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[[Central Nervous System Infectious Inflammation]]
 
[[Central Nervous System Infectious Inflammation]]
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==Routes of Entry==
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* CNS inflammation is usually the result of infection.
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** This may be caused by:
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*** Bacteria
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*** Fungi
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*** Protozoa
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*** Viruses
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* Organisms must first enter the CNS in order to establish infection.
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** There are several routes of entry that allow this:
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**# '''Haematogenous entry'''
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**#* This is the most common route.
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**# '''Entry via the peripheral nerves'''
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**#* Organisms track within the axoplasm of axons.
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**#* For example, ''Listeria monocytogenes''.
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**# '''Penetrating trauma'''
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**#* For example, dehorning wounds, skull fracture or tail docking.
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**# '''Direct spread of infection'''
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**#* From the nasal cavity, middle ear or paranasal sinuses.
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==Localisation of Infectious Organisms==
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* After entry, organisms may establish in one or more of four main areas:
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*# '''Epidural space'''
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*#* Infection tends to manifest as abscess formation.
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*# '''Subdural space'''
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*#* Manifests as abscess formation.
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*#* Fairly uncommon.
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*# '''Leptomeninges'''
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*#* Causes leptomeningitis, which may be:
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*#*# Suppurative
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*#*#* The most common form.
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*#*#* Neutrophils are the predominant cell type.
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*#*#* Caused by bacteria
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*#*#** E.g. ''E. coli'' and ''Streptococcus''
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*#*#* There are often no gross lesions, but the brain may appear swollen and the meninges opaque.
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*#*#* Usually results in death.
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*#*# Eosinophilic meningoencephalitis
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*#*#* The classic example of this is porcine salt poisoning, when water has been restricted and the suddenly replenished.
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*#*#* Perivascular eosinophilic cuffing is seen in the cerebrum and meninges.
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*#*# Lymphocytic
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*#*#* Usually of viral origin.
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*#*# Granulomatous
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*#*#* Caused by fungal diseases and Mycobacteriosis.
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*# '''CNS parenchyma'''
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==Bacterial Infections==
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[[Image:pneumococcalmeningitis.jpg|thumb|right|150px|Pneumococcal meningitis. Image courtesy of BioMed Archive]]
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* Bacterial infections typically result in abscesses.
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** These may be single or multiple depending on the route of entry, and vary in size.
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** They contain a central, liquefied cavity.
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* There are differences between cerebral abscesses and those occuring elsewhere.
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**  Encapsulation is slow.
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*** This is due to a lack of fibroblasts.
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*** There is therefore less collagen in the capsule.
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** Astrocytic glial fibers are not as strong as collagen
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* Other organisms may cause similar infections:
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** Rickettsial organisms
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*** E.g. ''Ehrlichia''
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** Spirochates
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*** E.g. Leptospirosis
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==Viral Infections==
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* Viral infections tend to reach the CNS by haematogenous spread and via peripheral nerves.
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* There are three hallmark lesions of CNS viral infections:
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*# Neuronal necrosis
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*# Gliosis
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*# Vascular changes
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* Several types of virus may cause inflammation in the CNS. [[Image:negribodies.jpg|thumb|right|150px|Negri bodies, as seen in rabies. Image courtesy of BioMed Archive]]
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** '''Neurotropic''', e.g.
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*** Rabies (rhabdovirus)
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*** Aujesky’s disease (herpesvirus)
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*** Visna (ovine lentivirus)
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** '''Endotheliotropic''', e.g.
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*** Infectious canine hepatitis (canine adenovirus)
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*** Classical swine fever (pestivirus)
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*** Equine herpesvirus type 1 (herpes)
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** '''Pantropic'''
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*** Infectious canine distemper (morbillivirus)
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*** Infectious bovine rhinotracheitis (bovine herpesvirus type 1)
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* Other examples of viruses affecting the CNS:
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** Distemper
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** Parvovirus
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** Parainfluenza
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** Herpes
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** FIP
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** FIV
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** FeLV
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** Pseudorabies
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** Rabies
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==[[Prion Disease]]==
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[[Category:Central Nervous System - Inflammatory Pathology]]
       
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