Further evaluation of the synthetic peptide vaccine S3Pvac againstTaenia soliumcysticercosis in pigs in an endemic town of Mexico

Research Progress on the Development of Porcine Reproductive and Respiratory Syndrome Vaccines

Porcine reproductive and respiratory syndrome (PRRS) is a highly contagious disease in the pig industry, but its pathogenesis is not yet fully understood. The disease is caused by the PRRS virus (PRRSV), which primarily infects porcine alveolar macrophages and disrupts the immune system. Unfortunately, there is no specific drug to cure PRRS, so vaccination is crucial for controlling the disease. There are various types of single and combined vaccines available, including live, inactivated, subunit, DNA, and vector vaccines. Among them, live vaccines provide better protection, but cross-protection is weak. Inactivated vaccines are safe but have poor immune efficacy. Subunit vaccines can be used in the third trimester of pregnancy, and DNA vaccines can enhance the protective effect of live vaccines. However, vector vaccines only confer partial protection and have not been widely used in practice. A PRRS vaccine that meets new-generation international standards is still needed. This manuscript provides a comprehensive review of the advantages, disadvantages, and applicability of live-attenuated, inactivated, subunit, live vector, DNA, gene-deletion, synthetic peptide, virus-like particle, and other types of vaccines for the prevention and control of PRRS. The aim is to provide a theoretical basis for vaccine research and development.

Improvement of cell suspension cultures of transformed and untransformed Carica papaya cell lines, towards the development of an antiparasitic product against the gastrointestinal nematode Haemonchus contortus

Parasitic diseases have a major impact on human and animal health worldwide. Despite the availability of effective anti-parasitic drugs, their excessive and uncontrolled use has promoted the emergence of drug resistance, severely affecting ecosystems and human health. Thus, developing environmentally friendly antiparasitic treatments is urgently needed. Carica papaya has shown promising effects against infectious diseases. C. papaya embryogenic calluses were genetically modified by our research team to insert immunogenic peptides with the goal of developing an oral anti-cysticercosis vaccine. Among these callus cell lines, one labeled as CF-23, which expresses the KETc7 immunogenic peptide, induced the highest protection levels against experimental cysticercosis. In the process of designing a natural antiparasitic product based on C. papaya that simultaneously induced immunity against cysticercosis, both transformed (SF-23) and untransformed (SF-WT) suspension cultures were produced and optimized. Our results showed a better duplication time (td) for SF-23 (6.9 days) than SF-WT (13.02 days); thus, the SF-23 line was selected for scale-up in a 2-L airlift bioreactor, reaching a td of 4.4 days. This is the first time that a transgenic line of C. papaya has been grown in an airlift bioreactor, highlighting its potential for scale-up cultivation in this type of reactor. Considering the previously reported nematocidal activity of C. papaya tissues, their activity against the nematode Haemonchus contortus of aqueous extracts of SF-WT and SF-23 was explored in this study, with promising results. The information herein reported will allow us to continue the cultivation of the transgenic cell suspension line of C. papaya under reproducible conditions, to develop a new anti-parasitic product.

Neurocysticercosis control for primary epilepsy prevention: a systematic review

Neurocysticercosis (NCC) is a leading cause of preventable epilepsy in lower- and upper- middle-income countries (LMICs/UMICs). NCC is a human-to-human transmitted disease caused by ingestion of Taenia solium eggs from a Taenia carrier. T. solium infection control is the key to reduce NCC incidence. This systematic review aims to identify T. solium control programs that can provide frameworks for endemic areas to prevent NCC-related epilepsy. A systematic search was conducted in PubMed/Medline, Embase, Web of Science, and Cochrane Library databases in March 2021. After title and abstract review, full texts were screened for qualitative analysis. Additional articles were identified via citation search. Of 1322 total results, 34 unique studies were included. Six major intervention types were identified: national policy (8.8%), community sanitation improvement (8.8%), health education (8.8%), mass drug administration (29.4%), pig vaccination and treatment (32.4%), and combined human and pig treatment (11.8%). Overall, 28 (82.4%) studies reported decreased cysticercosis prevalence following the intervention. Only health education and combined human and pig treatment were effective in all selected studies. NCC causes preventable epilepsy in LMICs/UMICs and its incidence can be reduced through T. solium control. Most interventions that disrupt the T. solium transmission cycle are effective. Long-term sustained results require comprehensive programs, ongoing surveillance, and collaborative effort among multisectoral agencies.

