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We investigated the reservoir role of European wild rodents for Anaplasma phagocytophila using polymerase chain reaction (PCR) analysis of blood collected from individually tagged rodents captured monthly over 2 years. The only tick species observed in the woodland study site was Ixodes trianguliceps , and ruminant reservoir hosts were not known to occur. A. phagocytophila infections were detected in both bank voles and wood mice but were restricted to periods of peak nymphal and adult tick activity. Most PCR-positive rodents were positive only once, suggesting that rodent infections are generally short-lived and that ticks rather than rodents may maintain the infection over winter. Bank voles were more likely to be PCR positive than wood mice, possibly because detectable infections are longer lived in bank voles. This study confirms that woodland rodents can maintain A. phagocytophila in Great Britain in the absence of other reservoir hosts and suggests that I. trianguliceps is a competent vector.

The importance of Ixodes ricinus in the transmission of tick-borne pathogens is well recognized in the United Kingdom and across Europe. However, the role of coexisting Ixodes species, such as the widely distributed species Ixodes trianguliceps, as alternative vectors for these pathogens has received little attention. This study aimed to assess the relative importance of I. ricinus and I. trianguliceps in the transmission of Anaplasma phagocytophilum and Babesia microti among United Kingdom field voles (Microtus agrestis), which serve as reservoir hosts for both pathogens. While all instars of I. trianguliceps feed exclusively on small mammals, I. ricinus adults feed primarily on larger hosts such as deer. The abundance of both tick species and pathogen infection prevalence in field voles were monitored at sites surrounded with fencing that excluded deer and at sites where deer were free to roam. As expected, fencing significantly reduced the larval burden of I. ricinus on field voles and the abundance of questing nymphs, but the larval burden of I. trianguliceps was not significantly affected. The prevalence of A. phagocytophilum and B. microti infections was not significantly affected by the presence of fencing, suggesting that I. trianguliceps is their principal vector. The prevalence of nymphal and adult ticks on field voles was also unaffected, indicating that relatively few non-larval I. ricinus ticks feed upon field voles. This study provides compelling evidence for the importance of I. trianguliceps in maintaining these enzootic tick-borne infections, while highlighting the potential for such infections to escape into alternative hosts via I. ricinus.Wild rodents are important reservoirs of numerous tickborne pathogens, including those that cause Lyme borreliosis, granulocytic anaplasmosis and babesiosis (32,33). That rodent populations commonly exist at high densities and are infested with large numbers of the key vector species underlies this importance. In the United States and Europe, it is the broadhost-range tick species such as Ixodes scapularis, Ixodes pacificus, and Ixodes ricinus that are considered as key vector species, but rodents may be infested with more specialized ticks that solely utilize small mammals as hosts for all developmental stages, such as Ixodes trianguliceps and Ixodes spinipalpis (6,26).We have previously reported on the role of I. trianguliceps as a vector for Anaplasma phagocytophilum (4,22), the causative agent of human anaplasmosis and tick-borne fever in livestock (7,35), while previous studies had demonstrated its competence as a vector for Babesia microti (29,36). More recently we reported that field voles (Microtus agrestis) in northern England are infested with both I. trianguliceps and I. ricinus (5), leading us to hypothesize, like others (13), that enzootic infections maintained in an I. trianguliceps-field vole cycle could escape into other hosts, including humans and domesticated animals, via I. ricinus. Furthermore, as I. ricinus nymphs and larvae feed concurr...

Genetically distinct subpopulations have adapted to different niches