micr 201 microbiology for health related sciences
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MICR 201 Microbiology for Health Related Sciences . Microbiology- a clinical approach by Anthony Strelkauskas et al. 2010 Chapter 24: Infections of the central nervous system. Why is this chapter important?. - PowerPoint PPT PresentationTRANSCRIPT
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MICR 201 Microbiology for Health Related Sciences
Microbiology- a clinical approach by Anthony Strelkauskas et al. 2010
Chapter 24: Infections of the central nervous system
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Infections that affect the central nervous system (CNS) can be catastrophic and potentially lethal.
Neurons do not regenerate, hence loss of neurons due to infection leads to permanent damage.
Why is this chapter important?
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Map for chapter 24
MENINGITIS, ENCEPHALITIS, BRAIN ABSCESS IN GENERAL
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The human nervous system
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CNS has two major parts◦ Brain◦ Spinal cord
Both surrounded by three layers of connective tissue – meninges.
Cerebrospinal fluid is found in the subarachnoid space.
The brain and spinal cord are protected from the body by the blood-brain barrier.◦ Protects against infectious
disease◦ Some pathogens can pass
through the blood-brain barrier
Anatomy of the CNS
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Inflammation is one of the first and most formidable responses.◦ Always causes swelling
No room for swelling in the CNS. Danger of brain herniation
Effects of edema on the brain
Normal Edema
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Infection can also affect proper brain function through: ◦ Acidosis◦ Hypoxia◦ Destruction of neurons
Effects of infection can be profound and irreversible.
Blood-brain barrier can make it difficult to treat CNS infections.
Effects of infection on brain function
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Skull or backbone fractures Medical procedures Along peripheral nerves
◦ Rabies virus, Herpes simplex virus Blood or lymph
◦ Infection originates from another body site◦ Neisseria meningitidis, Streptococcus pneumoniae◦ Must cross blood-brain barrier (capillaries)
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Spread of microorganisms into the brain
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CSF is obtained by lumbar puncture
Used for diagnoses of meningitis and other CNS disorders
Never refrigerate CSF for culture
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The meninges and cerebrospinal fluid (CSF)
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10http://doctorgrasshopper.files.wordpress.com/2010/01/lots-of-lumbar-puncture-pics.jpg
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Meningitis◦ Inflammation of meninges◦ Headaches, stiff neck, light sensitivity,
vomiting Encephalitis
◦ Inflammation of the brain◦ Mental disturbance, altered consciousness,
seizures Abscess
◦ Focal symptoms depending on the location of the abscess
◦ Often polymicrobial, anaerobes, amoeba
Main types of infections of the nervous system
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Fever, headache, stiff neck, light sensitivity Followed by nausea and vomiting May progress to convulsions and coma Bacterial meningitis can be severe and cause:
◦ Brain damage◦ Hearing loss◦ Learning disability
Diagnostics with CSF◦ Neutrophil exudate◦ Low glucose◦ Latex agglutination for selected microorganisms◦ Culture
Important to know type of bacterium◦ Antibiotic therapy can prevent its spread.◦ Cephalosporines
Bacterial meningitis
Streptococcus pneumoniaeHaemophilus influenzaeNeisseria meningitidisListeria monocytogenesEscherichia coliStreptococcus agalactiae
newborns
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Neisseria meningitidis sepsis
Septic Shock and bleeding into adrenal gland
Petechial skin lesions (bleeding into skin)
Death within 12 – 48 hours
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Waterhouse-Friderichsen Syndrome
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Most common cause of aseptic meningitis Lymphocytic pleocytosis in CSF Viral meningitis is generally less severe:
◦ Fever less elevated◦ Usually resolves without treatment.
90% of cases caused by enterovirus Also herpesvirus and mumps virus.
Viral meningitis
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Soil fungus associated with pigeon and chicken dropping (soil enriched for growth of fungus)
Transmitted by the respiratory route; spreads through blood to the CNS
Capsule Mortality up to 30% AIDS patients Treatment:
amphotericin B and flucytosine
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Fungal meningitis: Cryptococcus neoformans
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Infection of the brain
Fever, head aches, chills and altered consciousness
Abnormal EEG, MRI
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Encephalitis
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Most common is arboviral encephalitis (transmitted by arthropods)
◦ Western and Eastern equine Virus, West Nile Virus
◦ Seasonal occurrence◦ Subclinical to severe
symptoms including death
Herpes Virus 2 encephalitis
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Viral encephalitisEdema in right temporal lobe
33 y old female patient presented with agitation, confusion, mutism, and fever
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Free living amoeba found in fresh water
Infection during swimming Entry via nasal mucosa and ascension
into brain via olfactory nerve Naegleri fowleri infection has near
100% fatality rate Acantamoeba infection has better
prognosis
Amoeba meningoencephalitis
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Brain abscess
Cerebellar abscess in CT
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Many bacteria cause meningitis.◦ Increased cranial pressure and inflammation
Tetanus and botulism infections affect the CNS in different ways.◦ Produce exotoxins with an affinity for CNS tissue◦ Antibiotic therapy is ineffective once the exotoxin
has been produced.
