Toxicity of chlorophyllin in different wavelengths of visible light against Fasciola gigantica larvae.

Toxicity of chlorophyllin against redia and cercaria larvae of Fasciola gigantica was studied under irradiation of visible light. Highest and lowest toxicity of chlorophyllin against both larvae was noted under red (redia - 8 h LC50 7.88 mg/10 mL and cercaria - 11.99 mg/10 mL) and green (redia - 8 h LC50 32.12 mg/10 mL and cercaria - 8 h LC50 43.80 mg/10 mL) light irradiation respectively. The highest toxicity of chlorophyllin under red light irradiation against redia (8h LC50 7.88 mg/10 mL)/cercaria (8h LC50 11.99 mg/10 mL) was followed by white (8 h LC50 redia - 20.48 mg/10 mL, 8 h LC50 cercaria - 18.0 3mg/10 mL), blue (8 h LC50 redia - 33.10 mg/10 mL/ 8 h LC50 cercaria - 19.98 mg/10 mL) and yellow (8 h LC50 redia - 23.87 mg/10 mL/ 8 h LC50 cercaria - 23.48 mg/10 mL). Chlorophyllin treatment in darkness (control I) and without treatment of chlorophyllin, while all other conditions were same as treatment group (control II) caused no mortality of redia/cercaria larva. Chlorophyllin might be a promising new safe strategy to replace synthetic larvicide in fasciolosis control programme.

Protective effect of irradiated metacercariae of Fasciola gigantica and irradiated cercariae of Schistosoma bovis against fascioliasis in goats.

Sensitisation of goats for eight weeks with metacercariae of Fasciola gigantica gamma-irradiated at 3 kr resulted in significant resistance to an homologous challenge with normal metacercariae. However, serum sorbitol dehydrogenase assay suggested that, whereas little damage was produced by immunising infections, considerable hepatic damage was caused by flukes remaining from challenge infections. On the other hand sensitisation with cercariae of Schistosoma bovis gamma-irradiated at 3 kr did not stimulate any resistance against heterologous challenge with F. gigantica.

The protective effect of irradiated metacercariae of Fasciola gigantica against homologous challenge in sheep.

Five lambs were each sensitized with 400 metacercariae of Fasciola gigantica irradiated at 3 kr gamma rays. Eight weeks later, they were each challenged together with 5 controls with 500 non-irradiated metacercariae. Eight weeks later, all of the animals were necropsied and the worm burdens determined. The lambs which received the sensitizing infections had 80% less worms than the controls. The sensitized lambs also showed less hepatic damage compared with the controls as indicated by lower levels of the serum enzyme glutamate dehydrogenase. The blood indices showed insignificant reductions in the sensitized lambs whereas marked reductions were found in the erythrocytes, packed cell volume and haemoglobin values of the challenge controls. Bilirubinaemia was also evident in this latter group.

Immunization of zebu calves against Fasciola gigantica, using irradiated metacercariae.

The pathogenesis of unirradiated, 3 krad-irradiated and 20 krad-irradiated metacercarial infections was compared in zebu calves studied over a 10-week period. Calves exposed to 1000 unirradiated metacercariae (mc) became hypoalbuminaemic, and showed elevated serum concentrations of liver enzymes, whereas neither of the other groups was significantly affected. At slaughter, a mean of 332 flukes was recovered from the 0 krad group, while only 23% and 12% of this number were recovered from the 3 krad and and 20 krad groups, respectively. All the worms recovered from the 20 krad group were stunted, and found in biliary ductules, but a mean of 13% of the flukes recovered from the 3 krad group were large, and dwelling in main bile-ducts. Liver lesions typical of acute fascioliasis were present in the 0 krad group, but lesions in the other groups, and particularly the 20 krad group, were far less severe. Judged on clinico-pathological criteria, a single vaccination of calves with 1000 3 krad-irradiated mc induced partial resistance to a challenge with 1000 normal mc eight weeks later, but the reduction in worm recovery was not statistically significant. There was less evidence of protection when two vaccinating doses of 3 krad mc were given within four weeks, with challenge at week 8, and a single vaccination was ineffective against a challenge four weeks later. However, when the irradiation dose was increased to 20 krad, a hgh level of resistance (69% worm reduction) was induced by a single vaccination, given eight weeks before challenge, and liver pathology was strikingly reduced in the vaccinated animals.

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.

Assessment of the attenuation produced by irradiation of Fasciola gigantica metacercariae in hamsters.

Severe pathological changes were seen in hamsters given metacercariae of Fasciola gigantica irradiated at doses below 4 krads. No adult flukes were recovered from hamsters given metacercariae irradiated at doses above 4 krads and little hepatic damage was caused. It was not ascertained whether resistance resulted following these latter infections.