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Respiratory Viral Infections (view source)

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==In general==
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*Some viruses are thought to induce modifications of the pulmonary defences by:
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**Damaging the upper respiratory tract, thereby facilitating bacterial attachment and colonisation, with reduced [[Respiratory System General Introduction - Pathology#Mucociliary escalator|mucociliary clearance]]
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**Decreasing surfactant levels by destroying Type 2 pneumonocytes
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**Impairing the phagocytic ability of alveolar macrophages
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==In Dogs==
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===Canine distemper===
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*Caused by a [[Paramyxoviridae#Canine Distemper Virus (CDV)|morbillivirus]]
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*[[Nasal cavity - inflammatory#Infectious causes of rhinitis|Rhinitis]]
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*Although many organs can be affected by CDV, a relatively constant feature is the respiratory signs which occur in varying severity
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*A syndrome of catharral oculonasal discharge, [[Nasopharynx - inflammatory#Infectious causes of pharyngitis|pharyngitis]] and [[Bronchi and bronchioles - inflammatory#Infectious causes of bronchitis or bronchiolitis|bronchitis]] is relatively common in the initial stages
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*Since one of the primary sites of action of this virus is lymphoid tissue, the resultant immunosuppression -> predisposition to secondary bacterial infection
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*May cause [[Lungs - inflammatory#Interstitial pneumonia|interstitial pneumonia]] where [[General Pathology - Degenerations and Infiltrations#Cellular Inclusions|inclusions]] are found within alveolar macrophages
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*Gross pathology:
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**Oedematous lungs, diffuse interstitial pneumonia
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*Micro pathology:
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**Necrosis of pneumocytes, necrotising bronchiolitis, alveolar oedema, thickening of alveolar walls and type II pneumocyte hyperplasia
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===Parainfluenza- 2===
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*Caused by an [[Paramyxoviridae|parainfluenza- 2 virus]]
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*[[Nasal cavity - inflammatory#Infectious causes of rhinitis|Rhinitis]], [[Trachea - inflammatory|tracheo]][[Bronchi and bronchioles - inflammatory#Infectious causes of bronchitis or bronchiolitis|bronchitis]]
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===Infectious canine tracheitis===
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*Synonyms: '''Kennel cough''', '''Infectious tracheobronchitis'''
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*[[Trachea - inflammatory#Infectious causes of tracheitis|tracheitis]], [[Bronchi and bronchioles - inflammatory#Infectious causes of bronchitis or bronchiolitis|bronchitis]]
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*Multiple agents implicated:
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**[[Adenoviridae|Canine adenovirus-2]]
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**[[Paramyxoviridae|Canine parainfluenza-2 virus]]
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**[[Paramyxoviridae#Canine Distemper Virus (CDV)|Canine distemper virus]]
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**[[Bordetella bronchiseptica and Bordetella avium|''Bordetella bronchoseptica'']]
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*Symptoms are of a persistent, non-productive cough
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*Persistent tracheobronchial inflammation
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*The outcomes is generally recovery (may persist >3 weeks), but extension to [[Bronchi and bronchioles - inflammatory|chronic bronchitis]] or cranioventral [[Lungs - inflammatory#Infectious causes of pneumonia|bronchopneumonia]] may occur
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*In severe cases can extend to serous/mucopurulent [[Nasal cavity - inflammatory#Rhinitis|rhinitis]]
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*Lesions are neither specific nor always significant (catarrhal / mucopurulent tracheobronchitis)
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*Enlarged tonsils and retropharyngeal lymph nodes
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===Canine adenovirus===
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[[Image:Adenovirus pneumonia.jpg|right|thumb|100px|<small><center>Adenovirus pneumonia (Image sourced from Bristol Biomed Image Archive with permission)</center></small>]]
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*[[Adenoviridae|Adenoviridae]]
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*Usually mild [[Lungs - inflammatory#Bronchointerstitial pneumonia|bronchointerstitial pneumonia]], necrosis of bronchiolar and alveolar epithelium, oedema, type II pneumocyte hyperplasia
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*May cause necrotising [[Bronchi and bronchioles - inflammatory#Infectious causes of bronchitis or bronchiolitis|bronchiolitis]] in immune-deficient dogs ([[Paramyxoviridae#Canine Distemper Virus (CDV)|distemper]])
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*Can be associated with [[Viral infections#Infectious canine tracheitis|kennel cough]] described above
