Analysis of p67 allelic sequences reveals a subtype of allele type 1 unique to buffalo-derived Theileria parva parasites from southern Africa

Abstract

East Coast fever (ECF) and Corridor disease (CD) caused by cattle-and buffalo-derived T. parva respectively are the most economically important tick-borne diseases of cattle in the affected African countries. The p67 gene has been evaluated as a recombinant subunit vaccine against ECF, and for discrimination of T. parva parasites causing ECF and Corridor disease. The p67 allele type 1 was first identified in cattle-derived T. parva parasites from East Africa, where parasites possessing this allele type have been associated with ECF. Subsequent characterization of buffalo-derived T. parva parasites from South Africa where ECF was eradicated, revealed the presence of a similar allele type, raising concerns as to whether or not allele type 1 from parasites from the two regions is identical. A 900 bp central fragment of the gene encoding p67 was PCR amplified from T. parva DNA extracted from blood collected from cattle and buffalo in South Africa, Mozambique, Kenya, Tanzania and Uganda, followed by DNA sequence analysis. Four p67 allele types previously described were identified. A subtype of p67 allele type 1 was identified in parasites from clinical cases of CD and buffalo from southern Africa. Notably, p67 allele type 1 sequences from parasites associated with ECF in East Africa and CD in Kenya were identical. Analysis of two p67 Bcell epitopes (TpM12 and AR22.7) revealed amino acid substitutions in allele type 1 from buffalo-derived T. parva parasites from southern Africa. However, both epitopes were conserved in allele type 1 from cattle-and buffalo-derived T. parva parasites from East Africa. These findings reveal detection of a subtype of p67 allele type 1 associated with T. parva parasites transmissible from buffalo to cattle in southern Africa.

Variant analysis of the sporozoite surface antigen gene reveals that asymptomatic cattle from wildlife-livestock interface areas in northern Tanzania harbour buffalo-derived T. parva

“…The current study establishes that although a majority of the cattle in the northern Tanzania region are infected with cattle-transmissible T. parva genotypes, some of the animals are infected with T. parva genotypes with p67 sequences suggesting a likely recent origin from buffalo. This finding generally conforms to the distribution of p67 alleles at the interface area in Kenya that we evaluated (although the buffalo-derived p67 genotypes were different) and also to the situation reported in previous studies (Mukolwe et al 2020 ; Obara et al 2015 ; Sitt et al 2019 ). It is also important to note that this pattern of p67 allelic polymorphism is consistent with a scenario whereby frequent transmission of parasites from buffalo to cattle occurs, but many fail to permanently establish in cattle following initial infection, because insufficient progression of buffalo-derived parasites to the tick-infective erythrocytic piroplasm stage occurs to enable onward transmission between cattle by ticks (Mbizeni et al 2013 ; Morrison et al 1989 ).…”

“…The first of these two epitopes within the central region (TmM12 epitope) was conserved in all sequences categorised as cattle type (allele 1) or buffalo type (allele 2) except for one sequence from Kenya cattle (MT365007) which had a single substitution (TKEEVPPADLSDQV L ) (Table 2 ). This amino acid substitution has been observed among cattle type alleles from South Africa in a recent study (Mukolwe et al 2020 ). As shown in Table 2 , two buffalo p67 type 3 alleles had 7 substitutions in this epitope that have previously been reported in Kenya and South Africa (Sibeko et al 2010 ; Sitt et al 2019 ), while the remaining buffalo type 3 and 4 alleles had 5 substitutions (Table 2 ).…”

“…The fact that we did not detect the buffalo-derived allele type 4 of p67in our buffalo samples may have been the result of under sampling; hence, further in-depth sampling will improve the understanding of allele distribution patterns in the region. Previous analyses had suggested that this allele, which has been found in buffalo T. parva in South Africa, seems to be rare within East Africa (Mukolwe et al 2020 ; Obara et al 2015 ; Sibeko et al 2010 ; Sitt et al 2019 ). By contrast, buffalo-derived T. parva alleles 2 and 3 genotypes which we found in our Kenyan sample dataset were also reported in previous studies (Obara et al 2015 ; Sitt et al 2019 ), but not observed in the Tanzanian cattle samples studied.…”

“…Within East Africa, T. parva parasites that are transmissible between cattle by ticks have been frequently observed to carry the p67 allele type 1 which is relatively conserved and is characterised by a 129 bp deletion in the central region as exemplified by the Muguga strain of T. parva (Nene et al 1996 ). By contrast, the T. parva carrying the more heterogeneous p67 allele types 2–4 is known to originate from buffalo and has been shown to be associated with Corridor disease in livestock-wildlife interface areas, where cattle are exposed to infective ticks that have fed on infected African Cape buffalo (Mukolwe et al 2020 ; Obara et al 2015 ; Sibeko et al 2010 ; Sitt et al 2019 ). Recently however, a type 1 allele also associated with buffalo T. parva from South Africa but differing from the East Africa cattle type 1 p67 alleles by amino acid changes in the areas flanking the deletion and the epitope regions has been described (Mukolwe et al 2020 ).…”

“…By contrast, the T. parva carrying the more heterogeneous p67 allele types 2–4 is known to originate from buffalo and has been shown to be associated with Corridor disease in livestock-wildlife interface areas, where cattle are exposed to infective ticks that have fed on infected African Cape buffalo (Mukolwe et al 2020 ; Obara et al 2015 ; Sibeko et al 2010 ; Sitt et al 2019 ). Recently however, a type 1 allele also associated with buffalo T. parva from South Africa but differing from the East Africa cattle type 1 p67 alleles by amino acid changes in the areas flanking the deletion and the epitope regions has been described (Mukolwe et al 2020 ). In addition to assessing the level of exposure of Tanzanian pastoralist cattle to buffalo type T. parva based on p67 gene polymorphism, we also determined how similar the p67 alleles at the interface areas in Tanzania were to alleles carried by buffalo-associated T. parva strains in Kenya.…”