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;

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.