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EQUINE
Clinical review of Hendra virus infection in 11 horses in New South Wales, Australia
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CASE SERIES
MC Ball,a* TD Dewberry,b PG Freeman,c PD Kemsleya and I Poed
Case series Between 2006 and 2012, there were 11 horses diagnosed with Hendra virus (HeV) on 9 independent premises in New South Wales (NSW). We defined a case of HeV as premises where one or more horses were confirmed to be infected with HeV by PCR. All the cases occurred in the north-eastern region of NSW. In 8 of the 9 cases, infection occurred within 2 months over the winter of 2011. With no exception, the affected horses were kept at pasture on properties visited by flying foxes. Of the 11 horses testing positive for HeV, 5 had an association with a fence, with the horses dead or dying on a fence line. In the majority of cases, disease was an acute illness leading to death within 48 h. When signs of disease were observed, neurological signs predominated. There was limited spread to in-contact horses, with only two properties having more than one horse affected. There was significant variation in the sampling strategies undertaken by veterinarians. Conclusion Caution is needed to interpret a negative diagnosis when only swabs have been collected. Keywords
flying foxes; Hendra virus; horses; New South Wales
Abbreviations DPI, Department of Primary Industries; HeV, Hendra virus; LHPA, Livestock Health and Pest Authority; NSW, New South Wales; PBGS, phosphate-buffered glycerol saline Aust Vet J 2014;92:213–218
doi: 10.1111/avj.12170
H
endra virus (HeV) remains a relatively rare condition of horses in New South Wales (NSW). It had been diagnosed only once, near Murwillumbah, in 2006, but in 2011, there were eight further cases diagnosed in north-eastern NSW. For this review, a case of HeV is defined as an infected premises where one or more horses in residence were confirmed by PCR to be infected with HeV.
Suspected to be a result of sporadic ‘spillover’ from a natural reservoir of infection in pteropid bats (grey-headed (Pteropus poliocephalus) and black (P. alecto) flying foxes), the likely epidemiological interaction between horses, flying foxes and the environment has been well documented.4–10 Ongoing research into a rare and sporadic disease such as HeV is assisted by the documentation of accurate case studies. History, clinical signs and sampling strategies are described in details for the eight cases that were investigated in north-eastern NSW in 2011, plus the case in 2006. Epidemiological factors and laboratory testing are summarised in Tables 1 and 2. Case series Case 1 On the evening of 27 October 2006, a 19-year-old Thoroughbred gelding in a 12-ha paddock near Murwillumbah, NSW, was noticed by the owner to be lethargic. The following day, the horse was mildly ataxic, disorientated, had submandibular oedema, was reluctant to lower its head and had a persistent erection. It also had a heavy tick burden of both bush ticks and paralysis ticks and was being treated weekly with an organophosphate spray. Although usually kept at pasture with another horse, the gelding was fed in a stable twice daily and would often also eat from the other horse’s feed bin in the paddock. There was a large flying fox colony located 2–3 km from the property. A small number of flying foxes often came to the property to feed on native trees, especially the flowers of the silky oak (Grevillea robusta) in the horses’ paddock. The gelding also liked to eat the flowers from this tree.
Previously published reports have focused on HeV events in Queensland, often involving multiple horses and including both stabled and pastured horses.1–3 The NSW case series reported here, with the exception of the 2006 incident at Murwillumbah, occurred within a short period of time, in pastured horses and mainly involved a single affected horse.
A private veterinarian examined the gelding 2 days later and found it to be tachycardic, tachypnoeic, dyspnoeic, febrile and with hypermotile gastrointestinal sounds. The horse was listless, ataxic and had a wide-based stance. On locomotion, a hypermetric forelimb gait was noted. The tongue was occasionally protruding from the left side of the mouth, there was excessive bilateral lacrimation and grossly swollen submandibular lymph nodes. The gelding was given dexamethasone and penicillin. The dexamethasone was repeated twice over the following 12 h.
