A panel of 16S ribosomal RNA gene probes has been developed for the study of the
epidemiology of heartwater; five of these detect different cowdria genotypes, one detects five
distinct genotypes; one detects any Group III Ehrlichia
species other than Cowdria and one
detects any Group II Ehrlichia species. These probes have been used on PCR-amplified
rickettsial 16S rRNA genes from over 200 Amblyomma hebraeum ticks. Control ticks were
laboratory-reared and either uninfected or fed on sheep experimentally infected with different
cowdria isolates, field ticks were collected from animals in heartwater-endemic areas. All tick-derived DNA samples were also examined by PCR amplification and probing for two other
cowdria genes (map1 and pCS20) which have previously been used for heartwater
epidemiology. This paper describes the first direct comparison of all currently available DNA
probes for heartwater-associated organisms.