Vaccination against cestode parasites: anti-helminth vaccines that work and why

Immunoprotective effect and mechanism of rEg.P29 against CD4 + T cell-deficient mice with Echinococcus multilocularis infection

Alveolar echinococcosis (AE) is a zoonotic parasitic disease caused by infection with the larval stage of Echinococcus multilocularis and a major challenge to human public health. Vaccines are the most effective way to prevent and control infectious diseases. We previously revealed that the Echinocuccus granulosus recombinant protein P29 is a good vaccine candidate against E. granulosus. However, the protective and immunological mechanism of rEg.P29 against E. multilocularis remain unclear. In this study, CD4 + T cell-deficient mice are transferred with spleen CD4 + T cells isolated from wild-type mice and subjected to rEg.P29 immunization, and then these immunized mice are infected with E. multilocularis. The cyst inhibition rate is calculated by weighing the body and cyst weights. The level of antibody is detected by ELISA. Flow cytometry is used to detect the level of IFN-γ production by CD4 + T and CD8 + T cells. The cytokines in culture supernatant are detected by ELISA. The expressions of CD44 and CD62L on memory T cells are determined by flow cytometry. The results show the cyst inhibition rate is 41.52% after adoptive transfer of CD4 + T cells. Furthermore, the levels of IgG, IgM, IgA and IgE in serum are significantly increased compared with those in the PBS group. The IFN-γ-secretion by CD8 + T cells and the level of IFN-γ in culture supernatant are obviously increased; and the number of CD4 + T cells is increased, but the number of IFN-γ producing CD4 + T cells has no significant difference compared with PBS group. In addition, the number of CD44 +CD62L ‒CD8 + memory T cells in the spleen is significantly increased, while the number of CD44 ‒CD62L + CD8 + memory T cells is not significantly altered. Collectively, rEg.P29 can alleviate E. multilocularis infection by inducing humoral immune responses and CD8 + T cell responses.

Protective efficacy of six recombinant proteins as vaccine candidates against Echinococcus granulosus in dogs

BACKGROUND

Cystic echinococcosis (CE) is caused by the infection of Echinococcus granulosus sensu lato (E. granulosus s.l.), one of the most harmful zoonotic helminths worldwide. Infected dogs are the major source of CE transmission. While praziquantel-based deworming is a main measure employed to control dog infections, its efficacy is at times compromised by the persistent high rate of dog re-infection and the copious discharge of E. granulosus eggs into the environment. Therefore, the dog vaccine is a welcome development, as it offers a substantial reduction in the biomass of E. granulosus. This study aimed to use previous insights into E. granulosus functional genes to further assess the protective efficacy of six recombinant proteins in dogs using a two-time injection vaccination strategy.

METHODS

We expressed and combined recombinant E. granulosus triosephosphate isomerase (rEgTIM) with annexin B3 (rEgANXB3), adenylate kinase 1 (rEgADK1) with Echinococcus protoscolex calcium binding protein 1 (rEgEPC1), and fatty acid-binding protein (rEgFABP) with paramyosin (rEgA31). Beagle dogs received two subcutaneous vaccinations mixed with Quil-A adjuvant, and subsequently orally challenged with protoscoleces two weeks after booster vaccination. All dogs were sacrificed for counting and measuring E. granulosus tapeworms at 28 days post-infection, and the level of serum IgG was detected by ELISA.

RESULTS

Dogs vaccinated with rEgTIM&rEgANXB3, rEgADK1&rEgEPC1, and rEgFABP-EgA31 protein groups exhibited significant protectiveness, with a worm reduction rate of 71%, 57%, and 67%, respectively, compared to the control group (P < 0.05). Additionally, the vaccinated groups exhibited an inhibition of worm growth, as evidenced by a reduction in body length and width (P < 0.05). Furthermore, the level of IgG in the vaccinated dogs was significantly higher than that of the control dogs (P < 0.05).

CONCLUSION

These verified candidates may be promising vaccines for the prevention of E. granulosus infection in dogs following two injections. The rEgTIM&rEgANXB3 co-administrated vaccine underscored the potential for the highest protective efficacy and superior protection stability for controlling E. granulosus infections in dogs.

Very low frequency waves as selective probe for Cysticercus tenuicollis, Hydatid cyst and Coenurus cerebralis bio-analysis using single cell-signal recording

Comparative electric behavior of Cysticercus tenuicollis, Hydatid cyst and Coenurus cerebralis at the Very Low Frequency (VLF) region has been studied in detail. This investigation could be significant, because of the economic and public health importance of these parasitic infections in domestic animals. In this report, a single cell signal recording technique has been adopted for comparison using a stainless steel (type: 316, diameter: ~ 300 µm, height: 2.00 cm) two identical electrode system, implanted on the surface of the tested cysts with inter electrode distance of 0.50 cm at a ~ 6.0 giga ohm (GΩ) sealed condition (based on the situation of the implanted electrode system). This process was achieved based on applying electrical interaction between the cysts and the VLF electrical signal. Relative to the measured time domain signal (Current-time diagram), the frequency domain (Current-frequency diagram) was estimated via applying a "Discrete Fast Fourier Transform" (DFFT) algorithm at a fixed time interval (5.0 min). Factors, having important influence on the sensitivity of the detection system including the type (waveform) of different alternating-current (AC) triggering stimulus signals (such as direct current, square wave, triangular, sin (t), etc.), the amplitude, as well as the frequency were optimized automatically through a written "Visual Basic 6" program by one-factor-at-a-time method. Direct applying this AC triggering VLF voltage to the cysts resulted in tracing an AC electrical current vs. time that considered as the time domain wave. However, this electrical current was decayed rapidly versus time during maximum 30.0 s time scale. Applying the DFFT algorithm to the measured time domain, resulted in accessing to the frequency domain at the selected frequency range between 2 and 5 kHz that was considered as the selected frequency for the selective differentiation of C. tenuicollis, Hydatid cyst and C. cerebralis. The related probable mechanism of this process may be attributed to the correlation between the triggering potential and the cyst's electrical surface charge (Zeta potential) as the current source under similar conditions. The results of this study may help to introduce a new detection system for in vivo recognition of the cysts in future.

