Failure of low level γ-irradiation of infective larvae to influence establishment or expulsion of Trichostrongylus colubriformis in guinea pigs

Trichostrongylus colubriformis infective larvae were subjected to various levels of γ-irradiation and administered to guinea pigs. The worms surviving were subsequently counted. Irradiation with 12.9 C kg⁻ inhibited worm establishment but lower doses neither influenced worm establishment nor survival.     

The consequences of short-term grazing of bioactive forages on established adult and incoming larvae populations of Teladorsagia circumcincta in lambs

The objective of this study was to investigate the consequences of short-term grazing on bioactive forages on (i) the viability and fecundity of established adult Teladorsagia circumcincta population and (ii) the establishment and development of incoming T. circumcincta infective larvae. Forty-eight, parasite naive, 3-month old, grazing lambs were artificially infected with 8000 infective larvae of T. circumcincta on day 1 of the experiment. On day 21 p.i., lambs were allocated to one of three bioactive forage grazing treatments; chicory (Cichorium intybus), sulla (Hedysarum coronarium), lotus (Lotus pedunculatus), and the control grass/clover (Lolium perenne/Trifolium repens) forage. On day 28 of the experiment a second dose of 8000 T. circumcincta infective larvae was administered to the lambs to investigate the effects of forages on the ability of infective larvae to establish within the host. All animals were slaughtered for worm recovery on day 35, while liveweight gain, feacal egg counts (FEC) and total worm egg output were monitored regularly throughout the experiment. Although FEC or total egg output were similar among the groups, adult worm burdens at slaughter were significantly affected (P<0.05) by forage treatment during the 2 week grazing period. Lambs grazing chicory had the lowest adult worm burdens and significantly lower numbers of male worms compared to those grazing on grass/clover (P<0.01), while the lambs grazing on sulla or lotus had similar adult populations to grass/clover fed animals. The results from the worm recoveries of the second dose (immature worm burdens) were affected by physiologically and/or immunologically mediated mechanisms, which reduced larval establishment in all treatments. Nevertheless, immature worm burdens at slaughter were similar between chicory, sulla and grass/clover group, while the immature worm recoveries from the lotus group were significantly higher (P<0.05) compared to those from lambs grazing grass/clover. Overall, the results of the present study support the view that chicory can be a promising candidate species in pasture management practices to control T. circumcincta burdens.     

Persistence of acquired immunity to Trichostrongylus colubriformis in sheep after termination of infection

Lambs were infected with 6000 Trichostrongylus colubriformis L3 per week for 18, 12 or 6 weeks, beginning at ages 14, 20 and 26 weeks, respectively. At the end of the primary infection subgroups had geometric mean adult worm burdens of 5000, 15,000 and 18,000, respectively. In the remaining sheep the worm population was removed with anthelmintic, and sheep had no further larval intake until challenged with T. colubriformis 1,6, 12, 18 or 24 weeks later. In the groups given 18 or 12 weeks primary infection, establishment of challenge doses was low (less than 25% of establishment in helminth naive controls) in most animals at all challenge times. However, for the groups given 6 weeks primary infection, establishment was low only at the first two challenge times. Thereafter it had similar mean to control groups, but much greater variance. Other subgroups were challenged with T. colubriformis, Ostertagia circumcincta and Haemonchus contortus 1 week after worm removal. In these animals T. colubriformis establishment was not different to animals challenged at the same time with T. colubriformis alone, however immunity to T. colubriformis afforded little protection against the other species. The results of this experiment were incorporated into a simulation model of the population dynamics of T. colubriformis.     

