Neurotropic Agents Flashcards
List the 5 viruses discussed
- HSV encephalitis
- Rabies virus
- West Nile virus
- Enteroviruses
- Spongiform encephalopathies
Define encephalitis, meningitis and aseptic meningitis.
- encephalitis: infection of brain parenchyma
- meningitis:infection of meninges
- aseptic meningitis: viral infection of meninges
Define myelitis, encephalomyelitis, and meningoencephalitis
myelitis: infection of spinal cord
encephalomyelitis: infection of brain and spinal cord
meningoencephalitis: infection of brain and meninges
Neurotropism and neurovirulence
- NT: ability of an infectious agent to infect cells of the nervous system
- NV: potential to cause disease once within the nervous system
Blood-brain barrier is due to meninges and the endothelial cells extremely tight junctions. Give 4 impacts of this barrier.
- barrier to entry of infectious agents
- barrier to protective components of the immune response like antibodies, complement, inflammatory cells
- barrier to penetration of antimicrobial drugs
- restrictive nature of intracranial and intravertebral spaces leading to increase in pressure during swelling and inflammation
2 ways to gain entry into the CNS
- hematogenous route: infect endothelial cells, enter at choroid plexus due to no tight junctions, migration of infected inflammatory cells
- neural route: anterograde movement in axons from site of infection; olfactory nerve endings which is only CNS in direct contact with environment
Clinical signs of encephalitis
- acute onset of febrile illness with headache and altered mental status
- KEY: early mental status changes, can be focal or diffuse
- more commonly due to viruses
- behavioral or speech problems, neurological signs, seizures
Most common causes of sporadic and epidemic encephalitis
- sporadic: HSV
- epidemic: WNV
Differences in symptoms between encephalitis and meningitis
-encephalitis is less likely to have fever, more likely to have personality/behavior changes
Meningitis clinical signs
- classic triad: fever, headache (severe, frontal, photophobia), neck stiffness
- can have altered mental status
- symptoms usually appear rapidly and may include nausea and vomiting
3 signs to test for meningitis
- Jolt accentuation: tear head rapidly, does HA increase?
- Kernig sign: one leg with hip flexed, pain in back with extension of knee
- Brudzinski sign: flexion of legs and thighs when neck is flexed
* *idea is to stretch the meninges, and if meningitis is present, there will be inflammation around the nerve roots and this causes pain upon stretching. Specific, not sensitive
Aseptic meningitis: what is it? most common viruses causing it?
- inflammation of meninges without involvement of the brain due to a viral infection
- enteroviruses (echo and coxsackie), HSV-2, Mumps (rarely)
- usually self-limited unless parenchyma becomes involved and it turns into meningoencephalitis
What can be used to identify what virus is responsible for meningitis?
-PCR from CSF
Compare CSF cell type, protein levels, glucose levels, gram stain, and pressure between bacterial vs. viral meningitis
- bacterial: PMNs, increased protein, decreased glucose, 60% gram stain +, increases pressure
- viral: lymphocytes, normal protein levels, normal to slight decrease in glucose, negative gram stain, normal pressure
How does one treat HSV encephalitis?
- acyclovir immediately, IV, for 14-21 days
- detect viral DNA in CSF
HSV encephalitis: how will it look on an MRI?
-fronto-temporal lesions
Rabies virus: family and structure. What animals to be aware of in US.
- rhabovirus
- negative-stranded RNA
- enveloped
- NON-segmented
- raccoons> skunks> bats> foxes
T/F: almost any mammal can be infected with rabies.
-true
What is the most common vector for human rabies? Why does this cause many cases to miss preventative immunization?
- bats in US, dogs in other countries
- exposure was not recognized because the bat bite was too small or because there was no bite at all
2 types of rabies virus spread
- centripetal: from muscle, through nerve, to CNS; site of inoculation influences time to symptoms
- centrifugal: from CNS to cornea and salivary glands (sets up for transmission)
What do we expect to see in rabies-infected neurons in CNS?
-negri bodies and lymphocyte infiltration