Epidemiological perspectives on Hendra virus infection in horses and flying foxes.

H endra virus was first described in 1994 in Australia after a sudden outbreak of an acute respiratory syndrome in Thoroughbred horses in a Brisbane racing stable. The syndrome was characterised by severe respiratory signs and high mortality. A previously undescribed virus of the family Paramyxoviridae , initially named equine morbillivirus, was identified as the causal agent. 1 The virus was later renamed Hendra virus after the Brisbane suburb where the outbreak occurred. Thirteen of 20 infected horses died, and a stablehand and the trainer were infected, the latter fatally. Fruit bats of the genus Pteropus (family Pteropodidae ), colloquially known as flying foxes, were subsequently shown to be the likely reservoir host of Hendra virus and the putative source of infection for horses. 2,3 The second identified outbreak in horses (involving the fatal infection of two horses on a Thoroughbred stud near Mackay in central Queensland) actually preceded the Brisbane outbreak by several weeks but was identified retrospectively after the Hendra virus–attributed death of the stud owner 15 months later. 4,5 The third known incident involved a single fatal case in a 9-year-old Thoroughbred mare in the Cairns region of northern Queensland in January 1999. 6 No human cases were involved. Two new cases of Hendra virus infection (or probable infection) in horses in northern Queensland, described below, prompt this review of epidemiological aspects of Hendra virus infection in horses and flying foxes.