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===Canine herpes virus===
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*Caused by [[Herpesviridae|canine herpes virus 1]]
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*Part of '''fading puppy syndrome'''
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*Presents with necrotising [[Nasal cavity - inflammatory#Infectious causes of rhinitis|rhino]][[Trachea - inflammatory#Infectious causes of tracheitis|tracheitis]] and secondary [[Lungs - inflammatory#Bronchopneumonia|bronchopneumonia]] in older dogs
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*Seems to be common subclinically
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===Canine respiratory coronavirus===
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*(CRCV)
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*Shown to be involved in an outbreak of disease in large kennels with rapidly changing population and high incidence of respiratory disease
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*Erles, K., Toomey, C. ''et al.''(2003) "Detection of a group 2 coronavirus in dogs with canine infectious respiratory disease." Virology '''310'''(2):216-223
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==In Cats==
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===Feline viral rhinotracheitis===
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*Caused by a [[Herpesviridae|herpesvirus]]
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*Tends to be more [[Nasal cavity - inflammatory#Infectious causes of rhinitis|rhinitis]] than [[Trachea - inflammatory#Infectious causes of tracheitis|tracheitis]], may extend to [[Paranasal sinuses - inflammatory#Infectious causes of sinusitis|sinusitis]]
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*Feline herpesvirus -1
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**One of the causes of Feline viral rhinotracheitis
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***Viruses and bacteria are involved in the complex. The most frequent aetiologic agent is [[Herpesviridae|FHV-1]], and less frequently [[Caliciviridae|feline calicivirus]] and/or [[Chlamydia and Chlamydophila species|''Chlamydophila psittaci'']] (NB: previously called ''Chlamydia psittaci'' var felis)
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*All three agents infect URT respiratory epithelium, although FHV-1 has the highest affinity for this epithelium
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*Feline calicivirus more frequently infects the oral mucosa -> ulcerative stomatitis
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*''C.psittaci'' more frequently infects the conjunctival epithelium -> chronic conjunctivitis
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*Infection of the respiratory epithelium by FHV-1 results in a typical neutrophilic rhinitis with intraepitheial intranuclear eosinophilic [[General Pathology - Degenerations and Infiltrations#Cellular Inclusions|inclusion bodies]]
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*Uncomplicated cases resolve in 2-3 weeks
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*FHV-1 remains latent in the trigeminal ganglion, and can reactivate at times of stress
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*Can infect the cornea -> ulcerative keratitis
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*Mortality may be high in young kittens, debilitated and immune-suppressed animals, usually associated with secondary bacterial infection.
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===Feline calicivirus===
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*Causative agent: [[Caliciviridae|feline calicivirus]]
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*[[Nasal cavity - inflammatory#Infectious causes of rhinitis|Rhinitis]],
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*Suggested in the presence of ulceration of the dorsal and lateral edges of the [[Oral Cavity - Tongue - Anatomy & Physiology|tongue]], hard palate and external nares
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*Lesions present may include [[Lungs - inflammatory#Interstitial pneumonia|interstitial pneumonia]] with necrotising [[Bronchi and bronchioles#Infectious causes of bronchitis or bronchiolitis|bronchiolitis]]
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*Also see Feline viral rhinotracheitis above
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==In Horses==
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[[Image:Equine respiratory viruses concept map.jpg|right|thumb|100px|<small><center>Equine respiratory viruses Concept Map (Courtesy of B. Stanikova)</center></small>]]
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===Equine rhinovirus===
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*Causative agent: [[Picornaviridae|equine rhinovirus]]
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*[[Nasal cavity - inflammatory|Rhinitis]]
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*Most common in young horses
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*May cause acute upper respiratory disease
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===Equine influenza===
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*Causative agent: [[Orthomyxoviridae|equine influenza virus (Orthomyxovirus)]]
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*[[Nasal cavity - inflammatory#Infectious causes of rhinitis|Rhinitis]],
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*Pathogenesis:
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**Inhalation -> replication in epithelial cells of upper and lower airways (attaches  via haemaglutinin spike and gains entry into cell) -> neuramidase alters efficiency of [[Respiratory System General Introduction - Pathology#Mucociliary escalator|mucociliary apparatus]]
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*Sloughing of the affected area
