Microbial Diseases Of The Nervous System |
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Objectives: Bacterial Diseases of the Nervous System
For each microbial disease listed give the following if applicable:
Diseases:
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The Meninges And CSF
The three major causes of bacterial meningitis are Haemophilus influenzae, Streptococcus pneumoniae, and Neisseria meningitidis.
Nearly 50 species of opportunistic bacteria can cause meningitis.
Prodromal symptoms are like a mild cold.
Later symptoms usually include headache, nausea and vomiting.
Haemophilus influenzae Meningitis
Cultured on chocolate agar containing:
Most common cause of meningitis in children under 4 years of age.
Often a secondary infection following viral infections such as the flu.
Capsular polysaccharide conjugated vaccine (1988) is available and produces effective immunity.
Since introduction of the vaccine the incidence of meningitis in infants and children has been reduced 99%.
Incidence in older children and adults has remained unchanged.
Mortality rate is 6%
Diagnosis is based on culture and identification from the CSF.
Incidence Of H. influenzae Meningitis In The U.S.
Neisseria meningitidis (Meningococcal meningitis)
Aerobic, gram-negative coccus with a polysaccharide capsule, which makes it very resistant to phagocytosis. It is found in the throats of healthy carriers (10% of the population).
Probable mode of spread to the meninges is through the blood. The bacteria may live in leukocytes in CSF.
The symptoms are due to endotoxin. The disease occurs most often in young children.
Purplish spots appear on the skin.
Problem in military training camps, therefore a purified capsular polysaccharide vaccine is administered to military recruits to prevent epidemics.
Diagnosis based on isolation and identification of the organisms from either the blood or the CSF.
Cultivation requires blood agar and incubation in 5% to 10% carbon dioxide atmosphere.
Neisseria meningitidis
Streptococcus pneumoniae Meningitis (Pneumococcal Meningitis)
Hospitalized patients and children are the most susceptible. It is rare but has a high mortality rate (26%).
Because of a capsule the organism is resistant to phagocytosis.
Capsular vaccine is available but not effective in children under age 2. A conjugated vaccine was recently introduced.
Diagnosis and Treatment of the Most Common Types of Bacterial Meningitis
Cephalosporin may be administered before identification of the pathogen.
Diagnosis is based on Gram stain and serological tests of the bacteria in CSF.
Cultures are usually made on blood agar and incubated in an atmosphere containing reduced oxygen levels.
Listeriosis
Listeria monocytogenes causes meningitis in newborns, the immunosupressed, pregnant women, and cancer patients.
Contracted by the ingestion of contaminated food, especially diary products.
Can be ingested by phagocytes but is not destroyed and can divide in them.
The disease is usually asymptomatic in adults.
The organism can cross the placenta and cause spontaneous abortion and stillbirth.
Cell-To-Cell Spread Of L. monocytogenes, The Cause Of Listeriosis
Caused by a local infection of a wound by Clostridium tetani.
Produces the neurotoxin tetanospasmin, which causes the symptoms of tetanus:
Blocks relaxation pathway so antagonists contract at the same time agonists contract.
Anaerobic organism that grows in unclean wounds and wounds with little bleeding.
Prevention: DPT vaccine which contains tetanus toxoid.
Immunized persons may receive a booster of tetanus toxoid. An unimmunized person may receive tetanus immune globulin (antitoxins).
Infection may be controlled by debridement and antibiotics.
An Advanced Case Of Tetanus
Caused by production of exotoxin when Clostridium botulinum grows in foods.
There are several different serological types which vary in virulence; type A is the most virulent.
The exotoxin is a neurotoxin which inhibits transmission of nerve impulses (blocks synaptic release of acetylcholine) resulting in respiratory failure and cardiac failure.
Symptoms:
The mortality rate is 60% to 70% in untreated cases.
The organisms does not grow in acidic food such as most fruits or in an aerobic environment.
Endospores can be killed by using a pressure cooker in canning. Addition of nitrites to commercially packaged foods inhibits growth after endospore germination.
The toxin can be destroyed by boiling for five minutes (100 degrees C).
Wound botulism occurs when C. botulinum grows in anaerobic wounds.
Infant botulism results from growth in infant’s intestines. Some cases (30%) have been associated with honey. This problem does not seem to occur in older children - reason unknown.
Diagnosis by mouse inoculation with food or with patient samples of blood, stool, or vomitus.
Treatment: Supportive care and antitoxins may be administered, but they will not affect toxin bound to nerve endings. Antibiotics are useless.
The nerve endings may regenerate but this occurs slowly - neurological impairment may exist for months.
Respiratory assistance may be required for an extended period.
Vaccines are not used.
Diagnosis Of Botulism By The Identification Of Botulinal Toxin Type
Leprosy is caused by Mycobacterium leprae.
Cannot be cultured on artificial media; armadillos were classically used due to their low body temperature but cultures are now usually done in the footpads of athymic nude mice.
The organism is very slow growing.
The tuberculoid form of the disease (neural) is characterized by areas of skin that exhibit a loss of sensation and are surrounded by nodules.
Laboratory diagnosis is based on identification of acid-fast rods in lesions or fluids and the lepromin test is positive. (The lepromin test consists of injection of an extract of lepromatous tissue into the skin; a localized reaction indicates cell-mediated immunity has developed.) So people with the tuberculoid form of the disease have mounted an immune response and may even recover spontaneously.
In the lepromatous form (progressive) nodules are disseminated and tissue necrosis occurs. The lepromin test is negative.
The disease is not highly contagious and is spread by prolonged contact with exudates and fomites (makes you wonder about those Texans who have been reported to have contracted leprosy from contact with armadillos - how do you have prolonged contact with an armadillo?).
While the disease is rarely fatal untreated individuals often die from secondary infections such as tuberculosis.
Patients can be rendered noncommunicable within four or five days by administration of sulfone drugs and then treated as outpatients.
The disease is primarily a disease of the tropics.
Leprosy Lesions
