Chapter 22: Microbial Diseases of the Nervous System

What is the central nervous system (CNS)?

brain and spinal cord

What is the Peripheral nervous system (PNS)?

nerves that branch from the CNS

What are the Meninges?

nerves that protect the brain and spinal cord

What consists of the Meninges?

Dura, arachnoid and pia mater; outer, middle, and innermost layers, respectively

• Subarachnoid space contains cerebrospinal fluid (CSF)

What is the blood-brain barrier?

• Drugs can cross if small and lipid-soluble

• immune cells

What is Meningitis?

Inflammation of the meninges

What is Encephalitis?

Inflammation of the brain

What is Meningoencephalitis?

Inflammation of both the meninges and the brain

What are the initial symptoms of Bacterial Meningitis?

• fever, headache, and stiff neck

• followed by nausea and vomiting

• can progress to convulsions and coma

How can someone die from Bacterial Meningitis?

from shock and inflammation

• due to endotoxin and cell wall release

How does bacterial Meningitis compare to viral meningitis?

it is more common and mild

What is Haemophilus influenzae Meningitis?

• Gram-negative aerobic bacteria; normal throat microbiota

• Can enter the bloodstream

• Pathogenicity due to capsule antigen type b

Who is affected by Haemophilus influenzae Meningitis?

children (6 months to 4 years old)

How is Haemophilus influenzae Meningitis prevented?

Hib vaccine

How many bacterial meningitis cases does Haemophilus influenzae Meningitis account for & what morality rate?

45%; 6% mortality

What is Neisseria meningitidis Meningitis (Meningococcal Meningitis)?

Aerobic, gram-negative diplococcus with a capsule

• six serotype associated with the disease

What is the percentage of healthy people that are nasopharyngeal carriers?

40%

How does Neisseria meningitisdis Meningitis begin?

a throat infection, rash (does not fade when pressed), and bacteremia

What is the morality rate of Neisseria meningitidis Meningitis?

9-12% with antibiotic therapy; 80% without

Where do outbreaks of Neisseria meningitidis Meningitis start?

dorms and military barracks

Which serogroups does the vaccination of Neisseria meningitidis Meningitis protext against and not protect against?

protects against serogroups A, C, Y, A and B but not X

What is Streptococcus pneumoniae Meningitis (Pneumococcal Meningitis)?

Gram-positive, encapsulated diplococcus

What is the percentage of nasopharyngeal carriers on Streptococcus pneumonia Meningitis?

70% of people are healthy nasopharyngeal carriers

What does Streptococcus pneumonia Meningitis cause?

pneumonia and otitis media

In what age is Streptococcus pneumonia Meningitis most common?

children (1 month to 4 years)

What is the morality rate of Streptococcus pneumonia Meningitis?

8% in children, 22% in the elderly

How is Streptococcus pneumonia Meningitis prevented?

conjugated vaccine

How is Bacterial Meningitis most commonly diagnosed?

• Sample cerebrospinal fluid CSF via a spinal tap or lumbar puncture

  • pathogens in CSF do not survive storage or changes in temp

• Latex agglutination tests

• Chemotherapy initiated before diagnosis

  • Broad-spectrum third-generation cephalosporins

What is Listeriosis caused by?

Listeria monocytogenes

• gram-positive rod

How is Listeriosis spread?

foodborne or symptomatic

• meningitis more common in the immunocompromised

What can Listeriosis invade?

bloodstream, which causes sepsis

How does Listeriosis reproduce?

in phagocytes

• spread phagocyte-to-phagocyte

How does Listeriosis affect pregnant women?

crosses the placenta which leads to still birth

What is tetanus caused by?

Clostridium tetani

• gram-positive, endospore-forming, obligate anaerobe

Where does tetanus grow?

in deep wounds with anaerobic conditions

What toxin is released in tetanus?

Tetanospasmin neurotoxin is released from dead bacterial cells

What is the process of the Tetanus toxin being released from bacterial cells?

• Enters CNS

• Blocks the relaxation pathway in muscles, causing muscle spasms

  • death occurs from spasms of respiratory muscles

How is Tetanus prevented?

vaccination with a Tetanus toxoid (DTaP)

• Stimulates antibodies that neutralize the toxin

• Booster required every 10 years

How many cases of Tetanus are there and what is the morality rate?

Fewer than 10 cases per year

• 25-50%

What is the treatment for Tetanus?

immune globuilin (TIG)

What has to be removed with Tetanus?

infected tissue removed via debridement

What is Botulism caused by?

Clostridium botulinum

• gram-positive, endospore-forming, obligate anaerobe

What does the intoxication of Botulism come from?

ingesting the botulinal endotoxin

• specific for the synaptic end of the nerve

• blocks release of the neurotransmitter acetylcholine causing flaccid paralysis

How do people die from Botulism?

respiratory or cardiac failure

What are the different types of Botulinal?

• Type A toxin

  • fatality: 60-70%

  • Heat-resistent and proteolytic

• Type B toxin

  • Fatality: 25%

• Type E toxin

  • produced by organisms in marine and lake sediments

  • less heat resistant than other strains

How are the different types of Botulinal types diagnosed?

inoculating immunized mice with patient samples

What is Infant botulism?

C. botulinum growing in the intestines of infants due to a lack of intestinal microbiota

• associated with honey

What is Wound botulism?

growth of C. botulinum in wounds

How do you treat infant and wound botulism?

respiratory assistance and antitoxins

How do you prevent infant and wound botulism?

proper canning and the use of nitrites in foods

What is Leprosy caused by?

aka Hansen’s disease

• Caused by Microbacterium leprae

  • Acid-fast rod that grows best as 30 degrees C

  • Generation time of 12 days

Where does Leprosy grow?

peripheral nerves and skin cells

• survives macrophages and invades the myelin sheath

How is Leprosy transmitted?

requires prolonged contract with an infected person or the inhalation of secretions

What is Tuberculoid (neutral) form?

