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Microbiology: A Systems Approach, 2 nd ed. Chapter 19: Infectious Diseases Affecting the Nervous System. 19.1 The Nervous System and Its Defenses. Two component parts to the nervous system CNS PNS Three important functions Sensory Integrative Motor

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Microbiology a systems approach 2 nd ed

Microbiology: A Systems Approach, 2nd ed.

Chapter 19: Infectious Diseases Affecting the Nervous System


19 1 the nervous system and its defenses
19.1 The Nervous System and Its Defenses

  • Two component parts to the nervous system

    • CNS

    • PNS

  • Three important functions

    • Sensory

    • Integrative

    • Motor

  • Brain and spinal cord: made up of neurons, both surrounded by bone, encased with meninges

  • PNS: cranial and spinal nerves


Defenses of the nervous system
Defenses of the Nervous System

  • Mainly structural

  • Bony casings

  • Cushion of CSF

  • Blood-brain barrier

  • Immunologically privileged site




19 2 normal biota of the nervous system
19.2 Normal Biota of the Nervous System

  • No normal biota

  • Any microorganisms in the PNS or CNS is a deviation from the healthy state


19 3 nervous system diseases caused by microorganisms
19.3 Nervous System Diseases Caused by Microorganisms

  • Inflammation of the meninges

  • Many different microorganisms can cause an infection

  • More serious forms caused by bacteria

  • If it is suspected, lumbar puncture is performed to obtain CSF

  • Typical symptoms: headache, painful or stiff neck, fever, and usually an increased number of white blood cells in the CSF


Neisseria meningitides
Neisseria meningitides

  • Gram-negative diplococcic lined up side by side

  • Commonly known as meningococcus

  • Often associated with epidemic forms of meningitis

  • Causes the most serious form of acute meningitis





Streptococcus pneumonia
Streptococcus pneumonia

  • Referred to as the pneumococcus

  • Most frequent cause of community-acquired meningitis

  • Very severe

  • Does not cause the petechiae associated with meningococcal meningitis- useful diagnostically

  • Small gram-positive flattened coccus that appears in end-to-end pairs


Haemophilus influenza
Haemophilus influenza

  • Tiny gram-negative pleomorphic rods

  • Sensitive to drying, temperature extremes, and disinfectants

  • Causes severe meningitis

  • Symptoms: fever, stiff neck, vomiting, and neurological impairment


Listeria monocytogenes
Listeria monocytogenes

  • Gram-positive

  • Ranges in morphology from coccobacilli to long filaments in palisades formation

  • Resistant to cold, heat, salt, pH extremes, and bile

  • In normal adults- mild infection with nonspecific symptoms of fever, diarrhea, and sore throat

  • In elderly or immunocompromised patients, fetuses, or neonates- affects the brain and meninges and results in septicemia



Cryptococcus neoformans
Cryptococcus neoformans

  • Fungus

  • More chronic form of meningitis

  • More gradual onset of symptoms

  • Sometime classified as a meningoencephalitis

  • Headache- most common symptom; also nausea and stiff neck

  • Spherical to ovoid shape and a large capsule




Coccidioides immitis
Coccidioides immitis

  • At 25°C forms a moist white to brown colony with abundant, branching, septate hyphae

  • Hyphae fragment into arthroconidia at maturity

  • Usually begins with pulmonary infection




Viruses
Viruses

  • Aseptic meningitis

  • Majority of cases occur in children

  • 90% caused by enteroviruses

  • Generally milder than bacterial or fungal meningitis


Neonatal meningitis
Neonatal Meningitis

  • Almost always a result of infection transmitted by the mother, either in utero or during passage through the birth canal

  • Two most common causes

    • Streptococcus agalactiae

      • Group B strep

    • Escherichia coli


Meningoencephalitis
Meningoencephalitis

  • Encephalitis: inflammation of the brain

  • Two microorganisms cause meningoencephalitis (both amoebas)

    • Naegleria fowleri

    • Acanthamoeba


Naegleria fowleri
Naegleria fowleri

  • Small, flask-shaped amoeba

  • Forms a rounded, thick-walled, uninucleate cyst

  • Infection begins when amoebas are forced into human nasal passages as a result of swimming, diving, or other aquatic activities

  • Amoeba burrows in to the nasal mucosa, multiplies, and migrates into the brain and surrounding structure

  • Primary amoebic meningoencephalitis (PAM)



Acanthamoeba
Acanthamoeba

  • Large, amoeboid trophozoite with spiny pseudopods and a double-walled cyst

  • Invades broken skin, the conjunctiva, and occasionally the lungs and urogenital epithelia

  • Granulomatous amoebic meningoencephalitis (GAM)


Acute encephalitis
Acute Encephalitis

  • Encephalitis can present as acute or subacute

  • Always a serious condition

  • Acute: almost always caused by viral infection

  • Signs and symptoms vary but may include behavior changes, confusion, decreased consciousness, seizures


