Ch. 22: Microbial Diseases of the Nervous System

central nervous system

brain and spinal cord

peripheral nervous system

nerves that branch from CNS

meninges

protect the brain and spinal cord

dura arachnoid and pia mater

outer, middle, and innermost layers respectively

subarachnoid space

contains cerebrospinal fluid

blood brain barrier

this is the reason why it’s difficult to treat meningitis and encephalitis since most antibiotics cannot penetrate it

bacterial meningitis

initial symptoms of fever, headache, and a stiff neck; followed by nausea and vomiting; progress to convulsions and coma; death from shock and inflammation due to endo toxin and cell wall release

viral meningitis

more common and mild

haemophilus influenzae meningitis

gram-negative aerobic bacteria part of normal throat microbiota, enters bloodstream; pathogenicity due to capsule antigen type b; occurs mostly in children 6 months to 4 years, prevented by the Hiv vaccine, 45% of bacterial meningitis cases; 6% mortality

neisseria meningitidis meningitis

meningococcal meningitis; gram-negative aerobic cocci with capsule, six serotypes associated with the disease; 40% of people are healthy nasopharyngeal carriers, begins as throat infection, rash, and bacteremia, mortality of 9-12% with antibiotic therapy, 80% without, common outbreaks in dorms and military barracks, vaccination protects against serogroups A, C, Y, and W but not B

streptococcus pneumoniae meningitis

gram-positive encapsulated diplococcus, 70% of people are healthy nasopharyngeal carriers, pneumonia and otitis media; most common in children 1 month to 4 years, mortality 30% in children and 80% in elderly, prevented by conjugated vaccine

diagnosis and treatment of the most common types of bacterial meningitis

sample CSF via a spinal tap or lumbar puncture and gram staining, latex agglutination test, chemotherapy initiated before diagnosis cephalosporins(broad spectrum third generation cephalosporins)

spinal tap immediately

pathogens in CSF do not survive storage or changes in temp

listeriosis

caused by Listeria monocytogenes, gram-negative aerobic rod, usually foodborne and asymptomatic, meningitis more common in the immunocompromised and infants; can invade the bloodstream, causing sepsis, reproduce in phagocyte to phagocyte; infects pregnant women, crossing the placenta and leading to stillbirth

tetanus

caused by Clostridium tetani, gram-positive, endospore forming, obligate anaerobe; grows in deep wounds with anaerobic conditions; tetanospasmin released from dead cells, enters CNS, clocks the relaxation pathway in muscles, causing muscle spasms, death occurs from spasms of respiratory muscles; prevented by vaccination with a tetanus toxoid(DTap); fewer than 50 cases per year mortality of 25-50%; initial treatment with tetanus immune globulin (TIG) for unimmunized people; infected tissue removed via debridement

DTap

stimulates antibodies that neutralize the toxin, booster required every 10 years

botulism

Clostridium botulinum, gram-positive, endospore forming, obligate anaerobe; intoxication come from ingesting the botulinum exotoxin, specific for the synaptic end of the nerve, blocks release of the neurotransmitter acetylcholine, causing flaccid paralysis; death usually comes from respiratory or cardiac failure

infant botulism

C. botulinum grows in the intestine of infants due to a lack of intestinal microbiota; associated with honey

wound botulism

growth of C. botulinum in wounds; treatments and preventions of botulism: respiratory assistance and antitoxins, proper canning the use of nitrites in foods

poliomyelitis

caused by the poliovirus, transmitted by the ingestion of water containing feces containing the virus, initial symptoms are sore throat and nausea; viremia may occur entering the CNS, 1% of cases become paralytic, destruction of motor cells, death from respiratory failure

postpolio syndrome

muscle weakness occurring decades after infection

vaccine for all three serotypes

salk vaccine and sabin vaccine; polio cases fell 99% from 1988 to 2000; persistent reservoirs of polio remain in Pakistan, India, Afghanistan, and Nigeria

salk vaccine

inactivated vaccine; injectable

sabin vaccine

attenuated vaccine; oral; lifelong immunity

rabies

caused by rabies virus, genus Lyssavirus (bullet shape), single stranded RNA, usually transmitted by the saliva of an animal bite, can also cross mucous membranes; in US silver-haired bats are common cause; virus multiples in the skeletal muscles and travels through PNS to the brain cells, causing encephalitis; average incubation of 30 to 50 days; postexposure prophylaxis, human rabies Ig, and 3 dose of vaccines