PCR Detection of Cowdria ruminantium Infection in Ticks and Animals from Heartwater‐Endemic Regions of Zimbabwe

Abstract

The development of a PCR assay for the detection of Cowdria ruminantium infection in ticks has been previously described. Here we report a further evaluation of this assay by comparison with a DNA probe and with the mouse inoculation assay (MIA). Application of the PCR assay in determining the prevalence of infection in ruminants and ticks from heartwater-endemic areas of Zimbabwe is also described. One hundred uninfected and 120 infected Amblyomma hebraeum ticks were analyzed by PCR, DNA probe and the MIA. These tests detected infection in 92%, 77% and 8% of the infected ticks, respectively, showing PCR to be the most sensitive assay. None of the uninfected ticks were positive by any of the 3 tests. The PCR assay detected infection rates of 10.5%, 12.5% and 3.2% in 200 male, 241 female and 95 nymphal A. hebraeum ticks, respectively, which were collected from a heartwater-endemic farm. The PCR test was also applied to cattle of different age groups and goats from the same heartwater-endemic farm. In a cross-sectional survey, the assay detected infection in 3.3% to 26.7% of the cattle and in 23.3% of the goats. The implications of these findings and the potential for the application of PCR in heartwater diagnosis is discussed.