4 microbial diseases of the nervous system

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The Human Nervous System


The Meninges and CSF


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


The Nervous System

Meningitis: Inflammation of meninges

-Meningitis can be caused by viruses, bacteria, fungi, and protozoa.

Encephalitis: Inflammation of the brain

Meningoencephalitis: Inflammation of both


A. Bacterial Diseases of the Nervous System

a.Bacterial Meningitis

3 major causes: Hemophilus

influenzae , Streptococcus pneumoniae , and Neisseria

meningitidis

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


Spinal Tap (Lumbar Puncture)


Haemophilus influenzae Meningitis

Occurs mostly in children (6 months to 4 years)

Gram-negative aerobic bacteria, normal throat

microbiota

Mortality rate (6%)

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


Neisseria Meningitis


Meningococcal Rash

Exotoxins damage blood vessel walls

blood leaks into skin

Purplish spots appear on the

skin.


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

Usually foodborne;

it can be

transmitted to

fetus

Reproduce in

phagocytes


Diseases in Focus: Meningitis and Encephalitis

A worker in a day-care center in eastern North Dakota became ill with fever, rash, headache, and abdominal pain. The patient had a precipitous clinical decline and died on the first day of hospitalization. Diagnosis was confirmed by Gram staining of cerebrospinal fluid.

Can you identify infections that could cause these symptoms?


Tetanus (Lockjaw)

Caused by Clostridium tetani

Gram-positive, endospore-forming, obligate

anaerobe

Grows in deep wounds

Tetanospasmin released from dead cells blocks

relaxation pathway in muscles Spasms

Contractions of the jaw muscles, Death - from

paralysis of the respiratory muscles

Prevention by vaccination with tetanus toxoid (DTP)

and booster (dT)

Treatment with tetanus immune globulin (antitoxin)


Tetanospasmin Action

Blockage of

inhibitory NT release

in CNS

Result ?


An Advanced Case of Tetanus

Characteristic condition: Opisthotonos


- The further the injury site from the CNS, the longer the

incubation period

- The shorter the incubation period , the more severe the

symptoms.


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


Botulism

Treatment: Supportive care and antitoxin

a. Infant botulism: due to ingestion of endospores;

results from C. botulinum growing in intestines

(Botulism Immune Globulin Intravenous-Human (BIG-IV

or BabyBIG)

b. Wound botulism: start ~ 4 days after wound

infection results from growth of C. botulinum in wounds

c. Foodborne botulism: Intoxication not infection!

Endospores survive improper canning procedures.

https://www.boundless.com/definition/immune/


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


Botulinum Toxin: Killer and Healer

Botox (Botulinum toxin type A)

Medical uses:strabismus, torticollis . . . . . etc.

Under investigation: migraine headaches,

hyperhidrosis

Cosmetic purposes


Leprosy

Also called Hansen’s 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

Incubation time: Months to 10 years


Leprosy

Tuberculoid (neural) form: Loss of sensation in

skin areas; positive lepromin test

Lepromatous (progressive) form: Disfiguring

nodules over body; negative lepromin test


Common symptoms:

Runny nose

Dry scalp

Eye problems

Skin lesions

Muscle weakness

Reddish skin

Smooth, shiny, diffuse thickening of skin on the face, ears, and hands

Loss of sensation in fingers and toes

Thickening of peripheral nerves

Flat nose due to destruction of nasal cartilage

There is also phonation and resonation of sound during speech. Often

there is atrophy of the testes and impotency.


Leprosy Lesions


Leprosy Lesions

Patient with active,

neglected nodulous

lepromatous leprosy.

With treatment, all

nodules could be

reversed.

©WHO/TDR/McDougall


Diseases in Focus: Diseases with Neurological Symptoms or Paralysis

After eating canned chili,

two children experienced

cranial nerve paralysis

followed by descending

paralysis. The children

are on mechanical

ventilation. Leftover

canned chili was tested

by mouse bioassay.

Can you identify

infections that could

cause these symptoms?


Viral Diseases of the Nervous System

VIRAL MENINGITIS: Usually

mild. Clears up within a week or

two without specific treatment.

Also called aseptic meningitis.Poliomyelitis

Rabies

Viral meningitis

Viral encephalitis


Poliomyelitis (Infantile Paralysis)

Poliovirus (Enteroviruses of picornaviridae)

Transmitted by ingestion of fecally contaminated water.

90% of cases asymptomatic

Initial symptoms: Sore throat and nausea

Symptoms: Headache, Fever, Stiffness of the back and neck, Occasionally

paralysis (less than 1%)

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.