A qualitative assessment of the context and enabling environment for the control of Taenia solium infections in endemic settings

BACKGROUND

Taenia solium (T. solium), is a zoonotic helminth causing three diseases namely; taeniasis (in humans), neurocysticercosis (NCC, in humans) and porcine cysticercosis (PCC, in pigs) and is one of the major foodborne diseases by burden. The success or failure of control options against this parasite in terms of reduced prevalence or incidence of the diseases may be attributed to the contextual factors which underpin the design, implementation, and evaluation of control programmes.

METHODOLOGY/PRINCIPAL FINDINGS

The study used a mixed method approach combining systematic literature review (SLR) and key informant interviews (KII). The SLR focused on studies which implemented T. solium control programmes and was used to identify the contextual factors and enabling environment relevant to successful inception, planning and implementation of the interventions. The SLR used a protocol pre-registered at the International prospective register of systematic reviews (PROSPERO) number CRD42019138107 and followed PRISMA guidelines on reporting of SLR. To further highlight the importance and interlinkage of these contextual factors, KII were conducted with researchers/implementers of the studies included in the SLR. The SLR identified 41 publications that had considerations of the contextual factors. They were grouped into efficacy (10), effectiveness (28) and scale up or implementation (3) research studies. The identified contextual factors included epidemiological, socioeconomic, cultural, geographical and environmental, service and organizational, historical and financial factors. The enabling environment was mainly defined by policy and strategies supporting T. solium control.

CONCLUSION/SIGNIFICANCE

Failure to consider the contextual factors operating in target study sites was shown to later present challenges in project implementation and evaluation that negatively affected expected outcomes. This study highlights the importance of fully considering the various domains of the context and integrating these explicitly into the plan for implementation and evaluation of control programmes. Explicit reporting of these aspects in the resultant publication is also important to guide future work. The contextual factors highlighted in this study may be useful to guide future research and scale up of disease control programmes and demonstrates the importance of close multi-sectoral collaboration in a One Health approach.

Taenia solium taeniasis/cysticercosis: From parasite biology and immunology to diagnosis and control

Infection with the pork tapeworm (Taenia solium) is responsible for a substantial global burden of disease, not only restricted to its impact on human health, but also resulting in a considerable economic burden to smallholder pig farmers due to pig cysticercosis infection. The life-cycle, parasitology and immunology of T. solium are complex, involving pigs (the intermediate host, harbouring the larval metacestode stage), humans (the definitive host, harbouring the adult tapeworm, in addition to acting as accidental intermediate hosts) and the environment (the source of infection with eggs/proglottids). We review the parasitology, immunology, and epidemiology of the infection associated with each of the T. solium life-cycle stages, including the pre-adult/adult tapeworm responsible for human taeniasis; post-oncosphere and cysticercus associated with porcine and human cysticercosis, and the biological characteristics of eggs in the environment. We discuss the burden associated, in endemic settings, with neurocysticercosis (NCC) in humans, and the broader cross-sectoral economic impact associated both with NCC and porcine cysticercosis, the latter impacting food-value chains. Existing tools for diagnostics and control interventions that target different stages of the T. solium transmission cycle are reviewed and their limitations discussed. Currently, no national T. solium control programmes have been established in endemic areas, with further work required to identify optimal strategies according to epidemiological setting. There is increasing evidence suggesting that cross-sectoral interventions which target the parasite in both the human and pig host provide the most effective approaches for achieving control and ultimately elimination. We discuss future avenues for research on T. solium to support the attainment of the goals proposed in the revised World Health Organisation neglected tropical diseases roadmap for 2021-2030 adopted at the 73rd World Health Assembly in November 2020.