*Corresponding author:
[email protected]. a North Coast Livestock Health and Pest Authority, Lismore, New South Wales, Australia b Faculty of Veterinary Science, The University of Sydney, Sydney, NSW, Australia c New South Wales Department of Primary Industries, Wollongbar, NSW, Australia d Mid Coast Livestock Health and Pest Authority, Kempsey, NSW, Australia
The following day, the gelding’s condition had deteriorated further with pronounced dyspnoea, coughing, circling to the right, head tilt to the left and distress when handled. The gelding was euthanased and a limited necropsy was undertaken to collect swabs of nasal secretions and a piece of lung tissue. Despite HeV having never been diagnosed in NSW, the private veterinarian suspected and requested testing for
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Table 1. Sampling, test results and class of veterinarian for the suspect cases of Hendra virus in New South Wales, Australia, between 2006 and 2012
Property no.
Status
Test
1
Live
PCR (AAHL) Viral isolation PCR (AAHL)
2, horse 1
Live
PCR (SDL)
2, horse 2
Live
3
Dead
4
Dead
5
Dead
6
Live
7, horse 1
Dead
7, horse 2
Dead
8
Dead
9
Dead
Viral isolation PCR (AAHL) PCR (SDL) PCR (AAHL) PCR (SDL) PCR (AAHL) PCR (SDL) PCR (AAHL) PCR (SDL) Viral isolation PCR (AAHL) PCR (EMAI) PCR (EMAI) Viral isolation PCR (AAHL) PCR (SDL) Viral isolation PCR (AAHL) PCR (SDL) Viral isolation G envelope ELISA PCR (AAHL) PCR (SDL) Viral isolation PCR (AAHL) PCR (SDL) Viral isolation
Nasal swab
Neg.b 29/06/11c Neg. 01/07/11 Pos. 29/06/11 Neg. 01/07/11 Pos. Pos. Pos. Pos. Pos. Pos. Pos. Pos. Pos. Pos. Pos.
Vaginal/ rectal swab
EDTA blood
Lithium heparin blood
Neg. 29/06/11 Pos. 1/07/11 Pos. 29/6/11 inconclusive 01/07/11 Pos. Pos. Pos.
Lymph node
Pos.
Lung
Class of veterinariana
Pos. Neg.
Private Private and public
Pos.
Pos. Pos. Public Public
Pos. Pos. Pos.
Pos. Pos.
Pos. Pos.
Pos. Pos.
Pos. Pos.
Pos. Pos.
Clotted blood
Pos. Pos.
Pos. Pos. Neg.
Private
Pos. Pos. Pos. Pos. Pos. Pos.
Pos. Pos. Pos. Pos. Pos. Neg. Pos. Pos. Pos.
Pos. Pos. Pos. Pos.
Private
Pos. Pos. Neg.
Public
Neg. Private Neg. Private Neg.
a
Public veterinarians are employed by a government agency whereas private veterinarians are independent of government. Nasal wash rather than a swab. cTwo swabs on two separate days were collected: the first swab was negative, the second was positive. AAHL, Australian Animal Health Laboratory, Geelong, Victoria; EMAI, Elizabeth Macarthur Agricultural Institute, Menangle, NSW; Pos., positive; Neg., negative; SDL, State Diagnostic Laboratory, Menangle, NSW. b
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HeV, which was positive by RT-PCR (Table 1). Subsequent serological testing of the paddock mate, a mature-age pony, was negative for HeV antibodies.
which the horses sheltered routinely. This tree was frequented by both grey-headed and black flying foxes. Mosquitoes were noted to be active as a result of recent wet weather.
Case 2 On 28 June 2011, a private veterinarian examined a 16-year-old Quarter Horse gelding, one of two horses on a 3-ha property near Wollongbar, NSW. The farm contained a strangler fig (Ficus watkinsiana) that was in fruit at the time of the incident and under
The horse was found to be febrile, tachycardic and tachypnoeic, with brick-red mucous membranes. The horse was stumbling on the left foreleg and had a wide forelimb stance. The lower lip drooped to the left. The horse was diagnosed with toxaemia of unknown origin and treated with an antibiotic, an anti-inflammatory and a diuretic.
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Property no.
