Characterisation of South African field Ehrlichia ruminantium using multilocus sequence typing

Area of Science:

• Veterinary Parasitology
• Molecular Epidemiology
• Bacteriology

Background:

• Heartwater, a significant tick-borne illness in African ruminants, stems from Ehrlichia ruminantium.
• The genetic variability of Ehrlichia ruminantium strains limits current vaccine efficacy against virulent types.

Purpose of the Study:

• To genetically characterize Ehrlichia ruminantium isolates from South African cattle ticks.
• To understand the genetic diversity of Ehrlichia ruminantium in South Africa for improved disease control.

Main Methods:

• DNA from 1004 Amblyomma hebraeum ticks was analyzed using real-time PCR (pCS20 Sol1).
• Multilocus sequence typing (MLST) with five housekeeping genes was employed for genetic characterization.
• Phylogenetic analysis was performed on sequenced isolates.

Main Results:

• Ehrlichia ruminantium was detected in 22% of tick samples across Mpumalanga, KwaZulu-Natal, and Limpopo provinces.
• Phylogenetic analysis identified three main lineages, with South African isolates clustering within the worldwide clade.
• MLST successfully differentiated South African genotypes from West African isolates, revealing genetic variations like SNPs.

Conclusions:

• The genetic characterization of Ehrlichia ruminantium field isolates is vital for effective heartwater management.
• This study provides foundational knowledge for developing more targeted and practical vaccines against heartwater.