Advances in diagnosis and control of anthelmintic resistant gastrointestinal helminths infecting ruminants

Infection with gastrointestinal helminths is widely spread among ruminant causing severe losses and adversely affects the livestock husbandry. Synthetic chemotherapeutics have been utilized throughout years, as a means of combating helminthiasis. Anthelmintic resistance (AR) has a serious concern on livestock industry which, mainly arises as outcome of misuse, improper dosing and frequent utilization of the synthetic drugs.Various gastrointestinal helminths have the capability to survive the therapeutic dose of anthelmintics and become resistant to the major anthelmintic classes. Early diagnosis might delay or reduce the risk of AR. Conventional phenotyping methods were commonly used for detection of anthelmintic resistant helminths, but appeared to lack of sensitivity, especially when the frequency of resistant allele is very low. Several molecular assays were carried out to detect the AR with greater accuracy. Sustainable effective preventive and control measures for gastrointestinal helminths infection remain the corner stone to overcome AR. Rational use of anthelmintics with keeping unexposed proportion of worm populations, could have the potentiality to maintain and prolong the efficacy of anthelmintics. Several alternative anthelmintic treatments might offer valuable solutions either alone or adjunct to synthetic drugs to dilute the spread of resistance alleles among the helminths population. This article reviews current status of various diagnostic methods and control measures for anthelmintic resistant gastrointestinal helminths infecting ruminants and tries to present a practical protocol to avoid or delay the development of AR.

Ultrasonography of Parasitic Diseases in Domestic Animals: A Systematic Review

Simple Summary

The aim of this literature review was to summarize the current knowledge on the application of ultrasonography in diagnosis, staging and monitoring of helminthic diseases in domestic animals. We selected and analyzed 122 papers about the application of ultrasonography in parasitic disease in ruminants, equids, swine, and companion animals. Helminths can be recognized in ultrasound images by their morphology, size, and location. In some cases, the parasites are not directly seen by ultrasound, but the lesions caused by them can be easily visualized. Ultrasound imaging is taking on an increasingly important role in veterinary parasitology.

Abstract

The aim of this review was to summarize the current knowledge on the application of ultrasonography in diagnosis, staging and monitoring of helminthic diseases in domestic animals. Only peer reviewed papers written in English language were included in this systematic review. All papers concerning unicellular parasites, wild animals, non-domestic experimental animals, or ex vivo or in vitro applications of ultrasonography were excluded from the review. A total of 122 papers met the inclusion criteria. Among them 47% concerned nematodes, 37% cestodes, and 16% trematodes with the genus Dirofilaria, Echinococcus, and Fasciola the most represented, respectively. Helminths can be recognized in ultrasound images by their morphology, size, and location. In some cases, the parasite stages are not directly seen by ultrasound, but the lesions caused by them can be easily visualized. Ultrasound imaging is taking on an increasingly important role in the diagnosis, staging, monitoring, and control of parasitic diseases in veterinary medicine. However, it cannot replace the clinical approach and the diagnostic tests commonly used in veterinary parasitology.

Road map to the treatment of neglected tropical diseases: Nanocarriers interventions

Neglected tropical disease (NTD) is a set of 20 deadliest endemic diseases which shows its presence in most of the developing countries worldwide. Nearly 1 billion of the population are affected by it and suffered from poverty yearly. These diseases offer their own unique challenges and limitations towards effective prevention and treatment methods. Neglected tropical diseases are severe infections they may not kill the patient but debilitate the patient by causing severe skin deformities, disfigurement and horrible risks for several infections. Existing therapies for neglected diseases suffer from the loopholes like high degree of toxicity, side effects, low bioavailability, improper targeting and problematic application for affected populations. Progress in the field of nanotechnology in last decades suggested the intervention of nanocarriers to take over and drive the research and development to the next level by incorporating established drugs into the nanocarriers rather than discovering the newer drugs which is an expensive affair. These nanocarriers are believed to be a sure shot technique to fight infections at root level by virtue of its nanosize and ability to reach at cellular level. This article highlights the recent advances, rationale, targets and the challenges that are being faced to fight against NTDs and how the novel therapy tactics are able to contribute to its importance in prevention and treatment of NTDs.

Vaccination with a DNase II recombinant protein against Trichinella spiralis infection in pigs

Trichinellosis caused by Trichinella spiralis (T. spiralis) is an important public health problem. DNase II is an acidic endonuclease that catalyzes the degradation of DNA into oligonucleotides. DNase II-7 has been detected at the adult stage of T. spiralis and has been examined in excretory/secretory products. Previous studies have indicated that the DNase II-7 recombinant protein has a high rate of protection against T. spiralis infection in mice. In the present study, the protective effect of DNase II-7 recombinant protein against T. spiralis infection in Large White pigs was further explored. The humoral and cellular immune responses to the DNase II-7 recombinant protein were evaluated, including the dynamic trends of specific IgG, IgG1, IgG2a and IgM antibodies levels, as well as the levels of Th1 (IFN-γ and IL-2) and Th2 (IL-10 and IL-4) cytokines in serum. Our results showed that a Th1 dominated Th1/Th2 mixed immune response was induced by the DNase II-7 recombinant protein for all the time or a short period after vaccination. And the DNase II-7 recombinant protein induced partial protection against T. spiralis infection in pigs, compared to the control group. Our results showed that the DNase II-7 recombinant protein group displayed a 45.7 % reduction in the muscle larvae burden five weeks after being challenged. This study suggested that DNaseII-7 recombinant protein could be used as a potential candidate vaccine against T. spiralis infection in pigs.

