TY - JOUR AU - Weyer, Camilla AU - Grewar, John AU - Burger, Phillippa AU - Rossouw, Esthea AU - Lourens, Carina AU - Joone, Christopher AU - le Grange, Misha AU - Coetzee, Peter AU - Venter, Estelle AU - Martin, Darren AU - MacLachlan, N. James AU - Guthrie, Alan T1 - African Horse Sickness Caused by Genome Reassortment and Reversion to Virulence of Live, Attenuated Vaccine Viruses, South Africa, 2004–2014 T2 - Emerging Infectious Disease journal PY - 2016 VL - 22 IS - 12 SP - 2087 SN - 1080-6059 AB - 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. KW - live attenuated vaccine KW - vaccine transmission KW - genome reassortment KW - reversion KW - virulence KW - asymptomatic viral infections KW - veterinary epidemiology KW - vaccine progenitor availability KW - environmental vaccine identification KW - African horse sickness KW - viruses KW - South Africa DO - 10.3201/eid2212.160718 UR - https://wwwnc.cdc.gov/eid/article/22/12/16-0718_article ER - End of Reference