Protection against Fasciola hepatica in rats with adult fluke antigen in Freund’s adjuvant: influence of antigen batch, antigen dose and number of sensitising injections

Immunodiagnosis as an aid for early detection of Fasciola gigantica by glutathione S-transferase (GST)

In the present study, effort to isolate purified GST from Fasciola gigantica homogenate and its early detection for confirmation of infection has been successful. In this study, immunoprotection studies with GST and antibody titer post-infection has revealed GST to be an immunogenic protein with high sensitivity to detect anti-Fasciola antibody as early as two weeks post-infection in large ruminants.

Epizootiology, pathogenesis and immunoprophylactic trends to control tropical bubaline fasciolosis: an overview

On the Indian sub-continent, nearly 5,000 years ago, the domestication of the riverine buffalo-the incredible Asian dairy animal was initiated. It plays a versatile role in socio-economic upliftment of its owners from the rural agricultural communities in Asian, African, South American and a few European countries. Comparatively, buffaloes are lesser evolved and susceptible to infectious diseases than cattle. However, poor body thermoregulation and wallowing nature predisposed them to snail borne infections, especially tropical fasciolosis-an incessant major constraint on buffalo production and improvement programmes. This review article is an insight into the global prevalence, varied epizootiological factors, offers possible explanation to pathophysiological clinical signs, deleterious effects of the tropical liver fluke, involving hepato-biliary system, haemopoitic system, endocrine glands and their secretions, oxidative stress, altered metabolism and significant fall in food conversion efficiency with unaffected digestibility of nutrients. Besides, the authors have briefly discussed and reviewed the developments and significance of successful immunodiagnostic approaches for detecting and forecasting the disease during early pre-patency and feasibility of developing a cost effective immunoprotection strategies against tropical fasciolosis.

Immunology of the host–parasite relationship in fasciolosis (Fasciola hepaticaandFasciola gigantica)

The protective resolution of liver fluke (Fasciola hepatica and Fasciola gigantica) infection is a dynamic interplay between the host's effector responses and the parasite's defence and immunomodulatory systems. The evidence suggests that the juvenile or immature parasite is the target of protective host immune responses but the effector mechanisms employed vary between hosts. Moreover, F. hepatica and F. gigantica differ in their susceptibility to these killing mechanisms. In the rat, in vitro killing of juvenile F. hepatica involves an antibody-dependent cell cytotoxicity mediated by nitric oxide produced by activated monocytes and (or) macrophages. However, monocytes and (or) macrophages from Indonesian sheep do not produce nitric oxide yet can effectively kill juvenile F. gigantica in vitro and in vivo by a mechanism that is ineffective against F. hepatica. These data show that disease progression or resolution in fasciolosis is determined both by biochemical differences between Fasciola species and by host-dependent factors. Understanding the genetic basis for these differences is a key question for the future. Fasciola hepatica and F. gigantica actively modulate the host immune response, downregulating type 1 responses during infection. It is important to determine whether such modulation of the immune response by Fasciola spp. directly leads to enhanced parasite survival in the various hosts.

Juvenile Fasciola hepatica are resistant to killing in vitro by free radicals compared with larvae of Schistosoma mansoni

Free radicals have previously been shown to kill the immature stages of the trematode, Schistosoma mansoni but their effect on newly excysted juvenile (NEJ) flukes of Fasciola hepatica has not been established. Using acetaldehyde and xanthine oxidase to chemically generate reactive oxygen intermediates (ROI), up to 61% of NEJ were killed but only when exposed to high levels of ROI. At low concentrations of acetaldehyde and xanthine oxidase as sources of reactive oxygen intermediates, only 6-29% of NEJ were killed compared with 70-92% of schistosomula. Incubation with lipopolysaccharide (LPS)-stimulated rat peritoneal lavage cells (PLCs) killed only 7-15% of NEJ whereas 78-87% of schistosomula were killed under the same conditions by a mechanism dependent on the production of reactive nitrogen intermediates. Relative to immature and adult parasites, NEJ expressed 2.5-20-fold lower levels of superoxide dismutase and glutathione S-transferase but no catalase activity was detected. Incubation of NEJ with inhibitors of peroxidases and glutathione metabolism increased the mean killing of NEJ by LPS-stimulated rat PLCs to 40-75%. These results demonstrate that, in comparison to schistosomula of S. mansoni, NEJ of F. hepatica are relatively resistant to killing by free radicals and this resistance could, in part, be due to the activity of oxidant scavenger enzymes of NEJ.