Identification and control of sources of Taenia solium infection – the attempts to eradicate the parasite

Taenia solium is a parasite causing porcine cysticercosis and human taeniosis and cysticercosis, parasitic zoonoses with a serious public health and economic influence. It has been globally ranked as the top foodborne parasite by the Food and Agriculture Organisation of the United Nations (FAO) and the World Health Organisation (WHO). This parasite is transmitted mainly in countryside regions where animals are free roaming, having access to human faeces, and infected pork is widely available. More developed countries eliminated cysticercosis; nonetheless, there are insufficient data about the current endemicity status of T. solium, due to increased human migration from endemic areas. Formally submitted statistics on cysticercosis in pigs are extremely inadequate. This is the result of not reporting all cases of the disease by some countries and lack of molecular verification during identification of the parasite. There is a need to develop diagnostic tests with increased sensitivity and specificity. The purpose of the present review is to summarise current knowledge about diagnostic and control methods concerning T. solium infection. The article does not address the diagnostics of human cysticercosis, since there is a distinct medical field which should be discussed separately. The paper focuses mainly on identifying the sources of T. solium infection, presenting the methods to detect and control porcine cysticercosis and taeniosis in humans.

Identification and Control of Sources of Taenia Solium Infection - the Attempts To Eradicate the Parasite

Taenia solium is a parasite causing porcine cysticercosis and human taeniosis and cysticercosis, parasitic zoonoses with a serious public health and economic influence. It has been globally ranked as the top foodborne parasite by the Food and Agriculture Organisation of the United Nations (FAO) and the World Health Organisation (WHO). This parasite is transmitted mainly in countryside regions where animals are free roaming, having access to human faeces, and infected pork is widely available. More developed countries eliminated cysticercosis; nonetheless, there are insufficient data about the current endemicity status of T. solium, due to increased human migration from endemic areas. Formally submitted statistics on cysticercosis in pigs are extremely inadequate. This is the result of not reporting all cases of the disease by some countries and lack of molecular verification during identification of the parasite. There is a need to develop diagnostic tests with increased sensitivity and specificity. The purpose of the present review is to summarise current knowledge about diagnostic and control methods concerning T. solium infection. The article does not address the diagnostics of human cysticercosis, since there is a distinct medical field which should be discussed separately. The paper focuses mainly on identifying the sources of T. solium infection, presenting the methods to detect and control porcine cysticercosis and taeniosis in humans.

Human taeniasis: current insights into prevention and management strategies in endemic countries

Human taeniasis is a zoonotic condition resulting from infection with the adult stages of Taenia saginata ("beef tapeworm"), Taenia solium ("pork tapeworm") or Taenia asiatica ("Asian tapeworm"). Although these parasites have a worldwide distribution, the overwhelming burden is felt by communities in low- and middle-income countries. This is particularly true for T. solium, whereby infection of the central nervous system with the larval stage of the parasite (neurocysticercosis) is a major cause of acquired epilepsy in low-resource settings. With a focus on endemic countries, this review provides an insight into the prevention and management of human taeniasis, concluding with some recent case studies describing their implementation. Discussion of the opportunities and challenges regarding current fecal and serological diagnostic assays for detecting Taenia spp. highlights the importance of accurate and accessible diagnostic options for the field situation. The lack of long-term impact on the parasites' lifecycle from human anthelmintic treatment, coupled with the propensity for adverse reactions, highlights the importance of a "two-pronged" approach that considers the relevant animal hosts, particularly in the case of T. solium. Aside from the therapeutic options, this review reiterates the importance of adequate assessment and consideration of the associated behavioral and policy aspects around sanitation, hygiene and meat inspection that have been shown to support parasite control, and potential elimination, in endemic regions.

