Difference between revisions of "Paramyxoviridae"

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===[[Canine Distemper Virus (CDV)]]===
 
===[[Canine Distemper Virus (CDV)]]===
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====Hosts====
 
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*Dogs, ferrets, seals, lions, mink
 
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*Has been a major pathogen of dogs prior to vaccination
 
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====Pathogenesis====
 
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*Variable mortality depending on virulence
 
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*May occur subclinically
 
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*Involvement of central nervous system generally results in death
 
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*Aerosol infection
 
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*Infects alveolar [[Macrophages - WikiBlood|macrophages]] or [[Oropharynx - Pathology|oropharynx]]
 
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*Multiplies in the bronchial and other lymph nodes, infects monocytes and dendritic cells
 
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*Viraemia
 
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*Spreads via monocytes to a variety of epithelium depending upon the strain of virus
 
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*[[Respiratory Viral Infections - Pathology#Canine distemper|Respiratory]] and alimentary tracts, skin and later (1-5 wk. post infection) to the brain
 
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*'''Clinical signs''':
 
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**Mucopurulent oculonasal discharge
 
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**Keratitis
 
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**[[Lungs Inflammatory - Pathology#Interstitial pneumonia|Interstitial pneumonia]]
 
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**Severe clinical pneumonia follows secondary infection with [[Bordetella bronchiseptica and Bordetella avium|''Bordetella bronchiseptica'']]
 
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**Smelly sometimes bloody diarrhoea
 
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**Eruptions on the skin including hyperkeratosis of the nose and pads (hardpad)
 
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**[[PNS Repsonses to Injury - Pathology#Segmental Demyelination|Demyelination]] (especially in cerebellum) -> incoordination or muscle tremors -> paralysis and coma or convulsions -> death
 
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**Encephalitis
 
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**Secondary pyogenic infections associated with immunosuppression and damage to epithelia
 
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**Recovered animals may have persistent or spasmodic chorea
 
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**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.
 
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====Diagnosis====
 
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*May present as series of infections
 
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*'''Immunocytochemistry''' of inclusion bodies
 
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**Intracytoplasmic inclusions may be found in most affected tissues
 
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**Inclusions persist longest in the brain (may be intranuclear) and the alveolar macrophages
 
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**Sections of fixed bronchial tissue, lung, macrophages, bladder may be used or nasal or conjunctival epithelium from live animals
 
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*Giant cells may be seen in the alveoli
 
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====Control====
 
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*Live attenuated virus vaccines given at 10 and 12 weeks of age
 
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**Some now given at 7 and 10 weeks to allow socialisation
 
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*Homeopathic vaccines do not work
 
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*Live attenuated vaccines may kill some wildlife therefore '''Iscom vaccine''' is used in seal sanctuaries
 
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====Secondary Concerns====
 
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*Can contribute to [[Respiratory Viral Infections - Pathology#In Dogs|Infectious canine tracheitis]]
 
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*May be involved in [[Pancreas Inflammatory - Pathology#Chronic interstitial pancreatitis|chronic interstitial pancreatitis]]
 
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*May cause [[Bones Developmental - Pathology#Retention of elongated primary trabeculae|growth retardation lattice]]
 
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*May also trigger latent [[Tissue cyst-forming coccidia|Toxoplasmosis]] due to suppressing effect on lymphoid tissue
 
  
 
==Bovine==
 
==Bovine==

Revision as of 18:42, 13 October 2008


 This article is still under construction.


Infectious agents and parasitesWikiBugs Banner.png
VIRUSES



Introduction

Morphology

  • Single-stranded negative-sense unsegmented RNA virus
  • Reassortment and antigenic shift cannot occur
  • Spike proteins include
    • HN (Haemagglutinin and Neuraminidase)
    • F (Fusion glycoprotein), which allows the virus to fuse directly to the plasma membrane and release its RNA
      • F also causes syncitium to form, which aids diagnosis
      • Host antibody response to the F protein is the basis for vaccination

Virulence

  • Paramyxoviruses replicate in the epithelium of the upper respiratory tract as well as occasionally in the gut
    • Sites of spike protein cleavage
  • Virulence varies by virus, see below

Types and Subtypes

Paramoyxoviridae was reclassified in 2000 to include 2 subfamilies and 5 genera:

Antigenic Variation

  • Antigenic conservation allows some cross protection by vaccination:
    • Conservation of major virus-specific F/HN antigens means vaccines protect against all isolates of the same virus
    • Minor morbillivirus-specific epitopes on F allows some cross protection between canine distemper, measles, and rinderpest
  • Antigenic "fingerprinting" is possible for some viruses based on minor variable epitopes of HN, F and NP on specific isolates as detected by monoclonal antibodies
    • These are detected by immunostaining infected cells

Paramyxoviridae by Species

Avian

Newcastle Disease Virus (NDV)

Canine

Canine Parainfluenza - 2 (aka Parainfluenza - 5)

Canine Distemper Virus (CDV)

Bovine

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 [Respiratory Viral Infections - Pathology#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

Equine

Hendra Virus

  • Equine Paramyxovirus
  • Causes respiratory infections with respiratory distress and paralysis
  • Potentially zoonotic (beware palpating inside the throat for obstruction)

Porcine

Nipah Virus

  • Infects pigs and humans
  • Humans exposed to pig blood are at risk

Reptiles

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

Rodentia

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

Other resources


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