A form of leprosy where there is a loss of sensation in skin areas

What is Lepromatous (progressive) form?

A form of Leprosy in which disfiguring nodules over the body; mucous membranes are affected

How many cases of Tuberculoid and Lepromatous are there?

100 per year, most immigrants from endemic countries

How do you diagnose Tuberculoid and Lepromatous?

skin biopsy or skin smear, blood test

How do you treat Tuberculoid and Lepromatous?

antibiotics (Capsone, Rifampin, and Clofazimine) for 6 to 24 months

What is Poliomyelitis caused by?

Poliovirus

How is Poliomyelitis transmitted?

ingestion of water containing feces containing the virus

What are the initial symptoms of Poliomyelitis?

sore throat and nausea

What can occur in Poliomyelitis?

Viremia may occur; enters the CNS

• One percent of cases become paralytic

• Destruction of motor nerve cells

• death from respiratory failure

What are the vaccines of Poliomyelitis?

• Salk vaccine: inactivates vaccine; injected

• Sabin vaccine: attenuated vaccine; oral; lifelong immunity

What is the cure for Polio?

no cure, but fell 99% from 1988 to 2000

Where is Polio still present?

Nigeria, Pakistan, and Afghanistan

What is Rabies caused by?

rabies virus

• Genus Lyssavirus; bullet-shaped

• Single-stranded RNA; easily developed mutants

How is rabies transmitted?

saliva of an animal bite

• can also cross mucous membranes

What is the most common cause of Rabies?

Silver-haired bats

What are the initial symptoms of Rabies?

muscle spasms of the mouth and pharynx; hydrophobia

Where does the Rabies virus multiply?

skeletal muscles and travels through the PNS to the brain cells, causing encephalitis

• average incubation of 30-50 days

• forms Negri bodies in the brain stem

What is furious (classical) rabies?

animals are restless, then highly excitable

What is paralytic (dumb or numb) rabies?

animals seems unaware of their surroundings; minimally excitable

What is the pathology of Rabies infection?

1. Rabies virus enters the host via a bite from a rabid animal

2. Virus proliferates in the PNS

3. Virus travels up the PNS to the CNS

4. Virus reaches the brain (CNS) and causes fatal encephalitis

How do you diagnose Rabies?

bodily fluids with the direct fluorescent-antibody (DFA) test

What is postexposure prophylacis (PEP)?

vaccine plus immune globulin

• human diploid cell vaccine (HDCV)

• human rabies immune globulin (RIG)

Describe the treatment for Rabies?

very little effective treatment

What kinds of animals does Rabies occur in?

bats. skunks, foxes, raccoons, and domestic animals

• rarely in squirrels, rabbits, rats, and mice

How many humans get rabies annually?

6

What are related Lyssavirus Encephalitis with Rabies?

• Clinically indistinguishable from classic rabies

• Found in countries free of rabies

• Australian bat lyssavirus (ABLV)

• European bat lyssavirus (EBLV)

What is Congenital infections?

cross the placenta and cause serious damage to a fetus

What are some viral diseases with the vertical transfer that are harmful to developing babies?

• Zika virus disease

• Neonatal herpes

• Cytomegalovirus (CMV) infections

What are some bacteria and protozoan that can cross the placenta and cause disease

• Treponema pallidum

• Listeria monosytogenes

• Group B Streptococcus

• Elizabethkingia

• Toxoplasma gondii

What is the test that screens pregnant women for diseases that transmit vertically?

TORCH

What is the TORCH test?

• Panel of tests that screen for antibodies to infections in pregnant women

• Toxoplasmosis

• Other (Such as syphalis, chickenpox, HIV, measles, mumps, and hep B)

• Rubella

• Cytomegalovirus

• Herpes simplex virus

What is Arbovirus Encephalitis?

anthropod-borne virus

• belong to several families

What is Arboviral Encephalitis caused by?

mosquito-borne viruses

What are the two different types of Erboviral Encephalitis?

• Eastern equine encephalitis (EEE) and western equine encephalitis (WEE)

What is the morality of Eastern equine encephalitis (EEE) and western equine encephalitis (WEE)?

30% in humans

What does Eastern equine encephalitis (EEE) and western equine encephalitis (WEE) cause?

brain damage, deafness, and neurological

What is St. Louis encephalitis (SLE)?

• Distributed mostly in the central and eastern US

• Fewer than 1% of the infected show symptoms

What is California encephalitis (CE)?

Mild and rarely fatal

What is West Nile virus (WNV)?

• Maintained in the bird-mosquito-bird cycle

• Carried by Culex mosquitos

• Can cause polio-like paralysis and fatal encephalitis

What is Heartland virus disease?

Neurological problems, thrombocytopenia, leukopenia

What is Powassan virus (POW)

• Distributed mostly in northeastern US and Great Lake region

• Long-term neurological problems may occur

• Morality of 10-15%

What is Japanese encephalitis?

• found in the Far East and South Asia

• One percent show symptoms, but there is a 20-30% morality in those with symptoms

How is Abroviral Encephalitis diagnosed?

ELISA tests (to identify IgM antibodies)

How can you prevent Arboviral Encephalitis?

controlling mosquitos

How is Zika Virus transmitted?

the bite of infected Aedes spp. moquitos

• other include sexual intercourse, mother to child, and blood transfusions

What perfect of people infected with the Zika virus show symptoms?

20%, symptoms are usually mild

What happens if a pregnant women gets the Zika Virus?

increases the risk of microcephaly in infants