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*Severity of signs will depend on dose of virus
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*Acute [[Trachea - inflammatory#Infectious causes of tracheitis|tracheo]][[Bronchi and bronchioles - inflammatory#Infectious causes of bronchitis or bronchiolitis|bronchitis]] with coughing, and fever
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*May be accompanied by secondary bacterial infections
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*No viraemia
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*In severe cases may cause [[Lungs - inflammatory#Bronchointerstitial pneumonia|bronchointerstitial pneumonia]]
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*Secondary invaders are usually [[Streptococci|''Streptococci'']]
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===Equine rhinopneumonitis ===
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*Causative agent: [[Herpesviridae|equine herpesvirus type 1 and type 4]]
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*Primary viral lesions in [[Nasal cavity - inflammatory|nasal mucosa]] and [[Lungs - inflammatory#Infectious causes of pneumonia|lungs]]
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*Mild, transient [[Lungs - inflammatory#Bronchointerstitial pneumonia|bronchointerstitial pneumonia]]
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*Latent infection acting as a reservoir
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*Sites of latency: bronchial lymph nodes and trigeminal ganglia
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*Replicates in upper respiratory tract epithelium
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*Disseminated to lower respiratory tract
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*Transported to other organs in T-lymphocytes - viraemia up to 3 weeks
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*Vasculitis, abortion
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*May be accompanied by secondary bacterial infection
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===Equine viral arteritis (EVA)===
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*Causative agent: [[Arteriviridae|equine arterivirus]]
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*[[Nasal cavity - inflammatory|Rhinitis]], peripheral oedema, [[Bronchi and bronchioles - inflammatory|bronchitis/bronchiolitis]], conjunctivitis, periorbital oedema
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*Replicates in macrophages and endothelial cells
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*Disseminates via the circulatory system causing necrotising arteritis
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*[[Lungs - inflammatory#Interstitial pneumonia|Interstitial pneumonia]]
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*Transmitted by respiratory and venereal routes through direct contact with infected horse or its secretions
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*Stallion are a reservoir of infection as they are chronic shedders
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===Equine adenovirus===
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[[Image:Adenovirus in equine lung.jpg|right|thumb|100px|<small><center>Adenovirus in equine lung (Image sourced from Bristol Biomed Image Archive with permission)</center></small>]]
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*[[Adenoviridae|Adenoviridae]]
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*May cause necrotising [[Bronchi and bronchioles - inflammatory#Infectious causes of bronchitis or bronchiolitis|bronchiolitis]] in immune-deficient foals (Arabian foals)
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*Grossly:
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**[[Lungs - ventilation#Atelectasis (Collapse)|Atelectasis]] and consolidation of lobules in cranioventral region
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**Mucopurulent exudate in airways
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*Histologically:
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**Severe bronchiolitis, necrotising -> proliferative
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**Bronchiolar obstruction by sloughed debri and neutrophils -> alveolar atelectasis
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*May lead to secondary bacterial infections
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===African horse sickness===
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[[Image:Lung oedema in African horse sickness.jpg|right|thumb|100px|<small><center>Lung oedema in African horse sickness (Image sourced from Bristol Biomed Image Archive with permission)</center></small>]]
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*Caused by [[Reoviridae|orbivirus]], family reoviridae
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*Respiratory distress or cardiovascular failure
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*Rapid death due to massive [[Lungs - circulatory#Pulmonary oedema|pulmonary oedema]]
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*[[Pleural cavity and membranes - degenerative#Hydrothorax|Hydrothorax]] may also develop
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*Large amounts of froth present in airways
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===Hendra virus===
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*Causative agent [[Paramyxoviridae|equine morbillivirus]]
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*Oedematous lungs with distention of [[Pleural cavity and membranes - inflammatory|pleura]]
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*Micro: diffuse [[Lungs - circulatory#Pulmonary oedema|alveolar oedema]], syncytial cells
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==In Cattle==
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===Infectious bovine rhinotracheitis (IBR)===
