Infectious Diseases of the Nervous System

what is choroiditis?

inflammation of the choroid plexus

what is encephalitis?

inflammation of the brain

what is encephalomyelitis?

inflammation of the brain and spinal cord

what is ependymitis?

inflammation of the ependymal cells

what is gliosis?

proliferation of glial cells in response to injury

what is leptomeningitis?

inflammation of the meninges when it involves the pia-arachnoid

what is leukoencephalomalacia?

necrosis of white matter

what is malacia?

descriptive term indicating abnormal softness of brain tissue, commonly used to refer to areas of brain necrosis 

what is meningitis?

inflammation of the meninges

what is myelitis?

inflammation of the spinal cord

what is pachymeningitis?

inflammation of the meninges when it involves the dura

what is perivascular cuffing?

accumulation of inflammatory cells around blood vessels in the CNS

what is polioencephalomalacia?

necrosis of gray matter (aka laminar/cerebrocortical necrosis)

what is polyradiculoneuritis?

inflammation affecting multiple nerve roots 

what forms of “direct extension” can result in entry of diseases into the brain and spinal cord?

• penetrating trauma to the skull or vertebrae

• spreads from middle or inner ear infections

• extension from the nasal cavity or sinuses

• osteomyelitis affecting adjacent bone

how can diseases spread hematogenously to the brain or spinal cord?

• Capillary beds of the meninges, parenchyma, or choroid plexus

• Cerebrospinal fluid following vascular infiltration. 

how does “leukocyte trafficking” result in disease of the brain or spinal cord?

Some leukocytes carry pathogens into the CNS, facilitating infection (aka Trojan horse transit)

how does “retrograde axonal transport” result in disease of the brain/spinal cord?

pathogens move along neurons via retrograde axoplasmic flow, allowing direct nervous system invasion

what causes abscesses int he CNS?

pyogenic bacteria or fungal infections that spread hematogenously, through direct extension, trauma or iatrogenic injection

when do abscesses in the CNS commonly form?

in cattle, they may develop as a complication of dehorning wounds

what is neonatal bacterial suppurative meningitis?

certain bacteria can lead to bacteremia and suppurative meningitis in neonatal production animals; resulting in inflammation of the meninges

what gross lesions are seen with neonatal bacterial suppurative meningitis?

meningeal cloudiness or opacity, most prominently observed at the base of the brain

what bacteria can cause neonatal bacterial suppurative meningitis?

Streptococcus spp., E. coli, Salmonella spp., Pasteurella spp., Histophilus spp., and Glaesserella parasuis

what effect does septic embolism have on the CNS?

these often arise as complications of active endocarditis, leading to localized infection, inflammation and potential neurological dysfunction

what is the pathogenesis of listeric encephalitis in ruminants?

the bacteria invades through oral wounds or mucosa, travels along cranial nerves and localizes in the brainstem 

what is the pathogen that causes listeric encephalitis?

Listeria monocytogenes (gram positive, facultatively intracellular and anaerobic)

what other clinical forms might listeriosis present as?

abortion and stillbirths, enteritis, and septicemia with visceral abscesses

what is listeriosis also called and why?

circling diseases, as diseases animals tend to circle to one side

what bacterium causes infectious thrombotic meningoencephalitis?

Histophilus somni is a Gram-negative coccobacillus, considered part of the normal flora of the bovine genital tract and upper respiratory tract

what does H. somni cause in infected calves?

septicemia, which can result in acute death or a subacute or chronic disease course, manifesting as pneumonia, polyarthritis, myocarditis, meningoencephalitis, or abortion 

what morphological features are associated with infectious thrombotic meningoencephalitis?

multifocal areas of hemorrhage and necrosis in the CNS, most commonly affecting the cerebrum at the cortical grey-white matter interface

includes vasculitis and thrombosis 

what bacterium causes sporadic bovine encephalomyelitis (SBE)?

Chlamydia pecorum

what is SBE characterized by?

inflammation of the brain and spinal cord, often accompanied by polyserositis (encephalitis is secondary to vasculitis)

what group of animals can be diseased with SBE?

calves under 6 months of age

what neurologic manifestations are seen with FIP?

leptomeningitis, chorioependymitis, focal encephalomyelitis, and ophthalmitis; triggered by virus-antibody complexes within post-capillary venules that initiate a severe inflammatory reaction

how do encephalitic herpesviruses cause cell injury?

