Fasciola hepatica: epidemiological surveillance of natural watercress ...

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A total of 59 natural watercress beds in the Limousin region (central France) was surveyed over a 15-year period (1990–2004) to detect the contamination of ...
Parasitol Res (2005) 95: 278–282 DOI 10.1007/s00436-004-1269-3

O R I GI N A L P A P E R

G. Dreyfuss Æ P. Vignoles Æ D. Rondelaud

Fasciola hepatica : epidemiological surveillance of natural watercress beds in central France

Received: 18 October 2004 / Accepted: 3 November 2004 / Published online: 29 January 2005  Springer-Verlag 2005

Abstract A total of 59 natural watercress beds in the Limousin region (central France) was surveyed over a 15year period (1990–2004) to detect the contamination of watercress by the metacercariae of Fasciola hepatica and to determine the presence of larval forms in the two species of lymnaeids which live in these waterholes in June and July. The number of beds contaminated with F. hepatica metacercariae varied over the years, and the burden of the larvae on plants was low: a mean of 2.6–6.3 per bed. The same variability was also noted for natural infections of Galba truncatula with F. hepatica, as the annual prevalences ranged from 1.2% to 2.4%. Natural infections of Omphiscola glabra with F. hepatica were only detected from 1996 and the annual prevalences subsequently increased up to 1.4–1.8% between 2001 and 2004. However, for both lymnaeids, the variations in these prevalences with year were insignificant. The contamination of these beds with F. hepatica over the past 15 years was similar to that recorded in the same sites between 1970 and 1986. The main changes were the appearance of another digenea, Paramphistomum daubneyi, in the beds, and the possibility for O. glabra to naturally sustain the larval development of F. hepatica.

Introduction In most human infections with Fasciola hepatica, Nasturtium officinale (common watercress) is cited as the metacercariae-carrying plant (Mas-Coma et al. 1998). The watercress involved in central France rarely originates from plantations cultivated at an industrial level. G. Dreyfuss Æ P. Vignoles Æ D. Rondelaud (&) Faculte´s de Me´decine et de Pharmacie, UPRES EA n 3174 (associe´e a` l’INRA), 87025 Limoges, France E-mail: [email protected] Fax: +33-555-435893

In most cases, it is directly collected from waterholes and springs in which the plant grows spontaneously or is cultivated at a family level (Rondelaud 1980). As these natural watercress beds were not subjected to legal investigations in France to detect any contamination of watercress with F. hepatica metacercariae or to find natural infections of snails with this parasite, a follow-up study has been carried out by our team since 1970 in 59 watercress beds located in the region of Limousin (central France). Two previous reports (Rondelaud 1991; Rondelaud et al. 2000) demonstrated that natural infections of the snail Galba truncatula with F. hepatica in these beds were often irregular over time. However, in spite of these reports, little information is available in the literature on the number of F. hepatica metacercariae found on natural watercress. In the region of Limousin, Rondelaud and Mage (1990) reported a mean of 0.9 encysted larva (range 0–37) in 247 beds studied between 1970 and 1979. In the same way, the data on the prevalences of natural infections in snails are still few. According to Rondelaud (1991), the infection rates with F. hepatica ranged from 0.5% to 5.4% in the habitats colonized by G. truncatula only, and from 14% to 66% in those inhabited by G. truncatula and another lymnaeid, Omphiscola glabra, due to the low numbers of G. truncatula in these snail communities. As two new events (the finding of metacercariae of Paramphistomum daubneyi on watercress since 1993, and the detection of naturally infected O. glabra with F. hepatica since 1996) were noted in these natural watercress beds, it was of interest to determine the changes which have occurred in these beds over the past 15 years. Our aim was to answer the two following questions: (1) How many metacercariae of each digenean species are detected by the inspection of watercress every year? (2) What have the changes in prevalences of F. hepatica and P. daubneyi infections in G. truncatula and O. glabra been over the past 15 years? To answer these questions, a retrospective study on watercress contamination with digenean metacercariae and snail infections was carried out by consulting the records of

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our team from 1990 to 2004 in 59 natural watercress beds located in the departments of Corre`ze, Creuse, and Haute Vienne (central France).

Materials and methods Watercress beds studied A total of 59 natural watercress beds were investigated every year in June or July from 1990 to 2004. These were located in the departments of Corre`ze (seven beds), Creuse (six) and Haute Vienne (46). The underlying subsoils constituted granite (27 beds), diorite (11), gneiss (four) or migmatites (17), so that the pH of the running water ranged from 5.5 to 6.9 and the contents of dissolved calcium from 5 to 15 mg/l (Rondelaud 1991). In 17 sites, watercress grew in the source of the spring, while the other beds were situated in small pools (27 sites), rivulets (three), or open drainage furrows (12) into which water coming from upstream springs ran. The area of the beds was always less than 12 m2. Populations of G. truncatula were found in 47 watercress beds, while each of the 12 others was colonized by the two species of lymnaeids. However, G. truncatula and O. glabra also inhabited downstream areas along the furrows which came from all of the beds, so that the species of snails at any site might change from one year to the next as both snail species are able to migrate upstream in winter and spring towards the watercress beds. Investigations of aquatic plants Every year, ten specimens of N. officinale and ten of another plant species, Apium nodiflorum, were collected from the periphery of each bed. After removal of the roots, the other segments of each specimen were put into a bag. In the laboratory, these were examined under a stereomicroscope (16· magnification) to find live metacercariae of F. hepatica, P. daubneyi, or those of other digenea. The encysted larvae of the former species were dome-shaped, with a mean diameter of 250 lm and a uniform yellowish or dark yellow colour (determined by their age). Those of P. daubneyi showed the same characteristics but were blackish grey and slightly refringent. The first parameter was the number of watercress beds contaminated by metacercariae of either of these digenea. The number of metacercariae found on A. nodiflorum or on N. officinale was also determined, taking into account the digenean species and the physiological state of the cysts (live or dead). A two-way analysis of variance (Stat Itcf 1988) was used to establish levels of significance. Investigations of snails A variable number of adult G. truncatula (4 mm and more in height), depending on the size of the population, was collected from each bed in June or July. As the popula-

tions of O. glabra were more numerous, the number of adult snails (‡8 mm) collected from each bed ranged from 30 to 40 per year up to 1993 and 60 per year thereafter. After collection, the snails were transported to the laboratory under isothermal conditions (16C) in the dark. Each snail was squashed in tap water under a stereomicroscope and the external epithelium surrounding the digestive gland broken to release the larval forms of digenean species, if present. The characteristics allowing the recognition of rediae and cercariae of F. hepatica from those belonging to P. daubneyi have already been described in previous reports (Abrous et al. 2000; Dreyfuss et al. 2003). The number of watercress beds in which natural infections of snails with F. hepatica or P. daubneyi were found was determined. Another variable was the prevalence of these natural infections in G. truncatula or in O. glabra for each bed and each year. Spearman correlation and two-way analysis of variance (Stat Itcf 1988) were used to determine the levels of significance.

Results Contamination of watercress by metacercariae The number of beds contaminated by the metacercariae of F. hepatica (Table 1) fluctuated with year, ranging from 15 (in 1994) to 32 (in 1999). The number of larvae encysted on A. nodiflorum or N. officinale was low: a mean of 2.6–6.3 per bed. Metacercariae of P. daubneyi were only found from 1993 in these beds. However, the number of beds contaminated by this digenea increased strongly from 1995 to 2004: from 2 to 45. The mean burden of P. daubneyi metacercariae on plants was significantly higher (F=4.18, P