Abstract
White-tailed deer are susceptible to heartwater (Ehrlichia [Cowdria] ruminantium infection) and are likely to suffer high mortality if the disease spreads to the United States. It is vital, therefore, to validate a highly specific and sensitive detection method for E. ruminantium infection that can be reliably used in testing white-tailed deer, which are reservoirs of antigenically or genetically related agents such as Ehrlichia chaffeensis, Anaplasma (Ehrlichia) phagocytophilum (HGE agent) and Ehrlichia ewingii. Recently, a novel but as yet unnamed ehrlichial species, the white-tailed deer ehrlichia (WTDE), has been discovered in deer populations in the United States. Although the significance of WTDE as a pathogen is unknown at present, it can be distinguished from other Ehrlichia spp. based on 16S rRNA gene sequence analysis. In this study it was differentiated from E. ruminantium by the use of the pCS20 PCR assay which has high specificity and sensitivity for the detection of E. ruminantium. This assay did not amplify DNA from the WTDE DNA samples isolated from deer resident in Florida, Georgia and Missouri, but amplified the specific 279 bp fragment from E. ruminantium DNA. The specificity of the pCS20 PCR assay for E. ruminantium was confirmed by Southern hybridization. Similarly, the 16S PCR primers (nested) that amplify a specific 405-412 bp fragment from the WTDE DNA samples, did not amplify any product from E. ruminantium DNA. This result demonstrates that it would be possible to differentiate between E. ruminantium and the novel WTDE agent found in white tailed deer by applying the two respective PCR assays followed by Southern hybridizations. Since the pCS20 PCR assay also does not amplify any DNA products from E. chaffeensis or Ehrlichia canis DNA, it is therefore the method of choice for the detection of E. ruminantium in these deer and other animal hosts.
Highlights
Heartwater is an acute infectious disease caused by Ehrlichia (Cowdria) ruminantium and is transmitted to domestic and wild ruminants by Amblyomma ticks (Walker & Olwage 1987)
No amplification was detected when the pCS20 PCR was done on white-tailed deer ehrlichia (WTDE) DNA but amplification of a 279 bp fragment was seen with E. ruminantium DNA
White-tailed deer play an important role in the epidemiology of infections which affect humans, as they are reservoirs of E. chaffeensis, E. ewingii and Anaplasma (Ehrlichia) phagocytophilum (Little, Stallknecht, Lockhart, Dawson & Davidson 1998)
Summary
Heartwater is an acute infectious disease caused by Ehrlichia (Cowdria) ruminantium and is transmitted to domestic and wild ruminants by Amblyomma ticks (Walker & Olwage 1987). Some wild animal species are refractory to E. ruminantium infection, while some serve as carriers and others, such as white-tailed deer (Odocoileus virginianus), springbok (Antidorcas marsupialis) and kafue lechwe (Kobus leche kafuensis) suffer high mortality when infected experimentally or naturally (Camus, Barré, Martinez & Uilenberg 1996; Peter et al 2002). It has been shown that E. ruminantium can be maintained in Amblyomma hebraeum ticks found exclusively in the Kruger National Park in South Africa where there has been no contact between the wild game species and cattle for at least 40 years (Peter, Bryson, Perry, O’Callaghan, Medley, Smith, Mlambo, Horak, Burridge & Mahan 1999), indicating that the ticks maintain their infection by feeding on infected wild animal species found in the Park
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