Assessing the impact of intervention strategies against Taenia solium cysticercosis using the EPICYST transmission model

BACKGROUND

The pork tapeworm, Taenia solium, and associated human infections, taeniasis, cysticercosis and neurocysticercosis, are serious public health problems, especially in developing countries. The World Health Organization (WHO) has set goals for having a validated strategy for control and elimination of T. solium taeniasis/cysticercosis by 2015 and interventions scaled-up in selected countries by 2020. Timely achievement of these internationally-endorsed targets requires that the relative benefits and effectiveness of potential interventions be explored rigorously within a quantitative framework.

METHODS

A deterministic, compartmental transmission model (EPICYST) was developed to capture the dynamics of the taeniasis/cysticercosis disease system in the human and pig hosts. Cysticercosis prevalence in humans, an outcome of high epidemiological and clinical importance, was explicitly modelled. A next generation matrix approach was used to derive an expression for the basic reproduction number, R 0. A full sensitivity analysis was performed using a methodology based on Latin-hypercube sampling partial rank correlation coefficient index.

RESULTS

EPICYST outputs indicate that chemotherapeutic intervention targeted at humans or pigs would be highly effective at reducing taeniasis and cysticercosis prevalence when applied singly, with annual chemotherapy of humans and pigs resulting, respectively, in 94 and 74% of human cysticercosis cases averted. Improved sanitation, meat inspection and animal husbandry are less effective but are still able to reduce prevalence singly or in combination. The value of R 0 for taeniasis was estimated at 1.4 (95% Credible Interval: 0.5-3.6).

CONCLUSIONS

Human- and pig-targeted drug-focussed interventions appear to be the most efficacious approach from the options currently available. The model presented is a forward step towards developing an informed control and elimination strategy for cysticercosis. Together with its validation against field data, EPICYST will be a valuable tool to help reach the WHO goals and to conduct economic evaluations of interventions in varying epidemiological settings.

Control of Taenia solium taeniasis/cysticercosis: The best way forward for sub-Saharan Africa?

Taenia solium taeniasis/cysticercosis is a neglected parasitic zoonosis with significant economic and public health impacts. Control measures can be broadly grouped into community health education, improvements in hygiene and sanitary conditions, proper meat handling at household and community level, improved standards of meat inspection, pig management, treatment of individual patients and possibly human populations, and treatment and/or vaccination of porcine populations. This manuscript looks critically into currently existing control options and provides suggestions on which (combination of) tools would be most effective in the control of T. solium taeniasis/cysticercosis in sub-Saharan Africa. Field data and disease transmission simulations suggest that implementation of a single intervention control strategy will not lead to a satisfactory reduction of disease morbidity or transmission. A feasible strategy to combat T. solium taeniasis/cysticercosis would include a combination of approaches focussing on both human (health education and treatment) and animal host (management, treatment and vaccination), which can vary for different communities and different geographical locations. Selection of the specific strategy depends on cost-effectiveness analyses based on solid field data, currently unavailable, though urgently needed; as well as on health priorities and resources of the country. A One Health approach involving medical, veterinary, environmental and social sectors is essential for T. solium to be controlled and eventually eliminated. Finally the success of any intervention is largely dependent on the level of societal and political acceptance, commitment and engagement.

