Hendra virus (HeV) is the prototype species of a new genus Henipavirus within the subfamily Paramyxovirinae, and was first identified in Australia in 1994. The viral agent is endemic in specific species of fruit bats (also called flying foxes), and close contact with these bats is suspected to have facilitated transfer of the HeV to horses. Horses are infected by oronasal routes and excrete HeV in urine, saliva, and respiratory secretions.
There have been multiple, sporadic incidents of human and equine disease in Australia occurring in 1994, 1995, 1999, 2004, 2008, and 2009. In the first outbreak, 14 of 21 horses died. During this outbreak, 2 human caretakers developed influenza-like signs; one did not survive. A morbillivirus cultured from his kidney was identical to the virus isolated from lungs of 5 affected horses. In 2008, Australia experienced the largest outbreak to date, which also resulted in the death of an equine veterinarian.
Very close contact is required to transmit the virus among horses and from horses to people, and the virus is not considered highly contagious. Infected horses develop severe and often fatal respiratory disease, characterized by dyspnea, vascular endothelial damage, and pulmonary edema. Depression, anorexia, fever, respiratory difficulty, ataxia, tachycardia, and frothy, nasal discharge are common clinical signs. (see Hendra Virus Infection.)
Last full review/revision March 2012 by Bonnie R. Rush, DVM, MS, DACVIM