Abstract

This study documented Bartonella infections in wild rodents in Saskatchewan, Canada and investigated the ecology and transmission of Bartonella infections in Richardson's ground squirrels (Spermophilus richardsonii).

To determine the prevalence of Bartonella infections in the rodent community in Saskatchewan, I collected samples from six species of wild rodents at ten sites in 2002 and 2003. Of 104 wild rodents examined, 57% were infected with Bartonella and prevalence within species varied from 49% for Richardson's ground squirrels to 90% for Franklin's ground squirrels (S. franklinii). Sequencing of a 379bp portion of the citrate synthase gene was performed on 54 isolates and revealed 13 distinct genotypes, eight of which had not been described previously. The most common genotype isolated from red-backed voles (Clethrionomys gapperi) was 99.1% to similar to B. grahamii, a known human pathogen.

I investigated the ecology of Bartonella infections in Richardson's ground squirrels at multiple sites from 2002 to 2004. Juvenile squirrels were more likely to be infected with Bartonella and were more likely to have high levels of bacteremia than were adult animals. Prevalence of infection was lowest in May (27%) and highest in late summer and early autumn (71%). I detected four genotypes of Bartonella in 176 animals. The majority (87%) of sequences were identified as genotype H, with genotypes I, J, and K accounting for 8%, 4%, and 1% of sequences, respectively. Of 47 RGS that were bacteremic on more than one occasion, 38 (81%) were infected with the same genotype on all occasions.

Finally, I investigated the role of ectoparasites in transmitting Bartonella infections among Richardson's ground squirrels at six sites from April to September, 2004. After initial counts of fleas and testing for Bartonella in squirrels trapped in April, burrows at three sites were treated with deltamethrin insecticide. Richardson's ground squirrels trapped on treated sites were less likely to have fleas and had fewer fleas than squirrels on control sites. Significantly fewer squirrels were infected with Bartonella on treated sites than control sites in June and July. I conclude that ectoparasites are a significant route of transmission for Bartonella infections among Richardson's ground squirrels.