Tetanus
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Tetanus Poliomyelitis Rabies Trypansomiasis Prion diseases (Chapter 8)
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Specific diseases of the central nervous System
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Tetanus is caused by Clostridium tetani.◦ Gram-positive◦ Anaerobic◦ Rod shaped◦ Produces terminal
endospores Commonly found in
soil Spores enter tissue
and germinate Vegetative bacteria
produce a neurotoxin call tetanospasmin or tetanus toxin
Tetanus
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Toxin enters the presynaptic terminals of the lower motor neurons.
From there, it gets into the CNS. Toxin acts at the anterior horn cells in the
spinal cord. Blocks postsynaptic inhibition of the spinal
motor reflexes Produces spasmodic contraction of the
muscles◦ Occur locally at first ◦ May extend up and down the spinal cord
Tetanus toxin
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Incubation period can vary between 4 days and several weeks.◦ The shorter the incubation period, the more severe the
infection. Tetanus leads to systemic muscle spasms.
◦ Masseter muscle of the jaw usually first to be affected.◦ Mouth cannot be opened (sometimes called lockjaw)◦ Muscles for respiration and swallowing can eventually
be compromised.◦ Severe cases can suffer from opisthotonus (head and
heels move toward each other) Death results from exhaustion and respiratory
failure. Mortality for untreated tetanus is 15 - 60%.
Tetanus
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Tetanus ophistotonus
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Antibiotics are not effective once toxin is produced.
Neutralization of the toxin with human tetanus immunoglobulin is important.
Additional supportive measures are:◦ Maintenance of a dark, quiet environment◦ Sedation◦ Provision of an adequate airway for breathing
Vaccination with toxoid
Tetanus treatment
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Transmitted by animal bite Virus multiplies in skeletal
muscles, then brain cells causing encephalitis
Initial symptoms may include muscle spasms of the mouth and pharynx and hydrophobia, saliva overproduction
Develops into acute fatal encephalitis
Furious rabies: animals are restless then highly excitable
Paralytic rabies: animals seem unaware of surroundings
Pre-exposure prophylaxis: Vaccine
Post-exposure treatment: Vaccine + immune globulin
Rabies
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Rabies infection pathway
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Condition first known as infantile paralysis◦ Risk of paralysis actually increases with age.
Essentially nonexistent in most modern countries◦ There is an effective vaccine.
Still a major problem in developing countries. Virus is an enterovirus with an affinity for the
CNS.◦ Normally crosses the blood-brain barrier◦ Can also use axons or the perineural sheath of the
peripheral nervous system Motor neurons are particularly vulnerable.
Polio
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Various levels of neuronal destruction cause:◦ Necrosis of neural tissue◦ Infiltration by mononuclear cells, primarily
lymphocytes 90% of poliomyelitis infections are very mild
and subclinical. Three types of polio infection:
◦ Abortive poliomyelitis◦ Nonparalytic poliomyelitis (aseptic meningitis)◦ Paralytic poliomyelitis
Polio
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Occurs in 2% of persons infected Characterized by asymmetric flaccid
paralysis◦ Extent varies from case to case
Temporarily damaged neurons can regain function◦ Recovery can take six months
Paralysis persisting after this period is permanent
Paralytic poliomyelitis
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Polio vaccine essentially wiped out this infection.
Two types of vaccine:◦ Inactive form – developed by Jonas Salk◦ Live attenuated form – developed by Albert Sabin
Polio vaccines
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Success of poliomyelitis vaccination
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Protozoa Transmitted by
tsetse fly Undulating
membrane Live in body fluids Escape immune
system by changing a surface protein (encoded by ~ 1000 different genes)
Enter brain and cause encephalitis◦ Sleeping disease◦ Fatal within 2- 3
years if left untreated
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Trypanosomiasis
http://www.cdc.gov/parasites/sleepingsickness/
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Central nervous system infections can be very dangerous and require immediate and aggressive therapy.
The central nervous system has a blood–brain barrier to prevent access of blood borne pathogens.
Pathogens that can move from the blood to the cerebrospinal fluid cause meningitis.
Most central nervous system infections result from bacteremia or viremia.
Many viruses have an affinity for the central nervous system.
Chapter 24 key concepts
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Viral infection of the central nervous system can be acute or persistent.
Acute viral CNS infections include rabies, polio, and encephalitis.
Persistent viral infections include measles and rubella.
Prions cause persistent central nervous system infections.
Fungal infections of the central nervous system are primarily opportunistic and occur in immunocompromised individuals.
Parasitic infections of the central nervous system are usually caused by free-living amebas.
Chapter 24 key concepts
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Final Examination –Wednesday, June 12, 2013 10:45am – 1:15pm Lecture, Chapter End Self Study Questions 100 Multiple Choice Questions: 2 points
each x 100 = 200 points ~65%: Chapters 14-26 ~35%: Chapters 1-13 Please bring Scantron and No. 2 pencil
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CORRECTION – Chapter Question Chapter 22 Infections of the Digestive
System 1. The most common source of
gastrointestinal infection in the developed world is◦ A. Salmonella◦ B. Shigella◦ C. Escherichia◦ D. Campylobacter◦ E. Staphylococcus aureus
Correct answer is D. Campylobacter