Population dynamics of the parasitic stages of Oesophagostomum dentatum in pigs in single and trickle infections

A mathematical model was developed to describe the dynamics of the parasitic stages of Oesophagostomum dentatam in pigs. An immigration-death model with constant establishment, development and death rates was fitted to L3, L4 and adult worm burdens observed in a single-infection experiment. Female worm length was modelled by a function of worm age and total worm burden, while worm egg production (eggs per gram faeces per female worm) was modelled by a function of worm age and worm length. The model was then used to predict worm burdens observed in a trickle-infection experiment. The predicted worm burdens were much higher than those observed, suggesting that worm death rates were higher during the trickle infection. After increusing worm death rates to fit the observed worm burdens, female worm lengths and egg production in the trickle infection were predicted. At the medium- and high-dose rates, predicted worm lengths and, thus, egg preduction were lower than observed, while at the low-dose rate predicted egg production was too high. It appeared that in the trickle infections, total worm burden had less influence on observed female worm length and egg production than in the single infections. The results suggest that the demography of O. dentatum in pigs differs between single and trickle infections.     

Concomitant and protective immunity in mice exposed to repeated infections with Echinostoma malayanum

Concomitant immunity and its consequence against infection play roles in regulating worm burdens in helminthiasis. Under natural conditions, this immunity is generated by exposure to repeated low dose or trickle infection. In this study, concomitant immunity was induced in mice exposed repeatedly to infection with Echinostoma malayanum and its protective effect on a challenge infection evaluated. A profile of worm burden from exposure to 10 metacercariae/mouse/week rose rapidly during the first 2 weeks reaching a plateau from week 3 to 8 post infection. Based on a cumulative dose of infection, worm recoveries were around 75% in the first 2 weeks, dropped to 50% at week 3 and 19% at week 8. After week 2, adult worm burden was constant and no juvenile worms were found after week 3 of the experiment. To examine the effect of resistance against reinfection, mice in the experimental group were primarily infected with 10 metacercariae/week for 5 weeks, treated with praziquantel and were challenged with 75 metacercariae/animal. The number of worms recovered from the experimental groups was significantly lower than that from naïve control groups beginning from 24 h to 28 days post challenge. The worms in the experimental group showed growth retardation and the proportion of adult worms was lower than that in the control animals especially during the first 3 weeks of the experiment. Parasite fecundity was also suppressed compared with that in the control group. The selective effects of protective immunity on establishment, growth, and fecundity of challenged worms affected the population dynamics of E. malayanum which is a similar phenomenon to concomitant immunity in schistosomiasis.     

Postnatal challenge infections of congenitally Schistosoma japonicum-infected piglets

The aim of the present study was to assess the effect of a congenital Schistosoma japonicum infection on the establishment, fecundity, and pathogenicity of a postnatal challenge infection. Five prenatally S. japonicum-infected piglets received a challenge infection (prenatal + challenge group), 5 prenatally infected piglets were followed without challenge (prenatal group), and 10 piglets, born by unexposed sows, served as challenge controls (challenge control group). Challenge infections were given 8 wk after the piglets were born (14 wk after the primary infection of the sows), and the study lasted another 11 wk. Variables included worm burden, tissue egg count, and liver pathology. Worm establishment and tissue egg count were comparable in the prenatal + challenge group and in the challenge control group, both exceeding at a statistically significant level those in the prenatal group. No difference in worm fecundity (eggs/female worms/g tissue) was seen between the 3 groups. Liver pathology (i.e., portal and septal fibrosis) was more severe in the challenge control group compared to the other groups. A congenital S. japonicum infection in piglets thus affected neither establishment nor fecundity of a postnatal challenge infection. In spite of this, the challenge infection gave rise to much less liver pathology than the similarly sized challenge control infection.     

Efficacy of UV-irradiated larval vaccine of Ancylostoma ceylanicum (Looss, 1911) in golden hamsters (Mesocricetus auratus)

A vaccination trial in golden hamsters with UV-irradiated infective larvae of Ancylostoma ceylanicum was attempted. One oral vaccination of hamsters with 100 infective larvae irradiated by means of UV-tube (390 nm) at different time intervals induced the development of resistance. As the time exposure of irradiation was increased, there was a corresponding decrease in the subsequent worm establishment. A high level of protection afforded by larvae irradiated for 15 min UV-exposure was recorded giving 99.0% and 95.0% worm reduction against the challenge doses of 100 and 1000 normal larvae respectively. There was no marked difference in worm establishment in hamsters vaccinated either orally or subcutaneously, followed by oral challenge. In the vaccinated hamsters, the manifestations of resistance at 15 min UV-exposure were shown by marked reduction in worm establishment and highly reduced epg in pellets with significantly higher blood haemoglobin levels compared with those given normal larvae as vaccine and challenge controls.     

