Diseases Of The Nervous System

Structure and Function of the Nervous System

Normal Flora - none

The most common route of infection is the blood, although microorganisms can enter the CNS by trauma, along peripheral nerves, and also through the lymphatic system.

The blood-brain barrier makes treatment more difficult because it prevents many substances, including antibiotics, from entering.

Terminology:

Bacterial Diseases of the Nervous System

Bacterial Meningitis

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

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

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 adminsitered 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.

Tetanus

Caused by a local infection of a wound byClostridium tetani.

Produces the neurotoxin tetanospasmin, which causes the symptoms of tetanus:

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 .

Botulism

Produces 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 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.

Leprosy (Hansen’s Disease)

Leprosy is caused by Mycobacterium leprae.

Cannot be cultured on artificial media; armadillos are usually used. (May be cultured in mouse footpads as well)

The organism is very slow growing.

The tuberculoid form of the disease (neural) is characterized by loss of sensation in skin surrounded by nodules. The lepromin test is positive.

Laboratory diagnosis is based on identification of acid-fast rods in lesions or fluids.

In the lepromatous form (progressive) disseminated nodules 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.

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.

 

Viral Diseases of the Nervous System

Poliomyelitis

Polio is caused by a picornavirus and is found only in humans.

It is transmitted by ingestion of fecally contaminated water.

Symptoms:

The virus first invades lymph nodes of the neck and small intestine. Viremia and spinal cord involvement may follow. Death may occur by respiratory failure.

Most cases are mild or asymptomatic. Vaccines keep the incidence low in the US.

Vaccines: Salk (IPV) (1954) - Formalin-inactivated virus; Requires boosters.

Sabin (OPV or TOPV) (1963) - Contains three strains of live virus – trivalent; Administered orally, no boosters.

Diagnosis is based on isolation of virus from feces and throat secretions and the presence of virus-neutralizing antibodies in the serum.

Rabies

Caused by a rhabdovirus, results in an acute, usually fatal encephalitis.

Rabies is contracted through the bite of rabid animal, by inhalation of aerosols, or invasion through minute skin abrasions. The virus multiples in the skeletal muscle and in connective tissue.

Encephalitis occurs when the virus moves along peripheral nerves to the CNS.

Symptoms: Spasms of mouth and throat muscles (hydrophobia) and brain and spinal cord damage and death.

Direct immunofluorescent (FA) test of saliva, serum or CSF or brain smears.

Reservoirs include skunks, foxes, raccoons.

Animals likely to contract the disease include domestic cattle, dogs and cats.

Rodents and rabbits seldom get rabies.

Bats are the only animal that can harbor the rabies virus without getting the disease

Treatment: Pasteur - Multiple subcutaneous injections of virus grown in rabbit brain tissue.

Postexposure treatment includes administration of human rabies immune globulin (RIG) and multiple intramuscular injections of human diploid cell vaccine.

Preexposure treatment consists of vaccination with human diploid cell vaccine.

Arboviral Encephalitis

Symptoms: Chills, fever, headache and eventual coma.

Several types of arboviruses which are transmitted by Culex mosquitoes cause the disease.

The reservoir is birds. Outbreaks more common in the summer months

when mosquitoes are most numerous.

Notifiable arboviral infections are Eastern equine encephalitis (EEE), Western

equine encephalitis (WEE), St. Louis encephalitis (SLE), California encephalitis (CE), and West Nile virus (WNV).

Diagnosis is based on serological tests.

Immune globulin is used to provide passive immunity.

Prevention: eliminate the vector.

Fungal Diseases of the Nervous System

Cryptococcus neoformans Meningitis (Cryptococcosis)

Encapsulated yeast-like fungus.

May be contracted by inhalation of dried pigeon or chicken droppings.

Begins as a lung infection and spreads to the brain and meninges.

Immunosupressed people are the most susceptible.

Diagnosis is based on serological tests (latex agglutination ) for cryptococcal antigens in serum or CSF.

Treatment: Amphotericin B and flucytosine in combination. Mortality rate may approach 30%.

Protozoan Diseases of the Nervous System

African Trypanosomiasis

Caused by Trypanosoma brucei gambiense and Trypanosoma brucei rhodesiense and is transmitted by the bite of the tsetse fly (Glossina).

The disease affects the nervous system causing lethargy and eventual coma. It is commonly called sleeping sickness. If untreated, death results.

Vaccine development is hindered by the protozoan's ability to change its surface antigens.

Naegleria Meningoencephalitis

Encephalitis caused by the protozoan Naegleria fowleri is almost always fatal.

It is contracted from stream or pond water and children are the most common victims.

N. fowleri infects nasal mucosa and spreads to the brain. Diagnosis is usually upon autopsy.

Nervous System Diseases Caused by Prions

Diseases of the CNS that progress slowly and cause spongiform degeneration are caused by prions.

Diseases Caused by Unidentified Agents

Chronic Fatigue Syndrome

Chronic fatigue syndrome may be caused gby an unidentified infectious agent.