Coronaviridae & Arteriviridae Flashcards
Describe Coronaviridae…
- Largest genomes of RNA viruses
- Linear +ve sense ssRNA
- non-segmented genome
- Envelopes
- Replicate in cytoplasm
- Bud from ER
- Exit cell by exocytosis
- Moderately fragile
- Don’t grow well in culture
- Use EM for diagnosis
What makes coronaviridae moderately fragile?
- Survive 1-2 days at room temperature
- Destroyed by lipid solvents and extremes of pH
- Naked RNA can be infectious
What are some diseases caused by coronaviruses?
- Feline infectious peritonitis (FIP)
- Transmissible gastroenteritis (TGE)
- Pig vomiting and wasting disease
- Pig epidemic diarrhoea
- Chicken Infectious bronchitis
- Calf, puppy, kitten, foal diarrhoea
- Human common colds
- SARS
What are some coronaviridae fundamentals?
- Most cause mild disease in adults but more severe disease in newborns
- except: FIP, TGE and SARS
- Most mammalian coronaviruses have a tropism for endodermal cells: liver, kidney, intestinal or respiratory epithelium
- Most species have only one serotype
- Serological cross- reactivity occurs between mammalian coronaviruses of different species
Describe Feline infectious peritonitis (FIP)/ Feline enteric coronavirus (FCV)…
- Peritonitis
- Pleuritis
- Neurological signs
- Ocular lesions
- Can get wet or dry effusive FIP
- Faecal-oral transmission
- Widespread in all cat populations
- FCV seropositivity is high but FIP is uncommon consequence of infection (only 1-5% develop this)
- Persists in intestinal tract and continues to replicates at low levels for months
How can FECV (feline enteric coronavirus) mutate into FIPV (feline infectious peritonitis virus)?
- Spontaneous mutations
- Recombination with other coronaviruses
Describe the epizootiology of FCV’s…
- Each cat develops and harbours is own distinct quasispecies
- Evidence is mounting that FIPV’s are mutants of FECV arising in each FECV infected animal
What cell does FECV have a tropism for?
Intestinal epithelial cells
What cell does FIPV have a tropism for?
Macrophages
How do you diagnose FIP?
Use a combination of findings
- History
- Physical Exam: ultrasound
- Clinical Pathology: Fluid analysis, serum biochemistry / CBC
- Histopathology
How do you control FIPV?
- Minimise immunosuppression due to stress/ other infections
- Eliminate FCoV from the cat’s environment (disinfectants etc.)
- Vaccination - difficult because of the ‘antibody-mediated enhancement of disease’
What are the three important Porcine Coronaviruses exotic to NZ?
- Transmissible Gastroenteritis (TGE)
- Haemagglutination Encephalomyelitis (Vomiting & Wasting disease, V & WD)
- Epidemic Diarrhoea
Describe Transmissible Gastroenteritis (TGE)…
- Outbreak of vomiting and diarrhoea
- Especially in winter
- Incubation period of 1-2 days
- Signs persist for 3-5 days
- Animals of all ages affected
- High mortality in piglets due to dehydration
- High morbidity , low mortality in animals over 5 wks
- May cause stunting, agalactia or subclin infection
- Carriers can excrete virus for 3-4 months
Describe Bovine Coronavirus…
- In NZ
- Causes diarrhoea in young calves
- Diarrhoea lasts 4-5 days
- Diagnosed by EM, Cell culture with trypsin or calf diarrhoea faecal Ag ELISA
- Checks for rota and coronaviruses and E.coli
- Zoonotic
Describe Infectious bronchitis in chickens…
- Gasping disease of chickens
- In NZ
- Explosive outbreaks of entire flock
- Can establish persistent infection in young birds
- Can be shed in faeces
- Diagnosed by flock serology; HI, virus isolation, , ID by ELISA or AGID
- Controlled by Modified live virus vaccination
Describe Canine Coronavirus…
- Present in NZ
- Diarrhoea in young animals
- Usually lasts 2-3 days
- Affected animals are less ill than with parvo and don’t become leucopenic
- Diagnosis by EM, serology, faecal Ag detection
- Vaccines are available
Describe Arteriviridae…
- Small (45-70nm) diameter
- Enveloped
- Icosahedral
- RNA genome
- Highly species specific
- Infection outcome can range from asymptomatic to abortion to lethal hemorrhagic fever
- Often establish persistent infections
- Macrophages are primary target cells
What are some examples of arteriviridae…
- Porcine Reproductive and Respiratory syndrome virus (PRRS)
- Equine Arteritis Virus (EAV)
- Lactate dehydrogenase- elevating virus in mice
- Simian haemorrhagic fever virus in monkeys
- Wobbly Possum disease virus
Describe Equine arteritis virus (EAV)…
- Asymptomatic
- Influenza like illness in adults
- Interstitial pneumonia in young foals
- Abortions in pregnant mares
Describe EAV pathogenesis…
Vasculitis due to virus associated vascular injury
Describe EAV abortions…
Foetuses are usually partially autolysed and are often devoid of any gross lesions
How is EAV transmitted?
