Cross-protection between the metacestodes of Mesocestoides corti and Taenia crassiceps in mice

Novak M. 1984. Cross-protection between the metacestodes of Mesocestoides corti and Taenia crassiceps in mice. International Journal for Parasitology14: 497–501. Infection with M. corti generated significant resistance against a challenge with T. crassiceps introduced either 2 or 6 weeks after primary infection. Challenge infection with T. crassiceps did not influence primary infection with M. corti. Infection with T. crassiceps protected significantly against challenge with M. corti given 2 weeks but not 6 weeks after the primary infection. Challenge infection with M. corti significantly suppressed primary infection with T. crassiceps.     

Further observations on the nature and characteristics of cross protection against Fasciola hepatica produced in sheep by infection with Cysticercus tenuicollis

Dineen J. K., Kelly J. D. and Campbell N. J. 1978. Further observations on the nature and characteristics of cross protection against Fasciola hepatica produced in sheep by infection with Cysticercus tenuicollis. International Journal for Parasitology8: 173–176. Previous studies showed that sheep infected with Cysticercus tenuicollis were protected against a subsequent infection with Fasciola hepatica given at 12 weeks (Campbell, Kelly. Townsend & Dineen, 1977). The present studies showed that these animals were again protected against re-challenge with F. hepatica at 9 months. Resistance was detected about 10 weeks after re-challenge with metacercariae.Sheep in which the initial C. tenuicollis infections were terminated by anthelmintic at 12 weeks, were resistant to the primary infection with F. hepatica but became fully susceptible to the re-challenge at 9 months.These results suggest that maintenance of resistance depends upon persistence of the C. tenuicollis infections. They also indicate that resistance is maintained by cysts in the peritoneum which is remote from the reactive site (liver).Infection with F. hepatica at 3 weeks after infection with C. tenuicollis prevented cross protection against both the primary infection with F. hepatica and re-challenge at 9 months.     

Schistosoma mansoni and Fasciola hepatica: Cross-resistance in mice

Cross-resistance in Schistosoma mansoni and Fasciola hepatica infections were studied in mice. A primary infection of S. mansoni, 7 to 28 days old, did not stimulate a significant level of resistance to heterologous challenge with F. hepatica. In contrast, in older S. mansoni infections (54–65 days old) there was a significant level of resistance to a challenge with F. hepatica. The F. hepatica worm burden was reduced by 34.0 to 72.5% in separate experiments. Challenge infection with F. hepatica did not influence the number of S. mansoni in primary infections. No heterologous resistance to S. mansoni was found in mice with 7- and 23-day-old F. hepatica infections. However, primary infections with F. hepatica, 28, 32, 42, and 50 days old, conferred significant resistance to a heterologous challenge with S. mansoni. The established schistosome worm burden was reduced by 41.5 to 50.4%. In no case was the primary F. hepatica burden reciprocally influenced by challenge infection with S. mansoni.     

The stimulation of resistance in sheep to Fasciola hepatica by infection with Cysticercus tenuicollis

Infection of sheep with Cysticerus tenuicollis for 12 weeks generated a high level of protection (> 95%) against intra-ruminal challenge with metacercariae of Fasciola hepatica as measured by recovery of flukes from liver and bile ducts and counts of fluke eggs in faeces. The animals were resistant to Fasciola whether challenge was superimposed upon the cestode infection or after removal of the cestode with mebendazole.Previous infection with C. tenuicollis also protected against the pathogenic effects of challenge infection with F. hepatica. Liver fibrosis was much less extensive in resistant sheep than controls and PCV's were not affected although these were reduced during fluke infection in the control animals.     

Immunological response of the rat to infection with Taenia taeniaeformis: protective antibody response to implanted parasites.

Intraperitoneally implanted metacestodes of either T. taeniaeformis or T. crassiceps in rats provoked a high degree of resistance to oral challenge with eggs of T. taeniaeformis. This resistance was passively transferred to normal recipients with serum. Immunoglobulin fractions of immune serum containing IgG₁ or IgM were most effective in passive transfer and little activity was associated with IgG₂ antibodies. No skin-sensitizing antibodies were detectable in immune sera. These findings are in sharp contrast to previous observations involving protective immunoglobulins and reaginic antibodies in serum from rats with hepatic cysticerci of T. taeniaeformis. Possible reasons for this are discussed. Cysticerci implanted into normal rats survived for at least 21 days with no sign of host rejection, whereas those implanted into rats with hepatic infections with T. taeniaeformis were killed and encapsulated. Similar results were obtained by implanting cysticerci in normal rats given inoculations of complete Freund's adjuvant. Repeated inoculations of immune serum had no effect on the survival of implanted cysticerci, and it was concluded that exposure to infection by oncospheres provokes cellular defense mechanisms which can be effective against cysticerci in abnormal sites. Why these mechanisms are inoperative against hepatic cysticerci remains unclear.     

