title: Limited genetic and antigenic diversity within parasite isolates used in a live vaccine against Theileria parva.
abstract: An infection and treatment protocol is used to vaccinate cattle against Theileria parva infection. Due to incomplete cross-protection between different parasite isolates, a mixture of three isolates, termed the Muguga cocktail, is used for vaccination. While vaccination of cattle in some regions provides high levels of protection, some animals are not protected against challenge with buffalo-derived T. parva. Knowledge of the genetic composition of the Muguga cocktail vaccine is required to understand how vaccination is able to protect against field challenge and to identify the potential limitations of the vaccine. The aim of the current study was to determine the extent of genetic and antigenic diversity within the parasite isolates that constitute the Muguga cocktail. High throughput multi-locus sequencing of antigen-encoding loci was performed in parallel with typing using a panel of micro- and mini-satellite loci. The former focused on genes encoding CD8(+) T cell antigens, believed to be relevant to protective immunity. The results demonstrate that each of the three component stocks of the cocktail contains limited parasite genotypic diversity, with single alleles detected at many gene/satellite loci and, moreover, that two of the components show a very high level of similarity. Thus, the vaccine incorporates very little of the genetic and antigenic diversity observed in field populations of T. parva. The presence of alleles at low frequency (<10%) within vaccine component populations also points to the possibility of variability in the content of vaccine doses and the potential for loss of allelic diversity during tick passage. The results demonstrate that there is scope to modify the content of the vaccine in order to enhance its diversity and thus its potential for providing broad protection. The ability to accurately quantify genetic diversity in vaccine component stocks will facilitate improved quality control procedures designed to ensure the long-term efficacy of the vaccine.
authors.affiliation: The Roslin Institute, Royal (Dick) School of Veterinary Studies, University of Edinburgh, Easter Bush, Roslin, Midlothian EH25 9RG, UK.
authors.forename: Johanneke D
authors.initials: JD
authors.lastname: Hemmink
authors.affiliation: College of Medical, Veterinary and Life Sciences, Institute of Biodiversity Animal Health and Comparative Medicine, University of Glasgow, Henry Wellcome Building, Garscube Campus, Bearsden Road, Glasgow G61 1QH, UK.
authors.forename: William
authors.initials: W
authors.lastname: Weir
authors.affiliation: The Roslin Institute, Royal (Dick) School of Veterinary Studies, University of Edinburgh, Easter Bush, Roslin, Midlothian EH25 9RG, UK.
authors.forename: Niall D
authors.initials: ND
authors.lastname: MacHugh
authors.affiliation: The International Livestock Research Institute, PO Box 30709, Nairobi, Kenya.
authors.forename: Simon P
authors.initials: SP
authors.lastname: Graham
authors.affiliation: The International Livestock Research Institute, PO Box 30709, Nairobi, Kenya.
authors.forename: Ekta
authors.initials: E
authors.lastname: Patel
authors.affiliation: The Roslin Institute, Royal (Dick) School of Veterinary Studies, University of Edinburgh, Easter Bush, Roslin, Midlothian EH25 9RG, UK.
authors.forename: Edith
authors.initials: E
authors.lastname: Paxton
authors.affiliation: College of Medical, Veterinary and Life Sciences, Institute of Biodiversity Animal Health and Comparative Medicine, University of Glasgow, Henry Wellcome Building, Garscube Campus, Bearsden Road, Glasgow G61 1QH, UK.
authors.forename: Brian
authors.initials: B
authors.lastname: Shiels
authors.affiliation: The International Livestock Research Institute, PO Box 30709, Nairobi, Kenya.
authors.forename: Philip G
authors.initials: PG
authors.lastname: Toye
authors.affiliation: The Roslin Institute, Royal (Dick) School of Veterinary Studies, University of Edinburgh, Easter Bush, Roslin, Midlothian EH25 9RG, UK. Electronic address: ivan.morrison@roslin.ed.ac.uk.
authors.forename: W Ivan
authors.initials: WI
authors.lastname: Morrison
authors.affiliation: The International Livestock Research Institute, PO Box 30709, Nairobi, Kenya.
authors.forename: Roger
authors.initials: R
authors.lastname: Pelle
mesh_terms: D000483:Alleles; D019943:Amino Acid Substitution; D000818:Animals; D000940:Antigenic Variation; D001096:Arachnid Vectors / Q000469:parasitology; D002020:Buffaloes; D016827:CD8 Antigens / Q000235:genetics; D018414:CD8-Positive T-Lymphocytes / Q000276:immunology; D002417:Cattle; D016054:DNA, Protozoan / Q000737:chemistry / Q000302:isolation & purification; D014644:Genetic Variation; D059014:High-Throughput Nucleotide Sequencing; D018895:Microsatellite Repeats / Q000235:genetics; D018598:Minisatellite Repeats / Q000235:genetics; D016052:Protozoan Vaccines / Q000235:genetics / Q000276:immunology*; D048494:Rhipicephalus / Q000469:parasitology; D017422:Sequence Analysis, DNA / Q000662:veterinary; D016797:Theileria parva / Q000145:classification / Q000235:genetics / Q000276:immunology*; D013801:Theileriasis / Q000469:parasitology / Q000517:prevention & control*
chemical_list: D016827:CD8 Antigens; D016054:DNA, Protozoan; D016052:Protozoan Vaccines
keywords: Antigenic diversity; Cattle; Gene sequencing; Satellite DNA; Theileria parva; Vaccination