The contamination of wild watercress with Fasciola hepatica in central France depends on the ability of several lymnaeid snails to migrate upstream towards the beds

Abstract

As most natural watercress beds in central France are located upstream of the permanent habitats of two lymnaeid species, Galba truncatula and Omphiscola glabra, field investigations were made from 1999 to 2004 on 67 beds to determine why the contamination of watercress with Fasciola hepatica is irregular over time in these sites, while definitive hosts, especially lagomorphs, are regularly found infected around them. Snails are able to migrate upstream in winter and spring towards the beds, and a 4-year survey demonstrated the existence of annual variation in the colonization of these sites by snails. In the 45 beds irregularly contaminated with F. hepatica over time, 37.7-62.2%, according to the year, were not populated by lymnaeids, in spite of the presence of snail populations downstream. G. truncatula was found alone in 8.8-13.3% of sites and was the first colonizing snail in 24.3-33.3% when the two lymnaeid species successively settled in these waterholes. The colonizing ability of O. glabra was more limited, as it was observed alone in 2.2% of beds and was the first colonizing snail in only 2.2-20% of them. The distances covered by these snails significantly increased with increasing migration time. After migration, a few overwintering snails (3.8% of G. truncatula and 6.8% of O. glabra) are able to colonize the beds, but their numbers decreased when the distance of migration was greater. O. glabra migrated more quickly and reached more watercress beds than G. truncatula. However, this did not influence the natural infections of snails, which were more frequent in the F1 of G. truncatula. The variability observed in the colonization of beds by snails might explain the regular or irregular contamination of wild watercress by metacercariae of F. hepatica. One of the factors which may explain this variability is the occurrence of showers in spring, so that a few snails are able to reach watercress beds after their upstream migration.

Produce Contamination by Other Wildlife

“…The only zoonotic helminths linked to fresh produce are the trematodes Fasciola hepatica and gigantica, Fasciolopsis buski, and the nematodes Ascaris suum, Toxocara canis and cati, Toxascaris leonine, Lagochilascaris minor, and both Angiostrongylus cantonensis and costaricensis (Polley, 2005;Slifko et al, 2000). Only Fasciola hepatica has been responsible for outbreaks of produce-borne infections in humans (Macpherson, 2005;Mas-Coma, 2005;Rondelaud et al, 2005).…”

“…Human infection with F. hepatica in developed countries is almost exclusively due to ingestion of contaminated aquatic vegetation; primarily watercress (Macpherson, 2005;Rondelaud et al, 2005), and a number of aquatic plant-borne infections of F. hepatica have been reported . The primary routes of exposure to humans in developing countries are contaminated drinking water and food.…”

“…In hyperendemic areas, human prevalence is as high as 72% and is coassociated with proximity to aquatic sources of appropriate lymnaeid intermediate hosts (Mas-Coma et al, 1999. The primary wildlife reservoirs of Fasciola hepatica and gigantica are wild ruminants and equids (Polley, 2005;Slifko et al, 2000); F. hepatica is also common in wild lagomorphs (Rondelaud et al, 2005). The definitive host range for F. hepatica is expanding, and depending on geographic location, can include a wide variety of mammals and marsupials (Mas-Coma, 2005;Mas-Coma et al, 2005).…”

Aplexa hypnorum(Gastropoda: Physidae) exerts competition on two lymnaeid species in periodically dried ditches

“…Several authors (Økland, 1990;Moens, 1991;Vareille-Morel et al, 1999) have already reported the marginalization of most G. truncatula habitats at the peripheral extremity of open drainage and rainwater-draining furrows. According to these authors, G. truncatula was outcompeted by other lymnaeids, including O. glabra which may even drive G. truncatula to local extinction (Rondelaud et al, 2005). Our results demonstrate that A. hypnorum also exerted an evident negative effect on O. glabra, though to a lesser extent than on G. truncatula because of the two following reasons: (i) the complete colonization of O. glabra habitats by the physid took longer than that of the other lymnaeid (7 years instead of 4 years, respectively: Figs.…”

Tropische und subtropische Helminthosen

“…Der Mensch ist ein "Gelegenheitswirt". Die Aufnahme erfolgt durch an Grashalmen oder Gemüse enzystierte Erregerstadien oder durch das Garnieren von Speisen mit kontaminierten Gewürz-gräsern wie Brunnenkresse [9,13] …”