Parasitic nematodes of the genus Syphacia Seurat, 1916 infecting Muridae in the British Isles, and the peculiar case of Syphacia frederici
The latest Paper of the Month in Parasitology is Parasitic nematodes of the genus Syphacia Seurat, 1916 infecting Muridae in the British Isles, and the peculiar case of Syphacia frederici by Jerzy M. Behnke
In Europe wood mice (Apodemus sylvaticus) and yellow-necked mice (Apodemus flavicollis) are infected by two species of pinworms, Syphacia stroma and Syphacia frederici. In the UK, however, only S. stroma had previously been reported to infect our native wood mice. While conducting field studies of helminth communities in the UK we found wood mice that contained Syphacia restricted to the caecum and colon, a characteristic of S. frederici, S. stroma living mainly in the small intestine. Given that the UK has arguably one of the best studied rodent-helminth populations in the world we were intrigued that S. frederici had never been previously reported, despite our evidence to the contrary. We set out to resolve this issue by directly comparing the genetics and morphology of European specimens, known to be S. stroma and S. frederici, with our own UK population.
In order to compare the genetics of these worms we sequenced two regions of DNA, the cytochrome-c-oxidase 1 gene (CO1) and a section of ribosomal DNA that contains the 5.8S ribosomal subunit gene and two internal transcribed spacers. By comparing the sequences from both genetic targets we were able to demonstrate that samples suspected of being S. frederici from the UK did indeed match the sequences acquired from European specimens; confirming that this species is indeed found on the British Isles. Moreover, our analysis also used sequences of S. aff. frederici obtained from Apodemus speciousus in Japan that had been published online. We found that although these Japanese worms had been identified as S. frederici their genetics did not closely resemble our specimens from Europe and the UK, leading us to hypothesise (as have some authors before us) that these may be a distinct species.
Examination of both European and UK Syphacia at a morphological level corroborated our genetic analysis. We found the most consistent and easily discernible method for comparing both species was tail morphology. The tail of S. frederici tapers to a point more gradually than that of S. stroma, resulting in a longer thinner tail. Moreover, the tail of S. frederici is also often bent or twisted making this the simplest method of comparing species.
In this study we have therefore confirmed that on three lines of evidence (location in the gut, phylogenetics and morphology) that S. frederici is found in wood mice of the British Isles and we do so in a study that utilised extensive interdisciplinary and international collaboration. We suspect that the lack of previous reporting of S. frederici in the UK is because the female worms appear superficially quite similar and male worms, most commonly used to identify species, are extremely rare.
Our next objective is to sort out the Syphacia species affecting voles in the UK, both bank voles (Myodes glareolus) and short-tailed field voles (Microtus agrestis). For this we would very much welcome collaboration with anyone who can provide us with Syphacia worms from these animals from sites in the UK or further afield from Europe. We would be particularly grateful for any specimens from African rodents, especially those from W. Africa and specifically from the region in and around Nigeria. Our reason for this is the Syphacia nigeriana was originally described by Baylis 1928 on the basis of worms recovered from the African rodents Taterillus gracilis (slender gerbil from the district of Kano, Nigeria), Taterona kempi (northern savanna gerbil from Ibadan), Praomys tulbergi (Tullberg’s soft-furred mouse from Adu), Mastomys erythroleucus (Guinea multimammate mouse from Ife) and Lemniscomys striatus (typical striped grass mouse from Adu). And perhaps strangely and surprisingly given the distance and terrain involved, following Quentin 1971, was adopted as the type species infecting rodents of the genus Microtus throughout the Euro-Siberian region of the Palearctic. Using the combined tools of morphological and molecular analysis we hope to sort out the relationships between the Syphacia species in European voles and hopefully eventually to evaluate the status of S. nigeriana.
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