Transmission ecology of gastrointestinal trematodes of small mammals, malham tarn, North Yorkshire, UK

In 2007, Rogan et al. reported the rare occurrence of the digenean Plagiorchis muris from the wood mouse Apodemus sylvaticus at Malham Tarn Nature Reserve in North Yorkshire, UK. The life cycle of this trematode is not well understood. Therefore, in order to investigate the occurrence of this digenean and attempt to understand its transmission ecology at Malham Tarn, 180 rodents (117 A. sylvaticus, 54 Myodes glareolus and 9 Microtus agrestis) trapped between January 2010 and October 2011 were examined for helminths by dissection. The following helminth species were identified, including the following nematodes (overall prevalence rates and mean intensity in parentheses): Heligmosomoides polygyrus (67.5%, 9.2±12.7), Heligmosomoides glareoli (3.17%, 44±55.2), Syphacia stroma (29.1%, 32.5±37.2), Syphacia sp. (11.1%, 15.2±13.2) and Aoncotheca murissylvatici (7.6%, 3.0±2.7), the following cestode: Hymenolepis diminuta (7.9%, 1.0±0) and the following digeneans: Brachylaemus recurvum (1.7%, 2.0±1.4), Plagiorchis elegans (23%, 26.6±61.5) and Notocotylus malhamensis (14.3%, 65.6±104.6). The use of DNA sequencing of the partial 28S rRNA gene and the complete Internal Transcribed Spacer (ITS1-5.8SrDNA-ITS2) region confirmed the presence of Plagiorchis elegans at this location and not P. muris as originally reported. P. elegans was recorded in the wood mouse population but was not identified from any of the vole species despite careful observations. P. elegans was dispersed across the study site and demonstrated seasonal variation that is thought to be linked to the development of intermediate host species involved in transmission. Both mouse age and sex were determined to be associated with prevalence, with adult male mice carrying a statistically higher worm burden and prevalence. These significant differences are likely to be due to differences in the foraging behaviour between the sexes and age cohorts of the wood mouse. My. glareolus and Mi. agrestis were infected with N. malhamensis; this digenean was identified as a new species based upon morphological inspection and DNA analyses of the 28S rRNA gene and the complete ITS region. N. malhamensis was not identified from the wood mouse despite thorough examination. The N. malhamensis ITS sequence (GenBank: JQ766940) is the first to be published for a Notocotylus species and infection of My. glareolus furthermore represents a new UK host record. N. malhamensis appeared to be site-specific, being identified only from a wetland location with a prevalence of 66.7% and mean intensity of 94.6±119.4 in the bank vole and 50% prevalence and mean intensity of 4.3±2.9 in the field vole. This digenean did not demonstrate seasonality, rather infection is considered to be related to the ecology of this site and its associated flooding. Finally, PCR-based methodologies for detecting larval digeneans within their intermediate host were developed in an attempt to identify the invertebrate species involved in the transmission of both P. elegans and N. malhamensis. The use of morphological analysis, coupled with DNA sequencing, identified the larval stages of Haplometra cylindracea and Notocotylus sp. from Lymnaeid snails. However, the larval stages of P. elegans and N. malhamensis were not identified despite careful observations and the limitations encountered during this process are discussed