Chapter 22

Microbial Diseases of the Nervous System

 

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

¥       Meningitis: Inflammation of meninges

¥       Encephalitis: Inflammation of the brain

¥       Meningoencephalitis: Inflammation of both

 

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

¥       Treatment: Cephalosporins, vancomycin

 

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

¥       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 in U.S.

¥       Serotype B in Europe

¥       Serotype A in Africa, China, and Middle East

¥       Vaccination (B, C, Y, W-135 capsule) recommended for college students

 

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

 

Listeriosis

¥       Caused by Listeria monocytogenes

¥       Gram-negative aerobic rod

¥       Usually foodborne; it can be transmitted to fetus

¥       Reproduce in phagocytes

 

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 (DTP) and booster (dT)

¥       Treatment with tetanus immune globulin

 

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

¥       Treatment: Supportive care and antitoxin

¥       Infant botulism results from C. botulinum growing in intestines

¥       Wound botulism results from growth of C. botulinum in wounds

 

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

      25% fatality

      Found in marine and lake sediments

      Pacific Northwest, Alaska, Great Lakes area

 

Leprosy

¥       Also called HansenÕs 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

¥       Tuberculoid (neural) form: Loss of sensation in skin areas; positive lepromin test

¥       Lepromatous (progressive) form: Disfiguring nodules over body; negative lepromin test

 

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)

 

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

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

Prevention of Rabies

¥       Preexposure prophylaxis: Injection of human diploid cells vaccine (HDCV)

¥       Postexposure treatment: Vaccine plus rabies immune globulin (RIG)