Hendra virus

Background

Hendra virus infection was first recognised in 1994 in Australia, when it caused an outbreak of acute, fatal respiratory disease that killed 14 horses and was  initially called equine morbillivirus. 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) involving the death of two horses and a human. From 1994 to  2010, Hendra virus was confirmed on an additional 11 premises in Queensland and one premise in northern New South Wales. In June and July 2011, further cases have been identified in Queensland and  northern New South Wales.

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 infected people died.  One of the human deaths occurred 14 months after initial exposure during postmortem examination of an affected horse.

Hendra  virus is an RNA virus that is a member of the Paramyxoviridae family of viruses. It is closely related to Nipah  virus, which caused a major outbreak of acute fatal respiratory disease in pigs  and neurological and respiratory disease in humans (and dogs) in Malaysia in 1999. Like Hendra virus, Nipah virus has flying foxes as its natural  reservoir and periodically re-emerges in South East Asia.

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.

Transmission  of Hendra virus from horse to horse appears to be relatively inefficient, but has occurred among horses in close contact, including some horses in paddock situations. Transmission is more effective among stabled horses. There is no evidence of direct transmission of Hendra virus infection from flying foxes to humans. Transmission by fomites (e.g. contaminated tack) is also possible.

Currently,  no vaccine is available for use in humans. A monoclonal antibody preparation and anti-viral medications can be administered to people who have been exposed to Hendra virus. A vaccine against Hendra virus is being developed for use in horses  but is not yet available.

Hendra  virus infection is notifiable. Fees for tests undertaken to confirm or exclude a diagnosis of Hendra virus infection are paid by the Department of Primary Industries. Fees to confirm or exclude an alternative diagnosis other than  testing for another notifiable disease are not covered by the Department of  Primary Industries.

Clinical signs in horses

Clinical  signs in horses are highly variable but usually have an acute onset and include pyrexia (fever). Clinical signs may vary from mild to severe and include, discomfort  (weight shifting between legs), neurological changes (ataxia - “wobbly gait”, head-pressing, muscle twitching, depression, altered consciousness - “dazed”, aimless walking,  head tilting, circling, apparent blindness, urinary incontinence), respiratory distress  (dyspnoea, tachypnoea, white or blood-tinged frothy discharge from the mouth  and nares, particularly in the terminal stages), weakness, collapse with  inability to rise and/or death. Colic has been the initial sign in some cases. The  incubation period for Hendra virus in horses ranges from 5 to 16 days. There is  a high case fatality rate, particularly when there are multiple cases. Since  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.

Investigation of  suspected cases of Hendra virus infection

Veterinarians  should take rigorous biosecurity and safety precautions when examining horses  with suggestive clinical signs and when performing postmortem examinations of horses. This includes doing a risk assessment and deciding on suitable control measures. Veterinarians 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:

• Splash-proof overalls (long sleeves to prevent contamination of skin where there may be cuts and abrasions); or
• Cotton or disposable overalls with impervious or splash-proof apron; and
• Impervious boots;
• Double gloves;
• Face shield or safety glasses; and
• P2 particulate respirator mask to prevent inhalation of aerosols.

Please call the Customer Services Unit at the  State Veterinary Diagnostic Laboratory (1800 675 623) for advice.

Samples  should only be taken from live horses if veterinarians are confident of their  PPE and sampling procedure.

Minimally  invasive ("keyhole") techniques can be used to carefully collect  small portions of tissue from dead animals at postmortem examination. 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 Department of Primary Industries  website: in its document entitled "Guidelines for veterinarians handling potential  Hendra virus infection in horses". NSW Department of Primary Industry policy  is that these Guidelines must be followed. The Queensland website should be visited  regularly to ensure that the latest version of these guidelines is consulted.

NSW vets should also read Hendra virus- information for vets for state specific requirements

Caution Hendra virus is a zoonotic agent with the potential to cause serious illness and death  in humans. Provided appropriate personal protective equipment (PPE) and examination techniques are used it is considered that the risks of  veterinarians being exposed when examining infected horses is very low

Diagnosis

Clinical signs, postmortem findings, virology.

Specimens required for  diagnosis of Hendra virus infection:

Live  horses: From each horse:

1. 10 mL blood in lithium heparin collected  into an evacuated tube - for polymerase chain reaction (PCR).
2. 10 mL clotted blood collected into an  evacuated tube - for serology and PCR.
3. Nasal swabs from each nostril pooled in  phosphate buffered glycerol saline (PBGS) or equivalent virus transport medium  (VTM) - for PCR. If no PBGS is available, swabs should be placed in 2 mL  sterile saline.
4. Swabs from the oral cavity, rectum  (rectal mucosa not faeces) or urine collected separately into PBGS - for  PCR.

Dead  horses: From each horse:

1. 10 mL clotted blood from the jugular  vein collected into an evacuated tube - this sample can be used for  serology and PCR.
2. Submandibular lymph node collected into  a sterile container and chilled - this sample can be used for polymerase  chain reaction (PCR). There is less risk in taking this sample of tissue  compared to lung or other tissue.

Note: Due to the zoonotic  risk of Hendra virus, minimally invasive postmortem examination is recommended.  Dead horses can be sampled adequately for Hendra virus testing without conducting a complete postmortem examination.