Nano Based Approach for the Treatment of Neglected Tropical Diseases

Neglected tropical diseases (NTDs) afflict more than one billion peoples in the world’s poorest countries. The World Health Organization (WHO) has recorded seventeen NTDs in its portfolio, mainly caused by bacterial, protozoal, parasitic, and viral infections. Each of the NTDs has its unique challenges on human health such as interventions for control, prevention, diagnosis, and treatment. Research for the development of new drug molecules against NTDs has not been undertaken by pharmaceutical industries due to high investment and low-returns, which results in limited chemotherapeutics in the market. In addition, conventional chemotherapies for the treatment of NTDs are unsatisfactory due to its low efficacy, increased drug resistance, short half-life, potential or harmful fatal toxic side effects, and drug incompetence to reach the site of parasite infection. In this context, active chemotherapies are considered to be re-formulated by overcoming these toxic side effects via a tissue-specific targeted drug delivery system. This review mainly emphasizes the recent developments of nanomaterial-based drug delivery systems for the effective treatment of NTDs especially sleeping sickness, leishmaniasis, chagas disease, soil-transmitted helminthiasis, african trypanosomiasis and dengue. Nanomaterials based drug delivery systems offer enhanced and effective alternative therapy through the re-formulation approach of conventional drugs into site-specific targeted delivery of drugs.

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.

Advances in the Development of Anti-Haemonchus contortus Vaccines: Challenges, Opportunities, and Perspectives

The gastrointestinal nematode parasite Haemonchus contortus (H. contortus) is a resident of tropical and subtropical regions worldwide that imposes significant production losses, economic losses, and animal health issues in the small ruminant industry, particularly sheep and goats. Considerable efforts have been made to understand how immunity is elicited against H. contortus infection. Various potential vaccine antigens have been tested by different methods and strategies applied in animal models, and significant progress has been made in the development of vaccines against H. contortus. This review highlighted and shared the knowledge about the current understanding of host immune responses to H. contortus and ongoing challenges in the development of a protective, effective, and long-lasting vaccine against H. contortus infection. We have also pinpointed some achievements and failures in the development and testing of vaccines, which will establish a road map for future research directions to explore new effective vaccine candidates for controlling and preventing H. contortus infection.

Cystic echinococcosis in the endemic island of Sardinia (Italy): has something changed?

Cystic echinococcosis (CE) is a disease of livestock and humans caused by the larval stage of the Echinococcus granulosus sensu lato (s.l.) species complex and occurs especially in areas where sheep breeding is widespread. This survey evaluates, after more than a decade since the last epidemiological survey, the current situation and trend of CE in sheep of the highly endemic island of Sardinia (Italy). From 2012 to 2018, out of a total of 1416 sheep, 65.3% were found positive for CE. Cyst fertility has increased slightly from 10.3% in 2006 (Scala et al. 2006) to 11.7% in the present survey (χ2 = 1.07; P = 0.30018) with a peak of 14.0% in the province of Sassari. Overall, 6815 hydatids were found and classified as sterile (26.2%), fertile (14.4%), caseous (5.3%), or calcified (54.1%) based on their morphology. All isolates were identified as E. granulosus sensu stricto (former G1/G3, strains). Results shown as the implementation of new European Council Regulations and in particular of 21/2004 that established a system for the individual identification and tracking of sheep could be a step forward towards a better control of animal movement, preventing illegal slaughtering on the island as well as in other countries experiencing similar problems. Even if at first sight the general situation of Sardinia regarding CE seems a little better compared with the past, our findings indicate that in some Provinces the epidemiological situation is not improved since 2006.

Cloning, large-scale production and characterization of fusion protein (P-TUFT-ALT-2) of Brugian abundant larval transcript-2 with tuftsin in Pichia pastoris

Lymphatic filariasis is a "disease of poor people" due to a large section of affected people with economic backwardness. Therefore, successful elimination of this disease requires a cost-effective prophylactic agent such as vaccine along with conventional drugs. The Abundant Larval Transcript-2 (BmALT-2) protein of Brugia malayi has been recognized as the most potential vaccine candidate. Tuftsin, a tetra-peptide immunopotentiator has already shown the enhanced immunogenicity of various vaccine antigens in earlier studies. This study deals with the development of tuft-alt-2 fusion construct and a suitable culture condition for its large-scale production in Pichia pastoris. The recombinant P. pastoris/tuft-alt-2 with 9-11 copies of the gene construct exhibited the highest expression level. The molecular weight of P-TUFT-ALT-2 was determined as 28 kDa in SDS-PAGE including 3 kDa due to glycosylation. The dry cell biomass was 57.4 gL^-1 in the bioreactor. The P-TUFT-ALT-2 expression was measured as about 35 mg L^-1, which was 102% higher than flask culture. The P-TUFT-ALT-2 produced the highest 65,000 IgG peak titer in Balb/c mice. Moreover, P-TUFT-ALT-2 exhibited about 9.46% higher splenocyte proliferation than E. coli expressed E-ALT-2 alone. The enhanced secreted production of P-TUFT-ALT-2 in bioreactor would step up its commercialization as an inexpensive commercial vaccine for human lymphatic filariasis.

Influence of hydatid disease on the pregnancy outcomes: An experimental study

AIM

Hydatid disease during pregnancy may lead to various complications in both mother and child. Accordingly, enough knowledge is required to manage these complications. This study was done to evaluate the interaction between hydatid disease and pregnancy in laboratory mice.

METHODS

Twenty female BALB/c mice (Mus musculus) were divided into test and control groups, 10 animal in each. The mice of the test group were infected intraperitoneally by injection of 1000 protoescolices. Six months after infection, the mice of test and control groups were mated with male mice for a week. After parturition, the size and weight of babies were measured and compared between two groups.

