Chapter 22 Microbial Diseases of the Nervous System

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1

meninges

Both the brain and the spinal cord are covered and protected
by three continuous membranes called meninges

2

dura mater

outermost meninges

3

arachnoid mater

middle meninges

4

pia mater

innermost meninges

5

subarachnoid space

Between the pia mater and arachnoid
membranes

an adult has 100 to 160 ml of cerebrospinal fluid (CSF) circulating

6

Is meningitis an infection of the CNS or the PNS

...

7

meningitis

inflammation of the meninges

8

encephalitis

inflammation of the brain

9

meningoencephalitis

both
the brain and the meninges are affected, the inflammation

10

Why can the antibiotic chloramphenicol readily cross the
blood–brain barrier, whereas most other antibiotics cannot?

it is lipid soluble

11

Encephalitis is an inflammation of what organ or organ
structure?

the brain

12

Viral meningitis

is probably
much more common than bacterial meningitis but tends
to be a mild disease.

Most cases occur in the summer and fall
months and are usually caused by a varied group of viruses
termed enteroviruses

13

Enteroviruses

grow well in the throat and intestinal tract; they are responsible
for an assortment of mostly minor diseases.

Viral meningitis
can also be an occasional complication of viral infections such
as mumps, chickenpox, and influenza

14

three bacterial species have caused most
of the cases of meningitis

caused by Haemophilus influenzae type B,

about 80% of the cases are
now caused by Neisseria meningitidis and Streptococcus pneumoniae.

All three of these pathogens possess a capsule that
protects them from phagocytosis as they replicate rapidly in the
bloodstream, from which they might enter the cerebrospinal
fluid

15

Haemophilus influenzae Meningitis

is an aerobic, gram-negative bacterium
that is a common member of the normal throat microbiota

In addition to causing meningitis, it is also frequently
a cause of pneumonia (page 693), otitis media (page 685),
and epiglottitis

The carbohydrate capsule of the bacterium is
important to its pathogenicity, especially those bacteria with
capsular antigens of type b. (Strains that lack a capsule are called
nontypable.)

16

Neisseria Meningitis (Meningococcal Meningitis

caused by Neisseria meningitidis
(the meningococcus). This is an aerobic, gram-negative bacterium
with a polysaccharide capsule that is important to its virulence

A case of meningococcal meningitis
typically begins with a throat infection, leading to bacteremia
and eventually meningitis.

17

Streptococcus pneumoniae Meningitis
(Pneumococcal Meningitis)

Streptococcus pneumoniae, like H. influenzae, is a common inhabitant
of the nasopharyngeal region.

About 70% of the general population are healthy carriers

The pneumococcus, so called because
it is best known as a cause of pneumonia (Chapter 24), is a
gram-positive, encapsulated diplococcus

18

Listeria monocytogenes

is a gram-positive rod known to cause
stillbirth and neurological disease in animals long before it was
recognized as causing human disease

19

How is listeriosis contracted?

the organism is mostly foodborne.
It is frequently isolated from a wide variety of foods; ready-toeat
deli meats and dairy products have been involved in several
outbreaks.

L. monocytogenes is one of the few pathogens capable
of growth at refrigerator temperatures, which can lead to an increase
in its numbers during a food’s shelf life

20

Microscopically, what would you see in CSF from a healthy
person? A person with meningococcal meningitis?

clear CSF;Neisseria meningitidis

21

Why is meningitis caused by the pathogen Listeria monocytogenes
frequently associated with ingestion of refrigerated foods?

L. monocytogenes is one of the few pathogens capable
of growth at refrigerator temperatures, which can lead to an increase
in its numbers during a food’s shelf life

22

What body fluid is sampled to diagnose bacterial meningitis?

CSF

23

tetanus

Clostridium tetani, is an obligately
anaerobic, endospore-forming, gram-positive rod

24

tetanospasmin

symptoms of tetanus are caused by an extremely potent
neurotoxin that is released upon death and lysis
of the growing bacteria

25

What is the name of the toxin that causes opisthotonos?

tetanospasmin

26

tetanus vaccine

is a toxoid,
an inactivated toxin that stimulates the formation of antibodies
that neutralize the toxin produced by the bacteria

27

tetanus immune globulin (TIG),

temporary immunity can be
conferred by tetanus immune globulin (TIG), prepared from the
antibody-containing serum of immunized humans

28

antisera

Made by inoculating horses, antisera were very effective in
lowering the incidence of tetanus in injured people.

