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Twelve natural populations of Pseudosuccinea columella snails, sampled in the western and central regions of Cuba, were analyzed using the RAPD-PCR technique to screen for resistance to Fasciola hepatica. Ten OPA primers previously shown to produce marker bands for resistance and susceptibility were tested. A new population of P. columella (El Azufre, Pinar del Río) exhibited the amplification patterns of resistant snails, and its resistant status was confirmed after experimental exposure to miracidia. No genetic variability was detected across or within the susceptible isolates. Similarly, the novel resistant isolate displayed an RAPD profile identical to the profile of two other isolates previously identified as resistant to F. hepatica. However, clear differences in RAPD banding patterns and genetic distance were observed between resistant and susceptible isolates. [Copyright &y& Elsevier]

The abundance of freshwater snails in two rural sites of Pinar del Río, Cuba, which harbor Pseudosuccinea columella susceptible and resistant to miracidia of Fasciola hepatica was followed for one year. Susceptible snails were found in the most anthropic site (IPA) whereas the resistant population inhabited the most preserved one (El Azufre). Only two snail species coexisted with P. columella at IPA site (Physa cubensis and Tarebia granifera) while five species were found at El Azufre, including an endemic from that province (Hemisinus cubanianus). Populations of both resistant and susceptible snails showed stable densities throughout the year, although the susceptible strain attained higher abundance. The highest densities were observed in April-May 2004 for the susceptible population whereas the resistant strain attained its highest abundance in January 2004. No record of Fossaria cubensis was made and the thiarid T. granifera occurred only at low densities. One of the sampled sites (IPA) meets all the conditions for the first report of P. columella naturally infected with larvae of F. hepatica.

The variation of abundances of intermediate snail hosts of Fasciola hepatica in Cuba (Fossaria cubensis and Pseudosuccinea columella) was studied during one year under natural conditions at five sampling sites in San Juan y Martinez municipality, Pinar del Rio province, Cuba. The effect of some environmental variables on the lymnaeid abundances was also studied. A canonical correspondence analysis showed that both species do not generally occur together in the same habitat and that most factors affect them in an opposite fashion, although both of them correlate positively through time to the diversity of the habitats. F. cubensis prefers the sites that are in or closer to the city whereas P. columella is more abundant in rural sites. Lymnaeid abundances are mainly affected by nitrite and nitrate concentrations as well as by the abundance of the thiarid Tarebia granifera. F. cubensis is more abundant in polluted habitats with low densities (or absence) of T. granifera whereas P. columella prefers cleaner habitats and can coexist with the thiarid, even at its higher densities. The implications of divergent preferences of the two lymnaeids for the control of fasciolosis are discussed.

Isolates of Cuban Pseudosuccinea columella susceptible and non-susceptible to Fasciola hepatica miracidial infection were compared for cellular reaction to miracidial development, shell morphometrics, mantle pigmentation pattern, and egg laying behaviour. At 24 h post-exposure, non-susceptible snails showed an early cellular host reaction to encapsulate and phagocytise the miracidium, whereas viable transforming miracidia were observed in exposed susceptible snails, indicating that non-susceptibility resulted from resistance rather than physiological unsuitability. Susceptible isolates (more than 80% susceptible to infection) showed significantly higher values of the morphometric indices shell width/length and aperture width/length than resistant isolates (100% resistant). Mantle pigmentation pattern was analysed using Visilog software; the cumulative distances between mantle spots were plotted and compared between isolates, showing a clear distinction between groups. Egg-laying behaviour also showed significant differences with susceptible snails preferring to lay their eggs on the container's walls whereas resistant snails preferred to lay their eggs on the bottom of the container.

An uncommon snail-trematode interaction pattern was found for the Pseudosuccinea columella - Fasciola hepaticamodel under laboratory conditions. Week-old juveniles from two isolates showed very high rates of infection (90.0% and 93.3%) after exposure to five miracidia. They also showed differences in their life history traits when compared to a control group. However, they did not exhibit the increase in size and reduction/cessation in host fecundity which is usually observed in most of the other related snail-trematode systems. In contrast, infected juvenile P. columella showed increased egg laying after the onset of cercarial emission and there was no effect on growth. A third isolate of P. columella was found to be refractory to miracidial infection. This constitutes the first report of non-susceptibility to F. hepatica in a lymnaeid species which is usually susceptible. These non-susceptible snails exhibited lower fecundity and survival compared to non-exposed susceptible snails under identical laboratory conditions. The differences observed in terms of life span and reproduction could result from the cost of resistance for individuals from this isolate.