1 2 3 4 5 6 7 8 9
Month
Age of horse/s (years)
No. of at-risk horses
No. of horses affected
Sudden death
Flying fox sightings
Observed illness
Predominant respiratory signs
Predominant neurological signs
Fence association
October June July July July August August August August
19 16 and 4 16 15 15 25 6 and 2 4 10
2 2 4 2 5 3 6 2 1
1 2 1 1 1 1 2 1 1
No No No Yes Yes No Unknown Yes No
Frequent Frequent Occasional Occasional Frequent Frequent Frequent Frequent Frequent
Yes Yes Yes No No Yes No No Yes
No Yes (1 horse) No NA NA No NA NA No
Yes Yes Yes NA NA Yes NA NA Yes
No No Yes Yes No Yes Yes No Yes
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Table 2. Epidemiological factors for cases of Hendra virus infection of horses in New South Wales, Australia
NA, not applicable.
The practitioner re-examined the horse the following day and although its cardinal signs had improved, the neurological signs had progressed. The horse appeared to be blind and was moderately ataxic. The initial treatment was repeated and a nasal swab and clotted blood were collected and submitted for HeV exclusion. The nasal swab was submitted dry, not in phosphate-buffered glycerol saline (PBGS). On 30 June, the horse had deteriorated further and was euthanased by the private veterinarian approximately 36 h after the onset of the illness. Initial laboratory results on the blood were inconclusive and the dry swab was negative for HeV. Additional samples were collected at postmortem examination by a government veterinarian employed by the North Coast Livestock Health and Pest Authority (LHPA). The additional samples were prescapular and submandibular lymph nodes, blood collected from the dead horse’s jugular vein and a nasal swab placed in PBGS. These additional samples were positive for HeV (Table 1). A twice-daily observation schedule commenced for the companion horse, a 4-year-old Quarter Horse mare. On 10 July, 12 days after the onset of illness in the first horse, the mare also developed signs of lethargy, fever, nasal discharge, dyspnoea and ataxia. It tested positive for HeV (Table 1) and was euthanased on 12 July. Three in-contact dogs were tested for HeV with negative results. Case 3 On the afternoon of 1 July 2011, a 16-year-old Thoroughbred mare on a 33-ha property west of Macksville, NSW, was noted by the owner to be slightly off-colour. The mare was mildly lame on the right hindlimb and appeared depressed. Over the course of the following day, neurological signs progressed, with the horse appearing blind, walking through fences and becoming increasingly ataxic. Head pressing was also noted. The horse died early in the morning of 3 July after an illness of approximately 36 h. The owners had placed the horse in a small yard on the previous night and death occurred while the mare was pushing through a wire gate. There was a 16-year-old gelding in the same paddock as the deceased mare and two younger brumbies were running in a separate paddock
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that was well separated from the paddock where the deceased animal had been housed. The property also contained a small herd of beef cattle, approximately 30 breeders, and two pet cats. Although there were several fig trees (Ficus spp.) on the property, none was located in the paddock where the horses were currently grazing and the owners reported only occasional sightings of flying foxes. The paddock was bordered on one side by a river, along which were numerous species of native eucalypts that were not flowering at the time. A government veterinarian from the Mid Coast LHPA visited the property on 3 July, examined the dead mare and observed a small amount of blood from the nose and that the mucous membranes appeared congested. The blood from the nose was suspected to be associated with the trauma of pushing through the gate. Nasal swabs were collected from the dead horse and HeV infection was confirmed by laboratory testing (Table 1). Blood was collected from the in-contact paddock mate into EDTA and plain vacutainer tubes; these samples were negative for HeV. Repeated testing of the in-contact horse, the two brumbies and the two in-contact cats was undertaken, with all results negative for HeV. Case 4 On 14 July 2011, a cattle producer with a 77-ha property at Corndale, near Lismore, NSW, contacted a private veterinarian about a 15-yearold horse that had died with its head stuck through a wire fence. The horse had been observed by the owner to have no signs of disease 12–18 h earlier. The paddock in which the horse had been kept contained a fig tree. Flying foxes were suspected to visit the property but were not thought to be overly common. The private veterinarian indicated that it was unlikely to be HeV but advised the producer to contact the local government veterinarian employed by the local LHPA. After collecting a history from the farmer, two veterinarians from the North Coast LHPA independently considered that the case was likely to be an accident. Nevertheless, one of them attended the farm to investigate. A single dead horse with its head and neck through a wire fence was observed by the veterinarian. The fence line was at the bottom of a hill and the horse’s head and neck were on the ground underneath the
