Respiratory Viral Infections

()Map CARDIORESPIRATORY SYSTEM (Map) RESPIRATORY SYSTEM INFLAMMATION

In general

• Some viruses are thought to induce modifications of the pulmonary defences by:
  • Damaging the upper respiratory tract, thereby facilitating bacterial attachment and colonisation, with reduced mucociliary clearance
  • Decreasing surfactant levels by destroying Type 2 pneumonocytes
  • Impairing the phagocytic ability of alveolar macrophages

In Dogs

Canine Distemper Virus

Canine Parainfluenza - 2

Infectious canine tracheitis

Canine Adenovirus 1

Canine Adenovirus 2

Canine Herpesvirus 1

Canine Respiratory Coronavirus

In Cats

In Horses

Equine respiratory viruses Concept Map (Courtesy of B. Stanikova)

In Cattle

In Sheep

Parainfluenza -3

• As in cattle

In Goats

Caprine Arthrirtis Encephalitis Virus

In Pigs

Inclusion body rhinitis

Inclusion body rhinitis (Image sourced from Bristol Biomed Image Archive with permission)

• Herpesviridae, porcine cytomegalovirus
• Disease of suckling piglets 1-5 wks of age
• Clinical signs: those associated with acute/subacute rhinitis (ie: serous nasal discharge, progressing to catarrhal or purulent discharge with time and secondary bacterial infections; sneezing; pyrexia), fever in young piglets (3-8wks old)
• May progress to sinusitis, otitis media or pneumonia
• Morbitity high, mortality low
• Gross pathology - catarrhal discharge becoming purulent (secondary infection)
• Histology:
  • Large basophilic intranuclear inclusion bodies in the surface and subepithelium of nasal and sinus glandular epithelium with lymphocytic infiltration of the mucosa
  • Bursting of nucleus with cell necrosis and sloughing of necrotic epithelium
• Can develop viraemic stage, with inclusions and focal necrotising lesions in other organs eg: renal tubular epithelium
  • Usually younger piglets, can die during this phase
• Usually resolves if uncomplicated but rhinitis may persist if secondary infection is present
• May persist in pulmonary macrophages

Porcine reproductive and respiratory syndrome

• The syndrome is caused by a small enveloped RNA virus which belongs to the new Arteriviridae group
• Replicates in and destroys macrophages and endothelial cells causing vasculitis -> viraemia -> virus shedding (nasal secretions, faeces)
• Clinical signs: respiratory and reproductive failure, weaned pigs, tachypnoea, eyelid oedema, conjunctivitis
• Moderate to severe interstitial pneumonia in the cranial lobe
• Superimposed bacterial infections are common
• Infectious disease in swine that emerged 10 years ago
• Today, PRRS is endemic in many if not all the pig-producing countries

Postweaning multisystemic wasting syndrome (PMWS)

• Caused by a porcine circovirus alone or in combination with porcine parvovirus
• May cause mild interstitial pneumonia, failure of lungs to collpse on opening the thoracic cavity
• Microscopically: thickening of alveolar wall due to type 2 pneumocyte hyperplasia