South African Buffalo-Derived Theileria parva Is Distinct From Other Buffalo and Cattle-Derived T. parva

Distribution and Prevalence of Ticks and Tick-Borne Pathogens at the Wildlife-Livestock Interface in Africa: A Systematic Review

Ticks and tick-borne diseases (TBDs) significantly impact African animal health and agricultural productivity, especially at the wildlife-livestock interface. This systematic review analyzed 20 eligible studies from East, Southern, and limited parts of Central Africa to determine the distribution and prevalence of key tick species and associated pathogens. Rhipicephalus appendiculatus and Amblyomma variegatum were the most commonly reported tick species, with R. appendiculatus exhibiting up to 50.5% prevalence in cattle and buffalo in Uganda. The most frequently detected pathogens included Theileria parva, Anaplasma marginale, and Coxiella burnetii, with T. parva showing high prevalence in cattle populations coexisting with wildlife. Notably, geographic disparities were observed, with Central and West Africa being underrepresented. Most pathogen detections occurred in Kenya, Uganda, Tanzania, Botswana, and South Africa, indicating regional hotspots for tick-borne disease transmission. This review highlights the urgent need for enhanced surveillance, region-specific vector control programs, and integrated One Health approaches to address the ecological, agricultural, and zoonotic challenges of tick-borne pathogens across Africa.

Theileria parva genetics, prevalence and vaccination practices in Zimbabwe and the African region and the prospects for vaccine development: a systematic review

INTRODUCTION

January disease causes the deaths of over 55,000 cattle valued at approximately US$ 17 million annually in Zimbabwe. The locally developed Boleni stabilate vaccine is in use for controlling the disease. In the present review, we show the current knowledge of the genetic variation and population structure of Theileria parva parasite and its implications on the epidemiology and control of the parasite in eastern and southern Africa, with a major emphasis on Zimbabwe.

METHODS

A systematic review was conducted to analyse the reports available in literature in order to map the Theileria parva genetic diversity profile. A total of 103 studies met the criteria for analysis and were included in the review.

RESULTS

The reports retrieved in this study show that East Coast fever and Corridor disease have been extensively sequenced to establish the parasite population genetic structure. One report described genetic diversity in January disease, with no sequencing tools included. The live sporozoite stabilate administered as infection without concurrent treatment remains the vaccination approach of choice in January disease.

DISCUSSION

The adoption of population genetics led to the determination of genotypes that were employed in the development of the Muguga cocktail vaccine. To date, vaccination against East Coast fever is reported to reduce mortality rate. The Boleni isolate remains in use for vaccination against uncharacterized populations of January disease in spite of increased mortality rates extensively reported from 2015 to date. There is need to adopt comparative genomics in vaccine development for a more effective vaccine.

Conservation and variation in the region of the Theileria parva p104 antigen coding gene used for PCR surveillance of the parasite

The range of the protozoan parasite Theileria parva, which causes East Coast fever in cattle, has been expanding to countries where it has not previously been detected, as a result of cross-border domestic cattle movement. Countries where T. parva has not previously been observed until recently include Cameroon and South Sudan. This raises the issue of the conservation of the p104 antigen gene, on which the nested PCR assay that is widely used for T. parva surveillance in the blood of infected cattle is based. We sampled 40 isolates from six countries widely distributed across the geographical range of the parasite, including eastern, central and southern Africa, for p104 sequence polymorphism. These included parasites from both domestic cattle and the Cape buffalo (Syncerus caffer) wildlife reservoir. The most frequent allelic variants were present in cattle transmissible isolates from multiple widely separated geographical regions in Zambia, Uganda, Kenya, Tanzania, Rwanda and South Africa. These frequent p104 variants were also present in the three component stocks of the Muguga cocktail used for the infection and treatment live immunisation procedure to control T. parva in the field. Other isolates exhibited unique alleles. This includes some of the p104 sequences from Cameroon, which is outside the known range of the Rhipicephalus tick vector and whose origin is therefore unclear. The nested primer oligonucleotides used to generate the amplicons were universally conserved in cattle-derived parasites and a majority of buffalo-derived isolates across the geographical range of the parasite. However, some rare South African buffalo-derived isolates exhibited one or two mismatches with the primer sequences. It therefore remains possible that some p104 alleles may be so divergent that they do not amplify with the current diagnostic primers and are not detectable in surveys, hence the need for increasing knowledge of genetic heterogeneity of diagnostic targets. There was no evidence for positive selection among those p104 mutations that resulted in residue changes. Importantly, the data indicate that the p104-based PCR detection assay should be effective across the majority of the range of T. parva, and if the one or two mismatches are shown in future to result in the primers annealing less efficiently, then the assay can be further improved by introduction of degenerate bases to enable amplification of the less frequent South African buffalo-derived variant p104 genes.