Genetic diversity of Ehrlichia ruminantium field strains from selected farms in South Africa

Onderstepoort Journal of Veterinary Research

Field Value
Title Genetic diversity of Ehrlichia ruminantium field strains from selected farms in South Africa
Creator Steyn, Helena C. Pretorius, Alri
Subject Molecular Epidemiology Ehrlichia ruminantium; molecular epidemiology; phylogenetic analyses; qpCS20 real-time PCR; subtractive hybridisation polymorphic ORFs
Description Heartwater is a tick-borne disease caused by the intracellular rickettsial parasite Ehrlichia ruminantium and transmitted by Amblyomma hebraeum ticks. Heartwater is problematic in endemic areas because it causes high mortality in ruminants and leads to economic losses that threaten productivity and food security. This may indicate that there is augmented genetic diversity in the field, which may result in isolates that are more virulent than the Ball3 and Welgevonden isolates. The genetic diversity of E. ruminantium was investigated in this study, focussing on the pCS20 gene region and four polymorphic open reading frames (ORFs) identified by subtractive hybridisation. The 16S ribosomal ribonucleic acid gene confirmed E. ruminantium in brain, blood and tick genomic deoxyribonucleic acid samples (n = 3792) collected from 122 farms that were randomly selected from seven provinces of South Africa where heartwater is endemic. The conserved E. ruminantium pCS20 quantitative polymerase chain reaction (qPCR) assay was used to scan all collected field samples. A total of 433 samples tested positive with the qPCR using the pCS20 gene region, of which 167 were sequenced. The known stocks and field samples were analysed, and phylogenetic trees were generated from consensus sequences. A total of 25 new clades were identified; of these, nine isolates from infected blood could be propagated in cell cultures. These clades were not geographically confined to a certain area but were distributed amongst heartwater-endemic areas in South Africa. Thus, the knowledge of strain diversity of E. ruminantium is essential for control of heartwater and provides a basis for further vaccine development.
Publisher AOSIS
Date 2020-06-25
Type info:eu-repo/semantics/article info:eu-repo/semantics/publishedVersion — Epidemiological survey
Format text/html application/epub+zip text/xml application/pdf
Identifier 10.4102/ojvr.v87i1.1741
Source Onderstepoort Journal of Veterinary Research; Vol 87, No 1 (2020); 12 pages 2219-0635 0030-2465
Language eng
The following web links (URLs) may trigger a file download or direct you to an alternative webpage to gain access to a publication file format of the published article:
Coverage South Africa — Ehrlichia ruminantium positive samples
Rights Copyright (c) 2020 Helena C. Steyn, Alri Pretorius