Detection of the Agent of Heartwater, Cowdria ruminantium , in Amblyomma Ticks by PCR: Validation and Application of the Assay to Field Ticks

Abstract

We have previously reported that the pCS20 PCR detection assay forCowdria ruminantium, the causative agent of heartwater disease of ruminants, is more sensitive than xenodiagnosis and the pCS20 DNA probe for the detection of infection in the vectorAmblyomma ticks. Here, we further assessed the reliability of the PCR assay and applied it to field ticks. The assay detected DNA of 37 isolates of C. ruminantium originating from sites throughout the distribution of heartwater and had a specificity of 98% when infected ticks were processed concurrently with uninfected ticks. The assay did not detect DNA of Ehrlichia chaffeensis, which is closely related to C. ruminantium. PCR sensitivity varied with tick infection intensity and was high (97 to 88%) with ticks bearing 107 to 104 organisms but dropped to 61 and 28%, respectively, with ticks bearing 103 and 102 organisms. The assay also detected C. ruminantium in collections of Amblyomma hebraeum andAmblyomma variegatum field ticks from 17 heartwater-endemic sites in four southern African countries. Attempts at tick transmission of infection to small ruminants failed with four of these collections. The pCS20 PCR assay is presently the most characterized and reliable test for C. ruminantium in ticks and thus is highly useful for field and laboratory epidemiological investigations of heartwater.

Ehrlichia ruminantium infects Rhipicephalus microplus in West Africa

“…The female ticks exposed to E. ruminantium infection were all successfully infected and able to transmit the rickettsia to their offspring. Even if the specificity of the PCR-diagnosis method was already settled [ 16 , 17 ], we confirmed our results by sequencing the PCR-products obtained from the field-collected A. variegatum positive control, one field-collected R. microplus adult from Ivory Coast and the descent of the kimini females. This provided sequences of high quality (in both forward and reverse directions) except in three egg-pools.…”

Geographic distribution and genetic diversity of the Ehrlichia sp. from Panola Mountain in Amblyomma americanum

“…The overall prevalence of infection with PME, approximately 1–3%, was similar to that previously reported from Panola Mountain [ 1 ]. Similar prevalences of E. ewingii and E. ruminantium are seen in populations of Amblyomma infected with these agents [ 14 , 17 - 19 ].…”

Survey for the presence of White Spot Syndrome virus in Australian crustaceans

“…However, validated PCR tests routinely have specificities and sensitivities greater than 95% and usually in excess of 98%. 11,12 Although the specificity for the PCR test used was not known, the complete test regimen of retesting preliminary positive samples and the subsequent use of bioassay if required, was assumed to have an overall specificity of 100%. Based on the known sensitivity of other validated PCR tests, the sensitivity of the PCR testing regimen was assumed to be 95%.…”