title: African Horse Sickness Caused by Genome Reassortment and Reversion to Virulence of Live, Attenuated Vaccine Viruses, South Africa, 2004-2014.
abstract: African horse sickness (AHS) is a hemorrhagic viral fever of horses. It is the only equine disease for which the World Organization for Animal Health has introduced specific guidelines for member countries seeking official recognition of disease-free status. Since 1997, South Africa has maintained an AHS controlled area; however, sporadic outbreaks of AHS have occurred in this area. We compared the whole genome sequences of 39 AHS viruses (AHSVs) from field AHS cases to determine the source of 3 such outbreaks. Our analysis confirmed that individual outbreaks were caused by virulent revertants of AHSV type 1 live, attenuated vaccine (LAV) and reassortants with genome segments derived from AHSV types 1, 3, and 4 from a LAV used in South Africa. These findings show that despite effective protection of vaccinated horses, polyvalent LAV may, paradoxically, place susceptible horses at risk for AHS.
authors.forename: Camilla T
authors.initials: CT
authors.lastname: Weyer
authors.forename: John D
authors.initials: JD
authors.lastname: Grewar
authors.forename: Phillippa
authors.initials: P
authors.lastname: Burger
authors.forename: Esthea
authors.initials: E
authors.lastname: Rossouw
authors.forename: Carina
authors.initials: C
authors.lastname: Lourens
authors.forename: Christopher
authors.initials: C
authors.lastname: Joone
authors.forename: Misha
authors.initials: M
authors.lastname: le Grange
authors.forename: Peter
authors.initials: P
authors.lastname: Coetzee
authors.forename: Estelle
authors.initials: E
authors.lastname: Venter
authors.forename: Darren P
authors.initials: DP
authors.lastname: Martin
authors.forename: N James
authors.initials: NJ
authors.lastname: MacLachlan
authors.forename: Alan J
authors.initials: AJ
authors.lastname: Guthrie
mesh_terms: D000355:African Horse Sickness / Q000453:epidemiology* / Q000266:history / Q000517:prevention & control / Q000821:virology*; D000356:African Horse Sickness Virus / Q000145:classification / Q000235:genetics* / Q000276:immunology* / Q000472:pathogenicity; D000818:Animals; D004196:Disease Outbreaks; D016679:Genome, Viral; D005838:Genotype; D049674:History, 21st Century; D006736:Horses; D010802:Phylogeny; D020641:Polymorphism, Single Nucleotide; D016865:Reassortant Viruses / Q000235:genetics / Q000276:immunology; D012703:Serotyping; D013019:South Africa / Q000453:epidemiology; D014613:Vaccines, Attenuated / Q000235:genetics / Q000276:immunology; D014765:Viral Vaccines / Q000235:genetics / Q000276:immunology; D000073336:Whole Genome Sequencing
chemical_list: D014613:Vaccines, Attenuated; D014765:Viral Vaccines
keywords: African horse sickness; asymptomatic viral infections; environmental vaccine identification; genome reassortment; live attenuated vaccine; reversion; vaccine progenitor availability; vaccine transmission; veterinary epidemiology; virulence; viruses