Fasciola hepatica: Comparative studies on fascioliasis in rats and mice

Chapman C. B. and Mitchell G. F. 1982. Fasciola hepatica: comparative studies on fascioliasis in rats and mice. International Journal for Parasitology12: 81–91. Certain characteristics of infection differ between rats and mice exposed to metacercariae of the trematode parasite, Fasciola hepatica. Rats develop a degree of age-related resistance (and infected older females contain fewer parasites than older males), resistance to reinfection in infected rats is demonstrated readily though is partial, and a comparable degree of resistance can be obtained in recipients of infected rat serum provided the serum is given at about the time of challenge. None of these features of F. hepatica infection is seen in mice. Rats also differ from mice in that they can be vaccinated against infection (although again, resistance is incomplete) using larval antigen mixtures in adjuvants. Mice do respond to infection by production of antilarval antibodies and a slight IgG₁ hypergammaglobulinaemia and larvae will sensitize mice for delayed hypersensitivity. The results of this study indicate that sera from infected rats versus infected mice will be useful in pinpointing antigens of F. hepatica larvae which are involved in expression of partial host protection.     

Fasciola hepatica: The effect of challenge by the subcutaneous or intraperitoneal route with living adult flukes in sensitized rats

When rats, sensitized either by subcutaneous implantation of adult F. hepatica or by a normal oral infection with F. hepatica metacercariae, were challenged by implanting adult flukes in the peritoneal cavity, 23% of these flukes were killed in rats sensitized by subcutaneous implantation and 71% in the rats sensitized by the oral route. In contrast neither of these sensitization routes were effective against subcutaneous challenge with adult fluke. Histological evidence suggested that about half of the dead flukes found were killed shortly after transfer and these flukes were surrounded with mononuclear cells. The remaining dead flukes appear to have died after becoming surrounded with a cyst. These latter flukes were surrounded by neutrophils and this cell type was very prominent in the cysts of sensitized rats.     

Schistosoma mansoni and Fasciola hepatica: Cross-resistance in mice with single-sex schistosome infections

Primary Schistosoma mansoni single-sex infections in mice, i.e., either male only or female only, did not stimulate any detectable level of heterologous resistance to challenge with Fasciola hepatica after 22 to 76 days, while statistically significant resistance to a challenge with F. hepatica was demonstrated in the presence of patent mixed-sex S. mansoni infections. Simultaneous infections with S. mansoni and F. hepatica induced a statistically significant reduction in the number of schisto-some worms established, i.e., the burden being reduced by 40.1 and 43.9%, respectively. There was no reduction of the F. hepatica worm burden. Similar features could be observed with a time interval of 48 hr between the S. mansoni infection and the F. hepatica challenge, i.e., the schistosome burden being reduced by 34.2 and 45.6%, respectively. Furthermore, simultaneous infections with S. mansoni and F. hepatica induced a statistically significant reduction of the egg production capacity per paired female schistosome worm as compared with that of the S. mansoni control group. Tissue egg counts of the various intestinal sections were reduced by 92.8–99.6%.     

Experimental infections with African trypanosomes: IV. Immunization of cattle with gamma-irradiated Trypanosoma rhodesiense

Cattle immunized with gamma-irradiated Trypanosoma rhodesiense were protected against a challenge inoculation of unirradiated trypanosomes given 1 wk later. These animals were still resistant when rechallenged after 8 mo and some residual immunity persisted for 14 mo after immunization. Animals which had undergone self-cure after infection were resistant when challenged 14 mo later. No resistance was observed in animals challenged with a heterologous strain of T. rhodesiense. The infections observed in unprotected bovines were of a mild nature. Leukopenia and fever were common early in the course of infection, but no anemia was evident at any time.     

Fasciola hepatica: role of developmental stages in the rat's resistance to challenge

Rats were sensitized by subcutaneous implantation of either metacercariae, 4 week-old juveniles, adult worms, or eggs of Fasciola hepatica and then challenged with 30 metacercariae 2 weeks later. Worm burdens were determined 8 weeks after challenge. Apart from adult worms, all implanted stages conferred a significant degree of protection on the recipients. The effectiveness of adult worm implants was not improved by using worms from different sources (sheep and cattle rather than rats) nor by extending the period of sensitization prior to challenge.     

