Influence of vaccination of calves with recombinant cysteine proteinase of Fasciola hepatica on development and infectivity of miracidia

The aim of the study was to evaluate an influence of vaccination of the final host on F. hepatica development in intermediate hosts. Fluke eggs were isolated from the biliary tracts of calves vaccinated orally with recombinant cysteine proteinase of F. hepatica after the challenge infection and from control calves which received the infection only. To asses the ef fect of the vaccine on egg "hatch rate" the eggs were transferred to the Petri dishes with distilled water and incubated at 25°C for 16-19 days. They were subsequently exposed to light for about 2 h, at a temperature of 27 ± 1°C, to stimulate sprouting of the miracidia and asses the egg hatchability. In order to evaluate infectivity and pathogenicity of the miracidia, single miracidium infections of Lymnea truncatula by F. hepatica were carried out under laboratory conditions using 4-mm-high snails. The prevalence of snail infections with F. hepatica was calculated using the ratio between the number of cercariae-shedding snails in each group and that of surviving snails. It appeared that the eggs isolated from immunized calves demonstrated significantly lower hatchability than the eggs isolated from non-vaccinated control hosts. Also, the proportion of infected snails as well as their mortality were lower after exposition to miracidia originating from vaccinated calves. It is suggested that effectors of the immune response in vaccinated calves inhibited in part biological activity of cysteine proteinases of the fluke which are known to be involved in egg shell formation, penetration of host's tissues and worm feeding