Towards the development of an oral vaccine against porcine cysticercosis: expression of the protective HP6/TSOL18 antigen in transgenic carrots cells

The Taenia solium HP6/TSOL18 antigen was produced in carrot cells, yielding an immunogenic protein that induced significant protection in an experimental murine model against T. crassiceps cysticercosis when orally administered. This result supports the potential of HP6/TSOL18-carrot as a low-cost anti-cysticercosis vaccine candidate. Cysticercosis is a zoonosis caused by Taenia solium that can be prevented by interrupting the parasite life cycle through pig vaccination. Several injectable vaccine candidates have been reported, but the logistic difficulties and costs for its application limited its use in nationwide control programs. Oral plant-based vaccines can deal with this limitation, because of their easy administration and low cost. A stable expression of the HP6/TSOL18 anti-T. solium cysticercosis protective antigen in carrot calli transformed with an optimized transgene is herein reported. An antigen accumulation up to 14 µg g(-1) of dry-weight biomass was achieved in the generated carrot lines. Mouse immunization with one of the transformed calli induced both specific IgG and IgA anti-HP6/TSOL18 antibodies. A statistically significant reduction in the expected number of T. crassiceps cysticerci was observed in mice orally immunized with carrot-made HP6/TSOL18, in a similar extent to that obtained by subcutaneous immunization with recombinant HP6/TSOL18 protein. In this study, a new oral plant-made version of the HP6/TSOL18 anti-cysticercosis vaccine is reported. The vaccine candidate should be further tested against porcine cysticercosis.

Taenia solium taeniasis and cysticercosis control and elimination through community-based interventions

Taenia solium was declared potentially eradicable by the International Task Force for Disease Eradication in 1992. Yet, very few well-designed community-based randomized controlled trials have been conducted to measure the effectiveness of alternative control strategies. Most strategies have been tested in pre-post intervention designs in very few communities, often without a control group. The only two community-based randomized controlled trials suggest that an educational program alone or a combination of human and porcine mass treatment reduce porcine cysticercosis in the short term. A transmission dynamics model suggests that improved sanitation and pig management are more effective and sustainable than pig vaccination, human or porcine mass treatment. Current evidence does not support the eradication of Taenia solium in the foreseeable future. Investigators should follow international recommendations on the conduct of community-based randomized control trials to provide more valid estimates of the effect and cost-effectiveness of alternative control strategies for cysticercosis.

Coadministration of protoxin Cry1Ac from Bacillus thuringiensis with metacestode extract confers protective immunity to murine cysticercosis

The Bacillus thuringiensis Cry1Ac protoxin (pCry1Ac) is a promising mucosal immunogen and adjuvant that induces protective immunity against Naegleria fowleri and malaria infection models. We determined whether pCry1Ac acted as a protective adjuvant against infection with Taenia crassiceps. BALB/C mice were thrice i.p. immunized with (i) pCry1Ac, (ii) metacestode extract, (iii) extract + pCry1Ac or (iv) vehicle, challenged with metacestodes on day 26 and then sacrificed 35 days later. Cysticerci in the peritoneal cavity were counted, while the serum antibody response and cytokines were analysed after immunization and during infection. Only immunization with pCry1Ac plus extract conferred a significant protection (up to 47%). This group presented fluctuating antibody peaks during infection and the highest IgG1 and IgM titres. Immunization with extract alone elicited high IgG1 and the highest IgG2a responses after 25 days of infection, while nonimmunized mice presented a poor, mixed-Th1/Th2 response during infection. Sharp peaks of TNFα and IFN-γ occurred immediately after the first immunization with extract, especially in the presence of pCry1Ac, but not after the challenge, while in the control and pCry1Ac-alone groups, cytokines were only detected after the challenge. The data support the protective-adjuvant effect of co-administration of pCry1Ac in cysticercosis.