Respiratory route
- Aerosols from respiratory tract, aborted material etc.
- Fomites
- Close contact is necessary
Venereal Route
- Infected stallions can shed virus in semen for months- years without clinical signs
- Very efficient route of dissemination
Describe the epizootiology of EAV…
Need to ID shedder stallions!
- Positive serology = suspicious (seropositive stallion is not necessarily a shedder)
- Confirmation of virus in semen by virus isolation or PCR
- Breeding stallion with seronegative mares and checking for seroconversion of mares 4 weeks later
- Teasers can be a potential source of the virus
How do you diagnose EAV?
Based on clinical signs
- but remember there are other DDx e.g. EHV, lepto etc.
Laboratory Diagnosis
- Virus Isolation
- Ag detection
- RT-PCR
- Serology: Virus Neutralisation test is gold standard, ELISA
Describe EAV prevention/ management…
More important in breeding facilities
- Segregate pregnant mares
- ID carrier stallions
- Breed carrier stallions only to seropositive mares
- Semen test for AI
- Vaccination (prevents disease not infection)
When should horses be vaccinated for EAV?
- Colts before puberty to prevent infection establishment
- Mares before insemination by shedder stallions or AI
- Seronegative stallions to prevent infection
Describe Porcine reproductive and respiratory syndrome (PRRS) virus…
- Late term abortions increases the number of stillborn foetuses
- Premature weak piglets often die in respiratory distress
- Piglets also get: muscle tremours, eyelid oedema, conjunctivitis and/ or fever and splayed leg
- Reproductive disease occurs when sows are infected in the 3rd trimester of pregnancy
- they have normal litters after
What is respiratory PRRS characterised by?
- Difficulty breathing
- Eyelid oedema
- Sneezing
- Pyrexia
- Stunted growth
- Poor food conversion
What clinical signs are seen in sows with PRRS?
- Inappetance
- Lethargy
- Fever
- Respiratory distress
- Oestrus delay
- Early return to oestrus
- Abortion
- Early farrowing
- Birth of mummified dead, weak piglets
What clinical signs are seen in boars with PRRS?
- Lethargy
- Depression
- Reduction of ejaculate volume
What clinical signs are seen in suckling piglets with PRRS?
- Respiratory embarrassment
- Delayed development
- Depression
- Palpebral oedema
- Sneezing
- Conjunctivitis
- Rough hair coat
- High mortality
What clinical signs are seen in weaners and growing piglets with PRRS?
- Respiratory distress
- Secondary viral and bacterial infections
- Skin changes; blue ears
- Reduced growth rate
- Splay-legged piglets
How is PRRS controlled?
- Negative herd: biosecurity + testing to prevent new intro
- Removal of positive animals
- Management strategies to limit spread
- Maintenance of protective immunity by vaccination and simultaneous deliberate exposure to the virus
Describe wobbly possum disease virus…
- Inappetance
- Behaviour changes
- Neurological deficits
- Death
- Genomic sequence most closely related to arteriviruses
