Acute Fasciolosis Immature flukes track through liver causing bleeding and inflamation. Heavy infections can be rapidly fatal at this stage. Chronic Fasciolosis Adult flukes damage bile ducts and suck blood, causing anaemia in sheep. Infection causes gradual weight loss and anaemia. Because development in the environment is relatively slow and infection requires sheep to graze areas which have been infested with infected snails, the impact of climate on the disease is delayed.
Development starts in spring when temperatures are warm enough.
However, metacercariae are not eaten until sheep are forced to graze swampy areas where green herbage is present. This may not occur until there is an extended period of dry weather. The disease occurs several weeks later. Typically, in winter rainfall areas it is a summer disease and in summer rainfall regions, a winter disease. Because rainfall is so critical to the liver fluke life cycle, the pattern of disease varies with the weather from year to year and region to region.