Evolution, molecular epidemiology and perspectives on the research of taeniid parasites with special emphasis on Taenia solium

Human cysticercosis is known since old historical times in Greece and China; however, human infections by tapeworms have accompanied human beings for more that hundred thousand years. The disease is tightly bound to poverty and lack of hygiene, and has been eradicated in developed countries, but continues being a public health problem in developing countries of Latin-American, Sub-Saharan Africa and Asia, and is also remerging in a number of non endemic countries. It is considered a neglected disease. Here we revise a number of key scientific contributions on taeniid biology that open new avenues for more effective approaches to the control of cysticercosis. The evolution of flatworms and class Cestoda is analyzed, with special emphasis on the emergence of taeniid parasites and the colonization of the human species by tapeworms. The complex molecular host-parasite interplay in this relationship as result of co-evolution between two distantly related organisms. The relevant host and parasite's factors, in the prospect of identifying species-specific molecular markers useful in epidemiological studies carried out in endemic countries. The new possibilities arising with the characterization of the genomes for several species of tapeworms, including a deeper understanding of these organisms, as well as improved tools for diagnosis, vaccination and drug treatment. The need to revise the current control and management strategies for this tropical neglected disease.

Control of Taenia solium taeniasis/cysticercosis: past practices and new possibilities

Neurocysticercosis continues to be a major health burden on humans living in many regions of the world, despite the availability of highly effective taeniacides and identification of the cause, Taenia solium, as being potentially eradicable. Several T. solium control trials have been undertaken, generally achieving limited success and none that has been fully documented has achieved what was demonstrated to be a sustainable level of disease control. Pigs act as intermediate hosts for T. solium and two new control tools have become available for application in pigs – single-dose oxfendazole treatment of porcine cysticercosis and the TSOL18 vaccine. Three potential intervention scenarios for pigs are compared for control of cysticercosis, using either oxfendazole or vaccination. A control scenario involving vaccination plus oxfendazole treatment delivered at 4 monthly intervals was predicted to achieve the best outcome, with no pigs slaughtered at 12 months of age having viable T. solium cysticerci. Now that new control tools are available, there are opportunities to concentrate research attention on evaluation of novel control scenarios leading to the implementation of effective and sustainable control programmes and a reduction in the global burden of neurocysticercosis.

Development of the S3Pvac vaccine against porcine Taenia solium cysticercosis: a historical review

Herein we present a review of our research dealing with vaccination against experimental and naturally acquired porcine Taenia solium cysticercosis using Taenia crassiceps-derived antigens. Results strongly support that the different versions of S3Pvac vaccine are indeed effective against porcine T. solium cysticercosis. Immunological results related to vaccination prove that protection is at least partially mediated by specific immunity. The data also support the validity of T. crassiceps murine cysticercosis as an effective tool to identify vaccine candidates against some metacestode infections.

Edible vaccines against veterinary parasitic diseases--current status and future prospects

Protection of domestic animals against parasitic infections remains a major challenge in most of the developing countries, especially in the surge of drug resistant strains. In this circumstance vaccination seems to be the sole practical strategy to combat parasites. Most of the presently available live or killed parasitic vaccines possess many disadvantages. Thus, expression of parasitic antigens has seen a continued interest over the past few decades. However, only a limited success was achieved using bacterial, yeast, insect and mammalian expression systems. This is witnessed by an increasing number of reports on transgenic plant expression of previously reported and new antigens. Oral delivery of plant-made vaccines is particularly attractive due to their exceptional advantages. Moreover, the regulatory burden for veterinary vaccines is less compared to human vaccines. This led to an incredible investment in the field of transgenic plant vaccines for veterinary purpose. Plant based vaccine trials have been conducted to combat various significant parasitic diseases such as fasciolosis, schistosomosis, poultry coccidiosis, porcine cycticercosis and ascariosis. Besides, passive immunization by oral delivery of antibodies expressed in transgenic plants against poultry coccidiosis is an innovative strategy. These trials may pave way to the development of promising edible veterinary vaccines in the near future. As the existing data regarding edible parasitic vaccines are scattered, an attempt has been made to assemble the available literature.

