Postepizootic Persistence of Venezuelan Equine Encephalitis Virus, Venezuela

摘要

Five years after the apparent end of the major 1995Venezuelan equine encephalitis (VEE) epizootic/epidemic,focal outbreaks of equine encephalitis occurred inCarabobo and Barinas States of western Venezuela. Virusisolates from horses in each location were nearly identicalin sequence to 1995 isolates, which suggests natural per-sistence of subtype IC VEE virus (VEEV) strains in a genet-ically stable mode. Serologic evidence indicated thatadditional outbreaks occurred in Barinas State in 2003.Field studies identified known Culex (Melanoconion) spp.vectors and reservoir hosts of enzootic VEEV but a dearthof typical epidemic vectors. Cattle serosurveys indicatedthe recent circulation of enzootic VEEV strains, and possi-bly of epizootic strains. Persistence of VEEV subtype ICstrains and infection of horses at the end of the rainy sea-son suggest the possibility of an alternative, cryptic trans-mission cycle involving survival through the dry season ofinfected vectors or persistently infected vertebrates