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Chapter 22

Chapter 22. Microbial Diseases of the Nervous System. Figure 22.1 The human nervous system. Brain. Central nervous system (CNS). Spinal cord. Peripheral nervous system (PNS). The Nervous System. Meninges protect brain and spinal cord Dura mater: outermost layer

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Chapter 22

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  1. Chapter 22 Microbial Diseases of the Nervous System

  2. Figure 22.1 The human nervous system. Brain Central nervous system (CNS) Spinal cord Peripheral nervous system (PNS)

  3. The Nervous System • Meninges protect brain and spinal cord • Dura mater: outermost layer • Arachnoid mater: middle layer • Subarachnoid space contains cerebrospinal fluid (CSF) • Pia mater: innermost layer • Blood–brain barrier

  4. Figure 22.2 The meninges and cerebrospinal fluid. Skull bone Cerebrum Subarachnoid space (contains cerebrospinal fluid) Skull bone Dura mater Arachnoid mater Cranial meninges Pia mater Blood vessel Cerebrum Cerebellum Spinal cord Dura mater Spinalmeninges Arachnoid mater Pia mater Subarachnoid space of spinal cord Subarachnoid space (contains cerebrospinal fluid) Central canal

  5. The Nervous System • Meningitis: inflammation of meninges • Encephalitis: inflammation of the brain • Meningoencephalitis: inflammation of both

  6. Bacterial Meningitis • Initial symptoms of fever, headache, and stiff neck • Followed by nausea and vomiting • May progress to convulsions and coma • Diagnosis by Gram stain and latex agglutination of CSF

  7. Figure 22.4 Spinal tap (lumbar puncture). Spinal needle is inserted, usually between the fourth and fifth lumbar vertebrae Cerebrospinal fluid Spinal cord Fourth lumbar vertebra L4 Cauda equina L5 Sample of cerebrospinal fluid Longitudinal section of the spine Fifth lumbar vertebra

  8. Haemophilus influenzae Meningitis • Occurs mostly in children (6 months to 4 years) • Gram-negative aerobic bacteria, normal throat microbiota • Capsule antigen type b • Prevented by Hib vaccine

  9. Neisseria Meningitis • Also called meningococcal meningitis • Caused by N. meningitidis • Gram-negative, aerobic cocci with a capsule • 10% of people are healthy nasopharyngeal carriers • Begins as throat infection, rash • Serotypes B, C, Y, W-135 • Serotype B & C in United States • Serotype A in Africa • Vaccination (A, C, Y, W-135 capsule) recommended for college students

  10. Figure 22.3 Neisseria meningitis. N. meningitidis Cilia N. meningitidis

  11. Streptococcus pneumoniae Meningitis • Also called pneumococcal meningitis • Caused by S. pneumoniae (a gram-positive diplococcus) • 70% of people are healthy nasopharyngeal carriers • Most common in children (1 month to 4 years) • Mortality: 30% in children, 80% in elderly • Prevented by vaccination

  12. Listeriosis • Caused by Listeria monocytogenes • Gram-negative aerobic rod • Usually foodborne; it can be transmitted to fetus • Reproduce in phagocytes • Spread phagocyte-to-phagocyte

  13. Figure 22.5 Cell-to-cell spread of Listeria monocytogenes, the cause of listeriosis. Listeria monocytogenes Macrophage Macrophage Pseudopod

  14. A worker in a day-care center in eastern North Dakota becomes ill with fever, rash, headache, and abdominal pain. The patient has a precipitous clinical decline and dies on the first day of hospitalization. Diagnosis is confirmed by Gram staining of cerebrospinal fluid. Can you identify infections that could cause these symptoms? Diseases in Focus: Meningitis and Encephalitis

  15. Diseases in Focus: Meningitis and Encephalitis. Gram stain of cerebrospinal fluid.

  16. Tetanus • Caused by Clostridium tetani • Gram-positive, endospore-forming, obligate anaerobe • Grows in deep wounds • Tetanospasmin released from dead cells blocks relaxation pathway in muscles • Prevention by vaccination with tetanus toxoid (DTaP) and booster (Td) • Treatment with tetanus immune globulin (TIG)

  17. Figure 22.6 An advanced case of tetanus.

  18. Botulism • Caused by Clostridium botulinum • Gram-positive, endospore-forming, obligate anaerobe • Intoxication comes from ingesting botulinal toxin • Botulinal toxin blocks release of neurotransmitter, causing flaccid paralysis • Prevention • Proper canning • Nitrites prevent endospore germination in sausages

  19. Botulism • Treatment: supportive care and antitoxin • Infant botulism results from C. botulinum growing in intestines • Wound botulism results from growth of C. botulinum in wounds

  20. Botulinal Types • Type A toxin • 60–70% fatality • Found in CA, WA, CO, OR, NM • Type B toxin • 25% fatality • Europe and eastern United States • Type E toxin • Found in marine and lake sediments • Pacific Northwest, Alaska, Great Lakes area

  21. Figure 22.8 Diagnosing botulism by identifying botulinal toxin type.

  22. Leprosy • Also called Hansen’s disease • Caused by Mycobacterium leprae • Acid-fast rod that grows best at 30°C • Grows in peripheral nerves and skin cells • Transmission requires prolonged contact with an infected person