Fact or hypothesis: Taenia crassiceps as a model for Taenia solium, and the S3Pvac vaccine

Research undertaken over the past 40 years has established many of the general principals concerning immunity to taeniid cestodes. Although much is well understood about the host-protective mechanisms against taeniids and this knowledge has been exploited in studies on vaccine development, many aspects require further investigation or confirmation. Some phenomena have come to be regarded as being well established, while careful analysis of the published data would suggest that they may be better regarded as hypotheses rather than established facts. This review considers one selected issue pertaining to immunity to cestode infections and examines carefully the nature of the evidence that is available to support conclusions that have been made in this area. The issue examined is the use of Taenia crassiceps as a model for cysticercosis in pigs caused by Taenia solium, together with the S3Pvac vaccine, which has been developed based on this model. Strong evidence is found to support the conclusion that defined T. crassiceps antigens can limit intraperitoneal proliferation of the ORF strain of T. crassiceps in mice; however, the potential for these antigens to affect T. solium infection in pigs requires further confirmation.

Renewed hope for a vaccine against the intestinal adult Taenia solium

Review of experimental and observational evidence about various cestode infections of mammalian hosts revives hope for the development of an effective vaccine against adult intestinal tapeworms, the central protagonists in their transmission dynamics. As for Taenia solium, there are abundant immunological data regarding cysticercosis in humans and pigs, but information about human taeniasis is scarce. A single publication reporting protection against T. solium taeniasis by experimental primo infection and by vaccination of an experimental foster host, the immunocompetent female hamster, kindles the hope of a vaccine against the tapeworm to be used in humans, its only natural definitive host.

Characterization of S3Pvac anti-cysticercosis vaccine components: implications for the development of an anti-cestodiasis vaccine

Background

Cysticercosis and hydatidosis seriously affect human health and are responsible for considerable economic loss in animal husbandry in non-developed and developed countries. S3Pvac and EG95 are the only field trial-tested vaccine candidates against cysticercosis and hydatidosis, respectively. S3Pvac is composed of three peptides (KETc1, GK1 and KETc12), originally identified in a Taenia crassiceps cDNA library. S3Pvac synthetically and recombinantly expressed is effective against experimentally and naturally acquired cysticercosis.

Methodology/Principal Findings

In this study, the homologous sequences of two of the S3Pvac peptides, GK1 and KETc1, were identified and further characterized in Taenia crassiceps WFU, Taenia solium, Taenia saginata, Echinococcus granulosus and Echinococcus multilocularis. Comparisons of the nucleotide and amino acid sequences coding for KETc1 and GK1 revealed significant homologies in these species. The predicted secondary structure of GK1 is almost identical between the species, while some differences were observed in the C terminal region of KETc1 according to 3D modeling. A KETc1 variant with a deletion of three C-terminal amino acids protected to the same extent against experimental murine cysticercosis as the entire peptide. On the contrary, immunization with the truncated GK1 failed to induce protection. Immunolocalization studies revealed the non stage-specificity of the two S3Pvac epitopes and their persistence in the larval tegument of all species and in Taenia adult tapeworms.

Conclusions/Significance

These results indicate that GK1 and KETc1 may be considered candidates to be included in the formulation of a multivalent and multistage vaccine against these cestodiases because of their enhancing effects on other available vaccine candidates.

Eradication of Taenia solium cysticercosis: a role for vaccination of pigs

Taenia solium is the causative agent of neurocysticercosis, a disease responsible for substantial human morbidity and mortality. It is a zoonotic parasite, involving pigs as intermediate hosts. The parasite's full life cycle is restricted to poor people in developing countries. Attempts to date to control transmission of the parasite have been relatively poorly effective and not sustainable. Over the past decade research has been undertaken to develop practical vaccines for use in pigs to prevent transmission of T. solium. The most effective of these vaccines in controlled experimental trials has been the TSOL18 vaccine. More recently, TSOL18 has been proven to be highly effective against naturally acquired infection with T. solium in pigs. Application of TSOL18 together with a single treatment of pigs with oxfendazole achieved the complete elimination of transmission of the parasite by pigs involved in the field trial. This strategy may provide a relatively low cost and sustainable control tool which could assist towards the goal of achieving eradication of the parasite. An assessment is made of the potential value of various control measures that are available for T. solium, and two options are suggested as potential parasite control programs.

