In this issue – January/February 2017

The first two papers for Australian Veterinary Journal in 2017 both have clear One Health implications. Our first paper, on experimental Hendra virus (HeV) infection of dogs, concludes that that the virus is not highly pathogenic in that species. However, the authors suggest that an infected dog's oral secretions may be a potential risk for transmission of the virus to humans during the acute stages of the disease before they have established an adaptive immune response.1 HeV has a high mortality rate, particularly in horses and humans, as well as experimentally in ferrets and cats. In addition, antibodies have been found in asymptomatic dogs where HeV outbreaks have occurred. In this study, 16 dogs were infected via mouth and nose drops with HeV using tissue culture from the spleen of an infected horse or blood from ferrets. Results showed that dogs were infected with the virus following exposure and that gene copy numbers from oral swab samples were similar to those recovered from nasal swabs of experimentally infected unvaccinated horses. However, any clinical signs were minimal. Some but not all dogs had a short non-specific sinus infection, which only lasted up to 48 h, and all dogs were normal by 9 days post-infection. This is consistent with that seen in natural cases and the authors suggest that acute infections may not be noticed. In the early stages, canine oral fluids were able to induce disease in ferrets. Few abnormalities were noticed at postmortem examination, except for hyperplasia and hyperaemia of tonsil and tracheal lymph nodes. Immunohistochemical studies showed that the major sites of virus were tonsil epithelium and lymphoid follicles. The authors conclude that although such animals pose a potential transmission risk, the likelihood of CNS infection in dogs and any long-term consequences are currently unknown. They suggest that oral swabs should be used to confirm acute infection in suspect live dogs. A clinical review uses three different case reports to highlight the importance of recently emerged Brucella suis infection in dogs and the public health importance of taking care while performing necropsies, particularly on animals that have aborted.2 Most cases have occurred in dogs and people directly participating in pig hunting. The presence of B. suis in feral pigs is a security risk to commercial enterprises, although the domestic pig herd is currently free of the virus. As we mentioned last month,3 government recommendations are to euthanase such dogs as the only guaranteed way to prevent zoonotic transmission, although this is not a legal requirement as it is for animals infected with Hendra virus. The new guidelines also include antibiotic treatment as an alternative. The current study includes one case of a female dog diagnosed after 19 months of lameness, during which time it was in close contact with other dogs, all of which remained seronegative. Two other male dogs had a more standard presentation of orchitis; one had one testis removed, because the owners wanted to breed with it, and the other was castrated. The authors stress that this is not a purely rural disease; consumption of raw feral pig meat is the most probable route of infection and many recreational pig hunters reside in urban centres. Involvement of the reproductive tract is most likely in sexually intact animals, but spinal or appendicular skeleton involvement is a feature in neutered animals. As it is likely that transmission can be from sexual contacts and contact with aborted material, the authors make a strong recommendation that infected dogs should not be used for breeding and that bilateral castration using a closed technique is essential to maximise operator safety. It is a notifiable disease and so needs to be reported to the DPI. A study from Murdoch University in Western Australia reports on levels of cytokines produced in units of packed red blood cells collected at different times from retired Greyhounds.4 Cytokines accumulate during storage and leucocyte reduction before storage has been shown to prevent this occurring. The authors performed the third collection of whole blood from 12 healthy ex-racing Greyhounds. Platelet count was significantly higher in samples that were not leucoreduced and interleukin (IL)-8 increased from the first to third blood collection among the same samples. There was no difference over time in IL-1β. The authors discuss the possible biological reasons for their results, including the short time between taking the units, and the marked variation in IL-8 concentration between units. The authors address the possible study limitations but recommend the use of leucoreduction to prevent accumulation of inflammatory mediators in stored canine packed red blood cells. The presence of transitional lumbosacral vertebrae was assessed in a breeding colony of Labrador Retrievers and Labrador crosses.5 These transitional vertebrae are at either the thoracolumbar or lumbosacral junction and are