RESULTS

While all the mice of control group delivered healthy babies, 3 out of 10 mice of test group showed no pregnancy. The infected mice delivered lower number of babies than the mice of control group. The mean size of fetuses or babies obtained from the infected mice were statistically lower than those obtained from the mice of control group (P = 0.000). The weight of babies delivered by the infected mice not only at the time of birth (P = 0.005) but also 10 days after birth (P = 0.021), were significantly lower than those delivered by the mice of control group. The level of progesterone and estradiol in the mice of test group were significantly lower (P = 0.009) and higher (P = 0.043), respectively, in comparison to the mice of control group.

CONCLUSION

Hydatid disease during pregnancy may considerably affect the pregnancy outcomes.

Nanomedicine Approaches Against Parasitic Worm Infections

Nanomedicine approaches have the potential to transform the battle against parasitic worm (helminth) infections, a major global health scourge from which billions are currently suffering. It is anticipated that the intersection of two currently disparate fields, nanomedicine and helminth biology, will constitute a new frontier in science and technology. This progress report surveys current innovations in these research fields and discusses research opportunities. In particular, the focus is on: (1) major challenges that helminth infections impose on mankind; (2) key aspects of helminth biology that inform future research directions; (3) efforts to construct nanodelivery platforms to target drugs and genes to helminths hidden in their hosts; (4) attempts in applying nanotechnology to enable vaccination against helminth infections; (5) outlooks in utilizing nanoparticles to enhance immunomodulatory activities of worm-derived factors to cure allergy and autoimmune diseases. In each section, achievements are summarized, limitations are explored, and future directions are assessed.

K. G, Basnet S, Tiwari PK, Bahadur N, Mishra R. Time trend of neurocysticercosis in children with seizures in a tertiary hospital of western Nepal

Introduction

Neurocysticercosis is a common cause of seizure disorders in children of Western Nepal. The clinical presentation is variable. The incidence varies depending on the food habits and ethnicity of the population. The present study was undertaken with the objective of studying the mode of presentation, radiological findings and to determine the recent trend of the disease in children of Western Nepal.

Methods

Records from the Department of Pediatrics, Manipal Teaching Hospital, Pokhara, Nepal of children aged 0–17 years admitted from 2003 to 2015 and with the discharge diagnosis of seizure and neurocysticercosis (NCC) were reviewed. The diagnosis was primarily based on clinical features, neurological involvement and CT and MRI studies. Seizures due to other CNS pathologies were excluded. Patients with NCC were treated with Albendazole15mg/kg/day for 28 days with supportive treatments for seizures and raised intracranial pressure. Patients were followed up for one year after the completion of the treatment.

Results

There were 1355 cases of seizure disorders, out of which 229 (16.90%) were NCC. There were 99 (43.23%) in the age group 6–10 years followed by 91 (41.09%) in the age group of 11–15 years. Seizures were the most common presenting symptom in 88.65%, followed by raised ICP in 9.61%. Neuropsychiatric changes were noted in 38 cases (16.59%). CT scan findings revealed single lesion in 78.16% and multiple lesions in 21.83%. Poisson regression analysis showed statistically significant decline of year-wise incidence of NCC cases (p<0.05) from 2003 to 2015.

Conclusion

The decline in the incidence of NCC in recent years is most probably attributed to improved hygiene with the construction of household toilets to avoid open defecation and biannual deworming with Albendazole as a part of School Health and Nutrition Project.

Neurocysticercosis is a common parasitic infection of the central nervous system. It is caused by larval form of Taenia solium and it has been identified as a “Neglected Tropical Disease” endemic in south East Asia, including Nepal, by WHO. The clinical features in children are pleomorphic depending on the number, location and size of cysticerci. The parenchymatous lesions are presented as neurological symptoms like sudden onset seizures, encephalitis, raised intracranial pressure and neuropsychiatric symptoms. CT and MRI are the main diagnostic tools. Maximum incidence was found in school age children (6–15 years). Year wise review of percentage of NCC, revealed a declining trend from 20.83% in 2009 to 5.37% in 2014. The decline in the incidence of NCC noted in our study might be due to biannual deworming using Albendazole as a part of School Health and Nutrition Programme started by Ministry of Health Services, Nepal in 2008 and extended to all the districts of the country. In addition construction of household and school toilets to avoid open defecation, health education and hand washing facilities might have played a role. Large multicentre trials to evaluate role of biannual Albendazole to prevent cysticercosis is recommended.

Host protective ASP-based vaccine against the parasitic nematode Ostertagia ostertagi triggers NK cell activation and mixed IgG1-IgG2 response

The mucus-dwelling parasite Ostertagia ostertagi is one of the most important gastrointestinal nematodes in cattle. Our group has previously demonstrated the protective capacity of a vaccine against this parasite based on a native activation-associated secreted protein ASP1 (nASP) in combination with the saponin adjuvant QuilA. The aim of the current study was to analyse the effect of both antigen and adjuvant on the cellular and humoral vaccine-induced immune responses by comparing the native ASP to a recombinant version expressed in Pichia pastoris (pASP) and replacing QuilA by Al(OH)3. Immunization of cattle with the protective nASP+QuilA vaccine was associated with antigen-induced proliferation of natural killer (NK) cells combined with IFN-γ secretion and the induction of a mixed IgG1/IgG2 antibody response. ASP-specific activation and proliferation of NK cells was also observed in mice following the same vaccination regime. Replacing QuilA by Al(OH)3 or nASP by pASP significantly decreased the capacity of the vaccines to trigger both NK cell activation and antibody responses and failed to induce protection against a challenge infection. Reduction of the structurally anchoring disulphide bonds of the nASP completely abolished its ability to induce NK cell activation and antibody responses, highlighting the importance of protein conformation for the immunostimulatory activity.