Ivermectin against larval stages of Dirofilaria repens in dogs

The prophylactic efficacy of ivermectin against Dirofilaria repens infections in dogs was investigated. A first trial was carried out on 15 dogs exposed to four inoculations of L3 larvae at 15-day intervals and treated, in groups of five, with 0, 6 or 12 micrograms/kg body weight of ivermectin given per os 30 and 60 days after the first inoculation. Necropsy, performed about 9 months later, revealed that worm burdens were reduced by 86.6 and 92.8% for the 6 and 12 micrograms/kg dose levels, respectively. In a second trial with an otherwise identical protocol, a dose rate of 24 micrograms/kg of ivermectin was tested in 12 dogs. Only one of the six treated dogs was found worm free at necropsy. The worm burden was reduced by 87.9% in treated animals as opposed to controls. A lengthening of the prepatent periods, which might be considered dose related, was apparent in all treated groups. Ivermectin was not completely effective in preventing establishment of experimental infections with D. repens in dogs.     

Transforming growth factor-β and Th17 responses in resistance to primary murine schistosomiasis mansoni

Discovery of the T-helper (Th) 17 cell lineage and functions in immune responses of mouse and man prompted us to investigate the role of transforming growth factor-beta (TGF-β) and interleukin (IL)-17 in innate resistance to murine schistosomiasis mansoni. Schistosoma mansoni-infected BALB/c and C57BL/6 mice were administered with recombinant TGF-β or mouse monoclonal antibody to TGF-β to evaluate the impact of this cytokine on host immune responses against lung-stage schistosomula, and subsequent effects on adult worm parameters. Developing schistosomula elicited increase in peripheral blood mononuclear cells (PBMC) mRNA expression and/or plasma levels of IL-4, IL-17, and interferon-gamma (IFN-γ), cytokines known to antagonize each other, resulting in impaired Th1/Th2, and Th17 immune responses and parasite evasion. Mice treated with TGF-β showed elevated PBMC mRNA expression of IL-6, IL-17, TGF-β, and TNF-α mRNA and increased IL-23 and IL-17 or TGF-β plasma levels, associated with significantly (P < 0.02–<0.0001) lower S. mansoni adult worm burden compared to controls in both mouse strains, thus suggesting that TGF-β led to heightened Th17 responses that mediated resistance to the infection. Mice treated with antibody to TGF-β showed increase in PBMC mRNA expression and plasma levels of IL-4, IL-12p70, and IFN-γ, and significantly (P < 0.02 and <0.0001) reduced worm burden and liver worm egg counts than untreated mice, indicating that Th1/Th2 immune responses were potentiated, resulting in significant innate resistance to schistosomiasis. The implications of these observations for schistosome immune evasion and vaccination were discussed.     

Population dynamics of Trichostrongylus colubriformis in sheep: model to predict the worm population over time as a function of infection rate and host age

The developing immunity of sheep to Trichostrongylus colubriformis infections was described by a mathematical function. The rate of adult establishment was assumed to be a measure of the host's acquired immunity to this parasite. Prediction of establishment from infection rate and host age was used to estimate worm burden, worm rejection and arrested development.     