Immunological approaches for the control of fasciolosis

The immunological relationship between liver flukes and their mammalian hosts is being unravelled by in vivo and in vitro studies. Vaccine studies in cattle and sheep with purified antigens (fatty acid binding protein, FABP; glutathione S-transferase, GST; cathepsin L, CatL; hemoglobin) have shown that high reductions in worm burdens (31-72%) and egg production (69-98%) can be achieved, raising the realistic possibility that immunological control of Fasciola infection is a commercially achievable goal. Combination vaccines may also be feasible since a cocktail of CatL and hemoglobin elicits a significant 72% protection in cattle. Analysis of immune responses to Fasciola during infection in ruminants suggests that chronic infection correlates with a type 2 helper T cell response, implying that type 1 helper T cell responses are down-regulated in fasciolosis. Recent results studying the resistance of Indonesian Thin Tail (ITT) sheep to F. gigantica have shown that this breed exhibits high innate (or rapidly acquired) resistance to infection and acquires a higher level of resistance after a primary challenge. Initial studies suggest that the resistance of ITT sheep to F. gigantica may be determined by a major gene. Merino sheep also acquire resistance to F. gigantica. In contrast, ITT and Merino sheep do not exhibit resistance to F. hepatica. These results suggest that there are fundamental differences between these two species of Fasciola in the biology of their interaction with the sheep immune system. In vitro studies on immune mechanisms of killing of juvenile fluke have shown that juvenile larvae of F. hepatica are susceptible to antibody-dependent killing by activated rat macrophages in vitro which is mediated by nitric oxide. Future studies on the immune effector mechanisms expressed by resistant sheep which control infection by F. gigantica will lead to new knowledge which may allow the design of more effective vaccines for fasciolosis.

Separation of outer cysts from metacercariae of Fasciola gigantica in an aqueous two-phase system

The outer cysts (Oc) of Fasciola gigantica metacercariae (Mc) were separated in an aqueous two-phase system composed of polyethylene glycol and dextran in distilled water. A large number of separated Mc without Oc were recovered in the bottom layer rich in dextran in the system. Ten separated Mc in the layer were used to inoculate the mouse with a syringe and juveniles were recovered from the animals on the 14th day. When the number of juveniles recovered was compared with that from the mice infected orally with the same number of Mc, there was a significant difference between them (P < 0.05). The former method is easier than the latter for inoculation.

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.

Fasciola hepatica: comparison of immature and mature immunoreactive glycoproteins

A comparison of the 35S-methionine metabolically labelled immunoreactive glycoproteins of immature and mature F. hepatica was carried out by one-and two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Sera of rabbits infected for 3 weeks reacted much more strongly with glycoproteins of immature flukes than with glycoproteins of mature flukes as compared to sera of rabbits infected for 9 weeks. Several of the immunoreactive glycoproteins were also released by immature F. hepatica into the culture medium. At least one was a component of the T1 type granules. Analysis of the in vitro translation products of mature F. hepatica indicated that the initial humoral immune response of rabbit hosts may be directed against carbohydrate moieties.

Worm recovery, haemagglutinating antibodies and IgE-levels after immunisation against Fasciola hepatica in rats

Female inbred Hooded Lister (HL) rats were each infected with 20 metacercariae (Mc) of Fasciola hepatica. Remarkable variations between the number of flukes established in the bile ducts suggest the presence of individual, perhaps genetically controlled, differences in immune responsiveness of HL rats to F. hepatica. Serum (4 ml) from HL rats infected with 20 Mc 6 weeks prior to transfer partially protected rats against a F. hepatica challenge infection. However, 1 X 10(6) lymphoid cells originating from rats of the same age and stage of infection did not show the same protective qualities. Furthermore, attempts to immunise HL rats i.p. with either juvenile or adult excretory/secretory (ES) products, or somatic tissue antigens and AlOH3-gel as adjuvant failed. When compared to other investigations, the present results further suggest that both the adjuvant and the route of administration are crucial for the stimulation of a protective immunity to F. hepatica. Low titers and low anamnestic responses of haemagglutinating antibodies after prior immunisation with juvenile ES antigens or both juvenile ES and somatic tissue antigen suggest the occurrence of an immunosuppressive effect caused by juvenile ES products. The total serum IgE-levels in immunised groups were generally lower when compared to the challenge control group, whereas the F. hepatica ES-specific IgE-levels rose after challenge, but immediately decreased again when compared to challenge controls. These findings support the hypothesis of an immunomodulatory effect caused by the vaccination scheme.