Immunity to Haemonchus contortus and Vaccine Development

Sheep are capable of developing protective immunity to Haemonchus contortus through repeated exposure to this parasite, although this immune protection is the result of a complex interaction among age, gender, physiological status, pregnancy, lactation, nutrition and innate and adaptive immunity in the host animal. There are multiple effectors of the protective immune response, which differ depending on the developmental stage of the parasite being targeted, and our understanding of the effector mechanisms has developed considerably in the 2000s. The rational design of vaccines based on 'natural' or 'exposed' antigens depends on an understanding of this exposure-induced immunity. However, the most effective current vaccines rely on protection via the induction of high circulating antibody levels to 'hidden' gut antigens of H. contortus. The success of this latter strategy has resulted in the launch of a vaccine, which is based on extracts of the parasite's gut, to aid in the control of Haemonchus in Australia. The development of recombinant subunit vaccines based on the components of the successful native vaccine has not yet been achieved and most of the recent successes with recombinant subunit vaccines have focussed on antigens unrelated to the gut antigens. The future integration of an understanding of the immunobiology of this parasite with advances in antigen identification, expression (or synthesis) and presentation is likely to be pivotal to the further development of these recombinant subunit vaccines. Recent progress in each of the components underpinning this integrated approach is summarized in this review.

Pediatric neurocysticercosis: current challenges and future prospects

Neurocysticercosis (NCC) is an acquired infection of the nervous system caused by encysted larvae of Taenia solium. It is a major cause of epilepsy in the tropics and the commonest cause of focal seizures in North Indian children. T. solium teniasis-cysticercosis is considered a parasitic "Neglected Tropical Diseases" endemic throughout Southeast Asia. NCC in children has pleomorphic manifestations depending on the location, number and viability of the cysts, and host response. Even with advancing knowledge of the disease manifestations, many aspects related to diagnosis and treatment, particularly in children, still remain controversial and pose challenges to clinical practice. There is no gold standard test to diagnose NCC and the management recommendations are still emerging. This review provides an overview of diagnosis of NCC in children and its management with special focus on current challenges and future prospects.

A preliminary investigation into the genetic variation and population structure of Taenia hydatigena from Sardinia, Italy

Cysticercosis caused by the metacestode stage of Taenia hydatigena is endemic in Sardinia. Information on the genetic variation of this parasite is important for epidemiological studies and implementation of control programs. Using two mitochondrial genes, the cytochrome c oxidase subunit 1 (cox1) and the NADH dehydrogenase subunit 1 (ND1) we investigated the genetic variation and population structure of Cysticercus tenuicollis from Sardinian intermediate hosts and compared it to that from other hosts from various geographical regions. The parsimony cox1 network analysis indicated the existence of a common lineage for T. hydatigena and the overall diversity and neutrality indices indicated demographic expansion. Using the cox1 sequences, low pairwise fixation index (Fst) values were recorded for Sardinian, Iranian and Palestinian sheep C. tenuicollis which suggested the absence of genetic differentiation. Using the ND1 sequences, C. tenuicollis from Sardinian sheep appeared to be differentiated from those of goat and pig origin. In addition, goat C. tenuicollis were genetically different from adult T. hydatigena as indicated by the statistically significant Fst value. Our results are consistent with biochemical and morphological studies that suggest the existence of variants of T. hydatigena.

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.

Hydatid disease: vaccinology and development of the EG95 recombinant vaccine

Hydatid disease is a zoonotic parasitic disease that is distributed widely around the world and causes substantial human morbidity and mortality, particularly in developing countries. Reduction of human hydatid disease using anthelmintics, together with changes in human lifestyle and animal management practices, have been unsuccessful in some developing countries where the disease still persists. Substantial progress has been made towards developing a practical, recombinant vaccine in sheep, to interrupt the lifecycle of Echinococcus granulosus and to prevent subsequent transmission from dogs to humans. This review focuses on the scientific advances in the development of a recombinant vaccine for hydatid disease and the remaining challenges facing the widespread use of the vaccine for control of hydatid disease in endemic areas.

Characterization of the carbohydrate components of Taenia solium oncosphere proteins and their role in the antigenicity

This study examines the carbohydrate composition of Taenia solium whole oncosphere antigens (WOAs), in order to improve the understanding of the antigenicity of the T. solium. Better knowledge of oncosphere antigens is crucial to accurately diagnose previous exposure to T. solium eggs and thus predict the development of neurocysticercosis. A set of seven lectins conjugates with wide carbohydrate specificity were used on parasite fixations and somatic extracts. Lectin fluorescence revealed that D-mannose, D-glucose, D-galactose and N-acetyl-D-galactosamine residues were the most abundant constituents of carbohydrate chains on the surface of T. solium oncosphere. Lectin blotting showed that posttranslational modification with N-glycosylation was abundant while little evidence of O-linked carbohydrates was observed. Chemical oxidation and enzymatic deglycosylation in situ were performed to investigate the immunoreactivity of the carbohydrate moieties. Linearizing or removing the carbohydrate moieties from the protein backbones did not diminish the immunoreactivity of these antigens, suggesting that a substantial part of the host immune response against T. solium oncosphere is directed against the peptide epitopes on the parasite antigens. Finally, using carbohydrate probes, we demonstrated for the first time that the presence of several lectins on the surface of the oncosphere was specific to carbohydrates found in intestinal mucus, suggesting a possible role in initial attachment of the parasite to host cells.

