The Giant Liver Fluke in Bohemian Forest Ecosystem
Giant liver fluke (Fascioloides magna) is a parasitic flatworm non-native to Europe. This parasite lives mainly in the livers of ungulates where it usually forms a capsule of several adult individuals, producing the eggs. The eggs are released to the bile ducts from where they get to the intestine and later to the environment where they become further sources of infection.
Life cycle
This parasite also has a complicated life cycle with the intermediate host (aquatic snails), and final host (usually wild or farmed ungulates) (see picture 1 for a better overview). When the eggs get to the wet areas, they will develop into the stage Miracidium, which actively penetrates into the intermediate hosts, aquatic snails (Radix labiata or Galba truncatula). In the intermediate hosts, there is a series of multiplication of different larval stages, which results in the release of plenty “Cercaria”, which actively swims and forms a cyst called “Metacercaria” on the vegetation in the vicinity of water bodies. There the liver fluke waits until it’s ingested by the final host. In the stomach, the liver fluke sheds its hardcover and the juvenile fluke migrates through the intestine and abdominal cavity to the livers. There they migrate usually until they find a second individual for sexual reproduction. The capsule around flukes is formed as a response to the host immune system. The main damage is usually caused in the livers by the migration of flukes. Whereas for some species of final hosts, the moderate infection doesn’t seem to be an issue (e.g. red deer, whitetails), the others (e.g. sheep, roe deer) die in a few months after infection if untreated with antiparasitics. However, the massive infection can affect also the usually resistant species such as red deer.
1The schematic drawing of Giant Liver Fluke life cycle in Bohemian Forest Ecosystem © Pavel Procházka
Introduction
This species was introduced from North America to Italy in the second half of 19. Century. Since then, three main areas of occurrence in Europe have been established. The one covering middle Europe has been known for a century. However, the distribution in the bordering area between South Bohemia in Czechia and Bavaria in Germany, formed mainly by two National parks, has not been successfully examined yet.
Research project
This background established the idea of the cross-border research project, where participate Bavarian State Institute of Forestry, Bavarian Forest National Park, and Šumava National Park. Thanks to this project we have collected a huge dataset allowing us to find replies to questions connected with GLF occurrence in the ecosystem. What we already know:
1) GLF is distributed across all study areas on both sides of a border. The prevalence of GLF-positive red deer (percentage of infected individuals) is higher on the Czech side (18%), reflecting the longer occurrence of the parasite in Czechia.
2) When searching for the GLF also in the wild boar (almost 500 samples) and roe deer (150 samples), we revealed only a single roe deer sample infected. That illustrates, that red deer, similarly to many other regions, will be the most dominant host responsible for the GLF spread in the ecosystem.
3) Preliminary data from culls shows that both infected and non-infected individuals do not differ in their weight. That would support the theory that GLF infection is not crucial for red deer and they usually cope with that well.
The further processing of data will bring more detailed descriptions of GLF effects in these unique protected areas in middle Europe. For enthusiastic readers, there is a brochure available in German and Czech.