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EQUINE bottom wire. Another horse in the paddock had no signs of disease, but was observed to investigate the face of the dead horse. Oral and nasal swabs were collected from the dead horse and submitted in PBGS. It was noted that there was significant blood-stained froth in the nasal cavities. Testing was positive for HeV (Table 1). The remaining live horse was tested repeatedly for HeV with negative results. That horse continued to be kept in the paddock with the fig tree and became ill in early 2012. It was retested for HeV, but with negative results. Case 5 On the morning of 24 July 2011, a 15-year-old Australian Stock Horse mare was found dead in a paddock on a property near Mullumbimby, NSW, by the mare’s owner. The mare had been observed to be in normal health at lunchtime on the previous day. The owner suspected snakebite as she had noticed small puncture wounds on the leg of the dead horse and a brown snake had been seen on several occasions in the horse’s paddock. A fig tree was located in the paddock and the property also contained other fig and native trees that were in flower or fruit at the time. A plausible flying fox–horse interface was established by the presence of fruit debris and spats on the ground. A private veterinarian visited the property and collected nasal and vaginal swabs from the dead mare on 26 July, more than 48 h since the mare had died. At that visit, the veterinarian also sampled a sick 7-year-old Australian Stock Horse mare that had been running in a separate paddock distant to that of the dead horse. It had not had recent contact with the dead horse, but was depressed, anorexic and febrile, with a serous nasal discharge. Sampling to exclude HeV infection was undertaken. Laboratory testing confirmed HeV infection as the cause of death in the dead mare (Table 1). The sick mare tested negative for HeV and recovered after treatment for a respiratory infection. There was another horse running in the same paddock as the dead horse and 3 horses in an adjoining paddock were also classed as in-contacts. Another 4 horses, including the mare showing respiratory signs, were in a separate paddock with a 10-m tree-lined buffer preventing contact between horses in adjoining paddocks. There were also 35 sheep, 1 dog and 1 barn cat on the property. All horses and the barn cat were repeatedly tested for serological evidence of exposure to HeV and all results were negative. Case 6 A 25-year-old Thoroughbred gelding running in a 2-acre agistment paddock near Bangalow, NSW, was noticed by its owner on the afternoon of 14 August 2011 to be slightly unsteady in the hindquarters, although still bright and eating. Three paralysis ticks had been removed from the horse that morning, so it was suspected that the horse was suffering from a mild case of tick paralysis. Early the next morning, the horse was found recumbent and tangled in a wire fence, with a dull, semi-comatose demeanour and muscle fasciculation. The horse made several attempts to stand but was unable to rise and veterinary assistance was sought. A private veterinarian examined the recumbent horse and found that it did not have a fever or any respiratory signs. Attempts to get the horse to stand were unsuccessful. The veterinarian considered
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HeV infection as an unlikely cause of the illness but collected blood (EDTA and clotted) samples for HeV testing and administered an anti-inflammatory drug. The horse continued to deteriorate and was euthanased that same morning after an illness of less than 24 h. HeV infection was confirmed by laboratory tests (Table 1). There were no trees on the property itself, although the adjacent properties contained eucalypts, a mulberry tree and numerous other native trees that were in flower at the time. Many of these trees overhung the infected property and neighbours reported regular flying fox sightings in the wider region, which has a significant number of orchards and plantations. A single watering trough was located under one of the overhanging trees and feeding by the owner was also carried out under the overhanging trees. There were two other aged horses that were in direct contact with the affected horse. Repeated testing of these horses was unable to show any serological evidence of exposure to HeV infection. Case 7 On 16 August 2011, two dead horses in a neighbouring 4-ha block at Pimlico, NSW, were reported to the Department of Primary Industries (DPI). The owner of the horses on the property was absent at the time. A government veterinarian from the North Coast LHPA was tasked to perform a farm visit. The veterinarian observed and examined two dead horses in a small house paddock: a 2-year-old filly attached to a fence wire by a clip on its halter and a 6-year-old mare, the mother of the filly, in the middle of the lawn near the house. The mare appeared to have prolapsed material from both the rectum and vulva but the veterinarian considered it likely related to decomposition. The mare was estimated to have died at least 1 week earlier than the filly. The house paddock contained some native flowering trees, palms and an old orchard. Flying foxes had been seen frequently. Four live horses were observed not to have any obvious signs of disease. The initial field diagnosis by the veterinarian was an accident for the horse attached to the fence and a reproductive incident for the mare. Oral, nasal, vaginal and rectal swabs and jugular blood were collected from both of