Trypanosomes, fleas and field voles: ecological dynamics of a host-vector–parasite interaction
To investigate the prevalence of a flea-borne protozoan (Trypanosoma (Herpetosoma) microti) in its field vole (Microtus agrestis) host, we monitored over a 2-year period a range of intrinsic and extrinsic parameters pertaining to host demographics, infection status and vector (flea) prevalence. Generalized Linear Mixed Modelling was used to analyse patterns of both flea and trypanosome occurrence. Overall, males of all sizes and ages were more likely to be infested with fleas than their female counterparts. Flea prevalence also showed direct density dependence during the winter, but patterns of density dependence varied amongst body mass (age) classes during the summer. Trypanosome prevalence did not vary between the sexes but was positively related to past flea prevalence with a lag of 3 months, with the highest levels occurring during the autumn season. A convex age-prevalence distribution was observed, suggesting that individuals develop a degree of immunity to trypanosome infection with age and exposure. An interaction between age and whether the individual was new or recaptured suggested that infected animals are less likely to become territory holders than their uninfected counterparts.(Received January 18 2005)
(Revised February 23 2005)
(Accepted February 26 2005)
Key Words: Trypanosoma microti; Microtus agrestis; field vole; vector borne; Siphonaptera; acquired immunity; natural population; sex-bias; Kielder Forest.
c1 School of Biological Sciences, Biosciences Building, Crown Street, University of Liverpool, Liverpool L69 7ZB, UK. Tel: 0151 795 4533. Fax: 0515 795 4408. E-mail: firstname.lastname@example.org