SEASONAL-VARIATION IN THE CAPACITY OF THE BANK VOLE TO INFECT LARVAL TICKS (ACARI, IXODIDAE) WITH THE LYME-DISEASE SPIROCHETE, BORRELIA-BURGDORFERI

Seasonal variation in the capacity of bank voles, Clethrionomys glareo lus (Schreber), to infect larval Ixodes ricinus (L.) ticks with Borrel ia burgdorferi Johnson, Schmid, Hyde, Steigerwalt & Brenner was examin ed from May through October 1991 at Bogesund, near Stockholm in south- central Sweden. Although larval infestations of bank voles were greate st in June and July, nearly 70% of all larval ticks infected with spir ochetes by bank voles at this site became infected during August and S eptember. Seasonality of infectivity was related to the degree of earl ier nymphal infestation on voles as well as to the age composition of the vole population. These factors may influence the infectivity of ot her rodent reservoirs of B. burgdorferi, both in Europe and North Amer ica. Moreover, in determining the reservoir potential of tick hosts, a host population's spirochetal infectivity should be determined for th e entire period of larval infestation rather than just during the peri od of peak larval infestation.