Enzootic transmission of Anaplasma bovis in Nantucket cottontail rabbits

Abstract

Serological studies of cottontail rabbits sampled from Nantucket Island, Mass., have suggested exposure to at least two ehrlichiae. The agent of human granulocytic ehrlichiosis (Anaplasma phagocytophilum) is intensely enzootic in rabbits there, but the identity of the other ehrlichial infection remains undescribed. We sampled rabbits over five transmission seasons and tested their blood and tissues for evidence of infection using PCR targeting an Ehrlichia genus-wide 16S rDNA target. Sequence analysis of positive amplicons revealed the presence of Anaplasma bovis, an agent not known to be present in North America. The average annual prevalence of A. bovis within rabbits, as determined by PCR of blood samples, was 18%. Haemaphysalis leporispalustris appears to serve as vector. The public health (human or veterinary) significance of this finding remains speculative.

FIG. 1.

Phylogenetic analysis. Shown is a bootstrap consensus neighbor-joining tree of Ehrlichia spp.

FIG. 2.

Prevalence of A. bovis in rabbits by month. Black bars, 2000; dark gray bars, 2001; light gray bars, 2002. Data from 1998 and 1999 are not included in this graph because collections occurred only in the spring and fall. Hatched bars, mean prevalence for all years of collection, 1998 to 2002. Note that 2002 collections halted in August, and 2000 collections halted in September.