Hendra virus
Syn: Equine morbillivirus infection
Hendra virus infection was first recognised in 1994 in Australia, when it caused an outbreak of acute, fatal respiratory disease that killed 14 horses. During this outbreak the horse-trainer also died and there was a non-fatal infection of another person closely involved with the sick horses. A retrospective diagnosis was made of a prior case (also in 1994) which resulted in the death of two horses and a human. From 1994 to September 2009, an additional eleven sporadic outbreaks were associated with the deaths of at least 16 horses and four more human infections.
About 25% of horses can survive acute infection and become "recovered" horses. The current national policy is for these horses to be euthanased. Of the total of seven cases of human infection, four of the people died. One of the human deaths occurred 14 months after exposure at postmortem examination of an affected horse.
Flying foxes (fruit bats) are the subclinical reservoir of Hendra virus. All known cases have occurred in Queensland or northern NSW but could occur wherever there are flying foxes. There is a weak temporal association of cases with the birthing season of flying foxes between August and January.
Hendra virus is a member of the Paramyxovirus family of viruses, and is closely related to Nipah virus, which caused a major outbreak of acute fatal respiratory disease in pigs and humans (and dogs) in Malaysia in 1999. Like Hendra virus, Nipah virus has flying foxes as its natural reservoir.
Hendra virus infection is notifiable. Fees for tests undertaken to confirm or exclude a diagnosis of Hendra virus infection are paid by Industry and Investment NSW. Fees to confirm or exclude an alternative diagnosis other than testing for another notifiable disease is not covered by Industry and Investment NSW.
Caution: Hendra virus is a zoonotic agent with the potential to cause serious illness and death in humans.
Clinical signs in horses include pyrexia, respiratory distress (dyspnoea, blood-tinged foamy discharge from mouth and nares), sometimes neurological changes (head-pressing, muscle fasciculations) and death. Colic was the initial sign in at least two cases. As the clinical signs are not pathognomonic AND because this is an important zoonotic disease, it is important that samples are collected for laboratory confirmation or exclusion of Hendra virus infection.
Veterinarians should take rigorous biosecurity and safety precautions when examining horses with suggestive clinical signs and when performing post-mortem examinations of horses. This includes doing a risk assessment and deciding on suitable control measures. They should consider entry and exit procedures, the use of personal protective equipment (PPE) and disinfectants, disposal of potentially contaminated materials, and packing and dispatch of laboratory samples. Suitable PPE includes impervious boots and double gloves, waterproof overalls or apron, face shield or safety glasses, and P2 particulate respirator mask to prevent inhalation of aerosols. Call Customer Service (1800 675 623) for advice.
While blood samples are considered to be sufficient to confirm Hendra infection, it is important that wherever possible other specimens (e.g. nasal swabs and, from dead animals, fresh and fixed tissues) are collected to confirm alternative diagnoses. Nasal swabs should only be taken from live horses if veterinarians are confident of their PPE and sampling procedure.
"Key hole" techniques can be used to carefully collect small portions of tissue at postmortem. Infected horses have a high virus load throughout most organs and body fluids, and veterinarians collecting tissues from highly suspect horses must be fully confident with their PPE, infection control and sampling practices.
Detailed biosecurity guidelines can be found on the Queensland DPI website: www.dpi.qld.gov.au in its document entitled "Guidelines for veterinarians handling potential Hendra virus infection in horses". Industry & Investment NSW policy indicates that these Guidelines must be followed. The QLD website should be visited regularly to ensure that the latest version of these guidelines is followed.
Diagnosis
Clinical signs, postmortem findings, histopathology, virology.
Specimens required
- 10 mL of clotted and LiHep blood in evacuated tubes for virology
- Chilled lung for virology
- Fixed lung for histopathology
- Swabs from each nasal cavity pooled in PBGS.