Gastroenteritis old and new viruses

Transcription

1 Vet Times The website for the veterinary profession Gastroenteritis old and new viruses Author : SARAH CADDY Categories : Vets Date : February 25, 2013 SARAH CADDY discusses emerging viruses associated with this condition, reminding vets to be aware of all aetiologies and also looks at potential zoonoses Summary A multitude of new canine viruses associated with gastroenteritis have been identified by recent research. Such viruses include noroviruses, sapoviruses and kobuviruses. Ascertaining the pathogenic effects of these viruses and any possible zoonotic threats, are essential future avenues of investigation. In addition to these newly emerging viruses, certain enteric viruses identified decades ago are at risk of re-emergence, for example canine distemper virus. In the UK, canine parvovirus and canine enteric coronaviruses are typically held accountable for all cases of viral gastroenteritis in dogs, but it is increasingly apparent this is not the case. It is important veterinarians are aware of the other potential viral aetiologies of gastroenteritis in dogs. This will allow maintenance of appropriate isolation measures for infectious cases, may impact on vaccine selection, and could stimulate enhanced biosecurity in the face of potential zoonoses. Key words virus, gastroenteritis, diarrhoea, canine A WHOLE host of new viruses associated with gastroenteritis in dogs have been identified by research. These include noroviruses, sapoviruses and kobuviruses. In addition, certain viruses identified 1 / 6

2 decades ago are at risk of re-emergence, and zoonotic enteric viruses are another concern. In the UK, canine parvovirus and canine enteric coronaviruses are typically held accountable for viral gastroenteritis in dogs, but could this dogma be about to change? Dealing with diarrhoea cases can be a nightmare for vets and most certainly for kennel nurses. Diarrhoea is a common reason for visiting the vet, with a recent study showing that one in 14 consults in day practice are due to diarrhoea 1. The primary cause of diarrhoea in dogs is when the animal eats things it should not often politely referred to as dietary indiscretion on clinical notes. Bacterial causes are less frequent than many owners and clinicians think, but viruses are often not considered at all. Some studies have shown that up to 32 per cent of diarrhoea samples contain viruses 2, and this proportion can be up to 55 per cent for haemorrhagic diarrhoea 3. Recognised causes All clinicians are aware of canine parvovirus (CPV) as a major cause of viral gastroenteritis. CPV was first identified in 1978, when outbreaks of severe haemorrhagic gastroenteritis in young dogs were reported 4. Since then, widespread vaccination has served to limit its prevalence, but no specific therapy is available. Treatment is centred on maintaining hydration, avoiding secondary bacterial infection, preventing gastric ulceration and providing adequate analgesia ( Figure 1 ). Patient-side tests are available to detect the presence of CPV in stools. However, a negative test is often interpreted incorrectly. There are three possible ways to interpret a negative test. False negatives these are surprisingly common. Only 56 per cent of samples testing positive by PCR were detected using patient-side tests in a study 5. Some cases may be shedding very low amounts of virus, which cannot be detected by patient-side tests. The test should ideally be repeated in 48 hours if there is a high suspicion of CPV infection. CPV is not present, but another virus is causing signs as discussed later, there are many viruses capable of causing gastroenteritis. It is prudent to isolate any case with severe gastroenteritis to prevent spread of an unidentified viral infection. CPV is not present and a non-viral factor is causing gastroenteritis further investigations may be required, such as imaging to rule out foreign bodies ( Figure 2 ). Old virus, new tricks Infections with canine enteric coronavirus (CECoV) typically cause only mild gastroenteritis. However, young dogs can suffer from more severe disease and strains causing haemorrhagic gastroenteritis and systemic infections have been reported 6. CECoV is more prevalent than many 2 / 6

