Reduction In Number Of Worms Research Articles

Comparative analysis of transcriptional profiles of Schistosoma japonicum adult worms derived from primary-infected and re-infected water buffaloes

BackgroundSchistosoma japonicum (S. japonicum) is an important zoonotic parasite that is prevalent in China and parts of Southeast Asia. Water buffaloes are an important reservoir and the main transmission sources of S. japonicum. However, self-curing and resistance to re-infection have been observed in water buffaloes.ResultsIn this study, we compared the morphometry and differences in transcriptional expression of adult S. japonicum worms recovered from primary-infected and re-infected water buffaloes using Illumina RNA-sequencing (RNA-Seq) technology. Results of morphometry analysis revealed that adult S. japonicum worms recovered from re-infected water buffaloes were runtish with smaller organs. The ventral length of male worms was shorter in re-infected buffaloes (328 ± 13 vs 273 ± 8 µm, P < 0.05), and in female worms the oral sucker length (44 ± 3 vs 33 ± 5 µm, P < 0.05), ovary length (578 ± 23 vs 297 ± 27 µm, P < 0.05) and width (150 ± 8 vs 104 ± 9 µm, P < 0.05) were shorter, with fewer eggs in the uteri (41 ± 2 vs 12 ± 1, P < 0.05). Of 13,605 identified genes, 112 were differentially expressed, including 51 upregulated and 61 downregulated genes, in worms from re-infected compared with primary-infected water buffaloes. Gene ontology (GO) enrichment analysis revealed that GO terms such as “oxidation-reduction process”, “calcium-dependent phospholipid binding”, “lipid binding” and “calcium ion binding” were significantly enriched in downregulated genes, whereas GO terms related to metabolism and biosynthesis were significantly enriched in upregulated genes. The results revealed that the downregulation of some important genes might contribute to a reduction in worm numbers and maldevelopment of surviving worms in re-infected water buffaloes. Furthermore, upregulation of genes related to metabolic processes and biosynthesis might be a compensatory mechanism of worms in disadvantageous environments.ConclusionsTo our knowledge, our results present the first large-scale transcriptional expression study identifying the differences between adult S. japonicum worms from primary-infected and re-infected water buffaloes, and particularly emphasize differential expression that may affect the survival and growth of worms in re-infected water buffalo. This will provide new insight into screening for anti-schistosome targets and vaccine candidates.

Transcriptomic analysis of reduced sensitivity to praziquantel in Schistosoma mansoni

Schistosomiasis is an intravascular parasitic infection estimated to affect over 206 million people, the majority of whom live in Africa where the trematode worms Schistosoma mansoni and Schistosoma haematobium are the major causative agents. While a number of drugs have been used to treat schistosomiasis, praziquantel (PZQ) is the only one that is widely available, relatively cheap, and easy to use. The reliance on a single drug for the treatment of such a prevalent disease is a cause for concern due to the potential for resistance to render PZQ ineffective. In this study, we examine the transcriptome of three generations of a laboratory strain of S. mansoni (PR1) whose susceptibility to PZQ has been diminished across 9 passages through exposure to increasing sub-lethal doses of the drug. Miracidial susceptibility was significantly reduced after exposure to 2 × 50 mg/Kg PZQ during the first passage. Susceptibility of worms in vivo was first assessed during passage 5 when mice infected with PZQ-selected schistosomes were dosed with a lethal dose of 3 × 300 mg/kg PZQ resulting in only a 10% reduction in worm number compared to control treatment. The emergence of reduced sensitivity was marked by a shift in sex ratio from a predominantly male to a female population, a reduction in the length of females and ultimately the loss of the PZQ-selected line after passage 9. Analysis of differentially regulated transcripts did not suggest that any particular gene product or pathway was associated with drug resistance suggesting either a loss of function mutation to a single gene or an epistatic interaction of multiple gene products as the underlying cause of reduced susceptibility.