Isolation of Fasciola hepatica genus-specific antigens

Santiago de Weil N., Hillyer G. V. and Pacheco E. 1984. Isolation of Fasciola hepatica genus-specific antigens. International Journal for Parasitology14: 197–206. The Fasciola hepatica antigens which induce antibody formation in acute fascioliasis were isolated by acid elution after reacting an F. hepatica tegument antigen extract with a CNBr-Sepharose 4B column coupled with IgG obtained from the serum of rabbits infected with fascioliasis for 6–10 weeks. These isolated antigens were further separated by gel filtration using a column packed with Sephacryl S-200. In this manner three major peaks were obtained. The best serologic antigens were found in peak 2 which had a mol. wt range of 14,000–43,000. This peak contains genus-specific F. hepatica antigens which are highly reactive with fascioliasis serum. These antigens do not cross-react with either Schistosoma mansoni or with bovine serum albumin by gel diffusion. Monitoring by ELISA and gel diffusion with heterologous and homologous antisera showed that as purification by antibody affinity chromatography proceeded, cross reactivity with S. mansoni was eliminated. The rabbit antiserum obtained against peak 2, when tested by immunoelectrophoresis with a crude F. hepatica extract shows one main band identical to the main band observed with serum from acutely infected rabbits. Up to two other minor bands can be detected using concentrated homologous antisera. Fractions obtained from preparative iso-electric focusing of the F. hepatica tegument extract were reacted with sera from rabbits with acute fascioliasis. Two main bands were observed in immunodiffusion with antigens eluting in a pH range of 7.4–8.7. When these fractions were monitored with anti peak 2 antisera, two precipitin bands appeared with antigens eluting in a pH range of 7.4–7.9. The F. hepatica genus-specific antigen pool was applied to ELISA to evaluate its ability to detect antibody in a primary F. hepatica infection in rabbits. A rise in absorbance values could be detected by 2 weeks of infection, reached high levels by 6 weeks and remained high through 28 weeks of infection.     

The response of lambs to vaccination and challenge with Trichostrongylus colubriformis: Effect of plane of nutrition on,and the inter-relationship between,immunological responsiveness and resistance

Wagland B. M., Steel J. W., Windon R. G. and Dineen J. K. 1984. The response of lambs to vaccination and challenge with Trichostrongylus colubriformis: effect of plane of nutrition on, and the inter-relationship between, immunological responsiveness and resistance. International Journal for Parasitology14: 39–44. Merino lambs weaned at 8 weeks of age were fed either ground and pelleted (high plane, HP) or chopped (low plane, LP) lucerne hay ad libitum to achieve an approximate 2-fold difference in liveweight gain. When aged 17 and 21 weeks, 15 of the 20 lambs in each diet group were vaccinated with 80,000 irradiated T. colubriformis larvae. At 25 weeks, vaccinated and unvaccinated lambs were treated with anthelmintic and one week later challenged with 30,000 normal larvae. Four weeks after challenge the animals were killed for worm counts. After vaccination HP lambs had higher titres of antibodies to the parasite and after challenge had lower worm egg outputs, and lower worm burdens than LP lambs. Immunological responsiveness (serum titre of complement-fixing antibodies against worm antigen) and manifestations of resistance (eggs produced per female worm per day and percent protection calculated from worm counts) were significantly correlated within dietary groups. Percent protection and egg production per female worm were highly correlated (r = ?0.81) in individual animals pooled over dietary groups, suggesting that both manifestations of resistance respond to essentially the same immunological mechanism. Failure to obtain significant correlation between weight gain pre-vaccination and immunological and resistance parameters indicated that animal production and resistance to infection are not genetically linked. Negative correlation of weight gain during the vaccination period with serum antibody titre at challenge suggests that the developing immune response competes with weight gain for limited physiological resources of the animal.     

Characterization of sheep antibodies involved in precipitate formation with surface antigens of Fasciola hepatica in vitro

Sandeman R. M. and Howell M. J. 1982. Characterization of sheep antibodies involved in precipitate formation with surface antigens of Fasciola hepatica in vitro. International Journal for Parasitology12: 467–471. The role of sheep antibodies which precipitate with surface antigens of Fasciola hepatica is unclear. In an attempt to clarify their function these antibodies were characterized as to their immunoglobulin class and ability to affect the survival of fluke in rats. The ability of fluke antigens complexed with sheep antibody to vaccinate rats against infection was also tested. IgM antibodies were involved in precipitate formation on the teguments of fluke 3 weeks after infection but IgG₁ predominated at later stages of infection. The decreased survival of fluke in rats after culture with increasing levels of sheep antibodies suggests that the antibodies exert some deleterious effect on the fluke in vitro. The fluke antigen-sheep antibody complex failed to immunize rats against infection. Since sheep antibodies to F. hepatica can impair the ability of fluke to resist further attack in rats but not sheep, it is suggested that some effector mechanism other than antibody is defective in the latter.     

