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MICR 201 Microbiology for Health Related Sciences

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1 MICR 201 Microbiology for Health Related Sciences
Lecture 13: Microbial diseases of the skin and eyes Edith Porter, M.D. MICR 201 Microbiology for Health Related Sciences

2 Lecture outline Structure of the nervous system
Main types of infections of the nervous system Infections of the central nervous system Infections of the peripheral nervous system General and specific diseases of the nervous system Bacterial diseases Fungal diseases Parasitic diseases Prion diseases

3 The human nervous system

4 The meninges and cerebrospinal fluid (CSF)
CSF is obtained by lumbar puncture Used for diagnostics of meningitis and other CNS disorders Never refrigerate CSF for culture

5 http://doctorgrasshopper. files. wordpress

6 Spread of microorganisms into the brain
Skull or backbone fractures Medical procedures Along peripheral nerves Blood or lymph Must cross blood-brain barrier (capillaries)

7 Effects of edema on the brain
Increased intracranial pressure Never remove cerebrospinal by lumbar puncture in these patients Biochemical abnormalities Neural tissue necrosis with loss of function

8 Main types of infections of the nervous system
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

9 Meningitis Note the turbid appearance of the meninges and yellowish liquid accumulation

10 Bacterial Meningitis Fever, headache, stiff neck, light sensitivity
Followed by nausea and vomiting May progress to convulsions and coma Diagnostics with CSF Neutrophil exsudate Low glucose Latex agglutination for selected microorganisms Culture Treated with cephalosporins (broad spectrum antibiotic)

11 Bacterial Meningitis Streptococcus pneumoniae Haemophilus influenzae
Neisseria meningitidis Listeria monocytogenes In newborns: Group B streptococci From vaginal flora Transmitted during birth Prophylactic ampicillin treatment i.v. of mother during birth if mother tests positive for Group B streptococci

12 Haemophilus influenzae meningitis
Occurs mostly in children (6 months to 4 years) Gram-negative aerobic bacteria, normal microbiota in nasooropharynx (throat ) Pathogenic factor: capsule type b Prevented by Hib vaccine

13 Neisseria or meningococcal meningitis
N. meningitidis Gram-negative aerobic cocci, capsule 10% of people are healthy nasopharyngeal carriers Begins as throat infection, rash (doesn’t fade when pressed) Serotype B and Y is most common in the U.S. Vaccine against some serotypes (but not B) is available

14 Waterhouse-Friderichsen Syndrome
N. meningitidis sepsis Septic Shock and bleeding into adrenal gland Petechial skin lesions (bleeding into skin) Death within 12 – 48 hours

15 Listeria monocytogenes meningitis
Gram-positive rods Symptomatic in immunocompromised Intrauterine infections with abortion or stillbirth Pregnant woman asymptomatic or only very mild disease Proliferates at 4°C Intracellular survival and cell to cell spread

16 Viral meningitis Most common cause of aseptic meningitis
Lymphocytic pleocytosis in CSF Most commonly enteroviruses Fever less elevated Better prognosis

17 Fungal meningitis: Cryptococcus neoformans
Soil fungus associated with pigeon and chicken dropping Transmitted by the respiratory route; spreads through blood to the CNS Capsule Mortality up to 30% AIDS patients Treatment: amphotericin B and flucytosine

18 Encephalitis Infection of the brain
Fever, head aches, chills and altered consciousness Abnormal EEG, MRI

19 Viral encephalitis Arboviral (transmitted by arthropods)
Edema in right temporal lobe Arboviral (transmitted by arthropods) Most common Seasonal occurrence Subclinical to severe symptoms including death Herpes Virus 2 encephalitis This 33 year-old 33 y old female patient presented with agitation, confusion, mutism, and fever

20 Amoeba meningoencephalitis
Free living amoeba found in fresh water Infection during swimming Entry via nasal mucosa and ascension into brain via olfactory nerve Naegleri fowleri infection hasd near 100% fatality rate Acantamoeba infection has better prognosis

