Abstract:
Theileria parva is a protozoan parasite transmitted by the brown-eared ticks,
Rhipicephalus appendiculatus and Rhipicephalus zambeziensis. Buffaloes are the
parasite’s ancestral host, with cattle being the most recent host. The parasite has two
transmission modes namely, cattle–cattle and buffalo–cattle transmission. Cattle–cattle
T. parva transmission causes East Coast fever (ECF) and January disease syndromes.
Buffalo to cattle transmission causes Corridor disease. Knowledge on the genetic
diversity of South African T. parva populations will assist in determining its origin,
evolution and identify any cattle–cattle transmitted strains. To achieve this, genomic
DNA of blood and in vitro culture material infected with South African isolates (8160,
8301, 8200, 9620, 9656, 9679, Johnston, KNP2, HL3, KNP102, 9574, and 9581) were
extracted and paired-end whole genome sequencing using Illumina HiSeq 2500 was
performed. East and southern African sample data (Chitongo Z2, Katete B2, Kiambu
Z464/C12, Mandali Z22H10, Entebbe, Nyakizu, Katumba, Buffalo LAWR, and Buffalo
Z5E5) was also added for comparative purposes. Data was analyzed using BWA
and SAMtools variant calling with the T. parva Muguga genome sequence used as a
reference. Buffalo-derived strains had higher genetic diversity, with twice the number
of variants compared to cattle-derived strains, confirming that buffaloes are ancestral
reservoir hosts of T. parva. Host specific SNPs, however, could not be identified among
the selected 74 gene sequences. Phylogenetically, strains tended to cluster by host
with South African buffalo-derived strains clustering with buffalo-derived strains. Among
the buffalo-derived strains, South African strains were genetically divergent from other buffalo-derived strains indicating possible geographic sub-structuring. Geographic substructuring
was also observed within South Africa strains. The knowledge generated
from this study indicates that to date, ECF is not circulating in buffalo from South Africa. It
also shows that T. parva has historically been present in buffalo from South Africa before
the introduction of ECF and was not introduced into buffalo during the ECF epidemic.
