Chapter 22 - Microbial Diseases of the Nervous System
Terms in this set (24)
Normal Flora of Nervous System
The Nervous System
- Meninges protect the brain and spinal cord
- Dura mater: Outermost layer
- Arachnoid mater: Middle layer
- Subarachnoid space: contains cerebrospinal fluid (CSF)
- Pia mater: Innermost layer, in direct contact with the brain
- Blood-Brain barrier: selective as to what to let in.
- Brain = completely sterile area
Access to the Nervous System
1. Trauma to the head and back - physical method, common
2. Spinal tap - done to inject meds or withdraw CSF, invasive procedure
3. Movement along peripheral nerves - rabies
4. Bloodstream and lymphatic system - most common!!!
- Inflammation of the meninges - meningitis
- Inflammation of the brain - encephalitis
- Inflammation of both - Meningoencephalitis
Bacterial infection of the nervous system
rare, but when they do happen, they are very serious.
- Up to 50 species of bacteria can cause meningitis
- Initial symptoms of fever, headache, and stiff neck
- Followed by nausea and vomiting
- May progress to convulsions and coma, and ultimately death.
- Diagnosis from CSF, then Gram stain and latex agglutination tests (antibody test)
- Treatment: prompt broad spectrum: Cephalosporins, Vancomycin
- Mortality rate depends on organism
- Almost all will cause some kind of neurological problem
- 70% caused by these three organisms:
1. Streptococcus pnemoniae
2. Haemophillis influenzae
3. Naiserria meningitidis
Haemophilus influenzae Meningitis
- Occurs mostly in children (6 months to 4 yrs)
- Prevented by Hib vaccine given at 2 months.
- Also called meningococcal meningitis
- Caused by N. meningitidis (Gram-neg aerobic cocci with a capsule)
- 10% of people are healthy nasopharyngeal carriers
- Begins as throat infection, rash
- Varies in different parts of the world
- Vaccination (B, C, Y, W-135 capsule) recommended for college students
Streptococcus pneumoniae Meningitis
- Also called pneumococcal meningitis
- Caused by S. pneumoniae (gram-pos diplococcus)
- 70% of people are healthy nasopharyngeal carriers
- Most common in children (1 month to 4 yrs)
- Mortality: 30% in children, 80% in elderly (immuno-compromised)
- Prevented by vaccination usually given to children under the age of 2 yrs.
- Caused by Listeria monocytogenes
- Usually food borne in milk
- Pregnant women at risk : transmitted to fetus, spontaneous abortion
- Reproduce in phagocytes
- Caused by Clostridium tetani (gram-pos, endospore-forming, obligate anaerobe)
- Grows in deep wounds
- Tetanopasmin (toxin) released from dead cells blocks relaxation pathway in muscles (neurotoxin)
- Prevention by vaccination with tetanus toxoid (DTP) and booster (dT)
- Treatment: with tetanus immune globulin (TIG) (antibodies made toward toxins)
- If someone dies, its from respiratory failure
- Caused by Clostridium botulinum (Gram-pos, endospore-forming, obligate anaerobe)
- Intoxication comes from ingesting botulinal toxin
- Botulinal toxin blocks release of neurotransmitter, causing flaccid paralysis (muscle contractions)
- Prevention: proper canning, nitrites prevent endospore germination in sausages, cooking
- Get through digestive system, but its a disease of nervous system.
- Treatment: Supportive care and antitoxin
- Infant botulism: results from C. botulinum growing in intestines (honey)
- Wound botulism: results from growth of C. botulinum in wounds
- Most common way to get it is through consumption.
- Types: Type A toxin, Type B toxin, Type E toxin, BOTOX (botulinal toxin - contractions of muscles)
- Also called Hansen's disease
- Caused by Mycobacterium leprae
- Acid-fast rod that grows at 30C.
