Studies on the viability of metacercariae of Fasciola gigantica

The viability of metacercariae of Fasciola gigantica was tested by in vitro and in vivo methods. In vitro testing was based upon the motility of juven ile flukes within the inner cyst as examined under the light microscope. In vivo testing was undertaken through experimental infections of rabbits (tw o groups) and natural definitive hosts, lambs tone group). In the first gro up, out of six rabbits each given 25 metacercariae, worm establishment only took place in one rabbit with a single fluke recovery on 60 days post infe ction. Ln the second group of six rabbits each given 200 metacercariae, fiv e were infected, with two or three flukes per host. All the lambs given 250 metacercariae became infected showing prevalences of 7.2-40% in comparison with rabbits in which low prevalences (0-4%) were recorded. The results in dicated that even viable metacercariae which were already tested in vitro c ould not readily establish in rabbits. Such variability in worm establishme nt suggests that immunological and chemotherapeutic studies in rabbits infe cted with F. gigantica are Likely to be unreliable.