Probiotics and yogurt modulate oxidative stress and fibrosis in livers of Schistosoma mansoni-infected mice

BackgroundConsiderable morbidity, mortality, and economic loss result from schistosomiasis infection. Deposition of Schistosoma eggs in the hepatic portal vein is considered as the main causative agent for the development of liver fibrosis and subsequent liver cirrhosis. Probiotics are exogenous and beneficial microorganisms to living hosts against the harmful effect of many parasites. Strong evidence suggests the importance of probiotics in the control strategy of helminth. The ultimate goal of this study is to evaluate the protective effect of probiotics and yogurt on Schistosoma mansoni-induced oxidative stress and hepatic fibrosis in mice.MethodsMice were infected by tail immersion of schistosomal cercariae followed by an oral treatment with either probiotics or yogurt for one week before infection and immediately post-infection. Mice were scarified on day 56 following infection with S. mansoni and liver sample were obtained.ResultsWe showed that oral administration of probiotics or yogurt revealed a significant reduction in worm number, egg load, and granuloma size in liver tissue, which is mainly assigned to the decreased expression level of matrix metalloproteinases 9 (MMP-9) in liver tissue. A significant reduction in the oxidative stress markers-induced by S. mansoni infection including lipid peroxidation and nitrite/nitrate was also detected. The level of some antioxidant enzymes (superoxide dismutase, catalase, glutathione peroxidase and glutathione reductase) and reduced glutathione was greatly enhanced. Furthermore, treatment with probiotics or yogurt inhibited apoptosis in hepatic tissue, which is mainly assigned to the decreased expression level of caspases-3 in liver tissue.ConclusionOur findings represent the promising anti-schistosomal activities of probiotics and yogurt.

Anti-Inflammatory Effect of Hostacortin (Steroidal) or Vioxx (Non-Steroidal) on Mice Infected with Schistosoma Mansoni and Treated with Praziquantel

Background: Schistosoma mansoni, a helminthic parasite induces granulomatous inflammation following deposition of the eggs in the liver. The present study was conducted to evaluate the efficacy of two anti-inflammatory drugs; Hostacortin (steroidal) and Vioxx (non-steroidal) in ameliorating the damaging effects of S. mansoni infection in mice. The effects of the two anti-inflammatory drugs after treatment of schistosomiasis mansoni with praziquantel (PZQ) in mice were assessed for management of S. mansoni infection. Materials and Methods: The PZQ drug was administered to 6-weeks S. mansoni infected mice at one oral dose of 685 mg/kg body weight. The anti-inflammatory activity of the two drugs was evaluated at dose levels of 10, 50,100 and 200 mg/kg body weight in mice infected with 80 S.mansoni cercariae / mouse and treated for 10 consecutive days after 6-weeks of infection. Some biochemical parameters indicating the hepatic function as enzymatic activity of transaminases; alanine aminotransferase (ALAT), aspartate aminotransferase (ASAT) and alkaline phosphatase (ALP) in liver as well as serum albumin and liver total protein were performed to evaluate the possible anti-inflammatory effect of any of the two used anti-inflammatory drugs in ameliorating the severity of the disease. In addition, some parasitological parameters as worm burden, liver egg count, hepatic granuloma size and hepato-somatic index were performed to evaluate the possible anti-inflammatory effect of any of the two used anti-inflammatory drugs in ameliorating the severity of the disease. Results: The results indicated that Hostacortin had no marked effect on the parasite burden and liver egg count. However, it caused a percentage decrease by 14.9 in the elevated ALP activity and pronounced increases by 33.2% and 11.3% in ALAT and ASAT activities, respectively, in liver tissue homogenate. Also, a significant reduction in granuloma size by 22.5% and 31.6% for doses 100 and 200 mg/kg, respectively, was recorded. Hostacortin treatment with PZQ improved the liver status as indicated by a significant reduction in number of worms, eggs count and size of the liver granuloma. However, Vioxx did not affect the parasite burden and liver egg count, it caused high reduction in the enzymatic activities of ALAT, ASAT, and ALP in liver tissue homogenate. In contrast with Hostacortin, Vioxx significantly increased the granuloma size by 27.6% at a dose level of 200 mg/kg. Conclusion: the treatment with Hostacortin, after PZQ treatment, ameliorates to some extent the severity of the disease, but Vioxx treatment causes additional hepatotoxicity in the S. mansoni infected mice after treatment with PZQ.

Protective Potential of Antioxidant Enzymes as Vaccines for Schistosomiasis in a Non-Human Primate Model.