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[[Image:IBR nasal cavity.jpg|right|thumb|100px|<small><center>IBR in nasal cavity (Image sourced from Bristol Biomed Image Archive with permission)</center></small>]]
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[[Image:IBR trachea.jpg|right|thumb|100px|<small><center>IBR in trachea (Image sourced from Bristol Biomed Image Archive with permission)</center></small>]]
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*Causative agent is [[Herpesviridae|'''bovine herpesvirus, type 1''']]
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*URT infection with serous nasal discharge, increases respiratory rate, coughing and moderate fever,from nasal mucosa down to bronchioles
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*[[Nasal cavity - inflammatory|Rhinitis]], [[Nasopharynx - inflammatory#Infectious causes of pharyngitis|pharyngitis]], [[Larynx - inflammatory|laryngitis]], [[Trachea - inflammatory|tracheitis]], [[Bronchi and bronchioles - inflammatory|bronchiolitis]]
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*Morbidity is high, mortality is low
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*Highly infectious URT disease of cattle
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*Spread by movement of animals, aerosol transmission - requires close contact between animals
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*Early stages (only first few days) may show [[General Pathology - Degenerations and Infiltrations#Cellular Inclusions|intracellular inclusions]] in the respiratory mucosal epithelial cells
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*Leading to neutrophilic inflammation of varying severity.... serous -> catarrhal -> purulent
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*With secondary bacterial infection (eg: [[Pasteurella species and Mannheimia haemolytica|Pasturella spp.]], [[Mycoplasmas|Mycoplasma spp.]], [[Fusobacterium|Fusobacterium necrophorum]]) can lead to fibrinous to necrotizing inflammation; mucosal sloughing, ulceration... pyrexia, dyspnoea ... [[Lungs - inflammatory#Aspiration pneumonia|inhalation pneumonia]]... death
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*Underlying hyperaemic inflammatory response
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*Can become latent following primary infection
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*Clinical signs:nasal discharge, sneezing, coughing, lacrimation, and increased respiratory rate
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*Clinical disease most severe in young calves - can develop mucosal ulcerative lesions in the [[Oesophagus#Erosive & Ulcerative Pathology|oesophagus]] and forestomachs and viraemia with multiorgan infection
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*Cause of abortion >5 months of gestation
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*May contribute to [[Bacterial infections#Enzootic pneumonia of calves|Enzootic pneumonia of calves]]
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===Parainfluenza- 3===
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*Causative agent: [[Paramyxoviridae#Bovine Parainfluenza - 3 (PI-3)|parainfluenza- 3 virus]] (PI3)
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*On its own causes [[Nasal cavity - inflammatory#Infectious causes of rhinitis|rhinitis]]
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*Often part of multi-aetiology disease complex (e.g. [[Bacterial infections#Enzootic pneumonia of calves|Enzootic pneumonia of calves]]), often followed by [[Pasteurella species and Mannheimia haemolytica|''Pasteurella sp.'']] obscuring viral origin
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*Replicates in airway epithelial cells and results in an initial [[Bronchi and bronchioles - inflammatory#Infectious causes of bronchitis or bronchiolitis|bronchitis -> bronchiolitis]] -> extension into [[Lungs - inflammatory#Infectious causes of pneumonia|alveoli]], causing [[Lungs - inflammatory#Bronchointerstitial pneumonia|bronchointerstitial pneumonia]]
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*Early stages may show [[General Pathology - Degenerations and Infiltrations#Cellular Inclusions|intracytoplasmic inclusions]]
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*The resulting exudate is predominantly neutrophilic
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*Positive confirmation lies in a Fluorescent Antibody Test (FAT) to the specific virus on frozen sections of tissue
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===Bovine adenovirus===
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*Causative agent: [[Adenoviridae|bovine adenovirus]]
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*[[Nasal cavity - inflammatory#Infectious causes of rhinitis|Rhinitis]]
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*May contribute to [[Bacterial infections#Enzootic pneumonia of calves|Enzootic pneumonia of calves]]
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===Respiratory syncytial virus===
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*Causative agent [[Paramyxoviridae|Respiratory syncytial virus (RSV)]], synonym: bovine RSV (BRSV)
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*Outbreaks of RSV associated disease usually occur associated with winter housing
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*Gross pathology in severe cases
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**Cranioventral [[Lungs - ventilation#Atelectasis (Collapse)|atelectasis]] and consolidation
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**[[Lungs - ventilation#Emphysema|Interstitial emphysema]]
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***More prominent in the caudal lung lobes
