Chapter 22

1. Chapter 22 Microbial Diseases of the Nervous System

2. Microbes enter the nervous system via: • Skull or backbone fractures • Medical procedures • Along peripheral nerves • Blood or lymph

3. The Nervous System Figure 22.1

4. Microbial Diseases of the Nervous System • Bacteria can grow in the cerebrospinal fluid in the subarachnoid space of the CNS • The blood brain barrier (capillaries) prevents passage of some materials (such as antimicrobial drugs) into the CNS • Meningitis • Inflammation of meninges • Encephalitis • Inflammation of the brain

5. The Meninges and Cerebrospinal Fluid Figure 22.2

6. Bacterial Meningitis • Fever, headache, stiff neck • Followed by nausea and vomiting • May progress to convulsions and coma • Diagnosis by Gram stain of CSF • Treated with cephalosporins

7. Bacterial Meningitis Table 22.1

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. Haemophilus influenzae Meningitis Figure 22.3

10. Neisseria Meningitis, Meningococcal Meningitis • N. meningitidis • Gram-negative aerobic cocci, capsule • 10% of people are healthy nasopharyngeal carriers • Begins as throat infection, rash • Serotype B is most common in the U.S. • Vaccine against some serotypes is available

11. Neisseria Meningitis, Meningococcal Meningitis Figure 22.4

12. Streptococcus pneumoniae Meningitis, Pneumococcal Pneumonia • Gram-positive diplococci • 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

13. Listeriosis • Listeria monocytogenes • Gram-negative aerobic rod • Usually foodborne, can be transmitted to fetus • Reproduce in phagocytes

14. Listeriosis Figure 22.5

15. Tetanus • 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 (DTP) and booster (dT) • Treatment with tetanus immune globulin

16. Tetanus Figure 22.6

17. Botulism • Clostridium botulinum • Gram-positive, endospore-forming, obligate anaerobe • Intoxication due to ingesting botulinal toxin • Botulinal toxin blocks release of neurotransmitter causing flaccid paralysis • Prevention: • Proper canning • Nitrites prevent endospore germination in sausages

18. 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.

19. Botulism • Type A • 60-70% fatality • Found in CA, WA, CO, OR, NM • Type B • 25% fatality • Europe and eastern U.S. • Type E • Found in marine and lake sediments • Pacific Northwest, Alaska, Great Lakes area

20. Diagnosis Figure 22.7

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

22. Leprosy Figure 22.8

23. 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)

24. Poliomyelitis Figure 22.10

25. Rabies virus (Rhabdovirus) • 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 • Preexposure prophylaxis: Infection of human diploid cells vaccine • Postexposure treatment: Vaccine + immune globulin

26. Rabies virus (Rhabdovirus) Figure 22.11

27. Rabies virus (Rhabdovirus) Figure 22.12

28. Arboviral Encephalitis • Arboviruses are arthropod-borne viruses that belong to several families. • Prevention is by controlling mosquitoes

29. Cryptococcus neoformans Meningitis (Cryptococcosis) • Soil fungus associated with pigeon and chicken dropping • Transmitted by the respiratory route; spreads through blood to the CNS • Mortality up to 30% • Treatment: amphotericin B and flucytosine

30. Cryptococcus neoformans Meningitis (Cryptococcosis) Figure 22.14

31. African Trypanosomiasis • Trypanosoma brucei gambiense infection is chronic (2 to 4 years) • T. b. rhodesiense infection is more acute (few months) • Transmitted from animals to humans by tsetse fly • Prevention: elimination of the vector • Treatment: Eflornithine blocks an enzyme necessary for the parasite • Parasite evades the antibodies through antigenic variation

32. African Trypanosomiasis Figure 22.15

33. Naegleria fowleri • Protozoan infects nasal mucosa from swimming water Figure 22.16

34. Transmissible Spongiform Encephalopathies • Caused by prions • Sheep scrapie • Creutzfeldt-Jakob disease • Kuru • Bovine spongiform encephalopathy • Transmitted by ingestion or transplant or inherited • Chronic, fatal

35. Transmissible Spongiform Encephalopathies Figure 22.17a