Schistosomiasis remains a major cause of morbidity in the world. The challenge today is not so much in the clinical management of individual patients, but rather in population-based control of transmission in endemic areas. Despite recent large-scale efforts, such as integrated control programs aimed at limiting schistosomiasis by improving education and sanitation, molluscicide treatment programs and chemotherapy with praziquantel, there has only been limited success. There is an urgent need for complementary approaches, such as vaccines. We demonstrated previously that anti-oxidant enzymes, such as Cu–Zn superoxide dismutase (SOD) and glutathione S peroxidase (GPX), when administered as DNA-based vaccines induced significant levels of protection in inbred mice, greater than the target 40% reduction in worm burden compared to controls set as a minimum by the WHO. These results led us to investigate if immunization of non-human primates with antioxidants would stimulate an immune response that could confer protection as a prelude study for human trials. Issues of vaccine toxicity and safety that were difficult to address in mice were also investigated. All baboons in the study were examined clinically throughout the study and no adverse reactions occurred to the immunization. When our outbred baboons were vaccinated with two different formulations of SOD (SmCT-SOD and SmEC-SOD) or one of GPX (SmGPX), they showed a reduction in worm number to varying degrees, when compared with the control group. More pronounced, vaccinated animals showed decreased bloody diarrhea, days of diarrhea, and egg excretion (transmission), as well as reduction of eggs in the liver tissue and in the large intestine (pathology) compared to controls. Specific IgG antibodies were present in sera after immunizations and 10 weeks after challenge infection compared to controls. Peripheral blood mononuclear cells, mesenteric, and inguinal node cells from vaccinated animals proliferated and produced high levels of cytokines and chemokines in response to crude and recombinant antigens compared with controls. All together, these data demonstrate the potential of antioxidants as a vaccine in a non-human primate model.

Laboratory assessment of molluscicidal and cercariacidal effects of Glinus lotoides fruits

BackgroundThe negative impact of synthetic molluscicides on the environment and their high cost necessitated search for an alternative approach of using plant extracts for the control of schistosomiasis. The objective of this study was, therefore, to evaluate aqueous and ethyl acetate crude extracts of Glinus lotoides fruits for their cercariacidal activity and molluscicidal effect against schistosome snail intermediate hosts.MethodsAssessment of the molluscicidal activity against Biomphalaria pfeifferi was made by immersion method in accordance with WHO guideline. The results of mortality were statistically analyzed using probit analysis. The attenuating effect of the plant on Schistosoma mansoni cercariae was determined using establishment of adult worms as a parasitological parameter post exposure.ResultsThe 24 and 48 hour-LC50 values for the aqueous extract of G. lotoides fruits were 47.1 and 44.1 mg/L, respectively, whereas that of ethyl acetate were 66.1 and 59.6 mg/L, respectively. The 24 and 48 hour LC90 values for the aqueous extract of G. lotoides fruits were 56.96 and 51.0 mg/L, respectively, while that of ethyl acetate were 77.2 and 70.0 mg/L, respectively. The in vitro cercariacidal activity was determined after 2 hrs of exposure to the aqueous plant extract. It was found out that the LC50 and LC90 values were 18.7 and 41.7 mg/L, respectively. Besides, infectivity of Schistosoma mansoni cercariae to mice was determined by exposing mice to cercariae pre-treated with the sub-lethal concentrations (3.7, 11.6 and 18.7 mg/L) of the aqueous extract. A significant reduction in worm burden in mice was obtained at 11.6 mg/L (p < 0.05). Moreover, the reduction in number of worms recovered was highly significant at 18.7 mg/L (p < 0.001).ConclusionsThe results showed that G. lotoides has molluscicidal activity against B. pfeifferi snails and cercariacidal activity against S. mansoni. Yet, further comprehensive evaluation is recommended for the possible use of G. lotoides against B. pfeifferi and the schistosome parasite.