3 vets realise a European study showed 38.5 per cent of diarrhoea cases were CECoVpositive. Almost half of these cases were also positive for CPV, so the main cause of clinical disease is unclear. What is clear is that coinfections have a significantly poorer prognosis 7. Testing for CECoV is available commercially in the UK, which certainly perhaps should be considered more frequently. Nevertheless, it is important to be aware healthy dogs can shed CECoV, which makes the direct pathogenic effects of the virus uncertain. Bearing all this in mind, it is still unresolved as to whether dogs should be routinely vaccinated against CECoV. Only two of the licensed dog vaccine ranges in the UK protect against CECoV. Vaccine brand selection in practices is often a commercial choice, but if a positive CECoV case is identified locally, it might be worth re-evaluating the vaccine range offered to clients. The classic clinical signs of canine distemper virus infection can include gastroenteritis, respiratory signs and neurological abnormalities. A disease matching this description was first described in dogs in the early 1900s, and canine distemper is now highly prevalent worldwide. Despite this, successful vaccination programmes in the UK mean most vets never see a case. However, an outbreak of canine distemper was reported in ferrets in the midlands in 2010/2011. More than 300 animals are estimated to have succumbed to infection 8. This highlights the need to remain vigilant for signs of distemper, especially in areas of the UK where vaccination uptake is limited. Emerging viruses As molecular biology advances, a number of studies have used new techniques to screen diarrhoeic samples for novel viruses. The pathogenicity of most of these viruses is yet to be proven, but they are largely found in association with gastroenteric signs. Reports of the first canine picornavirus to be identified were published in , 10. This canine kobuvirus is genetically similar to the Aichi virus, a gastroenteritis-associated human picornavirus. The virus has identified in diarrhoea samples using high throughput sequencing. A study of 400 dogs in the US found 20 kobuvirus-positive samples 10. Human norovirus is the most common viral cause of diarrhoea and vomiting in humans in the UK. There are an estimated three million cases in people each year 11. When canine norovirus was identified in 2008, it was suspected that clinical signs of infection in dogs could be similar to human norovirus infection in humans. Canine norovirus has since been reported in diarrhoeic faecal samples from dogs across Europe 12, 13, 14, US 15 and Hong Kong16. Prevalence of canine norovirus in these samples ranged from 2.2 per cent to 40 per cent. Canine norovirus has also been identified in normal stools, so the pathogenic effect of infection is still yet to be elucidated. Noroviruses are members of the calicivirus family, alongside a number of other animal pathogens, including feline calicivirus and rabbit haemorrhagic disease virus. Caliciviruses causing gastroenteritis are not only limited to the norovirus genera; sapoviruses are another prominent 3 / 6

4 cause of enteric disease in humans. After canine norovirus, it seems it was only a matter of time before a canine sapovirus was reported. In 2011, canine sapovirus was first identified, but to date this virus has only been found in a handful of samples 10. Astroviruses deserve a mention at this point, despite the first canine astrovirus being identified more than 20 years ago 17. A PCR-based screen in 2011 of canine faecal samples from Italy showed astroviruses were detectable in 25 per cent of diarrhoea samples 18. However, canine astrovirus can be found in normal faeces, and in the Italian study 63 per cent of the positive samples were coinfected with either CPV, CECoV or both ( Figure 3 ). Is there a zoonotic risk? The most prevalent viral players in canine gastroenteritis are, thankfully, not transmissible to humans. An Australian study has even shown that owning a dog significantly decreases the incidence of gastroenteritis in young children 19. However, there are rare cases when dog-to-human transmission of enteric viruses has been reported, notably for rotaviruses and possibly for noroviruses. Rotaviruses are a serious pathogen of humans 800,000 cases are estimated to occur each year in the UK and up to a million children die from severe gastroenteritis worldwide each year. Calves, piglets and foals are also highly susceptible to rotavirus infection, but rotaviruses are not considered to be a major pathogen of dogs. Only a few reports of canine rotavirus infection exist, though recent evidence is emerging that shows canine strains can be spread to humans. A handful of individual case reports have identified rotavirus strains causing diarrhoea in children originating from dogs 20, 21. Human norovirus was identified in the faeces of four dogs in Finland in Importantly, their owners were suffering from suspected norovirus infections at the same time. None of the dogs showed significant signs of gastroenteritis. It is not yet known whether the dogs were merely acting as carriers of the virus, or if the virus was actually replicating in their gastrointestinal tract. While this report warrants further investigations, canine transmission of norovirus infections is not currently considered a major concern. It is well accepted that strict hygiene is essential during outbreaks of human gastroenteritis to reduce the likelihood of infection spread. Dogs, theoretically, can carry infection on their coats in much the same way as a used towel or cup can spread disease. Yet, dogs are often overlooked by owners as being potential vehicles of infection. Advising owners to maintain stringent cleanliness during outbreaks of gastroenteritis in both humans and dogs is a sensible precaution. Summary 4 / 6

