of flukes, tissues are mechanically destroyed and inflammation appears around migratory tracks of flukes. The second phase (the biliary phase) begins when parasites enter the biliary ducts of the liver. In biliary ducts, flukes mature, feed on blood, and produce eggs. Hypertrophy of biliar ducts associated with obstruction of the lumen occurs as a result of tissue damage. Resistance to infection Mechanisms of resistance have been studied by several authors in different animal species. These studies may help to better understand the immune response to F. hepatica in host and are necessary in development of vaccine against the parasite. It has been established that cattle acquire resistance to challenge infection with F. hepatica and F. gigantica when they have been sensitized with primary patent or drug-abbreviated infection. Resistance to fasciolosis was also documented in rats. On the other hand, sheep and goats are not resistant to re-infection with F. hepatica. However, there is evidence that two sheep breeds, in particular Indonesian thin tail sheep and Red maasai sheep, are resistant to F. gigantica.Wamae, L.W., 1996. Comparative pathogenesis and immunochemistry analysis of Fasciola gigantica infection in cattle and sheep. PhD Thesis. University of Edinburgh. Diagnosis Most immunodiagnostic tests will detect infection and have a sensitivity above 90% during all stages of the diseases. In addition antibody concentration quickly drops post treatment and no antibodies are present one year after treatment, which makes it a very good diagnostic method. In humans, diagnosis of fasciolosis is usually achieved parasitologically by findings the fluke eggs in stool, and immunologically by ELISA and Western blot. Coprological examinations of stool alone are generally not adequate because infected humans have important clinical presentations long before eggs are found in the stools. Moreover, in many human infections, the fluke eggs are often not found in the faeces, even after multiple faecal examinations. Furthermore, eggs of F. hepatica, F. gigantica and Fasciolopsis buski are morphologically indistinguishable. Therefore, immunonological methods such ELISA and enzyme-linked immunoelectrotransfer blot, also called Western blot, are the most important methods in diagnosis of F. hepatica infection. These immunological tests are based on detection of species-specific antibodies from sera. The antigenic preparations used have been primarily derived from extracts of excretory/secretory products from adult worms, or with partially purified fractions. Recently, purified native and recombinant antigens have been used, e.g. recombinant F. hepatica cathepsin L-like protease. Methods based on antigen detection (circulating in serum or in