Characterization of a Surface Glycoprotein from Echinococcus multilocularis and Its Mucosal Vaccine Potential in Dogs

Alveolar echinococcosis is a refractory disease caused by the metacestode stage of Echinococcus multilocularis. The life cycle of this parasite is maintained primarily between foxes and many species of rodents; thus, dogs are thought to be a minor definitive host except in some endemic areas. However, dogs are highly susceptible to E. multilocularis infection. Because of the close contact between dogs and humans, infection of dogs with this parasite can be an important risk to human health. Therefore, new measures and tools to control and prevent parasite transmission required. Using 2-dimensional electrophoresis followed by western blot (2D-WB) analysis, a large glycoprotein component of protoscoleces was identified based on reactivity to intestinal IgA in dogs experimentally infected with E. multilocularis. This component, designated SRf1, was purified by gel filtration using a Superose 6 column. Glycosylation analysis and immunostaining revealed that SRf1 could be distinguished from Em2, a major mucin-type antigen of E. multilocularis. Dogs (n = 6) were immunized intranasally with 500 µg of SRf1 with cholera toxin subunit B by using a spray syringe, and a booster was given orally using an enteric capsule containing 15 mg of the same antigen. As a result, dogs immunized with this antigen showed an 87.6% reduction in worm numbers compared to control dogs (n = 5) who received only PBS administration. A weak serum antibody response was observed in SRf1-immunized dogs, but there was no correlation between antibody response and worm number. We demonstrated for the first time that mucosal immunization using SRf1, a glycoprotein component newly isolated from E. multilocularis protoscoleces, induced a protection response to E. multilocularis infection in dogs. Thus, our data indicated that mucosal immunization using surface antigens will be an important tool to facilitate the development of practical vaccines for definitive hosts.

Efficacy of Procox® Oral Suspension for Dogs (0.1% Emodepside and 2% Toltrazuril) against Experimental Nematode (Toxocara cati and Ancylostoma tubaeforme) Infections in Cats

Two exploratory studies were performed to determine the optimum therapeutic dose of Procox(®) for the removal of experimental infection with mature adult Toxocara (T.) cati and Ancylostoma (A.) tubaeforme in kittens. Procox(®) is a new oral suspension containing a combination of the nematocidal and coccidiocidal active principles emodepside (0.1 %) and toltrazuril (2 %).In the first study, 18 eight-weeks-old kittens were inoculated with 450 L3 larvae of T. cati. 56 days after infection, the kittens were allocated to three treatment groups and were treated with 0.5 mg emodepside/kg body weight (group 1), 0.25 mg emodepside/kg body weight (group 2) and 0.1 mg emodepside/kg body weight (group 3), respectively. In the second study, 10 eight-weeks-old kittens were inoculated with 350 L3 larvae of A. tubaeforme. Four weeks after infection, the kittens were allocated to two treatment groups and were treated with 0.1 mg emodepside/kg body weight (group 1) or 0.25 mg emodepside/kg body weight (group 2). In both studies, all kittens received a reference treatment with Drontal(®) (230 mg pyrantel embonate and 20 mg praziquantel per tablet) at the recommended dose of one tablet/4 kg body weight 5 days after treatment with Procox(®). Anthelmintic efficacy was calculated by reduction in worm numbers expelled with the faeces following treatment with Procox(®) as compared with faecal worm numbers after reference treatment with Drontal(®), by thus avoiding necropsy of the animals.In the T. cati study, emodepside was at 99.9 %, 100 % and 96.5 % effective at a dosage of 0.5 mg, 0.25 mg and 0.1 mg per kg body weight, respectively. Against A. tubaeforme emodepside was at 95.7 % and 100 % effective at a dosage of 0.1 mg and 0.25 mg per kg body weight. No adverse events were seen during either study.It can be concluded that Procox(®) is efficacious for the control of mature adult T. cati and A. tubaeforme infections in cats at a single-dose rate of 0.25 mg emodepside/kg body weight.

The Schistosoma bovis Sb14-3-3ζ recombinant protein cross-protects against Schistosoma mansoni in BALB/c mice

Current control programs against schistosomiasis could be reinforced through the use of an effective vaccine. Schistosome 14-3-3 proteins have been proposed as candidates for vaccine against the respective infections, and were seen to elicit high protection levels against Schistosoma bovis in a previous work done by our group. We have therefore investigated the protective capacity of the 14-3-3 protein from S. bovis - Sb14zeta - against Schistosoma mansoni in mice. In addition, we have addressed the influence of the co-administration of three different immunomodulators with the 14-3-3 polypeptide. Protection was high when the Sb14zeta protein was combined in two independent experiments with the AA2829 and PAL immunomodulatory molecules as regards both the reduction of worm numbers (mean: 64.8%) and egg loads in liver (mean: 73.9%) or intestine (mean: 71.5%). In contrast, the degree of protection achieved with the Sb14zeta-CpG vaccine was very low (14.9% reduction in worm numbers, and 46.6% and 32% reduction in liver and intestinal egg loads). The immune responses observed in the vaccinated animals showed that the production of IFNgamma and the absence of IL-4, accompanied by a strong humoral response, are insufficient to elicit protection against S. mansoni.