Evidence for two distinct mechanisms of resistance in the rat to reinfection with Fasciola hepatica

Doy T. G. and Hughes D. L. 1982. Evidence for two distinct mechanisms of resistance in the rat to reinfection with Fasciola hepatica. International Journal for Parasitology12: 357–361. Congenitally athymic nude (rnu/rnu) and heterozygous hairy (rnu/ + ) rats were found to be equally highly resistant to oral reinfection with Fasciola hepatica. Accompanying the development of this resistance was a marked increase in intestinal eosinophil numbers. The sensitised rnu/ + rats showed a similar marked resistance to intraperitoneal challenge with newly excysted juvenile (NEJ) flukes. This was much less effective in the rnu/rnu rats, although there was some evidence of reduced numbers and stunting of parasites. Serum from infected rnu/rnu rats, unlike that from the infected rnu/+ rats, failed to induce the adherence of eosinophils to NEJ flukes in vitro. Flukes recovered from rnu/rnu rats were in general considerably larger than comparable flukes from their rnu/ + counterparts.There thus appears to be two distinct mechanisms of resistance to reinfection with F. hepatica operating in the rat. The first a T-independent system effective at the gut wall and the second, effective after penetration of the gut and requiring a T-dependent response for full expression. If eosinophils are involved in protection they can apparently function in the gut wall in the absence of an adherence promoting antibody in the serum.     

Elucidation of Schistosoma japonicum population dynamics in pigs using PCR-based identification of individuals representing distinct cohorts

The study reported here investigated the interactions of successive infections and acquired resistance of pigs to challenge infections of Schistosoma japonicum. Two morphologically indistinguishable geographical isolates from China (from Anhui and Zhejiang provinces) were used for the infections. The worms of the two isolates were distinguishable by PCR-linked restriction fragment length polymorphism analysis of the nicotinamide adenine dinucleotide phosphate dehydrogenase I gene of the mitochondrial genome. Thirty-two pigs divided into seven groups were used in the experiment. Two groups received a single infection by either the Anhui or the Zhejiang isolate. In Challenge Groups 1, 4, 6, 8 and 12, a primary infection of the Zhejiang isolate was followed by a challenge infection with the Anhui isolate at week 1, 4, 6, 8 or 12 after the primary infection. In this way it was possible to determine whether worms recovered by perfusion originated from the primary or the challenge infection. Only the challenge infection at week 1 resulted in a higher worm burden when compared with a single primary infection with the Zhejiang isolate. The results showed that challenge worms were able to establish, and that the proportion of worms originating from challenge infection increased at the later challenge infections, however without an increase in the total number of worms. In addition, mixed pairs of the two isolates were found in all challenge-infected groups. The results indicate that pigs are able to mount a partial resistance against re-infection with S. japonicum by 4 weeks after a primary infection, but that worms of the challenge infections eventually replace the primary infection. The finding of mixed pairs of the two isolates indicates that worms of S. japonicum are either polygamous or able to wait in solitude for up to 12 weeks for a partner.     

Leishmania donovani: Acquired resistance to visceral leishmaniasis in the golden hamster

The ability to acquire resistance to visceral leishmaniasis was studied in the golden hamster. Hamsters were infected subcutaneously with Leishmania donovani and challenged 6 weeks later by an intracardial route of inoculation. Parasitization in previously infected and control hamsters after challenge was followed by spleen and liver impression smears. Hamsters receiving a previous subcutaneous infection showed significantly lower numbers of visceral parasites after challenge than control animals. Differences in parasitization between the two groups were detectable as early as 2 days after challenge. Promastigotes and both hamster or cotton rat infected spleen tissue were effective in inducing acquired resistance to infection. The golden hamster is discussed as a model for the study of immunity to kala-azar.     

Immunological Interactions between 2 Common Pathogens,Th1-Inducing Protozoan Toxoplasma gondii and the Th2-Inducing Helminth Fasciola hepatica

Background

The nature of the immune response to infection is dependent on the type of infecting organism. Intracellular organisms such as Toxoplasma gondii stimulate a Th1-driven response associated with production of IL-12, IFN-γ, nitric oxide and IgG2a antibodies and classical activation of macrophages. In contrast, extracellular helminths such as Fasciola hepatica induce Th2 responses characterised by the production of IL-4, IL-5, IL-10 and IgG1 antibodies and alternative activation of macrophages. As co-infections with these types of parasites commonly exist in the field it is relevant to examine how the various facets of the immune responses induced by each may influence or counter-regulate that of the other.

