Infections of the Nervous System

=Objectives=

List the most common bacteria causing meningitis in different age groups

 * Neonates
 * gram negatives (E. Coli)30+%, strep B 30+%, listeria 10%, staph 5%


 * unvaccinated children
 * H influenza 40+%, Meningicoccal 25+%, S. pneumonia 10+%


 * adults
 * S. pneumonia 30+%, meningicoccal 20+%, staph, gram negatives, listeria

Relate the route of CNS entry to the type infection

 * 1) Hematogenous:
 * 2) *Retrograde venous spread can occur through veins in the face, eventually spreading to the cavernous sinus
 * 3) *source for meningitis, brain abscess, neurosyphillis
 * 4) Direct implantation: traumatic or iatrogenic (surgery)
 * 5) *Associated with brain abscess
 * 6) Local Extension: secondary to sinus infection, osteomyelitis, mastoiditis, infected tooth, etc
 * 7) * Associated with brain abscess, subdural empyema
 * 8) Spread through peripheral nervous system
 * 9) *Viral meningoencephalitis (herpes), rabies,

Describe lumbar puncture (LP) findings in meningitis

 * bacterial/pyogenic
 * cloudy CSF, increased pressure, marked neutrophils, markedly raised protein, markedly reduced glucose


 * viral
 * clear CSF, ~ normal pressure, lymphocytic pleocytosis, slightly elevated protein, normal glucose


 * fungal (cryptococcus)
 * clear CSF, increased pressure, india-ink positive encapsulated yeasts, markedly elevated protein

Describe the anatomical patterns associated with viruses

 * Herpes, type 1: inferior and medial regions of the frontal and temporal lobes. may be unilateral.
 * Herpes, type 2: meningitis or hemorrhagic necrotizing panencephalitis (AIDS).
 * CMV: periventricular necrosis
 * Rabies: midbrain, floor of 4th ventricle, basal ganglia, dorsal root ganglions
 * Measles:
 * acute measles encephalitis: diffuse encephalitis
 * post infection leukoencephalitis: white matter tracts, perivascular
 * subacute sclerosing panencephalitis
 * West nile virus: infects substantia nigra, diffuse symptoms
 * JC virus: white matter tracts, demyelination

Describe the pathology of subactue progressive encephalitis

 * PML (progressive multifocal leukoencephalopathy): Only associated with acquired immunodeficiency. This virus preferentially infects oligodendrocytes resulting in demyelination.  The oligodendrocytes contain intranuclear inclusions.
 * SSPE: (subacute sclerosing pan-encephalitis): progressive syndrome of progressive cognitive decline, spasticity, and seizures. Associated with microscopic gliosis, demyelination, neurofibrillary tangles, and neurodegeneration.  Typically occurs in children who had measles as infants.

Describe the patterns of fungal infections in the CNS

 * 1) granulomatous meningitis
 * 2) *example: histoplasmosis
 * 3) hematogenous abscess
 * ex: candida, cryptococcus
 * 1) vasculitis
 * ex: aspergillosis, zygomycetes
 * 1) subacute/indolent meningitis
 * 2) * ex: cryptococcus

Toxoplasmosis gondii

 * [[File:Toxoplasma_LifeCycle_BAM1.gif]]


 * The only known definitive hosts for Toxoplasma gondii are members of family Felidae (domestic cats and their relatives). Unsporulated oocysts are shed in the cat’s feces  .  Although oocysts are usually only shed for 1-2 weeks, large numbers may be shed.  Oocysts take 1-5 days to sporulate in the environment and become infective.  Intermediate hosts in nature (including birds and rodents) become infected after ingesting soil, water or plant material contaminated with oocysts  .  Oocysts transform into tachyzoites shortly after ingestion.  These tachyzoites localize in neural and muscle tissue and develop into tissue cyst bradyzoites  .  Cats become infected after consuming intermediate hosts harboring tissue cysts  .  Cats may also become infected directly by ingestion of sporulated oocysts.  Animals bred for human consumption and wild game may also become infected with tissue cysts after ingestion of sporulated oocysts in the environment  .  Humans can become infected by any of several routes:

eating undercooked meat of animals harboring tissue cysts. consuming food or water contaminated with cat feces or by contaminated environmental samples (such as fecal-contaminated soil or changing the litter box of a pet cat). blood transfusion or organ transplantation. transplacentally from mother to fetus.

Taenia solium

 * [[File:Cysticercosis.gif]]
 * This infection is caused by ingestion of eggs shed in the feces of a human tapeworm carrier .  Pigs and humans become infected by ingesting eggs or gravid proglottids ,  .  Humans are infected either by ingestion of food contaminated with feces, or by autoinfection.  In the latter case, a human infected with adult T. solium can ingest eggs produced by that tapeworm, either through fecal contamination or, possibly, from proglottids carried into the stomach by reverse peristalsis.  Once eggs are ingested, oncospheres hatch in the intestine  ,   invade the intestinal wall, and migrate to striated muscles, as well as the brain, liver, and other tissues, where they develop into  cysticerci  .  In humans, cysts can cause serious sequellae if they localize in the brain, resulting in neurocysticercosis.  The parasite life cycle is completed, resulting in human tapeworm infection, when humans ingest undercooked pork containing cysticerci  .  Cysts evaginate and attach to the small intestine by their scolex  .  Adult tapeworms develop, (up to 2 to 7 m in length and produce less than 1000 proglottids, each with approximately 50,000 eggs) and reside in the small intestine for years.

=References= =Links=
 * Video of Hyatid cyst