Persistence of the protective immunity to Schistosoma japonicum in Chinese yellow cattle induced by recombinant 26 kDa glutathione- S-transferase (reSjc26GST)

To observe the long lasting effect of the recombinant Sj26GST sub-unit vaccine against Schistosoma japonicum in cattle, animals aged from 5 to 12 months were vaccinated with reSjc26GST, and were challenged by natural infection 6 months or 12 months after vaccination. Worm burdens per cattle and egg burden in tissue (per gram) of cattle with or without vaccination were compared. The results showed that anti-reSjc26GST antibodies were produced in vaccinated cattle. Following natural infection, the vaccinated and the control non-vaccinated cattle were all found to be infected with S. japonicum. A 30% reduction in worm number was observed in the vaccinated cattle when compared with the control cattle. The anti-fecundity effect was characterized by an average of 60% decrease in eggs deposited in the liver of vaccinated cattle; such a decrease is obviously very significant. In addition to the anti-fecundity effect induced in the vaccinated cattle, the number of miracidum hatched per 50 g faeces and the number of eggs released in intestinal tissues per gram were reduced or decreased. Results suggested that the immune responses induced by reSjc26GST in cattle were similar to that in buffaloes and in pigs. In addition, our result demonstrated that the lasting effect of immunity to S. japonicum induced in cattle after vaccination with reSjc 26 GST could persist at least 12 months.

Prospects for a schistosome vaccine.

After some 20 years experience it is generally agreed that chemotherapy against schistosomiasis, a parasitic disease which should be considered a consequence of a chronic infection, does have significant limitations. In particular, chemotherapy does not affect transmission of the infection or the high re-infection rates and so limits the success by demanding frequently re-scheduled mass treatments. For this reason, a complementary approach that can be integrated and could sustain chemotherapy-based control programs, i.e. vaccination, is very much needed. The rationale is that drug treatment would provide short-term reduction of worm burdens and vaccination, long-term protective immune response. Vaccination can either be targeted towards the prevention of infection or to the reduction of parasite fecundity. A reduction in worm numbers is the "gold standard" for anti-schistosome vaccine development but, as schistosome eggs are responsible for both pathology and transmission, a vaccine targeted on parasite fecundity and egg viability also appears to be entirely relevant. This review considers various aspects of anti-schistosome protective immunity that are important in the context of vaccine development. The current status in the development of vaccines against the African (Schistosoma mansoni and S. haematobium) and Asian (S. japonicum) schistosomes is then discussed as the new approaches that may improve on the efficacy of the available vaccines and aid in the identification of new targets for immune attack.

In vitro and in vivo studies on the bioactivity of a ginger (Zingiber officinale) extract towards adult schistosomes and their egg production.

The bioactivity of an ethyl acetate extract of ginger (Zingiber officinale) towards Schistosoma mansoni adult pairs, both cultured in vitro and in vivo in laboratory mice, was investigated by monitoring worm mortality and fecundity. In vitro, a concentration of 200 mg l(-1) of extract killed almost all worms within 24 h. Male worms seemed more susceptible than female under these conditions. Cumulative egg output of surviving worm pairs in vitro was considerably reduced when exposed to the extract. For example, after 4 days of exposure to 50 mg l(-1), cumulative egg output was only 0.38 eggs per worm pair compared with 36.35 for untreated worms. In vivo efficacy of the extract was tested by oral and subcutaneous delivery of 150 mg kg(-1) followed by assessment of worm survival and fecundity. Neither delivery route produced any significant reduction in worm numbers compared with untreated controls. Worm fecundity was assessed in vivo by cumulative egg counts per liver at 55 days post infection with mice treated subcutaneously. Such infections showed egg levels in the liver of about 2000 eggs per worm pair in 55 days, in both treated and control mice, with no significant difference between the two groups. To ensure that density-dependent effects did not confound this analysis, a separate experiment demonstrated no such influence on egg output per worm pair, at intensities between 1 and 23 worms per mouse.