The relationship of abnormal mucosal microtopography with distribution of Trichostrongylus colubriformis in the small intestines of lambs

The relationship of abnormal mucosal microtopography with distribution of Trichostrongylus colubriformis in the small intestines of lambs. International Journal for Parasitology4: 153–163. The distribution of T. colubriformis was studied by counting worms in sequential 1-m segments from the guts of 14 infected lambs. Mucosal morphology was described at corresponding 1-m intervals and compared with similar samples from uninfected controls. A mean of 90 per cent of worms was recovered in the first 6 metres of gut. Maximum worm counts occurred in the first (eight lambs) second (three lambs) or third (three lambs) metre. Less than 0·8 per cent of worms were found in the abomasa of five lambs. Flat mucosae or abnormal surface patterns were seen frequently in the anterior small intestine of infected lambs. Degree of mucosal abnormality was positively associated with magnitude of worm numbers/m, and negatively correlated with distance of the sample from the pylorus, by analysis of partial correlation of worm numbers/m, mucosal type score, and distance from the pylorus. Mucosae from areas with > 4000 worms/m tended to have significantly shorter villi than intestine of control lambs. Factors influencing worm distribution and pattern of establishment are discussed, as is the association of extreme villus atrophy with poor performance by infected lambs.     

Population dynamics of Trichostrongylus colubriformis in sheep: the effect of infection rate on the establishment of infective larvae and parasite fecundity

The establishment of Trichostrongylus colubriformis was estimated in helminthologically naive 20-week-old Merino sheep given third stage infective larvae (L3) at rates of 2000, 632 or 200 L3 per day, 5 days per week. After varying periods of continuous L3 intake, a levamisole-susceptible strain of T. colubriformis was replaced with a highly resistant strain for 1 week. The animals were then treated with levamisole to remove the susceptible population, and establishment of the cohort of resistant worms was estimated. In previously uninfected sheep, approximately 65% of the L3 given in the first week became established as adults. This fell to low levels (less than 5%) after 7, 10 and 14 weeks of continuous L3 intake for the high, medium and low infection rates, respectively. At the low infection rate, establishment remained at maximum levels for the first 4 weeks, but then fell at a rate similar to that observed for the higher infection rates. This implied that a threshold of worm exposure was required before resistance to establishment developed. Parasite egg production, expressed as eggs per gram of faeces, was proportional to infection rate and is explained by higher worm burdens occurring at high infection rates. However, estimates of fecundity in eggs per female per day showed the opposite relationship with rate of infection. Fecundity stayed high (approximately 600) for 5 weeks at the low infection rate but only maintained this level for 3 weeks and 1 week at the medium and high rates, respectively. This suggests that fecundity, like establishment, was similarly affected at threshold levels of immunological recognition.     

Meningeal worm in a reintroduced elk population in Kentucky

Meningeal worm (Parelaphostrongylus tenuis) has been implicated in the failure of several elk (Cervus elaphus) restoration attempts in the eastern United States. However, limited post-release monitoring and a paucity of published literature prevents a clear understanding of this parasite's role in past failures. During winters of 1997-2001, the Kentucky Department of Fish and Wildlife Resources translocated 1,044 elk from western states to eastern Kentucky (USA) in an effort to restore a free-ranging population. We monitored 521 radio-collared elk over 4 yr to determine the impact meningeal worm had on population establishment. Thirty (23%) of 129 non-capture related mortalities were attributed to meningeal worm. Twenty-two (73%) of these meningeal worm-caused mortalities were animals < 3 yr old. If younger elk born in Kentucky suffer higher mortality rates than older translocated elk, the population growth observed during the initial years of restoration may be temporary. Additional research is necessary to determine the influence meningeal worm will have on elk population growth in Kentucky.     

