Prevalence of Cowdria ruminantium infection in Amblyomma hebraeum ticks from heartwater-endemic areas of Zimbabwe

Analysis of the transmission dynamics of Cowdria ruminantium, the tick-born e rickettsial agent of heartwater in ruminants, requires accurate measures of infection in vector populations. To obtain these, Amblyomma hebraeum tic ks were collected at two heartwater-endemic locations in the lowveld and hi ghveld regions of Zimbabwe and assessed for C. ruminantium infection with s pecific polymerase chain reaction (PCR) and DNA probe detection assays. At the lowveld site, 11.2 % (50/446) of adult ticks and 8.5 % (23/271) of nymp hs carried C. ruminantium, as detected by PCR. At the highveld site, the pr evalence of infection in adult ticks was 10.2 % (40/392). DNA probe analysi s revealed that most infections at both sites were of low intensity; only 9 % and 23 % of all nymph and adult tick infections, respectively, were grea ter than 70000 organisms, the detection limit of the DNA probe. However, th e majority (70 %) of probe-detectable adult tick infections were high, betw een 10(7) and 10(9) organisms/tick, while those within nymphs were lower, b etween 10(5) and 10(6) organisms/tick.