The role of nuclear technologies in the diagnosis and control of livestock diseases--a review

Nuclear and nuclear-related technologies have played an important role in animal health, particularly in relation to disease diagnosis and characterization of pathogenic organisms. This review focuses primarily on how and where nuclear technologies, both non-isotopic and isotopic methods, have made their impact in the past and where it might be expected they could have an impact in the future. The review outlines the extensive use of radiation attenuation in attempts to create vaccines for a multiplicity of pathogenic organisms and how the technology is being re-examined in the light of recent advances in irradiation techniques and cryopreservation/lyophilization that might obviate some of the problems of maintenance of viable, attenuate vaccines and their transport and use in the field. This approach could be used for a number of parasitic diseases where vaccination has been problematic and where investigations into the development of molecular vaccines have still failed to deliver satisfactory candidates for generating protective immune responses. Irradiation of antigens or serum samples also has its uses in diagnosis, especially when the samples need to be transported across international boundaries, or when handling the pathogens in question when carrying out a test presents serious health hazards to laboratory personnel. The present-day extensive use of enzyme immunoassays and molecular methods (e.g., polymerase chain reaction) for diagnosis and characterization of animal pathogens has its origins in the use of isotope-labeled antigens and antibodies. These isotopic techniques that included the use of 75Se, 32P, 125I, and 35S isotopes enabled a level of sensitivity and specificity that was hitherto unrealized, and it is prescient to remind ourselves of just how successful these technologies were, in spite of their infrequent use nowadays. Finally, the review looks at the potential for stable isotope analysis for a variety of applications--in the tracking of animal migrations, where the migrant are potential carriers of transboundary animal diseases, and where it would be useful to determine the origins of the carrier, e.g., Highly Pathogenic Avian Influenza and its dissemination by wild water fowl. Other applications could be in monitoring sequestered microbial culture (e.g., rinderpest virus) where in the case of accidental or deliberate release of infective culture it would be possible to identify the laboratory from which the isolate originated.

Vaccination of mice with an antigenic serine protease-like protein elicits a protective immune response against Trichinella spiralis infection

Trichinellosis has major economic impacts on animal husbandry and food safety, and the control and elimination of trichinellosis is a major objective of veterinary medicine. A gene encoding serine protease of Trichinella spiralis (Ts-Adsp) was identified by immunoscreening an adult T. spiralis cDNA library. In this study, the recombinant Ts-Adsp protein (rTs-Adsp) was cloned and expressed in a prokaryotic expression system and purified by Ni-affinity chromatography. To determine whether the purified rTs-Adsp is a potential vaccine candidate for the control of T. spiralis infection, we immunized BALB/c mice with this protein in combination with an alum adjuvant and subsequently challenged with T. spiralis larvae. The results showed that mice vaccinated with rTs-Adsp exhibited an average reduction in the muscle larvae burden of 46.5% relative to the control group. Immunization with the rTs-Adsp antigen induced both humoral and cellular immune responses, which manifested as elevated specific anti-rTs-Adsp IgG and IgE antibodies and a mixed Th1-Th2 response, as determined by Th1 (IFN-γ and IL-2) and Th2 (IL-4, IL-10, and IL-13) cytokine profiling, with the Th2 predominant. Thus, purified rTs-Adsp is able to limit the invasion of T. spiralis , and this protein could be an effective vaccine candidate for trichinellosis.

Helminth parasite proteomics: from experimental models to human infections

Schistosomiasis is a major human helminth infection endemic in developing countries. Urogenital schistosomiasis, caused by S. haematobium, is the most prevalent human schistosome disease in sub-Saharan Africa. Currently control of schistosome infection is by treatment of infected people with the anthelmintic drug praziquantel, but there are calls for continued efforts to develop a vaccine against the parasites. In order for successful vaccine development, it is necessary to understand the biology and molecular characteristics of the parasite. Ultimately, there is need to understand the nature and dynamics of the relationship between the parasite and the natural host. Thus, my studies have focused on molecular characterization of different parasite stages and integrating this information with quantitative approaches to investigate the nature and development of protective immunity against schistosomes in humans. Proteomics has proved a powerful tool in these studies allowing the proteins expressed by the parasite to be characterized at a molecular and immunological level. In this review, the application of proteomic approaches to understanding the human-schistosome relationship as well as testing specific hypotheses on the nature and development of schistosome-specific immune responses is discussed. The contribution of these approaches to informing schistosome vaccine development is highlighted.

To B or not to B: B cells and the Th2-type immune response to helminths

Similar T helper (Th)2-type immune responses are generated against different helminth parasites, but the mechanisms that initiate Th2 immunity, and the specific immune components that mediate protection against these parasites, can vary greatly. B cells are increasingly recognized as important during the Th2-type immune response to helminths, and B cell activation might be a target for effective vaccine development. Antibody production is a function of B cells during helminth infection and understanding how polyclonal and antigen-specific antibodies contribute should provide important insights into how protective immunity develops. In addition, B cells might also contribute to the host response against helminths through antibody-independent functions including, antigen presentation, as well as regulatory and effector activity. In this review, we examine the role of B cells during Th2-type immune response to these multicellular parasites.

Control of important helminthic infections vaccine development as part of the solution

Among the tools available for the control of helminth infections, chemotherapy has come to totally dominate the field. In the veterinary field, development of drug resistance has appeared but this is not (yet) a problem in the control of human diseases. Although there is no vaccine commercially available for any human parasitic infection yet, recent progress in vaccine development is making this a future possibility for several diseases. The goal of chemotherapy is to alleviate infection and morbidity in the definitive host, or reduce transmission, while the effect of available vaccine candidates would mainly be to influence transmission through targeting the intermediate or reservoir host, when the infection is zoonotic. Apart from this general scheme, there are also vaccine candidates targeting the parasites in the definitive host, in particular the early developmental stages, which should reduce the risk of drug failure. Since the biological targets in most cases are different, vaccination would be synergistic with drug therapy. This review covers diseases caused by helminthes in both humans and animals and includes examples of diseases caused by cestodes, nematodes and trematodes. The focus is on infections for which vaccine development has been undertaken for a long time, resulting in products that could realistically become integrated into control strategies in the near future.

