Adaptation of Lymnaea fuscus and Radix balthica to Fasciola hepatica through the experimental infection of several successive snail generations

Table 2 Characteristics of Fasciola hepatica infection in Lymnaea fuscus (F5 generation), Radix balthica (F5 generation) and Galba truncatula subjected to individual bimiracidial exposures and raised at 20°C (second experiment)

Population	*Lymnaea fuscus*	*Radix balthica*	*Galba truncatula*	Significant differences*
Number of snails:
- at exposure	100	100	100
- at day 30 p.e. (%)	54 (54.0)	65 (65.0)	74 (74.0)	χ² = 8.74, p < 0.05
Number of snails:
- CS	7	13	43
- NCS	12	14	11
Prevalence of infection (%)	35.1	41.5	72.9	χ² = 21.99, p < 0.001
Shell growth (mm):
- CS	7.7 ± 1.5	6.0 ± 1.1	3.7 ± 0.9	F = 14.32, p < 0.001
- NCS	7.3 ± 1.1	5.7 ± 0.8	3.5 ± 1.1	F = 16.63, p < 0.001
Prepatent period in days	55.7 ± 6.5	57.1 ± 8.3	43.3 ± 5.2	F = 4.42, p < 0.05
Patent period in days	11.2 ± 4.7	16.1 ± 5.2	28.8 ± 7.3	F = 10.21, p < 0.001
Number of shed cercariae	80.3 ± 35.8	66.8 ± 21.2	157.1 ± 55.2	F = 7.10, p < 0.01
Cadavers of NCS snails:
- Free rediae	15.7 ± 5.2	18.3 ± 4.5	31.5 ± 5.3	F = 11.71, p < 0.001
- Free cercariae	137.6 ± 37.0	154.2 ± 52.9	236.5 ± 67.1	F = 4.68, p < 0.05
Percentage of shed cercariae**	58.3	43.3	66.4

*Mean values are given with their standard deviations for seven parameters. Each statistical comparison was performed using values recorded for the three lymnaeid species. CS, cercariae-shedding snails; F, value of ANOVA; NCS, non cercarial shedding snails containing cercariae; NS, non significant difference; p, probability; p.e., post-exposure; χ², value of the χ² test.
**Number of cercariae shed by CS snails / overall cercarial production in NCS snails.

ISSN: 1756-3305