Worm wounding increases levels of pollen-related food allergens in soybean (Glycine max)

The levels of food allergens in worm-wounded or non-wounded green soybeans (edamame) and mature soybeans were investigated by immunoblotting and enzyme-linked immunosorbent assay (ELISA), using allergen-specific antibodies. Non-wounded and worm-wounded soybeans showed similar total protein profiles after Coomassie brilliant blue staining, but some protein bands were observed to have been changed by worm wounding. Immunoblotting with specific antibodies for major soybean allergens (Gly m 5, Gly m 6, Gly m Bd 30 K, and Kunitz soybean trypsin inhibitor) revealed that protein band profiles and intensities were not significantly changed by worm wounding. In contrast, levels of the pollen-related soybean allergens Gly m 4 and Gly m 3 were strongly increased by worm wounding in both green and mature soybeans, as detected by immunoblotting and ELISA. These results suggested that the pollen-related food allergen risk (i.e., oral allergy syndrome; OAS) from soybeans might be enhanced by worm wounding of soybeans.     

Diet texture modifies outcome of a primary infection with Heligmosomoides polygyrus (nematoda) in mice.

To determine if dietary texture altered the establishment, survival and reproduction of Heligmosomoides polygyrus during a primary infection, commercial mouse chow (Purina Chow) was fed in either pelleted or powdered form to 2 groups of infected BALB/c mice, and a semipurified, biotin-fortified, egg-white-based diet was provided in powdered form to a third group of mice. Diet texture (powdered vs. pelleted) modified parasite establishment, as evidenced by higher worm recovery 6 days postinfection (PI) in both groups of mice fed powdered diets compared with the group fed the pelleted diet, but diet texture had no detectable effect on net or per capita egg production or on day 30 worm survival. However, almost twice as many worms were recovered from mice fed the semipurified, powdered diet than those fed either textural formulation of the commercial mouse chow on day 30 PI, indicating that a dietary component in the semipurified diet, such as the single fiber source cellulose, facilitated parasite survival, or that other ingredients in the commercial mouse chow, perhaps the more complex fiber components, reduced worm survival, or both. We conclude that dietary texture influences parasite establishment and that specific fibers that change texture can individually and independently modify H. polygyrus survival.     

Immunization of Mastomys coucha with Brugia malayi Recombinant Trehalose-6-Phosphate Phosphatase Results in Significant Protection against Homologous Challenge Infection

Development of a vaccine to prevent or reduce parasite development in lymphatic filariasis would be a complementary approach to existing chemotherapeutic tools. Trehalose-6-phosphate phosphatase of Brugia malayi (Bm-TPP) represents an attractive vaccine target due to its absence in mammals, prevalence in the major life stages of the parasite and immunoreactivity with human bancroftian antibodies, especially from endemic normal subjects. We have recently reported on the cloning, expression, purification and biochemical characterization of this vital enzyme of B. malayi. In the present study, immunoprophylactic evaluation of Bm-TPP was carried out against B. malayi larval challenge in a susceptible host Mastomys coucha and the protective ability of the recombinant protein was evaluated by observing the adverse effects on microfilarial density and adult worm establishment. Immunization caused 78.4% decrease in microfilaremia and 71.04% reduction in the adult worm establishment along with sterilization of 70.06% of the recovered live females. The recombinant protein elicited a mixed Th1/Th2 type of protective immune response as evidenced by the generation of both pro- and anti-inflammatory cytokines IL-2, IFN-γ, TNF-α, IL-4 and an increased production of antibody isotypes IgG1, IgG2a, IgG2b and IgA. Thus immunization with Bm-TPP conferred considerable protection against B. malayi establishment by engendering a long-lasting effective immune response and therefore emerges as a potential vaccine candidate against lymphatic filariasis (LF).     

Parasitological and immunological responses of genetically resistant Merino sheep on pastures contaminated with parasitic nematodes.

