Recovery of Fascioloides magna (Digenea) population in spite of treatment programme? Screening of Galba truncatula (Gastropoda, Lymnaeidae) from Lower Austria
Introduction
The large American liver fluke Fascioloides magna (Digenea: Fasciolidae) is an important parasite of wild and domestic ruminants in North America, causing considerable economic losses. The life cycle of F. magna involves free-living parasitic stages as well as endoparasitic stages and two successive hosts (Pybus, 2001). F. magna has repeatedly been introduced to Europe, with first records from the late 19th century from Italy. In Europe, definitive hosts are red deer (Cervus elaphus) and fallow deer (Dama dama) (Erhardová-Kotrlá and Kotrly, 1968) and the snail species Galba truncatula (Erhardová-Kotrlá, 1971, Erhardová-Kotrlá, 1968) and Radix peregra (Faltýnková et al., 2006) are confirmed natural intermediate hosts. Dependent on temperature and snail species, the development inside the snail host takes about 40–58 days (Swales, 1935, Erhardová, 1961) and includes sack-like sporocysts, two redial generations, and a cercarial stage with a long, unforked tail.
Austria is a classic example where the parasite has been probably repeatedly introduced over many years, but become endemic only relatively recently and only in a small area. In Austria, the parasite was first detected in fallow deer in a game reserve close to the Danube in Lower Austria (Pfeiffer, 1983). The first infected free-living cervids were found in autumn 2000 in the Danube floodplain forests of Fischamend, Lower Austria (Winkelmayer and Prosl, 2001). During the past 10 years, the parasite spread through wild red and roe deer populations in riparian zones east of Vienna, particularly in Fischamend, Regelsbrunn, Orth and Mannswörth (Winkelmayer and Prosl, 2001, Ursprung, 2002, Ursprung and Prosl, 2011). Cervidae endemic in Austria can be severely affected by the parasite, as its migrations within the tissue lead to severe liver damage and may cause death of the hosts. In contrast, livers of red deer show chronic changes and, dependent on the parasite load, the animals become weakened or die spontaneously without marked symptoms (Erhardová-Kotrlá and Kotrly, 1968). Already one year after the first finding in the wild a monitoring and control programme was launched in the wetlands south of the Danube. In brief, free-living deer was treated with Fasinex® (Novartis Animal Health Inc.), a 10% suspension of triclabendazole, admixed with the winter feed, thus administering 10–15 mg triclabendazole per kg body weight within a period of six days. Treatment was performed 3–4 times (2001–2005), respectively 2 times (since 2006) per annum. Consequently, the number of infections in definitive hosts markedly decreased within the following years (Ursprung et al., 2006). Also, a very low prevalence of F. magna in G. truncatula was recorded, when a first screening was conducted in 2004/2005 (Hörweg et al., 2011). However, a complete eradication of F. magna in Austria was not achieved. Starting in 2006, a shift to the northern side of the Danube and a significant resurgence of F. magna infections in definitive hosts was recorded, with prevalences up to 72% (Ursprung and Prosl, 2011).
Thus, in 2008 the current study was initiated, in order to analyse the infection dynamics in the intermediate host – after the observed relapse in wild ruminants. In a GIS-based risk analysis of the Danubian wetlands east of Vienna the region around Orth was identified as a risk area (Reckendorfer and Groiss, 2006). Therefore we determined the infection rates in G. truncatula with F. magna and other digeneans in this risk area north of the Danube. Furthermore, we performed an evaluation of the distribution of infected snails and of a possible seasonality of infections, as well as investigations on population dynamics of the intermediate host snail G. truncatula. The screening was performed by microscopy as well as by molecular methods.
Section snippets
Study sites
The sampling was carried out from April to October 2008 on three distinct locations in the area Orth/Danube (Lower Austria) in the Danube wetlands east of Vienna, Austria. As shown in Fig. 1, the first sampling site, Entenhaufen, was located at the estuary area of the river Große Binn. This location is characterized by plane river banks, small vegetation and an abundance of periodically flooded, sandy-muddy sampling islets. At location 2 (Märchenteich), bank borders flanking an “animal
Snail distribution and seasonality
Most G. truncatula snails were found at location 1 (Entenhaufen), i.e. 1975 individuals, followed by location 2 (Märchenteich) with 1347 snails. At location 3 (Neubruchwiese), only 122 snails were found. The highest numbers of G. truncatula were found in August and September, while fewest snails were found in April. Population densities were also highest in August and September, with 45 and 36 snails, respectively found within 10 min per person. The shell size distribution of the 3444 examined
Distribution and life cycle of G. truncatula
In this study, G. truncatula was mainly found on periodically flooded, sandy-muddy habitats and in running waters, which confirmed former studies on G. truncatula in the Danube Wetlands National Park (Reckendorfer and Schaefer, 2003, Hörweg et al., 2011). Location 1 (Entenhaufen) obviously provided the most favourable living conditions for the dwarf pond snail with extensive, periodically flooded shores. As the collection areas at location 2 (Märchenteich) were very small, it is possible that a
Acknowledgements
This study was funded partly by grants of the Österreichische Bundesforste AG. The authors wish to thank the Museum of Natural History Vienna and the Institute of Specific Prophylaxis and Tropical Medicine, Medical University Vienna for providing reference material and financial support. We further want to thank Mag. Verena Pecavar and Florian Astelbauer, PhD for excellent technical assistance.
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