5 Over the past few decades, only one or two viruses have been considered as causes of gastroenteritis in the UK dog population. In contrast, human gastroenteritis is known to be caused by a variety of viruses, most notably noroviruses, astroviruses and rotaviruses. It is increasingly understood that canine strains of the human pathogens can cause diarrhoea in dogs as well. It is important veterinarians are aware of the other possible viral etiologies of gastroenteritis in dogs. This will allow maintenance of appropriate isolation measures for infectious cases, may impact on vaccine selection, and could stimulate enhanced biosecurity in the face of potential zoonoses. Key points A large number of viruses are known to cause gastroenteritis in dogs, only three of which can be vaccinated against: canine parvovirus, canine distemper and canine enteric coronavirus. A number of new enteric viruses have been associated with diarrhoea in dogs, including canine norovirus and canine kobuvirus. The pathogenic role of several enteric viruses is uncertain. Further research is essential to determine if vaccine development would be beneficial for control of these viruses. Isolation of diarrhoea cases demands careful consideration. A negative parvovirus test may actually be positive, or another infectious agent may be the cause. Remember some viral causes of gastroenteritis in dogs may be able to be transmitted to humans biosecurity must be taken seriously. References 1. Stavisky J et al (2010). Prevalence of canine enteric coronavirus in a cross-sectional survey of dogs presenting at veterinary practices, Veterinary Microbiology 140: Vieler E et al (1995). Electron microscopic demonstration of viruses in feces of dogs with diarrhea, Tierarztl Prax 23: Schulz B S, Strauch C, Mueller R S, Eichhorn W and Hartmann K (2008). Comparison of the prevalence of enteric viruses in healthy dogs and those with acute haemorrhagic diarrhoea by electron microscopy, The Journal of Small Animal Practice 49: Thomson G W and Gagnon A N (1979). Canine gastroenteritis associated with a parvovirus-like agent. The Canadian Veterinary Journal (La revue vétérinaire canadienne) 19: Desario C et al (2005). Canine parvovirus infection: which diagnostic test for virus?, Journal of Virological Methods 126: Decaro N and Buonavoglia C (2008). An update on canine coronaviruses: viral evolution and pathobiology, Veterinary Microbiology 132: Pratelli A et al (1999). Fatal coronavirus infection in puppies following canine parvovirus 5 / 6

6 Powered by TCPDF ( 2b infection, Journal of Veterinary Diagnostic Investigation 11: Thomas S (2012). Canine distemper outbreak in ferrets in the UK, Veterinary Record 170: Kapoor A et al (2011). Characterization of a canine homolog of human Aichi virus, Journal of Virology 85(21): 11,520-11, Li L et al (2011). Viruses in diarrhoeic dogs include novel kobuviruses and sapoviruses, The Journal of General Virology 92: 2,534 2, Tam C et al (2012). Longitudinal study of infectious intestinal disease in the UK (IID2 study): incidence in the community and presenting to general practice, Gut 61: Martella V et al (2009). Genetic heterogeneity and recombination in canine noroviruses, Journal of Virology 83(21): 11,391 11, Ntafis V, Xylouri E, Radogna A, Buonavoglia C and Martella V (2010). Outbreak of canine norovirus infection in young dogs, Journal of Clinical Microbiology 48: 2,605-2, Mesquita J R, Barclay L, Nascimento M S J and Vinjé J (2010). Novel norovirus in dogs with diarrhea, Emerging Infectious Diseases 16: Azevedo M et al (2012). Detection of norovirus in dogs in Arkansas, American Society of Virology Conference Tse H et al (2012). Complete genome sequences of novel canine noroviruses in Hong Kong, Journal of Virology 86(17): 9,531-9, Williams F P (1980). Astrovirus-like, coronavirus-like, and parvovirus-like particles detected in the diarrheal stools of beagle pup, Archives of Virology 66: Martella V et al (2011). Detection and characterization of canine astroviruses, Journal of General Virology 92: 1,880-1, Heyworth J S, Cutt H and Glonek G (2006). Does dog or cat ownership lead to increased gastroenteritis in young children in South Australia? Epidemiology and Infection 134: Wu F et al (2012). Putative canine origin of rotavirus strain detected in a child with diarrhea, Taiwan, Vector-Borne and zoonotic diseases 12: Luchs A, Cilli A, Morillo S G, Carmona Rde C and Timenetsky Mdo C (2012). Rare G3P[3] rotavirus strain detected in Brazil: possible human-canine interspecies transmission, Journal of Clinical Virology 54: Summa M, von Bonsdorff C H and Maunula L (2012). Pet dogs a transmission route for human noroviruses?, Journal of Clinical Virology 53: / 6