The vaccine efficacy of native paramyosin (Sj-97) against Chinese Schistosoma japonicum

One of the promising anti-schistosome vaccine candidates currently under investigation is paramyosin, a 97-kDa myofibrillar protein located in the muscles and tegument of schistosome worms. Here we describe the results of two vaccination\\challenge experiments undertaken in mice using native paramyosin isolated from adult worms of a Chinese strain of Schistosoma japonicum. In both sets of experiments, a relatively low but consistent and significant reduction in worm burden was evident in mice vaccinated subcutaneously with S. japonicum paramyosin and Freunds adjuvant. In contrast, intraperitoneal vaccination of mice with Chinese strain S. japonicum paramyosin without adjuvant did not result in any reduction in worm numbers when compared with a saline control group. These data contrast with the impressive protection figures reported by another group who used a similar intraperitoneal vaccination protocol with native paramyosin extracted from Philippine strain S. japonicum.

Anti-fecundity immunity to Schistosoma japonicum induced in Chinese water buffaloes ( Bos buffelus) after vaccination with recombinant 26 kDa glutathione- S-transferase (reSjc26GST)

We have shown previously that immunisation of mice and pigs with recombinant 26 kDa GST (reSjc26GST) induces a pronounced anti-fecundity effect after experimental infection with Chinese Schistosoma japonicum. We report here that anti-fecundity immunity can also be induced against reSjc26GST in Chinese water buffaloes ( Bos buffelus), important reservoir hosts for S. japonicum in China. Anti-Sjc26GST antibodies were produced in immunised buffaloes and, following challenge with S. japonicum cercariae, a 22.3% reduction in worm numbers was evident in vaccinated when compared with control animals. The anti-fecundity effect was characterised by a significant decrease in faecal egg output and eggs deposited in host tissues with those in the liver and intestine being reduced by about 50%. In addition to the anti-fecundity effect, reSjc26GST reduced by nearly 40% the egg-hatching capacity of S. japonicum eggs into viable miracidia. In terms of vaccination strategy, these effects would combine to diminish pathology in animals immunised with reSjc26GST and reduce transmission of schistosomiasis japonica.

The relationship between the frequency distribution of Ascaris lumbricoides and the prevalence and intensity of infection in human communities

Observed field data from a range of geographically distinct human communities suggest a consistent non-linear relationship between prevalence and mean intensity of Ascaris lumbricoides infection. Utilizing the negative binomial distribution as a description of observed aggregation, maximum-likelihood analysis reveals that the degree of aggregation is a negative linear function of mean worm burden. The factors responsible for this relationship in human populations require further study but may involve some combination of (i) density-dependent reduction in worm numbers within individuals, (ii) density-dependent parasite-induced host mortality or (iii) self-treatment by heavily infected hosts. Variability in the degree of aggregation appears dependent on the level of infection in a community and independent of geographical differences in the host or parasite populations.

Toxicity of cyclosporin A (CsA) against developmental stages of Schistosoma mansoni in mice

It has been shown elsewhere that the immunosuppressive drug cyclosporin A (CsA) exerts profound schistosomicidal activity when given to infected mice via a multiple administration regime. We show here that a single treatment regime also effects significant reductions in worm burden. Moreover, drug efficacy is maintained at CsA concentrations shown to be subimmunosuppressive in other systems. Subcutaneous treatment effected higher levels of schistosomicidal activity than intraperitoneal or oral treatment, irrespective of whether the drug was given prior to or during infection. Topical application of CsA to the skin site of cercarial penetration, prior to infection resulted in no reduction in worm burden. Systemic release of CsA from a slowly adsorbed, oil-based drug-vehicle combination effected greater levels of killing than when CsA was dissolved in an aqueous drug vehicle. All developmental stages of Schistosoma mansoni were susceptible to killing by a single dose of CsA but, in the case of liver-stage worms, an increased concentration of drug and a longer period between treatment and portal perfusion were needed for killing to be measurable as a reduction in worm numbers.

