After infection of three groups of rabbits by 50, 25 and 10 F. gigantica encysted metacercariae (EMC) for each animal, a rabbit appears as an unsuitable host for the development of this species of flukes. Rabbits need special precautions to help the worms to reach maturity before death of the infected animals. The juveniles wander in the liver tissue away from the main bile ducts, and may accidentally emerge back to the peritoneal cavity and can remain there or return back by chance to the liver. Survival of the infected rabbits, the degree of pathogenisty produced and the number of extracted worms are affected by the dose of the EMC and the general health conditions of the rabbit. Infective dose (ID) of 50 EMC led to mortalities from 28th to 58th day post infection (dpi.). This was accompanied by detection of flukes in the peritoneal cavity, and the anterior cones of several worms were found penetrating the liver toward the abdominal cavity. At 58th dpi, dead animals showed marked liver cirrhosis and adhesions with the surrounding organs. Decreasing the ID to 25 EMC increased the rabbits survived till 74th dpi. The liver looked enlarged and juveniles successfully reached the main bile ducts. Successful fluke development, with low adverse changes in the liver appearance was recorded in the group infected by 10 EMC, and the animals survived till 98th dpi. The problem, at this low ID, was the decreasing in the infection rate in the exposed rabbits to 37.5%. In all groups, using ELISA technique, IgM & IgG anti-Fasciola antibodies (AFAb) increased gradually in sera. Higher titters were recorded in the group infected by 25 EMC. Prolonged migration and
retardation of F. gigantica growth in the infected rabbits associated with either a high or a low titters. this means that the produced AFAb lack the capacity to mediate responses that can influence parasite survival. So failure of development of F. glgantlca growth in rabbit appears to be related mainly to its innate resistance against this Fasciola sp.