Elimination of Taenia solium transmission to pigs in a field trial of the TSOL18 vaccine in Cameroon

A pilot field trial of the TSOL18 vaccine was undertaken in Cameroon. Two hundred and forty, 2–3 month-old piglets were distributed to 114 individual households in pairs. Vaccinated animals received three immunisations with 200 μg TSOL18 plus 5 mg Quil A and 30 mg/kg oxfendazole at the time of the second immunisation. Necropsies were undertaken when the pigs were approximately 12 months of age. Viable Taenia solium cysticerci were identified in 20 control pigs (prevalence 19.6%); no cysticerci were found in any of the vaccinated animals (P < 0.0001). Combined application of TSOL18 vaccination and a single oxfendazole treatment in pigs may be a relatively simple and sustainable procedure that has the potential to control T. solium transmission in endemic areas and, indirectly, reduce the number of new cases of neurocysticercosis in humans.

Inexpensive anti-cysticercosis vaccine: S3Pvac expressed in heat inactivated M13 filamentous phage proves effective against naturally acquired Taenia solium porcine cysticercosis

In search of reducing vaccine production costs', a recombinant M13 phage version of the anti-cysticercosis tripeptide vaccine (S3Pvac) was developed. The efficacy of S3Pvac-Phage vs. placebo was evaluated in a randomized trial that included 1,047 rural pigs in 16 villages of Central Mexico. Three to five months after vaccination 530 pigs were examined by tongue inspection. At 5-27 months of age, 331 pigs (197 vaccinated/134 controls) were inspected at necropsy. Vaccination reduced 70% the frequency of tongue cysticercosis and, based on necropsy, 54% of muscle-cysticercosis and by 87% the number of cysticerci.

Echinococcosis: serological detection of patients and molecular identification of parasites

Alveolar (AE) and cystic echinococcosis (CE) are two of the most dangerous helminthic zoonoses worldwide, representing chronic hepatic diseases, often with lethal outcome. Since early diagnosis of echinococcosis is essential for effective treatment, an overview of serological methods for the detection of echinococcosis and differentiation between AE and CE is given. Recombinant antigens Em18 and Antigen B8/1 are highly recommended for patient screening and identification of AE and CE, respectively, in combination with imaging techniques. Novel aspects of molecular phylogenetic studies on the genus Echinococcus will also be addressed, including the description of Echinococcus shiquicus as a new sister-species of Echinococcus multilocularis. Both the serological detection of the disease and molecular phylogeny will be discussed in perspective.

Zoonotic helminth infections of humans: echinococcosis, cysticercosis and fascioliasis

PURPOSE OF REVIEW

Tissue parasites of humans are still prevalent in most regions of the world, and are also seen more frequently in developed countries due to increasing travel patterns. In particular, Echinococcus infections still account for hepatic and pulmonary pathology, cysticercosis is a major cause of seizures and epilepsy, and fascioliasis also causes significant liver pathology. This review summarizes current knowledge on clinical and epidemiologic aspects of zoonotic disease caused by tissue helminths.

RECENT FINDINGS

Tissue helminth infections remain as a public health concern. Recent research has provided new insights into clinical disease in humans and improved methods for diagnosis, treatment and control, arising mostly from the application of new techniques for immune and molecular diagnosis, availability of data from controlled trials, and development of new vaccines. Specific antiparasitic therapies are now better characterized, and new control tools are available.

SUMMARY

Recent research has provided new diagnostic technologies applicable to diagnosis, treatment and control, but effective interventions to reduce transmission are rarely applied. Despite some progress in their control, these zoonoses continue to be a major public health problem in many regions both in developing countries and in some more developed ones.