Hendra Virus Infection in Horses

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. The case fatality rate in horses and people is high, with reports of 81 horses and 4 people succumbing to Hendra virus infection, including an equine veterinarian investigating an outbreak.

Very close contact is required to transmit the virus among horses and from horses to people, and the virus is not considered highly contagious. Equine veterinarians are considered at occupational risk of contracting HeV. 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. (Also See Overview of Hendra Virus Infection.) A commercial HeV vaccine for use in horses is available under a Minor Use Permit for release to veterinarians who have completed an online training program. Horses must have a microchip to be vaccinated, and the information must be entered into the HeV Vaccine National Online Registry. The vaccine consists of soluble forms of G glycoprotein of HeV; it does not contain modified or inactivated virus.