Persistence mechanisms in tick-borne diseases.

Onderstepoort J Vet Res. 2009 Mar;76(1):53-8.

Barbet AF.

Department of Infectious Diseases & Pathology, College of Veterinary
Medicine, University of Florida, Gainesville, Florida, USA.

The use of new, highly sensitive diagnostic methods has revealed persistent
infections to be a common feature of different tick-borne diseases, such as
babesiosis, anaplasmosis and heartwater. Antigenic variation can contribute
to disease persistence through the continual elaboration of new surface
structures, and we know in several instances how this is achieved. Known or
suspected mechanisms of persistence in babesial parasites include
cytoadhesion and rapid variation of the adhesive ligand in Babesia bovis and
genetic diversity in several merozoite stage proteins of different Babesia
spp. In Anaplasma, extensive variation in the pfam01617 gene family
accompanies cycling of organism levels in chronic infection. One result from
the pioneering research at Onderstepoort is the definition of a related
polymorphic gene family that is likely involved in immunity against
heartwater disease. We are beginning to understand the sizes of the
antigenic repertoires and full definition is close, with the possibility of
applying simultaneous high-throughput sequencing to the order of 1000 small
genomes. We also, for the first time, can consider modifying these genomes
and looking at effects on persistence and virulence. However, important
biological questions remain unanswered; for example, why we are seeing a new
emerging Anaplasma infection of humans and is infection of endothelial cells
by Anaplasma significant to persistence in vivo.

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PMID: 19967928 [PubMed - indexed for MEDLINE]