the dead horses, with positive results for HeV (Table 1). The remaining horses were repeatedly tested, with negative results. On 23 August 2012, one of the remaining horses died and was found in a creek on the property. This horse was tested for HeV and found to be negative. Case 8 On 12 August 2011, a private veterinarian was contacted by a horse owner in Mullumbimby, NSW, regarding the sudden death of a 4-year-old Quarter Horse mare on their 35-ha hobby farm. According to the owner, the horse was well and moving freely the previous afternoon but was found dead the following morning. The paddock housing the deceased horse contained a number of palms, flowering eucalypts and fig trees. One adult pony was also running in this paddock. Flying fox faeces were identified close to an area of flattened grass where the horses regularly grazed. The owner’s dog had been sighted near the carcass before the arrival of the practitioner.
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On veterinary examination, there was blood present in both nostrils, but no other abnormalities were observed. Blood samples (clotted and lithium heparin) and swabs from the rectum, vagina and nostrils were submitted for HeV testing with positive results (Table 1). Samples from the in-contact pony and dog were collected, but these and the repeat samples were negative for HeV.
This NSW case series supports previous findings that HeV illness is typically acute, leading to death within 48 h.2,3 Indeed, 5 of the 11 horses were found dead, suggesting a rapid illness. In cases 4, 5, 6, 8 and 9, the duration of illness appeared very rapid, with the horses having been observed as well 12–18 h earlier. However, case 1 clearly indicates that HeV infection can also be associated with a more prolonged clinical illness.
Case 9 On the morning of 28 August 2011, a private veterinary practitioner was called to a horse death on a 31-ha property in Tintenbar, NSW. The owners reported that the previous morning their 10-year-old gelding had been depressed, febrile and swaying from side-to-side, with a wide forelimb stance. The owner had observed unsuccessful attempts by the horse to pick up feed. By 4:30 pm that day, the gelding was recumbent and resting its weight against a fence. The horse died in this position during the night.
All horses that were examined before death displayed clinical signs that match the case definition for a highly suspect case of HeV infection.12 To a varying degree, these horses displayed fever, weight shifting, depression and other neurological signs. Although fever was typically reported, it was not present at the time of examination in case 6. It is also of interest that only 1 of the 11 horses had respiratory signs as the predominant finding (Table 2). Overall, only 6 of the 11 horses showed any signs of illness, with predominantly neurological signs. Although 5 horses were found dead and had not been observed as ill by their owners, 2 were found tangled in fences, which is also suggestive of severe nervous system dysfunction.
The property was surrounded by extensive rainforest and contained a mandarin orchard, with evidence of ripe fruit half-eaten by flying foxes on the ground. The horse paddock also contained a fig tree and other flowering natives. Large numbers of flying foxes were reported to visit the property every night. The owners had a dog that had been in contact with the sick horse during the time it was displaying clinical signs. The practitioner collected blood samples (clotted and lithium heparin) and two nasal swabs from the deceased horse, which were found to be HeV positive (Table 1). Repeat sampling of the dog was negative for HeV on laboratory testing. Discussion Without exception, the affected horses in this case series were kept at pasture on premises in the north-east of NSW that are visited by flying foxes. Both species of flying fox are endemic to the region and present in large numbers. Despite ongoing interaction between flying foxes and horses, HeV infection has remained uncommon, so the unprecedented number of cases in the winter of 2011 suggests that some factor at that time was enhancing transmission of HeV from the bats to horses, with subsequent disease expression in the horses. Environmental, nutritional and reproductive stressors affecting the flying fox populations are likely to be important in increasing the potential for virus spillover.6,9 The events of 2011 could be explained by an increased prevalence of viral shedding in the flying foxes; however, no systems were in place for assessing excretion of virus by flying foxes in the vicinity of these cases. This information is now being obtained across NSW and Queensland as a result of the response by authorities to the outbreak. Of the 11 horses that tested positive for HeV, 5 were found dead or were dying in association with a fence (Table 2). Some had been trying to push through a fence while others had collapsed against the fence. The high prevalence of this scenario suggests that horses found dead in or near a fence should never be assumed to have died simply from misadventure. The neurological effects of HeV infection are severe and involve significant brain pathology.11 The ability to identify objects such as barriers would be compromised. Placement reflexes would also be diminished and it is therefore not surprising that affected horses get caught up in fences.