Arborviruses
Arborviruses

  • Borne by insects; most feed on the blood of hosts

  • Common outcome: acute fever, often accompanied by rash


Western equine encephalitis wee
Western Equine Encephalitis (WEE)

  • Appears first in horses then in humans

  • Carried by mosquito

  • Extremely dangerous to infants and small children


Eastern equine encephalitis eee
Eastern Equine Encephalitis (EEE)

  • Eastern coast of North American and Canada

  • Usually appears first in horses and caged birds

  • Very high case fatality rate


California encephalitis
California Encephalitis

  • May be caused by two different viral strains: California strain and the LaCrosse strain

  • Children living in rural areas: primary target group


St louis encephalitis sle
St. Louis Encephalitis (SLE)

  • May be most common of all American viral encephalitides

  • Epidemics in the US occur most often in the Midwest and South


West nile encephalitis
West Nile Encephalitis

  • Increasing in numbers in the United States


Herpes simplex virus
Herpes Simplex Virus

  • Can cause encephalitis in newborns born to HSV-positive mothers

  • Prognosis is poor


Jc virus
JC Virus

  • Infection is common

  • In patients with immune dysfunction, cause progressive multifocal leukoencephalopathy (PML)- uncommon but generally fatal


Subacute encephalitis
Subacute Encephalitis

  • Symptoms take longer to show up and are less striking

  • Most common cause: Toxoplasma


Toxoplasma gondii
Toxoplasma gondii

  • Flagellated parasite

  • Most cases go unnoticed

  • In the fetus and immunodeficient people, severe and often fatal

  • Asymptomatic or marked by mild symptoms such as sore throat, lymph node enlargement, and low-grade fever



Measles virus subacute sclerosing panencephalitis sspe
Measles Virus: SubacuteSclerosingPanencephalitis (SSPE)

  • Occurs years after an initial measles episode

  • Seems to be caused by direct viral invasion of neural tissue


Prions
Prions

  • Transmissible spongiform encephalopathies (TSEs): neurodegenerative diseases with long incubation periods but rapid progression once they begin

  • Human TSEs

    • Creutzfeldt-Jakob disease (CJD)

    • Gerstmann-Strussler-Scheinker disease

    • Fatal familial insomnia



Rabies
Rabies

  • Slow, progressive zoonotic disease

  • Characterized by fatal encephalitis

  • Average incubation time: 1-2 months or more

  • Prodromal phase begins with fever, nausea, vomiting, headache, fatigue, and other nonspecific symptoms

  • Furious rabies

    • Periods of agitation, disorientation, seizures, and twitching

    • Spasms in the neck and pharyngeal muscles lead to hydrophobia

  • Dumb rabies

    • Patient is not hyperactive but is paralyzed, disoriented and stuporous

  • Both forms progress to the coma phase, resulting in death




Poliomyelitis
Poliomyelitis

  • Acute enteroviral infection of the spinal cord

  • Can cause neuromuscular paralysis

  • Often affects small children

  • Most infections are contained as short-term, mild viremia

  • Some develop mild nonspecific symptoms of fever, headache, nausea, sore throat, and myalgia

  • Then spreads along specific pathways in the spinal cord and brain

  • Neurotropic: the virus infiltrates the motor neurons of the anterior horn of the spinal cord

  • Nonparalytic: invasion but not destruction of nervous tissue

  • Paralytic: various degrees of flaccid paralysis

  • Rare cases: bulbar poliomyelitis




Tetanus
Tetanus

  • Also known as lockjaw

  • Clostridium tetani

  • Gram-positive, spore-forming rod

  • Releases a powerful neurotoxin, tetanospasmin, that binds to target sites on peripheral motor neurons, spinal cord and brain, and in the sympathetic nervous system

  • Toxin blocks the inhibition of muscle contraction

  • Results in spastic paralysis

  • First symptoms : clenching of the jaw, followed in succession by extreme arching of the back, flexion of the arms, and extension of the legs

  • Risussardonicus





Botulism
Botulism

  • Intoxication associated with eating poorly preserved foods

  • Can also occur as a true infection

  • Three major forms

    • Food-borne botulism

      • Ingestion of preformed toxin

    • Infant botulism

      • Entrance of botulinum toxin into the bloodstream

    • Wound botulism

      • Entrance of botulinum toxin into the bloodstream



Figure 19.23 dizziness; later symptoms include descending muscular paralysis and respiratory compromise


African sleeping sickness
African Sleeping Sickness dizziness; later symptoms include descending muscular paralysis and respiratory compromise

  • Trypanosomabrucei

  • Also called trypanosomiasis

  • Affects the lymphatics and areas surrounding blood vessels

  • Usually a long asymptomatic period precedes onset of symptoms

  • Symptoms include intermittent fever, enlarged spleen, swollen lymph nodes, and joint pain

  • Central nervous system is affected with personality and behavioral changes that progress to lassitude and sleep disturbances


Figure 19.24 dizziness; later symptoms include descending muscular paralysis and respiratory compromise


Figure 19.25 dizziness; later symptoms include descending muscular paralysis and respiratory compromise


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