Resistance to Fasciola hepatica in rats and rabbits following sensitising infection and treatment

A novel ex vivo rat infection model to study protective immunity against Fasciola hepatica at the gut level

We describe an ex vivo rat infection model to study protective immunity against Fasciola hepatica at the gut level. An exact number of newly excysted juveniles (NEJs) was injected into a gut segment with an intact blood supply and which was still attached to a live anaesthetized rat. NEJs that penetrated the gut wall during the following 6 h were recovered from a beaker filled with medium and were counted under a microscope. This infection model was validated and enabled us to exactly quantify the infection dose whilst at the same time exactly quantifying the number of NEJs penetrating the gut wall. The mean sum of NEJs that migrated through the gut wall into the beaker (peritoneal fraction), plus NEJs that remained in the gut wall and the gut lumen was 87% of the infective dose (+/-3.6% SEM; n=18). The function of the ex vivo segments was well-preserved, as demonstrated by only minor leakage of an inert liquid marker. The ex vivo model enabled us to measure protection against F. hepatica at the gut level. In naive rats 52% (+/-2.4% SEM; n=40) of the injected NEJs penetrated the gut wall, whereas in previously infected rats only 12% (+/-1.8% SEM; n=40) were able to do so, irrespective of the infection dose. Thus, when rats were orally primed, the migration of NEJs through the gut wall was 77% less than the migration in naive rats. We conclude that the ex vivo model should be valuable in studies of the induction and expression of protective immunity against F. hepatica in the intestine, and will aid in development and optimization of vaccines.

Studies on helminthosis at the Centre for Tropical Veterinary Medicine (CTVM)

The research work relating to helminths, which has been conducted within the Helminthology Section of the CTVM, often in collaboration with colleagues from the tropics is reviewed and placed into a historical perspective. The research has, in the main, concentrated on the trematodes Fasciola hepatica and Fasciola gigantica and the cestodes Taenia saginata and Taenia solium, but work on other parasites including gastro-intestinal nematodes is also considered. All of these parasites are of obvious veterinary/economic importance particularly in the tropics and subtropics. While the zoonotic importance of T. saginata and T. solium has been recognised for many years, it is only more recently that the zoonotic impact of Fasciola spp. has been generally acknowledged.

Cellular reactions in the small intestine of rats after infection with Fasciola hepatica

Groups of five rats each were infected with metacercariae of Fasciola hepatica according to two experimental procedures. In the first experiment, they received 20 metacercariae 0, 1, 2 or 3 times at intervals of 4 weeks. In the second, both the inoculation dose and the interval between doses were varied. After the animals had been killed, the small intestine was prepared for histology and tissue sections were stained for the detection and quantification of mucosal mast cells (MMCs), eosinophils and goblet cells. The density of eosinophils and MMCs increased significantly with each reinfection in the first experiment; in the second, the MMC reaction reached a peak at 4 weeks post-infection (p.i.), whereas the eosinophils peaked at 4 and 17 weeks p.i. In addition, the reaction of these cells depended on the infectious dose. In both experiments, goblet cells reacted only weakly. These findings thus clearly reflect a considerable intestinal response against migrating juvenile F. hepatica. The pattern of these defence reactions in the small intestine suggests some similarities with the mechanisms of antibody-dependent cell-mediated cytotoxicity that have been shown to take place during Schistosoma mansoni reinfection.

Response of goats to repeated infections with Fasciola gigantica

One or two mature primary infections with Fasciola gigantica which had been removed by anthelmintic treatment resulted in a significant reduction in the number of flukes recovered from challenge infection as compared with that from controls. Characteristic lesions of fascioliasis were seen in the livers of the 3 groups, however, goats with two primary abbreviated infections prior to challenge showed more severe lesions than those of animals with one primary abbreviated infection or those of challenge controls. The former group also showed the highest serum glutamate dehydrogenase and sorbitol dehydrogenase peaks following challenge infections and pulmonary fascioliasis was encountered in one of the goats of this group. Haemoglobin concentration and packed-cell volume decreased after infection in the three groups of goats.

Resistance to fascioliasis--a review

Attempts to actively stimulate or passively transfer resistance to Fasciola hepatica or F. gigantica in various laboratory and farm animals including mice, rats, rabbits, sheep, goats and cattle have been reviewed. These attempts comprised sensitization by primary homologous or heterologous normal or irradiated infections per os, sensitization by subcutaneous, intramuscular or intraperitoneal implantation with the various fluke stages, sensitization by somatic extracts or metabolic products of mature or immature flukes and passive transfer of resistance by immune serum or sensitized lymphocytes.

The serum antibody response of infected rats, rabbits, lambs and calves to Fasciola hepatica adult antigen fractions separated by preparative flatbed iso-electrofocusing

Electrofocusing of F. hepatica adult antigen in granulated gels separated the material into 22 arbitrary fractions. Polyacrylamide gel analysis demonstrated groups of proteins with similar iso-electric points in 19 of the fractions. A microplate ELISA detected antigens in all 22 fractions and was used to test the serum antibody response in infected rats, rabbits, lambs and calves to these antigen fractions. The results indicated that rat and calf sera gave a much stronger response than rabbit and lamb sera to the antigens which separated above pH 7.0. It is possible that the greater efficiency of the rat and bovine immune systems in combating re-infection with F. hepatica may be related to this response.