East Coast Fever and vaccination at the livestock/wildlife interface

Theileria parva causes an acute, often fatal disease in cattle (east coast fever; ECF) in eastern and southern Africa (annual losses >$300 million). The African buffalo (Syncerus caffer) is also a host for T. parva, but infected buffalo do not suffer disease. Buffalo parasite strains are readily transmitted to cattle by ticks, but they differentiate poorly to the tick-infective stage and transmission by ticks is inefficient. Recent evidence suggests that cattle-maintained T. parva are less genotypically diverse than the buffalo population. All infected buffalo, as well as recovered cattle, remain long-term low-level carriers of the parasite. Immunity to T parva is T cell-mediated and shows parasite strain restriction. A live vaccine currently employed to control the disease incorporates 3 parasite isolates. The vaccine protects against experimental challenge with most cattle isolates but only partially protects against buffalo parasites.
The proposed project builds on an existing collaborative research programme (with Glasgow University, Liverpool School of Tropical Medicine and SRUC) in N. Tanzania studying animal disease at the interface of livestock and wildlife populations around the Serengeti NP. Cattle in this area have a high prevalence of infection with T. parva and ECF is recognised as the most important cause of mortality. Significant populations of buffalo are also present. As part of ongoing research, large numbers of blood samples are being collected from cattle and buffalo, with detailed records of location and clinical information.
The aim of the proposed project is to determine the nature and extent of antigenic diversity in the T. parva population in this region, in cattle, buffalo and the tick vector, to provide an understanding of the transmission dynamics of infection and to compare the diversity with that in the live T. parva vaccine.
Objectives:
1. Determine parasite genotype diversity in carrier cattle and buffalo, by high throughput sequencing of selected polymorphic parasite genes (including genes encoding known T cell antigens).
2. Use host species-specific PCR to determine the proportions of adult ticks that have fed on cattle and buffalo.
3. Determine the levels of infection and genotypes of parasites present in ticks, to assess the host species of origin of the parasites.
4. Examine the parasite genotypes in clinical cases of ECF, to assign the likely sources of infection to parasite genotype (cattle and buffalo).
5. Compare the genotype diversity in the cattle T. parva with that in the live vaccine and a geographically distant cattle population of T. parva (Zambia, Malawi).
Methodology
i. Design and carry out a cross-sectional field sampling strategy of sympatric cattle, buffalo and ticks, with support of ongoing project in N. Tanzania (Years 1-2; Milestone 1)
ii. Molecular methodologies will include DNA extraction, diagnostic PCR for T. parva and blood meal species, and genotyping (multiplexed sequence analysis of PCR amplicons) (Years 2-3; Milestone 2). A selected subset of samples will be taken forward for genome sequence capture and diversity analysis (Years 3-4; Milestone 3), and comparison with vaccine strains.
iii. Analyse molecular epidemiological data; clustering & principal component analyses, genetic sub-structuring by host, vector, time or space.
These results will provide a foundation for future hypothesis-driven research, but will also inform vaccine development and validation of vaccine efficacy.