Submitted to: Journal of Medical Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/23/2009
Publication Date: 5/1/2009
Citation: Baldridge, G.D., Scoles, G.A., Burkhardt, N.Y., Schloeder, B., Kurtti, T.J., Munderloh, U.G. 2009. Transovarial Transmission of Francisella-Like Endosymbionts and Anaplasma phagocytophilum Variants in Dermacentor albipictus (Acari: Ixodidae). Journal of Medical Entomology. 46(3):625-632.
Interpretive Summary: The winter tick, Dermacentor albipictus (also known as the moose tick), is widely distributed in North America. This one-host tick is frequently found on large animal hosts including deer and cattle. Although this species is known to be a competent vector of Anaplasma marginale to cattle its other vector relationships have been little studied. In this paper the microbial flora of D. albipictus collected from deer has been studied using PCR for detection of bacterial DNA in the ticks. Anaplasma species and Francisella-like endosymbionts were present in nymphal and adult ticks of both sexes at prevalences of 45% and 94%, respectively, but no other bacterial species were found. The Anaplasma and Francisella-like endosymbionts were transmitted to their larval offspring (transovarially transmitted) at efficiencies of 10 – 40% and 95 – 100%, respectively. The Francisella-like endosymbionts were transovarially transmitted to a second generation of larval ticks obtained as progeny of adult ticks from the first generation reared to maturity on a calf, but the Anaplasma endosymbionts were not. This demonstration of co-infection and maintenance of Francisella and Anaplasma spp. in D. albipictus fed on an alternative host (cattle) provides a foundation for further investigations of the relationships between endosymbionts and tick-transmissible disease agents in this tick species.
Technical Abstract: Dermacentor albipictus (Packard) is a North American Ixodid tick that parasitizes deer species but also infests livestock. It is a suspected vector of the agent of anaplasmosis in cattle herds, Anaplasma marginale, but its microbial flora and emerging pathogen vector potential remain under-evaluated. We screened D. albipictus ticks collected from white-tailed deer in Minnesota for bacteria of the genera Anaplasma, Borrelia, Ehrlichia, Francisella, and Rickettsia using PCR amplification and sequence analyses of bacterial genes. Anaplasma phagocytophilum and Francisella-like endosymbionts (FLE) were present in nymphal and adult ticks of both sexes at prevalences of 45% and 94%, respectively, but members of the other genera were not. Both A. phagocytophilum and the FLE were present in extracts of pooled larvae and were transovarially transmitted to F1 larvae by four female ticks at efficiencies of 10 – 40% and 95 – 100%, respectively. The FLE were transovarially transmitted to an F2 generation of larval ticks obtained as progeny of adults from F1 larval ticks reared to maturity on a calf, but A. phagocytophilum was not. The calf showed no evidence of infection with either bacterium. Sequences of the A. phagocytophilum 16S rRNA gene amplification products were identical, or nearly so, to those of the Ap-Variant WI-1 and WI-2 strains detected in white-tailed deer from central Wisconsin. The amplified FLE 16S rRNA gene sequences were highly similar to those previously amplified from various Dermacentor tick species and were identical to that obtained from a D. albipictus tick collected from a horse in Texas.