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This case series also demonstrates that many of the signs associated with HeV are relatively non-specific, which makes risk assessment prior to laboratory testing difficult. Whether or not HeV testing is to occur, for welfare reasons, all acutely ill horses need a private veterinarian to undertake other diagnostic tests and implement a treatment plan. In north-eastern NSW, veterinarians assume that almost any sick horse could have HeV despite it being an uncommon diagnosis compared with colic, toxicity or other infectious disease. Thus, there has been frequent HeV testing of sick horses in the region since the 2011 cases. NSW DPI laboratory data indicate that during 2012 there were 198 exclusion tests undertaken and all were found to be negative for HeV. The majority of HeV exclusions are undertaken by private veterinarians. The initial contact in 5 of the 9 cases was by private veterinarians (Table 1). Cases 2, 3, 4 and 7 are examples of dead horses that would likely not have had a diagnosis unless a local public veterinarian was available to undertake an investigation. However, these diagnoses can be considered to be chance findings where the horse owner and the public veterinarian have been motivated, usually by public health concerns, to request testing of a dead horse. There was limited spread to in-contact horses in these cases of HeV (Table 2). More than one horse was present on 8 of the 9 properties, but on only 2 properties (25%) was more than one horse affected. This supports the relatively low transmissibility of HeV reported previously.13 This low transmissibility is further supported by observations on properties, such as those associated with cases 4 and 8, where an animal was seen to have face-to-face contact with an affected horse but remained well. Exposure by this route is likely limited by the poor survival of HeV in the environment.14 When two horses were affected on the same property, such as cases 2 and 7, the time period between the onset of illness in each horse was consistent with studies on the incubation period for HeV, suggesting that the virus was spread from horse to horse. In addition, the close association between the mare and its foal in case 7 would have made viral transmission between the two horses more likely. However, it is still possible that those horses, which shared the same paddocks, became infected from the same contaminated environment.
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EQUINE These cases demonstrate the variation in HeV sampling strategies undertaken by veterinarians (Table 1). Case 2 provides an example of the care needed to interpret a negative diagnosis when only swabs of supposed fluid have been collected. Advice regarding appropriate sampling strategies is readily available. A range of samples should be collected from suspect HeV cases and the use of appropriate transport medium is essential.12,15 The recommended range of samples for HeV exclusion from the live horse are 10 mL of clotted, EDTA and heparin blood; pooled nasal swabs from each nostril; swabs from other mucosal surfaces (e.g. oral cavity, rectum, or conjunctiva); or urine collected in PBGS. If PBGS is not available, the swabs can be placed in 2 mL of sterile saline. It is recommended that when sampling dead horses, veterinarians collect 10 mL of blood from the jugular vein in addition to the submandibular lymph node and swabs as per a live horse. Field experience suggests that it is relatively easy to safely collect jugular blood from recently dead horses.16–18 HeV is a serious zoonotic infection. Veterinarians who work with horses should be familiar with both the risk assessment process and the personal protective equipment that should be worn.19 When a veterinarian suspects there will contact with body fluids or aerosols from a horse, then overalls, washable boots, disposable gloves and hand washing after the examination are essential. If the horse is located on premises where flying foxes visit and it is displaying systemic signs of illness, a higher level of protection is required, including appropriate respiratory protection. HeV is a sporadic illness of horses that is likely to remain uncommon in NSW. The documentation of 9 cases of HeV is hoped to benefit both clinicians and researchers. Important aspects were the location of all cases in the north-east region of the state, the affected horses all being kept at pasture on properties visited by flying foxes, the majority of cases being an acute illness dominated by neurological signs, an association with fences in many cases and limited spread to in-contact horses. Acknowledgments We thank private veterinarians Karen Teasdale, John Clunie, Greg Plummer and Neil Farquhar for the provision of clinical data and their work with Hendra virus in NSW.
