Comparative evaluation of 16S, map1 and pCS2O probes for the detection of Cowdria and Ehrlichia species in ticks

We have developed a panel of 16S ribosomal RNA gene probes for heartwater epidemiology; five of these detect different Cowdria genotypes (Ball3, Senegal, Omatjenne, Crystal Springs, and Mars 87/7); one detects all five of these genotypes; one detects any Group III Ehrlichia species other than Cawdria; one detects any Group II Ehrlichia species. We have used these probes on PCR-amplified rickettsial 16S rRNA genes from over 200 Amblyomma ticks. Control ticks were laboratory-reared and either uninfected or fed on sheep experimentally infected with different Cowdria isolates, field ticks were harvested from animals in heartwater-endemic and heartwater-free areas. All the samples were also examined by PCR amplification and probing for two other Cowdria genes (map1 and pCS20) which have been used for heartwater epidemiology, This paper describes the first direct comparison of all the currently available DNA probes for heartwater-associated organisms.