Post-encystment/established immunity in cystic echinococcosis: is it really that simple?

In 1982, Rickard & Williams stated that immunity to larval taeniid cestodes could be divided into two different phases: the establishment phase, operating against oncospheres, and the established phase, operating against established metacestodes in the tissues. These concepts were largely based on experimental and veterinary data. As a result of subsequent research combined with clinical data, we can consider that, for metacestodes of Echinococcus spp, a single established phase is probably too simple a concept. These parasites show developmental changes in different hosts over time, the most significant being growth, fertility and degeneration. Recent clinical cyst classifications (WHO/IWGE) have highlighted that all hydatid cysts are morphologically not the same. This is important for treatment but fails to completely address variation in the host/parasite response and the understanding of parasite survival. This review attempts to relate the immunological and developmental data obtained from experimental, veterinary and medical studies to update our understanding of established immunity against E. granulosus. It proposes that a single 'Established' phase for E. granulosus could be subdivided into four additional phases: maturing; stable; unstable and degenerative. Combining this type of information with existing cyst classification systems could significantly benefit our understanding of the parasites immunobiology.

A molecular and ecological analysis of the trematode Plagiorchis elegans in the wood mouse Apodemus sylvaticus from a periaquatic ecosystem in the UK.

The prevalence of the digenean Plagiorchis sp. was investigated in a natural wood mouse population (Apodemus sylvaticus) in a periaquatic environment. Classical identification was complemented with the use of molecular differentiation to determine prevalence and verify species identity. Use of the complete ITS1-5.8S rDNA-ITS2 and partial 28S rDNA gene sequences have confirmed that the species reported at this location was Plagiorchis elegans and not Plagiorchis muris as reported previously. This underlines the difficulties in identification of these morphologically similar parasites. Plagiorchis elegans is typically a gastrointestinal parasite of avian species but has also been reported from small mammal populations. Although the occurrence of this digenean in A. sylvaticus in the UK is rare, in the area immediately surrounding Malham Tarn, Yorkshire, it had a high prevalence (23%) and a mean worm burden of 26.6 ± 61.5. The distribution of P. elegans followed a typically overdispersed pattern and both mouse age-group and sex were determined to be two main factors associated with prevalence. Male mice harboured the majority of worms, carrying 688 of 717 recovered during the study, and had a higher prevalence of 32.4% in comparison to only 8.7% in the small intestine of female mice. A higher prevalence of 43% was also observed in adult mice compared to 14% for young adults. No infection was observed in juvenile mice. These significant differences are likely to be due to differences in the foraging behaviour between the sexes and age cohorts of wood mice.