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***Results from bronchoconstriction which results in airway obstruction - this constriction is thought to arise from [[Mast cells - Anatomy & Physiology|mast cell]] degranulation and histamine release
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*Histologically
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**[[Bronchi and bronchioles - inflammatory#Acute bronchitis/bronchiolitis|Acute bronchiolitis]], characteristic of the bronchiolar response is the formation of syncytial giant cells  (formed by proliferating bronchiolar epithelial cells which may contain [[General Pathology - Degenerations and Infiltrations#Cellular Inclusions|intracytoplasmic inclusion bodies]]), alveolar epithelium sometimes affected
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**Obstruction of bronchioles by exudate - these may later become obliterated by the fibrous tissue of organisation
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*May contribute to [[Bacterial infections#Enzootic pneumonia of calves|Enzootic pneumonia of calves]]
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===Bovine rhinovirus===
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*Causative agent: [[Picornaviridae|bovine rhinovirus]]
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*May cause mild respiratory disease
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==In Sheep==
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===Maedi Visna===
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*Caused by a [[Retroviridae|retrovirus]]
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*The respiratory from of the disease caused by maedi-visna virus (Maedi) is also called '''lymphoid interstitial pneumonia'''
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*Transmitted by close contact and via milk
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*The pulmonary lesions develop very slowly hence this disease is uncommon in sheep < 2 years old
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*Increased respiratory rate upon exertion, loss of weight
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*Remains in monocytes and macrophages
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*Gross findings
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**Severe [[Lungs - inflammatory#Interstitial pneumonia|interstitial pneumonia]]
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**Lungs fail to collapse properly on opening the chest and can weigh more than twice the normal weight
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**Impressions of the ribs remain on the visceral pleura
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**Lungs are a mottled grey/ tan colour - the lesions can vary from irregular grey speckling to homogeneous grey consolidation
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**Rubbery in consistence
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**Diaphragmatic lobes most affected
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**Associated bronchial and mediastinal lymph nodes are often enlarged
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*Histologically
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**Major features are extensive lymphoid proliferation around perivascular, peribronchial and peribronchiolar sheaths associated with pulmonary lymphatics
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**Many of these areas contain germinal centres and smooth muscle hyperplasia (in walls of terminal bronchioles and alveoli)
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===Parainfluenza -3===
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*As in [[Viral infections#Parainfluenza- 3|cattle]]
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===Pulmonary adenomatosis===
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*See [[Lungs - hyperplastic and neoplastic#Sheep pulmonary adenomatosis (SPA/ Jaagsiekte)|neoplasia]]
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==In Goats==
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===Caprine Arthritis-Encephalitis (CAE)===
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*Caused by [[Retroviridae|retrovirus (lentivirus)]] similar to [[Viral infections#Maedi Visna|Maedi Visna]] in sheep described above
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*Two forms:
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**Non-suppurative leukoencephalomyelitis in young goats and kids
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**Chronic, non-suppurative arthritis-synovitis in adult goats
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*Also causes [[Lungs - inflammatory#Interstitial pneumonia|interstitial pneumonia]] which tends to be obscured by other clinical signs
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*Gross pathology:
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**Mainly caudal lobes
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**Lungs are firm, grey-pink with grey-white focal lesions on cut surface
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*Micro pathology:
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**Thickened alveolar wall
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**Lymphocyte infiltration and type II pneumocyte hyperplasia
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*Can be confused with or coexisting with [[Lungs - inflammatory#Verminous pneumonia|Parasitic pneumonia]]
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==In Pigs==
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===Inclusion body rhinitis===
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[[Image:Inclusion body rhinitis.jpg|right|thumb|100px|<small><center>Inclusion body rhinitis (Image sourced from Bristol Biomed Image Archive with permission)</center></small>]]
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*[[Herpesviridae|'''Herpesviridae, porcine cytomegalovirus''']]
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*Disease of suckling piglets 1-5 wks of age
