is detected in subacute or chronic fasciolosis from 12 to 15 weeks after ingestion of metacercariae. Economical effect of fasciolosis in sheep consists in sudden deaths of animals as well as in reduction of weight gain and wool production. In goats and cattle, the clinical manifestation is similar to sheep. However, acquired resistance to F. hepatica infection is well known in adult cattle. Calves are susceptible to disease but in excess of 1000 metacercariae are usually required to cause clinical fasciolosis. In this case the disease is similar to sheep and is characterized by weight loss, anemia, hypoalbuminemia and (after infection with 10,000 metacercariae) death. Importance of cattle fasciolosis consist in economic losses caused by condemnation of livers at slaughter and production losses especially due to reduced weight gain. In sheep and sometimes cattle, the damaged liver tissue may become infected by the Clostridium bacteria C. novyi type B. The bacteria will release toxins into the bloodstream resulting in what is known as black disease. There is no cure and death follows quickly. As C. novyi is common in the environment, black disease is found wherever populations of liver flukes and sheep overlap. Cause Fasciolosis is caused by two digenetic trematodes F. hepatica and F. gigantica. Adult flukes of both species are localized in the bile ducts of the liver or gallbladder. F. hepatica measures 2 to 3 cm and has a cosmopolitan distribution. F. gigantica measures 4 to 10 cm in length and the distribution of the species is limited to the tropics and has been recorded in Africa, the Middle East, Eastern Europe and south and eastern Asia. In domestic livestock in Japan, diploid (2n = 20), triploid (3n = 30) and chimeric flukes (2n/3n) have been described, many of which reproduce parthenogenetically. As a result of this unclear classification, flukes in Japan are normally referred to as Fasciola spp. Recent reports based on mitochondrial genes analysis has shown that Japanese Fasciola spp. is more closely related to F. gigantica than to F. hepatica. In India, a species called F. jacksoni was described in elephants. Transmission Human F. hepatica infection is determined by the presence of the intermediate snail hosts, domestic herbivorous animals, climatic conditions and the dietary habits of man. Sheep, goats and cattle are considered the predominant animal reservoirs. While other animals can be infected, they are usually not very important for human disease transmission. On