Principal Findings

Regardless, of whether F. hepatica infection preceded or succeeded T. gondii infection, there was little impact on the production of the Th1 cytokines IL-12, IFN-γ or on the development of classically-activated macrophages induced by T. gondii. By contrast, the production of helminth-specific Th2 cytokines, such as IL-4 and IL-5, was suppressed by infection with T. gondii. Additionally, the recruitment and alternative activation of macrophages by F. hepatica was blocked or reversed by subsequent infection with T. gondii. The clinical symptoms of toxoplasmosis and the survival rate of infected mice were not significantly altered by the helminth.

Conclusions

Despite previous studies showing that F. hepatica suppressed the classical activation of macrophages and the Th1-driven responses of mice to bystander microbial infection, as well as reduced their ability to reject these, here we found that the potent immune responses to T. gondii were capable of suppressing the responses to helminth infection. Clearly, the outcome of particular infections in polyparasitoses depends on the means and potency by which each pathogen controls the immune response.     

Age-associated responses in susceptible and resistant rats to infection with Fasciola hepatica

Rajasekariah G. R. and Howell M. J. 1981. Age-associated responses in susceptible and resistant rats to infection with Fasciola hepatica. International Journal for Parasitology11: 59–65. Groups of susceptible (5-week-old) and age resistant (25-week-old) outbred male Wistar rats were infected with metacercariae of Fasciola hepatica and the establishment of the parasite was assessed in terms of worm reocvery, and haematological, histopathological and immunological criteria, 2, 4, 6 and 8 weeks after infection. Apart from 2 weeks after infection, there was a significant difference between groups in the recovery of F. hepatica, with resistant rats infected with consistently fewer parasites than susceptible animals. The juvenile worms which invaded the livers of resistant rats elicited a number of host reactions, marked by an intensive cellular infiltration into migratory tracks of the parasite, heavy deposition of fibrous tissue in the liver parenchyma and a rapid antibody response. These responses were not as striking in susceptible animals even though more worms were present. The ability of resistant rats to mount an enhanced response seems related to the maturation of their haemopoietic system.     

Taenia taeniaeformis in mice: Protective immunization with oncospheres and their products

Taenia taeniaeformis oncospheres, injected parenterally with or without adjuvants, stimulated a high degree of protective immunity in mice against challenge infection with eggs. Furthermore, the supernatant from a centrifuged (twice for 30 min at 4500 g) preparation of oncospheres which had been frozen, thawed and sonicated, induced more than 90% protection when used as a vaccine with adjuvant. By contrast, centrifuged (1 h at 3500 g) supernatant medium collected during 72 h incubation of activated T. taeniaeformis oncospheres in vitro in serum-free culture medium was only marginally host-protective. The results indicate that materials from disrupted oncospheres should be a suitable starting preparation for identification and purification of ‘host-protective’ antigens.     

Fasciola hepatica demonstrates high levels of genetic diversity,a lack of population structure and high gene flow: possible implications for drug resistance

Fasciola hepatica, the liver fluke, is a trematode parasite of considerable economic importance to the livestock industry and is a re-emerging zoonosis that poses a risk to human health in F. hepatica-endemic areas worldwide. Drug resistance is a substantial threat to the current and future control of F. hepatica, yet little is known about how the biology of the parasite influences the development and spread of resistance. Given that F. hepatica can self-fertilise and therefore inbreed, there is the potential for greater population differentiation and an increased likelihood of recessive alleles, such as drug resistance genes, coming together. This could be compounded by clonal expansion within the snail intermediate host and aggregation of parasites of the same genotype on pasture. Alternatively, widespread movement of animals that typically occurs in the UK could promote high levels of gene flow and prevent population differentiation. We identified clonal parasites with identical multilocus genotypes in 61% of hosts. Despite this, 84% of 1579 adult parasites had unique multilocus genotypes, which supports high levels of genotypic diversity within F. hepatica populations. Our analyses indicate a selfing rate no greater than 2%, suggesting that this diversity is in part due to the propensity for F. hepatica to cross-fertilise. Finally, although we identified high genetic diversity within a given host, there was little evidence for differentiation between populations from different hosts, indicating a single panmictic population. This implies that, once those emerge, anthelmintic resistance genes have the potential to spread rapidly through liver fluke populations.