29

debridement

To minimize the production of more toxin, damaged
tissue that provides growth conditions for the pathogen
should be removed, a procedure called debridement (sounds
like “de-breed-ment”), and antibiotics should be administered

30

Is the tetanus vaccine directed at the bacterium or the toxin
produced by the bacterium?

toxin

31

Botulism

a form of food poisoning, is caused by Clostridium
botulinum, an obligately anaerobic, endospore-forming grampositive
rod found in soil and many aquatic sediments.

microorganism produces an exotoxin.

This neurotoxin
is highly specific for the synaptic end of the nerve, where
it blocks the release of acetylcholine, a chemical necessary for
transmitting nerve impulses across synapses

32

flaccid paralysis

botulism undergo a progressive
flaccid paralysis for 1 to 10 days and may die from respiratory
and cardiac failure

33

What are the symptoms of botulism?

flaccid paralysis

34

The very name botulism is derived from the fact that sausage was
the most common food causing the disease. Why is sausage now
rarely a cause of botulism?

nitrates added

35

Hansen’s disease

is the more formal
name for leprosy;

36

Which form of leprosy is more likely to occur in immunosuppressed individuals? Why?

If the immune system fails to control the
disease, the result is lepromatous (progressive) leprosy

37

skin biopsy
sample

The standard diagnostic test for leprosy

38

Why are nude mice and armadillos important in the study
of leprosy?

mice and armadillos are used to grow M. leprae

39

Salk
vaccine

consists of viruses of all three types
that have been inactivated (killed) by treatment with formalin.

Vaccines of this types, called inactivated polio vaccines (IPV)

40

Sabin vaccine

contains
living, attenuated (weakened) strains of the virus in a suspension
that is ingested

is more commonly called oral polio vaccine (OPV).
It usually contains the three types of polio virus (trivalent,
tOPV).

41

Why is it possible to eradicate
polio but not tetanus?

vaccine for polio

42

Why is paralytic polio more likely to occur than a mild or asymptomatic
infection in areas with high standards of sanitation?

Improved sanitation delayed
exposure to polioviruses in feces until after the protection provided
by maternal antibodies had waned. At one time, exposure
to the poliovirus was frequent (and is still so today in parts of the
world with poor sanitation).

Infants were usually exposed to poliovirus
while still protected by maternal antibodies.

The result was
usually an asymptomatic case of the disease and a lifelong immunity.

When infection is delayed until adolescence or early adulthood,
the paralytic form of the disease appears more frequently

43

Rabies

(the word is from the Latin for rage or madness) is a disease
that almost always results in fatal encephalitis

The causative
agent is the rabies virus, a member of the genus lyssavirus having
a characteristic bullet shape

44

paralytic (dumb or numb) rabies

which there is only minimal excitability. This form is especially
common in cats

45

postexposure
prophylaxis (PEP)

meaning a series of antirabies vaccine and immune
globulin injections

46

human diploid cell vaccine (HDCV)

rabies vaccine

vaccines are
administered in a series of four injections at intervals during
a 14-day period

47

human rabies immune globulin (RIG)

Passive immunization is provided simultaneously
by injecting human rabies immune globulin (RIG) that has
been harvested from people who are immunized against rabies

48

Sentinel animals

such as caged
chickens, are tested periodically for antibodies to arboviruses.
This gives health officials information on the incidence and types
of viruses in their area

49

cryptococcosis

caused by fungi of the genus Cryptococcus.
They form spherical cells resembling yeasts, reproduce by
budding, and produce extremely heavy polysaccharide capsules

50

What is the most common source of airborne cryptococcal
infections?

bird droppings

51

African trypanosomiasis

sleeping sickness, is a protozoan disease
that affects the nervous system

disease is caused by two subspecies of Trypanosoma
brucei that infect humans: Trypanosoma brucei gambiense and
Trypanosoma brucei rhodesiense

These protozoans are flagellates (see Figure 23.23
on page 667 for the appearance of a similar organism) that are
spread by tsetse fly vectors

52

primary amebic meningoencephalitis (PAM)

Naegleria fowleri is a protozoan (ameba) that causes a neurological
disease, primary amebic meningoencephalitis (PAM)

53

How is amebic meningoencephalitis transmitted?

swim in warm ponds or streams. The organism initially infects
the nasal mucosa and later penetrates to the brain and proliferates,
feeding on brain tissue

54

What insect is the vector for African trypanosomiasis

tsetse fly species that inhabits stream vegetation

55

a prion

abnormally folded protein

56

bovine spongiform encephalopathy
(BSE)

mad cow disease

57

What are the recommendations for sterilizing reusable surgical
instruments when prion contamination might be a factor?

a strong solution of sodium hydroxide combined
with extended autoclaving at 134°C.


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