[25], having reviewed the early history of the parasite, strongly

[25], having reviewed the early history of the parasite, strongly recommended that N. dubius should be dropped. However, in subsequent work, it became apparent that the parasites used in laboratory studies and those parasitizing wild wood mice (Apodemus sylvaticus) in Europe were quite distinct in a number of respects. At first, it was suggested that these

were subspecies and should be referred to as H. polygyrus bakeri for the laboratory-maintained parasite and H. p. polygyrus for that in wild rodents [26], but Cable et al. [27] raised both to full species status check details on the basis of molecular genetic data. This controversy about the exact taxonomic status of the parasite was reviewed again recently [28], although not everyone has accepted

PF2341066 the change in nomenclature proposed by Cable et al. [29], and for this reason in this article, we refer to it as H. p. bakeri. In the 1960s–1970s, a key research problem with H. p. bakeri was how to induce immunity to this parasite, as primary infections appeared to be so stable for so long. Many experimenters found that removing a primary infection and then challenging the mice with a second batch of larvae just did not induce marked immunity, that is, a substantial reduction in the success of challenge infections [30-32], and it was thought at the time that Adenosine triphosphate adult worms were not immunogenic [33]. Much effort was given therefore to devising various combinations of repeated infections, sometimes interspersed

with anthelmintic treatment or just superimposed on one another. The breakthrough came when it was realized that adult worms not only failed to induce effective resistance in many mouse strains and appeared not to be susceptible to mucosal responses in some strains of immune mice [34], but actually prevented the expression of host-protective effector mechanisms operating at the mucosal level [13, 31, 35]. The larval, tissue-dwelling stages of this parasite are in fact highly immunogenic [36] and can induce immunity even in poor responder strains of mice [37], as long as the period of residence of adult worms in the gut lumen is brief, as for example after infection with irradiated infective larvae [38], following treatment with ivermectin, which kills the larvae in situ in the intestinal walls [36], or by chemotherapy immediately after their emergence from the intestinal walls 7–9 days post-infection [31, 35]. It was shown that an average of just over 3 infective larvae per mouse was sufficient to generate an 84% reduction in challenge infection worm burdens in NIH mice when the immunizing larvae were killed by ivermectin on day 6 post-infection [37].

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