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*Clinical signs: those associated with acute/subacute [[Nasal cavity - inflammatory#Infectious causes of rhinitis|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)
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*May progress to [[Paranasal sinuses - inflammatory#Sinusitis|sinusitis]], otitis media or [[Lungs - inflammatory#Infectious causes of pneumonia|pneumonia]]
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*Morbitity high, mortality low
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*Gross pathology - catarrhal discharge becoming purulent (secondary infection)
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*Histology:
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**Large basophilic [[General Pathology - Degenerations and Infiltrations#Cellular Inclusions|intranuclear inclusion bodies]] in the surface and subepithelium of nasal and sinus glandular epithelium with lymphocytic infiltration of the mucosa
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**Bursting of nucleus with cell necrosis and sloughing of necrotic epithelium
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*Can develop viraemic stage, with inclusions and focal necrotising lesions in other organs eg: renal tubular epithelium
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**Usually younger piglets, can die during this phase
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*Usually resolves if uncomplicated but rhinitis may persist if secondary infection is present
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*May persist in pulmonary macrophages
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===Swine influenza===
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*Caused by [[Orthomyxoviridae|Swine influenza virus]]
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*[[Nasal cavity - inflammatory|Rhinitis]], may progress to [[Lungs - inflammatory#Infectious causes of pneumonia|pneumonia]]
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*Clinical signs: pyrexia, lethargy, skin erythema, anorexia, severe cough and sneezing, dyspnoea, conjunctivitis, pregnant sows may abort
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*Grossly:
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**[[Trachea - inflammatory|Tracheo]][[Bronchi and bronchioles - inflammatory#Infectious causes of bronchitis or bronchiolitis|bronchitis]], airway obstruction -> [[Lungs - ventilation#Atelectasis (Collapse)|atelectasis]]
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**[[Pleural cavity and membranes - inflammatory|Pleura]] normal or covered with serous or serofibrinous exudate
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**[[Pleural cavity and membranes - inflammatory|Pleural cavity]] filled with excess fluid
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**Lung lesions
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***Clear demarcation of lesions in cranial and middle lobes
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***[[Lungs - inflammatory#Interstitial pneumonia|Interstitial pneumonia]]
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*Histologically:
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**Acute inflammation of mucosa of trachea and bronchi
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*Zoonotic
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*Circumstantial evidence of mutation from human strain
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*Migrating [[Parasitic infections#Ascaris suum|ascarids]] thought to precipitate the disease, reservoir of infection in earthworms containing infected lungworm larvae
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===Porcine reproductive and respiratory syndrome===
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*The syndrome is caused by a small enveloped RNA virus which belongs to the new [[Arteriviridae|Arteriviridae]] group
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*Replicates in and destroys macrophages and endothelial cells causing vasculitis -> viraemia -> virus shedding (nasal secretions, faeces)
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*Clinical signs: respiratory and reproductive failure, weaned pigs, tachypnoea, eyelid oedema, conjunctivitis
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*Moderate to severe interstitial [[Lungs - inflammatory#Infectious causes of pneumonia|pneumonia]] in the cranial lobe
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*Superimposed bacterial infections are common
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*Infectious disease in swine that emerged 10 years ago
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*Today, PRRS is endemic in many if not all the pig-producing countries
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===Postweaning multisystemic wasting syndrome (PMWS)===
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*Caused by a [[Circoviridae|porcine circovirus]] alone or in combination with [[Parvoviridae|porcine parvovirus]]
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*May cause mild [[Lungs - inflammatory#Interstitial pneumonia|interstitial pneumonia]], failure of lungs to collpse on opening the thoracic cavity
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*Microscopically: thickening of alveolar wall due to type 2 pneumocyte hyperplasia
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===Porcine respiratory coronavirus (PRCV)===
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*Caused by a [[Coronaviridae|coronavirus]]
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*Usually mild [[Lungs - inflammatory#Infectious causes of pneumonia|pneumonia]] unless complicated by other agents
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*Virus replicates in epithelial lining of airways
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