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.

Neglected and endemic zoonoses

Endemic zoonoses are found throughout the developing world, wherever people live in close proximity to their animals, affecting not only the health of poor people but often also their livelihoods through the health of their livestock. Unlike newly emerging zoonoses that attract the attention of the developed world, these endemic zoonoses are by comparison neglected. This is, in part, a consequence of under-reporting, resulting in underestimation of their global burden, which in turn artificially downgrades their importance in the eyes of administrators and funding agencies. The development of cheap and effective vaccines is no guarantee that these endemic diseases will be eliminated in the near future. However, simply increasing awareness about their causes and how they may be prevented-often with very simple technologies-could reduce the incidence of many endemic zoonoses. Sustainable control of zoonoses is reliant on surveillance, but, as with other public-sector animal health services, this is rarely implemented in the developing world, not least because of the lack of sufficiently cheap diagnostics. Public-private partnerships have already provided advocacy for human disease control and could be equally effective in addressing endemic zoonoses.

Purification of polyclonal anti-conformational antibodies for use in affinity selection from random peptide phage display libraries: a study using the hydatid vaccine EG95

The use of polyclonal antibodies to screen random peptide phage display libraries often results in the recognition of a large number of peptides that mimic linear epitopes on various proteins. There appears to be a bias in the use of this technology toward the selection of peptides that mimic linear epitopes. In many circumstances the correct folding of a protein immunogen is required for conferring protection. The use of random peptide phage display libraries to identify peptide mimics of conformational epitopes in these cases requires a strategy for overcoming this bias. Conformational epitopes on the hydatid vaccine EG95 have been shown to result in protective immunity in sheep, whereas linear epitopes are not protective. In this paper we describe a strategy that results in the purification of polyclonal antibodies directed against conformational epitopes while eliminating antibodies directed against linear epitopes. These affinity purified antibodies were then used to select a peptide from a random peptide phage display library that has the capacity to mimic conformational epitopes on EG95. This peptide was subsequently used to affinity purify monospecific antibodies against EG95.

Isolation of antibodies specific to a single conformation-dependant antigenic determinant on the EG95 hydatid vaccine

EG95 is a recombinant vaccine protein that elicits protection against hydatid disease in sheep. Previous studies have shown that the host-protective epitopes on EG95 depend on correct conformation and cannot be represented by simple “linear” peptides. By screening random peptide phage display libraries with polyclonal antibodies directed against conformation-dependant epitopes of EG95, we have selected a number of peptides that mimic these epitopes. The selected peptides did not show sequence homology to EG95. Antigen binding assays involving these peptides have provided evidence of at least four conformationally-dependant epitope regions on EG95. One of the selected peptides, E100, has been used to purify antibodies from anti-sera raised in sheep vaccinated with EG95. This yielded monospecific antibodies capable of recognizing recombinant EG95 in ELISA and native EG95 in Western blot assays. This antibody was demonstrated to be effective in antibody-dependant complement-mediated in vitro killing of Echinococcus granulosus oncospheres. Peptide E100 may represent the basis for a quality control assay for EG95 production, and has the potential to become a component of a synthetic peptide-based vaccine against E. granulosus.

Vaccination with 73kDa recombinant heavy chain myosin generates high level of protection against Brugia malayi challenge in jird and mastomys models

We have earlier reported identification, expression and purification of a 2.0kb cDNA clone coding for Brugia malayi heavy chain myosin which exhibited strong immuno-reactivity with bancroftian sera from endemic normal (EN) human subjects which are considered to be putatively immune. In the present study, immunoprophylactic characterization of B. malayi recombinant myosin was carried out in rodent models and the protective efficacy was evaluated by assessing the microfilarial burden and adult worm counts in vaccinated host after an infective larval challenge. Data indicates that immunization resulted in to a significant reduction in microfilarial burden (approximately 76%) and adult worm establishment (54-58%), accompanied with embryostatic effect (70-75%) in both the animal models. The findings suggest that immune-protection by recombinant myosin was conferred through both humoral and cellular arms of immunity as indicated by an increased antibody titer with predominance of IgG2a and IgG2b isotypes along with elevated level of IgG1 apart from significant proliferation of lymphocytes, increased nitric oxide production and profound adherence of splenocytes causing cytotoxicity to microfilariae and infective larvae. The present study indicates that the recombinant B. malayi myosin is a promising vaccine candidate against human lymphatic filarial infection.

Echinococcus granulosus: variability of the host-protective EG95 vaccine antigen in G6 and G7 genotypic variants

Cystic hydatid disease in humans is caused by the zoonotic parasite Echinococcus granulosus. As an aid to control transmission of the parasite, a vaccine has been produced for prevention of infection in the parasite's natural animal intermediate hosts. The vaccine utilizes the recombinant oncosphere protein, EG95. An investigation into the genetic variability of EG95 was undertaken in this study to assess potential antigenic variability in E. granulosus with respect to this host-protective protein. Gene-specific PCR conditions were first established to preferentially amplify the EG95 vaccine-encoding gene (designated eg95-1) from the E. granulosus genome that also contains several other EG95-related genes. The optimized PCR conditions were used to amplify eg95-1 from several parasite isolates in order to determine the protein-coding sequence of the gene. An identical eg95-1 gene was amplified from parasites showing a G1 or G2 genotype of E. granulosus. However, from isolates having a G6 or G7 genotype, a gene was amplified which had substantial nucleotide substitutions (encoding amino acid substitutions) compared with the eg95 gene family members. The amino acid substitutions of EG95 in the G6/G7 genotypes may affect the antigenicity/efficacy of the EG95 recombinant antigen against parasites of these genotypes. These findings indicate that characterization of eg95 gene family members in other strains/isolates of E. granulosus may provide valuable information about the potential for the EG95 hydatid vaccine to be effective against E. granulosus strains other than the G1 genotype.