  23. Leprosy • Tuberculoid (neural) form: loss of sensation in skin areas; positive lepromin test • Lepromatous (progressive) form: disfiguring nodules over body; negative lepromin test

  24. Figure 22.9 Leprosy lesions. Tuberculoid (neural) leprosy Lepromatous (progressive) leprosy

  25. After eating canned chili, two children experience cranial nerve paralysis followed by descending paralysis. The children are on mechanical ventilation. Leftover canned chili is tested by mouse bioassay. Can you identify infections that could cause these symptoms? Diseases in Focus: Diseases with Neurological Symptoms or Paralysis

  26. Disease in Focus: Diseases with Neurological Symptoms or Paralysis Gram stain from canned chili.

  27. Poliomyelitis (Polio) • 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: vaccination (enhanced-inactivated polio vaccine)

  28. Figure 22.11 Worldwide annual incidence of poliomyelitis. 7,000 6,000 2,000 5,000 1,000 4,000 Number of confirmed polio cases 0 2008 2010 2009 3,000 2,000 1,000 0 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 Year

  29. Rabies • Caused by the rabies virus • Transmitted by animal bite • Furious rabies: animals are restless, then highly excitable • Paralytic rabies: animals seem unaware of surroundings

  30. Figure 22.12 Pathology of rabies infection. Virus reaches brain and causes fatal encephalitis. Virus ascends spinal cord. Virus enters salivary glands and other organs of victim. Virus moves up peripheral nervous system to CNS. Virus replicates in muscle near bite and enters neuron of peripheral nervous system. Virus enters tissue from saliva of biting animal.

  31. Figure 22.13 Reported cases of rabies in animals. Areas of the United States in which rabies predominates in certain wildlife species. Rabies-infected bats were reported in 47 of the 48 contiguous states. In eastern states in which raccoons are the predominant rabies-infected animal, many cases were also reported in foxes and skunks. KEY Skunk Raccoon Fox Fox and skunk

  32. Figure 22.13 Reported cases of rabies in animals. Rabies cases in various wild and domestic animals in the United States. Rabies in domestic animals such as dogs and cats is uncommon because of high vaccination rates. Raccoons, skunks, and bats are the animals most likely to be infected with rabies. Most human cases are caused by bites of bats. Worldwide, most human cases are caused by bites of dogs. Raccoons 35.5% Bats 24.8% Skunks 24.5% Foxes 7.7% Cats 4.6% Dogs 1.2% KEY Cattle 1.1% Wild Horses/mules 0.6% Domestic 0 10 20 30 40 50

  33. Clinical Focus: A Neurological Disease, Figure B. Silver-haired bat.

  34. Rabies Virus • Virus multiplies in skeletal muscles and then brain cells, causing encephalitis • Initial symptoms may include muscle spasms of the mouth and pharynx and hydrophobia

  35. Prevention of Rabies • Preexposure prophylaxis: injection of human diploid cells vaccine (HDCV) • Postexposure treatment: vaccine plus rabies immune globulin (RIG)

  36. Arboviral Encephalitis • Arboviruses • Arthropod-borne viruses that belong to several families • Prevention: controlling mosquitoes

  37. Figure 22.14 California serogroup arbovirus cases: 1964–2009. VT NH MA 1 366 58 586 1 RI 29 8 134 2 CT 898 143 241 28 1 3 NJ 1 14 22 215 154 DE 2 3 5 25 MD 2 14 7 4 25 DC 4 594 WV

  38. Arboviral Encephalitis

  39. Arboviral Encephalitis

  40. An 8-year-old girl in rural Wisconsin has chills, headache, and fever and reports having been bitten by mosquitoes. Which type of encephalitis is most likely? Diseases in Focus: Types of Arboviral Encephalitis

  41. Diseases in Focus: Types of Arboviral Encephalitis. Culex mosquito engorged with human blood.

  42. Cryptococcus neoformans Meningitis • Also called cryptococcosis • Soil fungus associated with pigeon and chicken droppings • Transmitted by the respiratory route; spreads through blood to the CNS • Mortality up to 30% • Treatment: amphotericin B and flucytosine

  43. Figure 22.15 Cryptococcus neoformans. Capsule

  44. African Trypanosomiasis • Trypanosoma brucei gambiense • Chronic (2 to 4 years) • T. b. rhodesiense infection • Acute (few months) • Transmitted from animals to humans by tsetse fly

  45. African Trypanosomiasis • Prevention: elimination of the vector • Treatment: eflornithine blocks an enzyme necessary for the parasite • Parasite evades the antibodies through antigenic variation

  46. Figure 22.16 How trypanosomes evade the immune system. Clone A Clone B Clone C Relative number of trypanosomes 0 2 3 1 4 Weeks after infection

  47. Naegleria fowleri • Protozoan infects nasal mucosa from swimming water • Ameboid-flagellate-cyst

  48. Figure 22.17 Naegleria fowleri. Dead ameba Naegleria fowleri

  49. Chapter 22, unnumbered figure, page 635. Flagellate Ameba Cyst

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