• Necrosis of infected neurons, glial cells, and/or endothelium

• Herpesvirus-induced apoptotic cell death

• Secondary effects of inflammation (cytokines and chemokines)

what causes bovine meningoencephalomyelitis?

Bovine herpesvirus 1 (BHV-1)

what lesions are associated with bovine meningoencephalomyelitis?

intranuclear herpetic inclusions may occasionally be present in affected neural tissues

primarily affecting young cattle

what causes canine herpesviral encephalitis?

Canine herpesvirus 1

how does canines herpesviral encephalitis manifest?

necrotizing polioencephalitis, with the most severe lesions occurring in the cerebellum and brainstem

rapidly fatal in puppies under 6 weeks old 

what causes equine herpesviral myeloencephalopathy?

EHV-1 reactivation in the endothelium of small blood vessels supplying the CNS

what lesions are associated with equine herpesviral myeloencephalopathy?

damage to endothelial cells, leading to vasculitis featuring multifocal petechial or ecchymotic haemorrhages in both white and grey matter of the brain and spinal cord

what clinical signs may be seen in a horse with equine herpesviral myeloencephalopathy?

rapidly progressing weakness, ataxia, paresis, urinary incontinence and cystitis 

what is malignant catarrhal fever caused by?

ovine herpesvirus type 2 (OHV-2)

how does malignant catarrhal fever manifest as CNS disease?

mononuclear vasculitis, most evident in the arteries of the rete mirabile surrounding the pituitary gland

what neurological effects does caprine arthritis encephalitis virus (CAEV) cause?

hindlimb lameness, head tilt, tremors, and ataxia, eventually leading to paresis and paralysis of all limbs.

The primary lesion associated with this infection is nonsuppurative leukoencephalomyelitis.

what impact does canine distemper virus have on the CNS?

the virus spreads to the brain and choroid plexus, infecting astrocytes and microglia, with primary demyelination thought to result from direct viral damage to oligodendrocytes.

what microscopic lesions are associated with canine distemper virus (CDV)?

multifocal necrotizing encephalitis with rare intranuclear or intracytoplasmic inclusion bodies

what causes Neosporosis? and which animals are most affected?

Neospora caninum, with young dogs infected in utero experiencing the most severe disease

what clinical signs are associated with neosporosis?

ataxia, head tilt, hindlimb paresis, and rigidity that ascends to progressive paralysis

what gross findings are associated with neosporosis?

foci of necrosis and hemorrhage in the central nervous system with vascular pattern

Histologically, lesions are characterized by a nonsuppurative encephalomyelitis and lymphohistiocytic and occasionally eosinophilic polyradiculoneuritis with secondary degeneration and necrosis in muscles or nerves.

what nervous system lesions are seen with toxoplasmosis in cats?

polyradiculoneuritis, resembling those seen in neosporosis 

what cestodes can cause CNS disease? and in which species?

Coenurus cerebralis can be found in the brains of sheep, less common in other herbivores and rare in horses

Cysticercus cellulosae in pigs (resulting in cysts in the meninges and brain in ~40% of pigs); same species has also been identified in the brains of dogs

what common fungal or algal infections cause CNS disease?

Aspergillus, Candida, Mucor, dematiaceous fungi, and the blue-green algae Prototheca spp

which fungi has the strongest affinity for the CNS?

Cryptococcus neoformans

what pathogens cause cryptococcosis and in which species?

Cryptococcus neoformans and Cryptococcus gattii, frequently affecting cats, dogs and horses 

what is the pathogenesis of cryptococcosis?

infection occurs via the cribriform plate, following nasal or sinus infections, or through leukocytic trafficking in cases of pulmonary infection

what lesions are present on the brain in animals with cryptococcosis?

multiple small “cysts”, characteristic of cryptococcal disease. The yeast cells are spherical, measuring 2-20 µm, and are surrounded by a non-staining capsule when viewed with hematoxylin and eosin (HE) staining

what pathogen cause encephalozoonosis and in which species?

Encephalitozoon cuniculi which primarily infects rabbits, but can also affect other mammals and birds

what nervous system lesions result from encephalozoonosis?

non-suppurative meningoencephalomyelitis; examination of the brain reveals granulomatous inflammation surrounded by moderate numbers of lymphocytes and plasma cells