Paramyxoviridae

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Overview


Classification


Virus properties

Structure

  • Negative sense RNA, unsegmented, single stranded
    • -> Reasortment and antigenic shift cannot occur
  • HN spike contains:
    • Haemagglutinin (H)- attachment protein
    • Neuraminidase (N)
  • Fusion glycoprotein (F) spike
    • -> Viral lipid bilayer can fuse directly with host plasma membrane
      • -> RNA released into cytoplasm
    • ->Syncytium (multinucleated giant cells) in lesions and cell culture
    • Host antibody response to this protein is most important
      • Best induced by live attenuated vaccines

Growth in vitro

  • Allantoic cavity of 10-day-old eggs
  • Followed by haemagglutination

In vivo

  • Cell tropism for upper respiratory tract epithelium
    • All replicate in these cells
  • Some replicate in the gut
  • Most virulent replicate in lymphoid cells and neurons (Distemper, NDV)
  • Links to the readiness to cleave Fo and Ho precursors in different cells

Antigenic differentiation

  • Major conserved immunodominant virus-specific antigens on F and HN
    • -> Vaccines protect against all isolates of the same virus
  • Minor morbillivirus-specific epitopes on F
  • Minor variable epitopes of F, HN and NP
    • Allows antigenic fingerprinting


Canine Distemper Virus (CDV)

{Canine distemper - a pantropic virus which has a suppressing effect on lymphoid tissue, and which may trigger latent Toxoplasmosis. After aerosol infection, the virus multiplies in the bronchial and other lymph nodes. It then spreads to a variety of epithelium depending upon the strain of virus including that of the respiratory and alimentary tracts, skin and later (1-5 wk. post infection) to the brain, causing a mucopurulent oculonasal discharge with keratitis and an interstitial pneumonia, a smelly sometimes bloody diarrhoea, eruptions on the skin including hyperkeratosis of the nose and pads, and encephalitis respectively. The essential feature of the last mentioned is demyelination particularly in the cerebellum resulting in ataxia. Convulsions, coma and paralysis may occur, and chorea (rhythmic motor movements) may be seen in recovered animals. Intracytoplasmic inclusions may be found in most affected tissues and inclusions persist longest in the brain (may be intranuclear) and the alveolar macrophages. Giant cells may be seen in the alveoli. The severity of the disease may vary; if enough neutralising antibody develops in the early stages, the virus maybe kept restricted largely to the lymph nodes. Severe clinical pneumonia follows secondary infection with Bordetella bronchiseptica.} From RVC respiratory notes 2006 by B.Smyth


Newcastle Disease Virus (NDV)

  • Hosts
    • Gallinaceous birds, pigeons, parrots, finches
    • Subclinical carriers: ducks, ostriches
    • Causes conjunctivitis in humans
  • Epidemiology
    • Air-born
    • Direct contact of poultry
  • Diagnosis
    • Samples of trachea and gut of 20 birds are tested in eggs
    • HI using anti-NDV serum (to differentiate HA caused by avian influenza
    • Animal test: virulence of isolate tested by the speed it kills chicks
    • Sequencing the cleavage site of H gene
      • The more basic amino acids the more virulent the virus
      • Now replacing the animal test
  • Control
    • Isolation of stock
    • Vaccination of chickens and racing pigeons
    • Surveillance of imported exotic birds
    • Notifiable disease
    • Infected premises to be culle and firebreak cull if spread


Reptilian Paramyxoviruses

  • Infect central nervous system and lungs
  • Kill particularly snakes
  • Healthy reptiles may be carriers
  • Testing by serology - HI test
  • Aim to keep virus free collection and prevent spread back into the wild


Murine Parainfluenza - 1 (Sendai virus)

  • Endemic in many mouse colonies
  • Most mice show no symptoms due to maternal antibodies
  • But minor respiratory lesions may invalidate carcinogenic or toxicological studies
  • Immunological studies also confused due to virus activating NK cells via high circulating IF 3-4 days post-infection
  • Control achieved by:
    • Purchasing specific pathogen free (SPF) mice
    • Kill whole colony in an outbreak -> disinfection -> formalin fumigation


Canine Parainfluenza - 2

  • or Parainfluenza - 5
  • Infects dogs
  • May cause mild upper respiratory infection, rhinitis
    • Virus shed for a short time only
  • Also part of kennel cough (Infectious canine tracheitis), together with Bordetella bronchiseptica
  • Control:
    • Live attenuated vaccine may be incorporated in multivalent vaccines
      • Immunity is short-lived
      • Only reduces severity of clinical signs


Bovine Parainfluenza - 3 (PI-3)

  • Virulence varies with isolates
  • Cessation of ciliary clearance and epithelial necrosis predisposes to secondary bacterial infections -> cough
  • May cause rhinitis of cattle
  • With other agents causes calf pneumonia
    • Together with managemental factors (overcrowding, poor ventilation, high humidity, deprivation of colostrum and stress caused by transport or mixing of stock)
  • Diagnosis
    • Diseased lung tissue from dead animals or centrifuged cells from lung lavage
    • Virus is too fragile for cell culture isolation (often inactivated intransport)
    • Antigen detection by immunocytochemistry for intracytoplasmic viral inclusions containing labelled viral protein
    • Serology: 4-fold rise in ELISA antibody in paired serum samples from several animals
  • Control
    • Improve managemental factors
    • All-in, all-out systems
    • Some vaccination
      • Temperature sensitive mutant that replicates at 34oC but not at 37oC
      • Re-infection is common


Bovine Respiratory Syncytial Virus (BRSV)

  • Pathogenesis:
    • More serious than PI-3
    • Causes [Viral infections#Respiratory syncytial virus|respiratory infection]]
    • Replicates in nasal epithelium -> throughout upper respiratory tract -> bronchial tree
    • Syncytia form -> shed into bronchioles
    • Complications include emphysema and oedema, drop in milk yield in adult cattle
  • Epidemiology:
    • Subclinical reinfections are important in spreading disease
    • More than 70% of cattle in the UK have antibodies to BRSV
  • Diagnosis is same as for PI-3
  • Control
    • Improve husbansry as in PI-3
    • Vaccines are available but not effective as need to stimulate cytotoxic T-cells
  • Reference: Bryson, 1999, Update on calf pneumonia, CPD Veterinary Medicine, 1,3, 90-95




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