-inflammatory functions. Schistosome annexins have been identified on the parasite's tegument surface and excretory/secretory products, but their functions are still unknown. Here we report the cloning, sequencing, in silico analysis, and functional characterization of a Schistosoma bovis annexin. The predicted protein has typical annexin secondary and tertiary structures. Bioassays with the recombinant protein revealed that the protein is biologically active in vitro, showing fibrinolytic and anticoagulant properties. Finally, the expression of the native protein on the tegument surface of S. bovis schistosomula and adult worms is demonstrated, revealing the possibility of exposure to the host's immune system and thus offering a potential vaccine target for the control of schistosomiasis in ruminants.

Screening trematodes for novel intervention targets: a proteomic and immunological comparison of Schistosoma haematobium, Schistosoma bovis and Echinostoma caproni

With the current paucity of vaccine targets for parasitic diseases, particularly those in childhood, the aim of this study was to compare protein expression and immune cross-reactivity between the trematodes Schistosoma haematobium, S. bovis and Echinostoma caproni in the hope of identifying novel intervention targets. Native adult parasite proteins were separated by 2-dimensional gel electrophoresis and identified through electrospray ionisation tandem mass spectrometry to produce a reference gel. Proteins from differential gel electrophoresis analyses of the three parasite proteomes were compared and screened against sera from hamsters infected with S. haematobium and E. caproni following 2-dimensional Western blotting. Differential protein expression between the three species was observed with circa 5% of proteins from S. haematobium showing expression up-regulation compared to the other two species. There was 91% similarity between the proteomes of the two Schistosoma species and 81% and 78·6% similarity between S. haematobium and S. bovis versus E. caproni, respectively. Although there were some common cross-species antigens, species-species targets were revealed which, despite evolutionary homology, could be due to phenotypic plasticity arising from different host-parasite relationships. Nevertheless, this approach helps to identify novel intervention targets which could be used as broad-spectrum candidates for future use in human and veterinary vaccines.

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.

Schistosomicidal activity of the antimalarial drug, mefloquine, in Schistosoma mansoni-infected mice

Therapeutic effects of racemic mefloquine were assessed in Schistosoma mansoni-infected mice, and evaluated by recording worm burden, the status of egg maturation and viability, and intestinal mast cell recruitment. Age-matched mice were divided into four groups, of which two were infected. At 8 weeks postinfection, one group of infected and one group of uninfected mice were treated with a single dose of mefloquine (150 mg/kg). Ten days after treatment, all animals were killed. Mefloquine at 150 mg/kg had no effect on worm burden, but significantly reduced the number of eggs in the first three developmental egg stages. Analysis of intestinal mast cell numbers showed that mefloquine induced mastocytosis both in infected and control animals. In conclusion, mefloquine significantly reduces egg production in S. mansoni-infected mice, suggesting a therapeutic potency in schistosomiasis therapy. Mefloquine also exerts a significant proinflammatory effect on the intestine. Through its effect on egg production, mefloquine may be a cause of silent schistosomiasis in travelers using mefloquine for malaria chemoprophylaxis. Further study of the anti-schistosomal activity of mefloquine is warranted, as its activity against other helminths.

Artemisinins and synthetic trioxolanes in the treatment of helminth infections

PURPOSE OF REVIEW

Helminthiases, including schistosomiasis and food-borne trematodiasis, affect millions of people. Just a few drugs are used for the treatment and control of these diseases. We review recent in-vitro and in-vivo observations with the artemisinins and synthetic trioxolanes against major trematode infections, update clinical findings, and discuss the potential impact that artemisinin-based combination therapy might have on trematode infections in settings where malaria and helminthiases are co-endemic.

RECENT FINDINGS

The artemisinins and synthetic trioxolanes possess a broad spectrum of activity against trematodes. High worm-burden reductions were obtained with these drugs in rodents with acute or chronic infections of Schistosoma japonicum, S. mansoni, Clonorchis sinensis, Fasciola hepatica and Opisthorchis viverrini. Clinical trials carried out in Africa, utilizing artemether or artesunate singly or as artemisinin-based combination therapies, following recommended malaria treatment schedules, found an effect against schistosomiasis.

SUMMARY

Artemisinin-based combination therapies are increasingly deployed against malaria, and hence there is a need to assess the potential auxiliary effects against schistosomiasis in settings where both diseases are endemic. Also, the effect of artemisinin-based combination therapies on food-borne trematodiasis should be assessed. In-vitro and in-vivo findings with the synthetic trioxolanes provide data to launch preclinical investigations.

Neutral N-glycan patterns of the gastropods Limax maximus, Cepaea hortensis, Planorbarius corneus, Arianta arbustorum and Achatina fulica

The N-glycosylation potentials of Limax maximus, Cepaea hortensis, Planorbarius corneus, Arianta arbustorum and Achatina fulica were analysed by investigation of the N-glycan structures of the skin and viscera glycoproteins by a combination of HPLC and mass-spectrometry methods. It is one of the first steps to enlarge the knowledge on the glycosylation abilities of gastropods, which may help to establish new cell culture systems, to uncover new means for pest control for some species, and to identify carbohydrate-epitopes which may be relevant for immune response. All snails analysed contained mainly oligomannosidic and small paucimannosidic structures, often terminated with 3-O-methylated mannoses. The truncated structures carried modifications by beta1-2-linked xylose to the beta-mannose residue, and/or an alpha-fucosylation, mainly alpha1,6-linked to the innermost N-acetylglucosaminyl residue of the core. Many of these structures were missing the terminal N-acetylglucosamine, which has been shown to be a prerequisite for processing to complex N-glycans in the Golgi. In some species (Planorbarius corneus and Achatina fulica) traces of large structures, terminated by 3-O-methylated galactoses and carrying xylose and/or fucose residues, were also detected. In Planorbarius viscera low amounts of terminal alpha1-2-fucosylation were determined. Combining these results, gastropods seem to be capable to produce all kinds of structures ranging from those typical in mammals through to structures similar to those found in plants, insects or nematodes. The detailed knowledge of this very complex glycosylation system of the gastropods will be a valuable tool to understand the principle rules of glycosylation in all organisms.

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.