- Grows in peripheral nerves and skin cells
- Transmission requires prolonged physical contact with an infected person (not very contagious; through nasal secretions)
- Tuberculoid (neural) form: Loss of sensation in skin areas; positive lepromin test (antibody test)
- Lepromatous (progressive) form: Disfiguring nodules over body; negative lepromin test; nodules in peripheral nervous system
- Incidence: worldwide, millions still suffer in Africa and Asia
- Viral Disease -
- Transmitted by ingestion of water
- Initial symptoms: Sore throat and nausea
- Viremia may occur; in persistent, virus can enter CNS
- Destruction of motor cells and paralysis occurs in <1% of cases
- Prevention: vaccination (enhanced-inactivated polio vaccine)
- Diagnosis is by culture of throat and feces
- Mortality is from respiratory failure
- Incidence is low due to vaccines
- Salk vaccine (inactivates virus) IPV (injected polio virus)
- Sabin vaccine (attenuated (weakened) strains) OPV (oral polio virus)
- Now, only Salk is used
- Humans are the only host for this virus
- Viral Disease -
- Caused by the rabies virus
- Transmitted by animal bite; can be inhaled
- Furious rabies: Animals are restless then highly excitable
- Paralytic rabies: Animals seem unaware of surrounding (usually associated with cats)
- Replicates near source of bite in CNS. If it gets to the brain, it causes encephalitis.
- Raccoon is most common culprit in the U.S.
- Virus multiplies in skeletal muscles and then brain, causing encephalitis
- Initial symptoms may include muscle spasms of the mouth (lock jaw) and pharynx and hydrophobia ( not swallowing = foaming at mouth)
- Prevention by preexposure prophylaxis or post exposure treatment
- Preexposure prophylaxis: Injection of human diploid cells vaccine (HDCV)
- Post exposure treatment: Vaccine plus rabies immune globulin (RIG) (antibodies) (5-6 injections over 28 day period)
Pathology of Rabies Infection
1. Virus enters tissue from saliva of biting animal.
2. Virus replicates in muscle near bite.
3. Virus moves up peripheral nervous system to CNS.
4. Viras ascends spinal cord.
5. Virus reaches brain and causes fatal encephalitis.
6. Virus enters salivary glands and other organs of victim.
- Worldwide most common carrier = canine
- In the U.S. = raccoon
- In the U.S.: 8,000 cases a yr in animals, 6 cases in humans
- 20-30,000 get rabies vaccine annually
- Squirrels, rabbits, mice, rats never get rabies
- Australia, New Zealand, Hawaii, Great Britain have no rabies.
- Viral Disease -
- Arthropod-borne viruses that belong to several families
- Transmitted mostly by mosquitos
- Prevention: controlling mosquitos
- Types: Western equine (horses), Eastern equine (horses), St.Louis (humans can get it), California (only in eastern U.S.), West Nile (came from Egypt; newest national endemic)
Fungal Diseases of the Nervous System
Fungi very rarely invade the CNS
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
Protozoan Diseases of the Nervous System
Protozoans capable of invading the CNS are rare but those that do have serious effects.
- Trypansoma brucei gambiense = chronic (2 to 4 yrs)
- T. b. rhodesiense infection = acute (few months)
- Transmitted from animals to humans by tsetse fly.
- Capable of changing surface antigen
- Causes African Sleeping Sickness
- Protozoan infects nasal mucosa from swimming water / lakes / ponds.
- Causes Naegleria disease
- Caused by an amoeba
- Causes fatal encephalitis
Nervous System Diseases Caused by Prions
- Prions are self-replicating proteins without nucleic acids.
- The disease they cause are on the nervous system.
- Diseases are slowly progressive with long incubation periods resulting in degeneration of brain tissue.
- There are 9 diseases - all are 100% fatal (Sheep-Scarpie, Bovine Spongiform encephalopathy (Mad Cow Disease), Creutzfelt-Jacob Disease (CJD), Kuru)
- Human forms = CJD and Kuru
- Acquired by Ingestion
- Difficult to destroy
Chronic Fatigue Syndrome
- Also called myalgic encephalomyelitis (ME)
- Associated with a couple diseases
- On your nervous system
- Can get from mono, etc.
- Unexplained fatigue that lasts at least 6 months + 4 of these symptoms: (Sore throat, tender lymph nodes, muscle pain, pain in multiple joints, headaches, unrefreshing sleep, malaise after exercise, impaired short-term memory or concentration.