Immunization of baboons with attenuated schistosomula of Schistosoma haematobium: levels of protection induced by immunization with larvae irradiated with 20 and 60 krad

We have shown previously that baboons ( Papio anubis) develop high levels (>80%) of protection against challenge infection following immunization with Schistosoma haematobium cercariae irradiated with 20 krad. In the present study baboons were immunized with schistosomula irradiated with either 20 krad or 60 krad, with variations in the timing and number of larvae comprising each vaccination. Baboons immunized 2 or 3 times with schistosomula irradiated with 20 krad were significantly more protected (85–90%) against challenge infection than baboons similarly immunized with larvae receiving 60 krad (56-50% protection). Baboons immunized with schistosomula irradiated with 20 krad were better protected against challenge infection at 8 weeks after immunization than at 28 weeks after immunization. Protection was manifest by a reduction in worm numbers, tissue and excreta egg counts, gross pathology and, to a lesser extent, by stability of body weight and haematological indices following challenge. Enzyme-linked immunosorbent assay (ELISA) results of selected baboon sera showed few differences related to irradiation dose alone, but titres were higher in baboons receiving booster immunizations, and there was a significant correlation between titres immediately preceeding challenge and the degree of resistance. Examination of responses to individual schistosomular surface antigens by immunoprecipitation and sodium dodecyl sulphate-polyacrylamide gel electrophoresis showed no correlation between the pattern of antigens recognized and resistance status. As with the ELISA assay, an anamnestic response was detected after vaccination, while the amount of antibody present declined markedly with increasing time after individual immunizations.

A dose-response investigation on the level of resistance to pyrantel citrate in nodular worms of pigs

This study was undertaken to determine the level of resistance against pyrantel citrate in strains of Oesophagostomum quadrispinulatum and Oesphagostomum dentatum which have previously been found resistant to this anthelmintic. Groups of pigs were artificially infected with batches of infective larvae which were previously found either susceptible or resistant to pyrantel citrate. After treatment with 1, 2 and 4 times the recommended dose (14 mg kg −1) of pyrantel citrate, the resistant O. quadrispinulatum population was reduced by 51.0, 76.2 and 86.1%, and O. dentatum by 41.2, 47.9 and 78.5%. The results indicated that O. dentatum was slightly more resistant ( P < 0.05) than O. quadrispinulatum to pyrantel citrate. Treatment of the susceptible worms with 1 and 2 times the recommended dose caused a reduction in worm numbers by 61.0 and 99.4%, respectively.

Tolerance of Kenyan Schistosoma mansoni to oxamniquine

Although 30 mg/kg oxamniquine produced high levels (85·5 to 99·5%) of egg reduction in Kenyan children infected with Schistosoma mansoni after a single oral treatment, cure rates from children at Mwea in Kirinyaga district were lower than those from Machakos (58% v. 74%). Redosing uncured children confirmed this lower cure rate (36% v. 83%). Isolates from infected children were passaged into mice and dosed with oxamniquine. Lower than expected reductions in worm numbers were obtained, suggesting that oxamniquine tolerant S. mansoni are present in the normal worm population in Kenya. It is concluded that mass use of oxamniquine at 30 mg/kg may produce problems of drug resistance.

Immunization with Infective Larvae of Strongyloides ratti (Nematoda) Exposed to Microwave Radiation

Microwaves have not been tested previously for possible application in producing immunogenic preparations of parasites. This study examines the immunizing capacity of microwave-irradiated, infective larvae of Strongyloides ratti in rats. Rats were inoculated subcutaneously with untreated, microwaved, or microwaved and homogenized larvae, or distilled water, and challenged with untreated larvae. Data were collected on egg production and worm number/rat during primary infections and on egg production, worm number/rat, worm size, and eggs in utero/worm following challenge. Our results demonstrated that microwaved, infective larvae (intact or homogenized) of S. ratti were immunogenic for rats, even though they were incapable of reaching the intestine and maturing to adult worms. The immunity elicited by exposure to microwaved larvae was characterized on challenge by a significant reduction in the number of eggs produced/worm, by the formation of perioral plugs, and by reductions in worm numbers and size. These results suggest that microwave radiation may provide a valuable new tool for parasitic vaccine production. In addition, we have demonstrated the occurrence of a feature of the immune response of rats to S. ratti that may have been overlooked previously; i.e., a gut-level response that was elicited by larvae, but manifested against adult worms in the intestine.