title: Passive transfer and rate of decay of maternal antibody against African horse sickness virus in South African Thoroughbred foals.
abstract: BACKGROUND
  African horse sickness is an insect-transmitted, noncontagious disease of equids caused by African horse sickness virus (AHSV). Mortality can exceed 90% in fully susceptible horse populations. A live-attenuated (modified live) cell-culture-adapted (MLV) polyvalent AHSV vaccine is widely used to control African horse sickness in endemic areas in southern Africa. Field studies detailing antibody responses of vaccinated horses are lacking.
  
  
  OBJECTIVE
  To determine antibody titres to the 9 known serotypes of AHSV in a cohort of broodmares that were regularly vaccinated with the MLV AHSV vaccine and to measure the passive transfer and rate of decay of maternal antibody to the individual virus serotypes in foals.
  
  
  METHODS
  Serum was collected from 15 mares before foaling and from their foals after foaling and monthly thereafter for 6 months. Antibody titres to each of the 9 AHSV serotypes were determined by serum virus neutralisation assay.
  
  
  RESULTS
  There was marked variation in the antibody response of the mares to individual AHSV serotypes even after repeated vaccination, with consistently higher titre responses to some virus serotypes. Likewise, the duration of maternally derived antibodies in foals differed among serotypes.
  
  
  CONCLUSIONS
  Data from this study confirm variation of the neutralising antibody response of individual mares to repeated vaccination with polyvalent AHSV vaccine. Virus strains of individual AHSV serotypes included in the vaccine may vary in their inherent immunogenicity. Passively acquired maternal antibodies to AHSV vary markedly among foals born to vaccinated mares, with further variation in the duration of passive immunity to individual AHSV serotypes.
  
  
  CONCLUSIONS
  These data are relevant to the effective utilisation of live-attenuated AHSV vaccines in endemic regions, and potentially to the use of vaccines in response to future incursions of AHSV into previously free regions. Further studies involving a larger population will be required to determine the optimal time for vaccinating foals.
authors.affiliation: Department of Veterinary Tropical Diseases, Faculty of Veterinary Science, University of Pretoria, Gauteng, South Africa.
authors.forename: J E
authors.initials: JE
authors.lastname: Crafford
authors.forename: C W
authors.initials: CW
authors.lastname: Lourens
authors.forename: I A
authors.initials: IA
authors.lastname: Gardner
authors.forename: N J
authors.initials: NJ
authors.lastname: Maclachlan
authors.forename: A J
authors.initials: AJ
authors.lastname: Guthrie
mesh_terms: D000355:African Horse Sickness / Q000453:epidemiology / Q000276:immunology*; D000356:African Horse Sickness Virus / Q000276:immunology*; D000818:Animals; D000914:Antibodies, Viral / Q000097:blood*; D005260:Female; D007112:Immunity, Maternally-Acquired; D011247:Pregnancy; D012703:Serotyping; D013019:South Africa / Q000453:epidemiology; D013997:Time Factors
chemical_list: D000914:Antibodies, Viral
keywords: African horse sickness virus; antibody half-life; horse; maternal antibody; neutralising antibody; passive transfer