CASE NOTES


HENDRA VIRUS CASE STUDIES

Matt Ball, District Veterinarian Lismore

Posted Flock & Herd September 2011

INTRODUCTION

In 2011 the North Coast of NSW has had multiple properties diagnosed with Hendra virus. The last known occurrence of the disease in NSW was in 2006. The events of 2011 have demonstrated that the region is prone to Hendra virus. The reason behind the sudden increase in Hendra virus cases on the North and Mid-coast is still not understood.

Over the last 5 years the North Coast LHPA has been involved in a number of Hendra virus exclusions. However, the vast majority of Hendra exclusions are serviced by private veterinarians because they can carry out diagnostic procedures and administer treatments that the LHPA is not legislated to perform.

Some Hendra cases studies will focus on attempts to understand the epidemiology of the outbreaks. In the absence of adequate data to comment on epidemiological factors, the following case studies instead outline cases where Hendra virus was diagnosed in circumstances where a private veterinarian was not employed or LHPA assistance was required. The case studies also highlight that Hendra virus needs to be considered when a horse is found dead in a fence.

Case One

HISTORY

In July 2011 a cattle producer near Lismore contacted their private veterinarian about one of their horses that had died with its head stuck through a wire fence. The horse was observed by the owner to have no signs of disease 12-18 hours earlier. The paddock that the horse had been grazing contained a fig tree. Flying foxes were suspected to visit the property but were not thought to be common. The private veterinarian indicated that it was unlikely to be Hendra virus but advised the producer to contact the LHPA. After collecting a history from the farmer, two district veterinarians in the LHPA independently considered that the case was likely to be an accident. Despite this, a district veterinarian attended the farm to investigate.

ON FARM EXAMINATION

A single dead horse was observed by the district veterinarian with its head and neck through a fence line. The fence line was at the bottom of a hill. The head and neck were on the ground underneath the bottom fence wire. Another horse was in the paddock with no signs of disease. Using appropriate personal protective equipment an oral and nasal swab was taken from the horse. It was noted that there was significant blood stained froth in the nasal cavities. Swabs were placed in PBGS viral transport medium.

LABORATORY TESTING

Both oral and nasal swabs were positive for Hendra virus on a N Gene TaqMan Assay done at the Australian Animal Health Laboratory (AAHL) and on a PCR test done at NSW EMAI State Diagnostic laboratory. To date 0 day and 16 day testing on the live horse has been negative.

Case Two

HISTORY

A neighbour to a sugarcane property near Ballina reported to NSW DPI that they had observed two dead horses in their neighbour's paddock. The owner of the property was currently away. A district veterinarian from the North Coast LHPA was tasked by NSW DPI to investigate.

ON FARM EXAMINATION

Wearing appropriate PPE the district veterinarian observed and examined two dead horses in a house paddock. Pictures are shown below. One dead horse was attached to a fence wire and the other horse was dead in the middle of the lawn near the house. This horse appeared to have prolapsed material from both the rectum and vulva but the district veterinarian considered that this may have been due to decomposition. The house paddock contained some native trees and an old orchard. Four live horses were observed without any obvious signs of disease. The initial field diagnosis by the district veterinarian was an accident for the horse attached to the fence and a reproductive incident for the other horse. Both swabs and jugular blood were collected from the dead horses.

LABORATORY TESTING

All samples collected from the horses were positive for Hendra virus on testing done at both the NSW State Diagnostic Laboratory and AAHL.

DISCUSSION

These case studies demonstrate the following:
1. Some cases of Hendra virus, especially mortalities, will only be diagnosed if a local government field service is available to attend.
2. Hendra virus should be suspected in horses stuck to or through a fence.
3. The use of swabs to collect a range of fluids from a dead horse appears satisfactory to detect a positive field case of Hendra virus.

The NSW livestock health system that combines the use of private veterinarians, LHPA and NSW DPI veterinarians and staff to undertake surveillance and control activities for disease is proving effective in the case of the Hendra virus outbreaks in northern NSW.

Advisory messages to horse owners should include that horses stuck in fences should not be assumed to be due to accidents. The neurological damage that Hendra virus can do may predispose horses to becoming stuck in fences.

LHPA management considers that the risk of exposure to Hendra virus by their veterinarians is increased from 'low' when no sharps are used to 'high' if sharps are used. These case studies suggest that if adequate bodily fluid in a dead horse can be found, then the use of sharps may not be required. Multiple swabs of bodily fluid is likely to detect infection. However if nasal cavities and other orifices are dry, without obvious discharge, it would be recommended to collect jugular blood or possibly a superficial lymph node.

 


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