considered to be a congenital abnormality. Lateral radiographs of the thorax were performed in those dogs in which an eighth lumbar vertebra was identified in AP radiographs. Fusion of the sacrum was also assessed. The study included 119 puppies from 18 litters; 9 of the puppies showed this abnormality even though all parents had been screened before breeding. The frequency was higher if either parent was affected, suggesting high heritability, although some normal progeny resulted from two abnormal parents. The authors suggest that a lateral radiographic projection would be valuable during screening, as well as a separate lateral view centred on the pelvis. Careful interpretation is needed to account for the maturity of the animal. They also note that the observed rate was higher than that seen in other populations, but that the study group was a relatively closed breeding colony in which there had been no active selection against this condition and thus may not reflect prevalence in the general Retriever populations. A retrospective case series describes the treatment of histiocytic sarcomas in 12 dogs that had confirmed metastases to lymph nodes.6 All dogs were treated surgically, with or without three different protocols of adjuvant chemotherapy. The endpoint was death from any cause, and the authors found that sex of the animal and whether the dogs received chemotherapy or not (median survival, 219 days vs. 57 days) were the only statistically significant differences for survival. The median survival was 77 days in animals that had postoperative macroscopic disease and 1638 days for those that did not. In spite of the lack of statistical significance, presumably because of the small number of dogs, this would seem to imply clinically that radical surgery including clear margins is essential to prevent tumour progression. It is important to note that Kaplan-Meier survival curves are usually produced for clinical trials involving large numbers of (human) patients. One should be wary of over interpretation of this, and the use of medians, in studies with small sample sizes. Management of oesophageal foreign bodies in dogs usually involves endoscopy or fluoroscopic guidance for oral removal or for advancing the foreign body into the stomach followed by thoracotomy or oesophagotomy.7 Pyothorax may result from perforation of the mediastinum following treatment and its occurrence has a poor prognosis. This case report is of two dogs that presented with oesophageal foreign bodies accompanied by pyothorax. One of the dogs was treated surgically according to standard recommendations. The owners did not want surgery for the other dog and so it was treated with supportive care, treatment by infusion and oesophageal rest, which was also successful, although the authors would still recommend surgical treatment as their preferred option. An equine case report is of an osteochondroma in a Thoroughbred gelding that had been lame with associated fluid in the extensor carpi radialis tendon sheath for 5 months. A firm mass could be felt on the cranial aspect of the distal radius, projecting 3 cm cranially, and it had the radiological features of an ostochondroma.8 The authors describe the surgical removal of the mass and report that the horse was sound at the trot 2 months after surgery, was in race training at 6 months and went on to race successfully. Although rare, the authors suggest that osteochondrosis should be considered when investigating horses with inflammation in this location. Bovine ephemeral fever is a vector-borne rhabdovirus disease. We have previously published a paper from this group that discussed the epidemiology of this virus.9 In the current paper they discuss the localisation of antigens in various tissues, as well as its presence within cell cultures, from a case that was confirmed using qRT-PCR.10 The authors note the presence of antigen in tissue sections morphologically consistent with macrophages. They identified the virus in isolated cells of which most were morphologically consistent with fibroblasts, and required trypsin to remove them from the tissue culture plates. I find it interesting that we have two studies using immunohistochemistry for viral antigen identification that have come to opposite conclusions about intracytoplasmic staining of macrophages. Middelton et al. make the point that identification of the antigen is not regarded as sufficient evidence that a particular tissue is the site of virus replication, as this may simply reflect sequestration of virus or fragments in phagocytes or cellular debris.1 However, Barigye et al. are more confident that their positive staining does demonstrate virus survival and replication in macrophages.10 It would be interesting to see immunohistochemistry results from animals in the earliest stages of BEFV infection to ascertain if it is indeed replication or if this macrophage antigen staining is, as Middleton suggests, phagocytic debris collection.

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