Prevention: vaccination (enhanced IPV)

Diagnosis is based on isolation of virus from

feces and throat secretions and the presence of

virus-neutralizing antibodies in the serum.


Rabies Virus (of Rhabdoviridae)

Zoonosis–Transmission from saliva of rabid animal

Virus multiplies in skeletal muscles, then retrograde axonal transport to CNS

(encephalitis), then back out to periphery (salivary glands etc.)

Initial symptoms may include muscle spasms of the mouth and pharynx and

hydrophobia.

Furious rabies: Animals restless then highly excitable.

Paralytic rabies: Animals unaware of surroundings.


Pathology of Rabies Infection


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

Arboviruses are arthropod-borne viruses that belong to several families.

Prevention by mosquito(Culex mosquito) control.

Horses and humans affected.

Incidence of arboviral encephalitis in summer, when mosquitoes are most

numerous.

Sentinel animals, e.g.: caged chickens

Diagnosis based on serological tests.

Symptoms from subclinical to coma and death


Notifiable Arboviral Encephalitis InfectionsEncephalitis Reservoir Mosquito vector U.S. distribution

Western equine Birds, horses Culex

Eastern equine Birds, horses Aedes, Culiseta

St. Louis Birds Culex

California Small mammals Aedes

West Nile Birds, mammals Culex, Aedes


Fungal Disease of Nervous System

Cryptococcus neoformans Meningitis

Also called cryptococcosis

Soil fungus associated with pigeon and chicken (aerosolization

of dried up contaminated droppings)

Transmitted by the respiratory route; spreads through blood to

the CNS

Begins as a lung infection and spreads to the brain and

meninges.


Mortality up to 30% –Primarily affects AIDS

patients

Diagnosis: Serology to detect cryptococcal

antigens in serum or CSF

Treatment: Amphotericin B and flucytosine


Protozoan Diseases of Nervous System

African Trypanosomiasis (Sleeping Sickness)

-Caused by Trypanosoma brucei; vector: tsetse fly(day-biting)

T.b. gambiense infection is chronic (2 to 4 years).

T.b. rhodesiense infection is more acute (few months).

Symptoms: chancre -intermittent fever –CNS invasion. Without

treatment: death


A woman caring for her comatose husband who is dying of

African trypanosomiasis, Uganda, 1990


Amoebic meningoencephalitis

-an often-fatal central nervous system infection caused

by Naegleria fowleri.

Naegleria fowleri nasal passage olfactory

bulbs forebrain death within 14 days

from initial exposure

- largely asymptomatic until its final stages

- Avoiding the infection by wearing nose plugs

when swimming in warm water is a good

preventative measure.

https://www.boundless.com/definition/asymptomatic/


Nervous System Diseases Caused by Prions

Transmissible Spongiform Encephalopathies

-Prions convert normal proteins into abnormal proteins

-Post mortem sponge-like appearance of brain tissue large

vacuoles in cortex and cerebellum due to loss of neurons

-Chronic and fatal

-Transmitted by ingestion or transplant or inherited.

Typical diseases

Sheep scrapie

Creutzfeldt-Jakob disease

Kuru

Bovine spongiform encephalopathy


Bovine spongiform encephalopathy (BSE)

-a fatal neurodegenerative disease in cows (mad cow

disease)

- caused by a misfolded protein known as a prion;

-Cooking of prions does not destroy them.

- about 30 months to 8 years, usually affecting adult

cattle at a peak age of four to five years, all

breeds being equally susceptible

https://www.boundless.com/definition/protein/

https://www.boundless.com/definition/prion/

https://www.boundless.com/definition/susceptible/


A cow suffering from BSE. The disease has progressed so far the

animal cannot stand.

https://www.boundless.com/microbiology/textbooks/boundless-microbiology-textbook/diseases-15/fungal-protozoan-prion-and-other-nervous-system-diseases-172/bovine-spongiform-encephalopathy-859-5455/images/bovine-spongiform-encephalopathy-bse/

https://www.boundless.com/microbiology/textbooks/boundless-microbiology-textbook/diseases-15/fungal-protozoan-prion-and-other-nervous-system-diseases-172/bovine-spongiform-encephalopathy-859-5455/images/bovine-spongiform-encephalopathy-bse/


In humans, it is known as new variant

Creutzfeldt–Jakob disease (vCJD or nvCJD)

*October 2009- 166 people died in the United

Kingdom and 44 elsewhere


Kuru


How can a protein be infectious?

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