DISEASES OF THE NERVOUS SYSTEM

How Microbes Enter the Nervous System Skull or backbone fractures Medical procedures Along peripheral nerves Blood or lymph

The Nervous System Figure 22.1

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.

The Meninges and Cerebrospinal Fluid Figure 22.2

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

Bacterial Meningitis Figure 22.3

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

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 United States Vaccination recommended for college students.

Neisseria Meningitis, Meningococcal Meningitis Figure 22.4

Streptococcus pneumoniae Meningitis, Pneumococcal Meningitis 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

Listeriosis Listeria monocytogenes Gram-negative aerobic rod Usually foodborne; it can be transmitted to fetus. Reproduce in phagocytes. Figure 22.5

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.

Tetanus Figure 22.6

Botulism 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.

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.

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

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

Leprosy Figure 22.9

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).

Poliomyelitis FDR- Polio Pioneer

Poliomyelitis First vaccine made in Canada by Connaught Medical Research Laboratories

Poliomyelitis Figure 22.11

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 plus immune globulin.

Rabies Virus (Rhabdovirus) Figure 22.12

Rabies Virus (Rhabdovirus) Figure 22.12

Rabies Virus (Rhabdovirus) Figure 22.12

Rabies Virus (Rhabdovirus) Figure 22.12

Rabies Virus (Rhabdovirus) Figure 22.12

Rabies Virus (Rhabdovirus) Figure 22.12

Rabies Virus (Rhabdovirus) Negri Bodies in Neurons of Brain Figure 22.12

Rabies Virus (Rhabdovirus) Figure 22.13

Arboviral Encephalitis Arboviruses are arthropod-borne viruses that belong to several families. Prevention is by controlling mosquitoes. Figure 22.14

Arboviral Encephalitis Reservoir Mosquito vector U.S. distribution Western equine Birds, horses Culex Eastern equine Aedes, Culiseta St. Louis Birds California Small mammals Aedes West Nile Birds, mammals Culex, Aedes

Cryptococcus Neoformans Meningitis (Cryptococcosis) Figure 22.15

Cryptococcus Neoformans Meningitis (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.

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.

African Trypanosomiasis Figure 22.16

Naegleria fowleri Protozoan infects nasal mucosa from swimming water. Figure 22.17

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

Transmissible Spongiform Encephalopathies Figure 22.18