2. Field HE, Barrat PC, Hughes RJ et al. A fatal case of Hendra virus infection in a horse in north Queensland: clinical and epidemiological features. Aust Vet J 2000;78:279–280. 3. Field H, Schaaf K, Kung N et al. Hendra virus outbreak with novel clinical features, Australia. Emerg Infect Dis 2010; 16:338–340. 4. Field HE, Breed AC, Shield J et al. Epidemiological perspectives on Hendra virus infection in horses and flying foxes. Aust Vet J 2007;85:268–270. 5. Barclay AJ, Paton DJ. Hendra (equine morbillivirus) [Review]. Vet J 2000;160: 169–176. 6. Field H, Kung N. Henipaviruses: unanswered questions of lethal zoonoses. Curr Opin Virol 2011;1:658–661. 7. Plowright RK, Field HE, Smith C et al. Reproduction and nutritional stress are risk factors for Hendra virus in little red flying foxes (Pteropus scapulatus). Proc R Soc Biol Sci 2008;275:861–869. 8. Thornley M. Hendra virus under the microscope. Aust Vet J 2005;83:2. 9. Plowright RK, Foley P, Field HE et al. Urban habituation, ecological connectivity and epidemic dampening: the emergence of Hendra virus from flying foxes (Pteropus spp.). Proc R Soc Biol Sci 2011;278:3703–3712. 10. Halpin K, Young PL, Field H et al. Newly discovered viruses of flying foxes. Vet Microbiol 1999;68:83–87. 11. Hooper P, Zaki S, Daniels P et al. Comparative pathology of the diseases caused by Hendra and Nipah viruses. Microbes Infect 2001;3:315–322. 12. Biosecurity Queensland. Guidelines for veterinarians handling potential Hendra virus in horses. 2011. http://www.daff.qld.gov.au/4790_13371.htm Accessed January 2013. 13. Williamson MM, Hooper PT, Selleck PW et al. Transmission studies of Hendra virus (equine morbillivirus) in fruit bats, horses and cats. Aust Vet J 1998; 76 (12): 813–818. 14. Fogarty R, Halpin K, Hyatt AD et al. Henipavirus susceptibility to environmental variables. Virus Res 2008;132:140–144. 15. NSW Department of Primary Industries. Vet Lab Manual. http://www.dpi.nsw .gov.au/agriculture/vetmanual. Accessed January 2013. 16. Kemsley P. Hendra virus experiences. In: Proceedings of the 94th District Veterinarian’s Conference, 26–30th March, 2012, Wollongong, NSW. District Veterinarians Association of NSW. http://www.flockandherd.net.au/edition/ conference_2012.html. 17. Ball M. Hendra virus experiences. In: Proceedings of the 94th District Veterinarian’s Conference, 26–30th March, 2012, Wollongong, NSW. District Veterinarians Association of NSW. http://www.flockandherd.net.au/edition/ conference_2012.html. 18. Poe I. Hendra virus experiences. In: Proceedings of the 94th District Veterinarian’s Conference, 26–30th March, 2012, Wollongong, NSW. District Veterinarians Association of NSW. http://www.flockandherd.net.au/edition/ conference_2012.html. 19. Australian Veterinary Association. Guidelines for veterinary personal biosecurity. http://www.ava.com.au/sites/default/files/AVA_website/pdfs/Biosecurity%20 Guidelines%202013%20FINAL.pdf. Accessed July 2013. (Accepted for publication 21 November 2013)
References 1. Baldock FC, Douglas IC, Halpin K et al. Epidemiological investigations into the 1994 equine morbillivirus outbreaks in Queensland, Australia. Sing Vet J 1996;20:57–61.
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