21 Brain abscess Cerebellar abscess in CT

22 Clinical Case N Engl J Med, Vol. 344, No. 18 May 3, 2001;www.nejm.org
Two hours after the onset of fever and malaise, a 15-year-old boy began to have tachycardia and tachypnea and became unconscious. He was taken to the intensive care unit, where he was found to be in septic shock (pulse, 180; blood pressure, 70/45 mm Hg; temperature, 40.2°C; and partial-thromboplastin time, 90 seconds). He had bullous lesions about the elbow and confluent petechial and purpuric lesions on his face, arms, and legs (Panel A). His hands and feet were cool and cyanotic. He had no signs of meningeal irritation. He was intubated, placed on cardiopulmonary support, and given large doses of catecholamines. A single dose of dexamethasone (3 mg per kilogram of body weight) was given immediately, and treatment with penicillin G (16 million IU per square meter of body-surface area) was started. Meanwhile, the petechiae spread rapidly, and four hours later peripheral pulses could not be detected in the arms or legs. Therapy with fresh-frozen plasma and heparin was also begun. Although the treatment led to resolution of the sepsis syndrome, local intravascular lysis with streptokinase failed to prevent severe ischemia-induced damage to the patient’s hands (Panel B) and feet (Panel C). Seven digits and both forefeet had to be amputated. After reconstructive surgery with free flaps, the patient was able to walk with orthopedic shoes and could use his remaining fingers in a pincer-like grip. N Engl J Med, Vol. 344, No. 18 May 3, 2001;www.nejm.org

23 Specific diseases of the nervous System
Tetanus Botulism Leprosy Poliomyelitis Rabies Trypansomiasis Prion diseases

24 Tetanus Clostridium tetani
Gram-positive, endospore-forming, obligate anaerobe Intoxication due to tetanus toxin Tetanospasmin, a neurotoxin, blocks relaxation pathway in muscles causing contractions Treatment Supportive care and antitoxin Prevention: Vaccination Wound cleaning

25 Tetanus

26 Botulism Clostridium botulinum
Gram-positive, endospore-forming, obligate anaerobe Intoxication due to ingesting botulinum toxin (dose: mg/kg)  food poisoning Botulinum toxin blocks release of neurotransmitter causing flaccid paralysis Treatment Supportive care and antitoxin Prevention: Proper canning Nitrites prevent endospore germination in sausages No honey for very young children!

27 Funeral of an Oregon family wiped out by botulism
Home-canned string beans 12 deaths (2 funerals held at a different location)

28 Diagnosis of botulism Decontaminate and inject suspicious material into laboratory mice Follow fate of mice over next 72 hours

29 Leprosy (Hansen’s disease)
Mycobacterium leprae 12 day generation time Survival in macrophages Spread in the myelin sheaths of peripheral nerves

30 Poliomyelitis Poliovirus Transmitted by ingestion
Initial symptoms: sore throat and nausea Viremia may occur; if persistent, virus can enter the CNS; destruction of motor cells and paralysis occurs in <1% of cases Prevention is by vaccination (enhanced-inactivated polio vaccine)

31 Success of poliomyelitis vaccination

32 Rabies virus 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 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

33 Rabies infection pathway

34 Reported cases of rabies in animals

35 Trypanosomiasis 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

36 Prion diseases Transmissible Spongiform Encephalopathies Sheep scrapie
Creutzfeldt-Jakob disease Kuru Bovine spongiform encephalopathy Proteinaceous infectious particle Transmitted by ingestion or transplant or inherited Chronic, fatal within months – a few years

37 Transmissible spongiform encephalopathies
Normal Spongiform encephalitis Neurological Damage Fibrillar deposit

38 Important to remember The CNS is covered by meninges, three layers of membranes called dura mater, arachnoid mater, and pia mater. Blood-brain barrier greatly limits access to the brain. Infection of the meninges is called meningitis, infection of the brain with its grey and white matter is called encephalitis. Bacteria, viruses, fungi and parasites can cause meningitis and encephalitis. Key symptoms of meningitis are fever, head aches and possibly vomiting. Encephalitis is characterized by fever, headache and impairment of brain function and consciousness. Specific diseases of the nervous system have unique symptoms

39 Check your understanding
Tetanospasmin and botulinum toxin are alike in that they both A) cause muscle spasm B) cause flaccid paralysis C) affect the smooth muscles (e.g. in the intestine) D) are produced by the aerobic spore former Bacillus anthracis E) None of the above In contrast to meningitis encephalitis A) leads to generalized bleeding B) rather causes disturbances of the mental status C) is best diagnosed by a lumbar tap D) All of the above. E) None of the above.


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