Vaccination with recombinant oncosphere antigens reduces the susceptibility of sheep to infection with Taenia multiceps

Taenia multiceps is a cestode parasite, the larval stage of which encysts in the brain of sheep, goats and cattle causing an often fatal condition. The parasite also causes zoonotic infections in humans. Homologues of the recombinant oncosphere vaccine antigens from Taenia ovis and other Taenia species were identified in T. multiceps. Sequencing of the associated T. multiceps genes and cloning of the encoding mRNA has revealed conserved features in the genes and proteins. The T. multiceps oncosphere proteins, designated Tm16 and Tm18, contain a predicted secretory signal and fibronectin type III domain. The recombinant Tm16 and Tm18 proteins were successfully expressed in Escherichia coli as fusion proteins with GST. The antigens, formulated with Quil A adjuvant, were tested in a vaccine trial in sheep. The antigens stimulated immunity in sheep against challenge infection with T. multiceps eggs. Five of nine control sheep died due to a challenge infection with T. multiceps whereas none of 20 vaccinated animals died as a result of the parasite challenge (P = 0.001). In addition, vaccination with the Tm16 protein, or Tm16 plus Tm18, induced significant protection against the number of parasites encysting in the brain as a result of the challenge infection (P = 0.023, P = 0.015, respectively). No clear relationship was apparent between the level of specific serum antibody in vaccinated animals and either the presence or absence of parasites or the number of parasites that occurred in some of the vaccinated animals. We believe this study is the first description of recombinant vaccine-related investigations for T. multiceps. The recombinant oncosphere antigens identified may allow development of effective vaccination strategies against T. multiceps infection in sheep. They raise the potential for the development of a combined vaccine with the Echinococcus granulosus EG95 antigen for prevention of T. multiceps as well as preventing the transmission of cystic hydatid disease.

Research approaches for improved pro-poor control of zoonoses

BACKGROUND

Developing countries face difficulties in sustainably utilizing tools to effectively implement control measures for zoonoses. This is mainly due to dispersed and heterogeneous smallholder livestock systems, predominance of informal markets, poor infrastructure and lack of resources to deliver information, interventions, and regulations. In addition, developing countries lack an evidence base for planning and targeting control efforts. Zoonotic infections are receiving more and more international attention as diseases of neglected and impoverished communities, at the intersection between livestock production, human health, and poverty.

OBJECTIVE

To review research innovations and trends that can help identify and test targeted control strategies for zoonoses tailored to poor communities, focusing particularly on Africa.

METHODS

Review of recommendations of relevant working groups and scientific literature.

RESULTS

New and innovative research approaches promise to better capture the impact of zoonoses from a societal perspective and the perspective of poor livestock owners through more comprehensive frameworks that consider benefits of the control of zoonoses to the public health, livestock, and private sectors. It is challenging to better assure food safety in informal markets. Risk-based approaches with participatory elements provide a framework in which stakeholders can decide an appropriate level of protection to balance the needs for safe food, cheap food, and pro-poor economic growth. Appropriate information for all stakeholders and capacity-building of national and regional authorities is an important element of this process. New diagnostic tools that are accurate and easily used in developing-country health centers and markets can assist in reporting of cases, detection of patients, and testing of control strategies.

CONCLUSIONS

A research agenda on zoonoses of the livestock sector should be interdisciplinary and participatory and include intersectoral collaborations, notably between the livestock and public health sectors.

Parasite vaccines: The new generation

Parasites cause some of the most devastating and prevalent diseases in humans and animals. Moreover, parasitic infections increase mortality rates of other serious non-parasitic infections caused by pathogens such as HIV-1. The impact of parasitic diseases in both industrialised and developing countries is further exacerbated by the resistance of some parasites to anti-parasitic drugs and the absence of efficacious parasite vaccines. Despite years of research, much remains to be done to develop effective vaccines against parasites. This review focuses on the more recent vaccine strategies such as DNA and viral vector-based vaccines that are currently being used to develop vaccines against parasites. Obstacles yet to be overcome and possible advantages and disadvantages of these vaccine modalities are also discussed.

Control of cystic echinococcosis/hydatidosis: 1863-2002

Echinococcosis/hydatidosis, caused by Echinococcus granulosus, is a chronic and debilitating zoonotic larval cestode infection in humans, which is principally transmitted between dogs and domestic livestock, particularly sheep. Human hydatid disease occurs in almost all pastoral communities and rangeland areas of the underdeveloped and developed world. Control programmes against hydatidosis have been implemented in several endemic countries, states, provinces, districts or regions to reduce or eliminate cystic echinococcosis (CE) as a public health problem. This review assesses the impact of 13 of the hydatid control programmes implemented, since the first was introduced in Iceland in 1863. Five island-based control programmes (Iceland, New Zealand, Tasmania, Falklands and Cyprus) resulted, over various intervention periods (from <15 to >50 years), in successful control of transmission as evidenced by major reduction in incidence rates of human CE, and prevalence levels in sheep and dogs. By 2002, two countries, Iceland and New Zealand, and one island-state, Tasmania, had already declared that hydatid disease had been eliminated from their territories. Other hydatid programmes implemented in South America (Argentina, Chile, Uruguay), in Europe (mid-Wales, Sardinia) and in East Africa (northwest Kenya), showed varying degrees of success, but some were considered as having failed. Reasons for the eventual success of certain hydatid control programmes and the problems encountered in others are analysed and discussed, and recommendations for likely optimal approaches considered. The application of new control tools, including use of a hydatid vaccine, are also considered.