One hundred and twenty lambs were grazed continuously from weaning until 9 months of age on 12 plots contaminated with larvae of three nematode species (Haemonchus contortus, Trichostrongylus colubriformis and Ostertagia circumcincta). The lambs were sired by either a genetically resistant ram or susceptible rams (determined by the response of previous progeny to artificial H. contortus infection). Half the resistant and half the susceptible lambs were given strategic anthelmintic treatment and the remainder remained untreated. Faecal egg counts and blood packed cell volume were measured frequently in all animals. One and 5 months after weaning, two lambs from each plot were slaughtered, and worm burdens and larval establishment rates of the three species of nematode were estimated. At the second slaughter, leukotriene levels and larval migration inhibitory (LMI) activity were measured in mucus collected from the small intestine. The dominant species in all faecal samples and the gastrointestinal tract was T. colubriformis. Lambs of the resistant genotype had lower faecal worm egg counts, lower worm burdens and higher levels of resistance to larval establishment. There were no differences in larval migration inhibition (LMI) activity, but resistant lambs had higher levels of the leukotriene LTC4/D4/E4. Further, the resistant genotype, identified on responsiveness to artificial infections with H. contortus, was more resistant to infections of three important species acquired naturally from contaminated pastures. All these genetic differences were maintained while the lambs were subject to strategic anthelmintic treatment.     

Immunization with Brugia malayi Myosin as Heterologous DNA Prime Protein Boost Induces Protective Immunity against B. malayi Infection in Mastomys coucha

The current control strategies employing chemotherapy with diethylcarbamazine, ivermectin and albendazole have reduced transmission in some filaria-endemic areas, there is growing interest for complementary approaches, such as vaccines especially in light of threat of parasite developing resistance to mainstay drugs. We earlier demonstrated recombinant heavy chain myosin of B. malayi (Bm-Myo) as a potent vaccine candidate whose efficacy was enhanced by heterologous DNA prime/protein boost (Myo-pcD+Bm-Myo) vaccination in BALB/c mice. BALB/c mouse though does not support the full developmental cycle of B. malayi, however, the degree of protection may be studied in terms of transformation of challenged infective larvae (L3) to next stage (L4) with an ease of delineating the generated immunological response of host. In the current investigation, DNA vaccination with Bm-Myo was therefore undertaken in susceptible rodent host, Mastomys coucha (M. coucha) which sustains the challenged L3 and facilitates their further development to sexually mature adult parasites with patent microfilaraemia. Immunization schedule consisted of Myo-pcD and Myo-pcD+Bm-Myo followed by B. malayi L3 challenge and the degree of protection was evaluated by observing microfilaraemia as well as adult worm establishment. Myo-pcD+Bm-Myo immunized animals not only developed 78.5% reduced blood microfilarial density but also decreased adult worm establishment by 75.3%. In addition, 75.4% of the recovered live females revealed sterilization over those of respective control animals. Myo-pcD+Bm-Myo triggered higher production of specific IgG and its isotypes which induced marked cellular adhesion and cytotoxicity (ADCC) to microfilariae (mf) and L3 in vitro. Both Th1 and Th2 cytokines were significantly up-regulated displaying a mixed immune response conferring considerable protection against B. malayi establishment by engendering a long-lasting effective immune response and therefore emerges as a potential vaccination method against LF.     

Growth and development of Gymnophalloides seoi in immunocompetent and immunosuppressed C3H/HeN mice

The growth and development of Gymnophalloides seoi were studied in C3H/HeN mice and effects of immunosuppression of the host on the worm development were observed. Two hundred metacercariae of G. seoi were orally administered to each mouse, and worms were recovered on days 1, 3, 5, 7, 14 and 21 post-infection (PI). The worm recovery rate was significantly higher in immunosuppressed (ImSP) mice than in immunocompetent (ImCT) mice except on days 1 and 3 PI. The worms attained sexual maturity by day 3 PI with eggs in the uterus, and worm dimensions and the number of uterine eggs continuously increased until day 14 PI in ImSP mice. Worms recovered from ImSP mice were significantly larger in size than those from ImCT mice on days 1 and 3 PI, and the number of uterine eggs was significantly larger in ImSP mice on days 5 and 7 PI. Genital organs such as the ovary, testes, and vitellaria, that were already developed in the metacercarial stage, grew a little in size until day 14 PI. The results show that the C3H/HeN mouse is, though not excellent, a suitable laboratory host for G. seoi.