Download CHAPTER 24 INFECTIONS OF THE CENTRAL NERVOUS SYSTEM

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Transcript

CNS consists of the brain and the spinal cord
&infections can be caused by:
›
›
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Normal bacterial flora
Pathogens acquired through ingestion
Pathogens acquired during the birthing process
Contamination of shunts
Infection of the meninges ( the system of
membranes which envelopes the central nervous
system).
 Usually caused by a bacterial infection
 Characterized by fever, irritability, and various
degrees of neurological dysfunction

Usually caused by Mycobacterium tuberculosis,
fungi, or protozoan parasites.
 Characterized by fever, headache, stiff neck and
back, nausea, and vomiting

Involves seizures, paralysis, or defective mental
faculties.
 Problem is not with the meninges, but the actual
nervous tissue.
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POLIOMYELITIS: Infection which destroys cells
associated with the anterior the spinal cord, and brain
stem.
Causes weakness or paralysis of muscle groups
& Can cause respiratory difficulties
Characterized by asymmetrical paralysis
ACUTE POLIOMYELITIS : Inflammatory infection of
the peripheral nervous system (consists of the nerves and
ganglia outside of the brain and the spinal cord)
Characterized by symmetrical paralysis
Can be caused by diphtheria toxin, enteric pathogens,
cytomegalovirus, and Epstein-Barr virus

Acute meningitis usually caused by:
› H. influenzae
› N. meningitidis
› S. pneumoniae
A vaccine is available to protect against H.
influenzae.
 Group B streptococci and E. coli often involved
in meningitis in newborns

› Acquired through the birthing process

Most common viral causes of acute CNS
infections:
› Enterovirus
› Herpes simplex virus
› HIV
› Epstein-Barr virus
› Also several arthropod-borne viruses

Deep fungal mycoses Cryptococcus neoformans
and Coccidioides immitis

Tetanus is caused by Clostridium tetani.
›
›
›
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Gram-positive
Anaerobic
Rod shaped
Produces a terminal spore
Toxin produced by C. tetani is neurogenic
© CDC

Etiologic agent is Clostridium botulinum.
›
›
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
Gram-positive
Anaerobic
Spore-forming
Rod-shaped
Found naturally in soil and sediments of ponds
and lakes.
Rabies is an acute and fatal viral CNS infection.
Can affect all mammals
Transmitted by infected secretions (usually
through a bite).
 Prevention is the best cure.
 Treatment consists of a course of injections.



› Only beneficial if administered before the onset of
symptoms

Mortality for rabies is 90%.

Enterovirus - Condition first known as infantile
paralysis
› Risk of paralysis actually increases with age.

Essentially nonexistent in most modern countries
› There is an effective vaccine.

Still a major problem in underdeveloped
countries

BSE (mad cow disease) was first identified in the
UK in 1986.
› Source of prions traced to cattle feed containing bone
meal from sheep that had scrapie.
› Cows ate the feed and became infected.
› The infection passed to humans who ate infected beef.

Infection in humans is known as variant
Creuztfeld-Jacob disease (vCJD).
› Cases frequently present in young adults.
Cryptococcosis is the most important fungal CNS
infection.
 Caused by Cryptococcus neoformans

› Encapsulated form of yeast
› Capsule production varies with the strain and
environmental conditions.
› Found throughout world, especially in soil
contaminated with bird droppings

Causes a chronic form of meningitis
Acanthamoeba & Naegleria: Both cysts and
trophozoites of amoeba can be found in lesions.
 AIDS patients can have:

› Cutaneous ulcers and hard nodules containing amebas
› Amebas in the cerebrospinal fluid.

Acanthamoeba occasionally ends in spontaneous
recovery.
› It is invariably fatal in the immunocompromised.
Courtesy of Dr. Andrew Bollen and Dr. Walter Finkbeiner.
Bacterial and fungal infections require prompt
and aggressive treatment.
 Treatment periods vary depending on the type of
infection.

› 10 days to 12 months for uncomplicated cases
› Longer if the infection is caused by M. tuberculosis
› Treatment of fungal infections can last for years.
› Treatment of viral infections is mostly supportive.
Infections in the blood easily become systemic
and systemic infections can have devastating
effects on the patient.
 Types:

›
›
›
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Bacteremia
Viremia
Fungemia
Parasitemia
Pathogenic organisms growing in the blood can
lead to major clinical conditions:
› Sepsis & Septic shock

Infections in the blood easily become systemic
and systemic infections can have devastating
effects on the patient.
Systemic nature of blood infections requires
aggressive treatment.
 Blood has access to the entire body:

› Can carry pathogens from one location to another.

Presence of circulating pathogens is a natural
progression of an infection:
› These are quickly removed from the blood by host
defenses.

In some cases pathogens in the blood reflect a
serious, uncontrollable infection.

Depending on type of organism blood infections
are classified as:
›
›
›
›
Bacteremia
Viremia
Fungemia
Parasitemia

Pathogenic organisms growing in the blood can
lead to major clinical conditions:
› Sepsis
› Septic shock
› Bacteremia and fungemia can also be caused by
pathogens growing inside or outside of intravenous
devices.
INTRAVASCULAR INFECTIONS-arise when
pathogens enter the blood and damage the structures
of cardiovascular system
› Endocarditis – infection of the heart
› Thrombophlebitis – infection in the veins
› Endoarteritis – infection of the arteries
Most commonly caused by bacteria
Fungi are sometimes involved.
Infections of the cardiovascular are very dangerous
& Can be fatal
 Commonly produce shedding of organisms into the
blood.



INFECTIOUS ENDOCARDITIS-Once referred to as
bacterial endocarditis
› Now known that organisms other than bacteria can cause it

Infection affects the heart valves
› Can also develop on the septa of the heart and cardiac
shunts.

Infectious endocarditis classified in two ways:
› Acute – high fever and toxicity
 Can result in death within few days or weeks
› Subacute – low fever, weight loss, and night sweats
 Death can take weeks to months
© CDC/Dr. Edwin P. Ewing, Jr.

Complications from infectious endocarditis:
›
›
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Risk of congestive heart failure
Rupture of the chordae tendineae
Perforation of the valves
Kidney damage
 Blood is found in urine.
SEPSIS AND SEPTIC SHOCK- both result from
the progression of bacteremia
› Gram-positive and Gram-negative bacteria can be
responsible
› Fungi, protozoa, and viruses can also be the cause

Sepsis – an infection which causes a host
response including: sepsis causing altered blood
flow to organs causing reduced urine ; changes in
mental status; Development of hypotension

Multiorgan failure and death.
Vector-transmitted to humans.
Most explosively virulent bacterial infection ever
known.
 Spreads from lymph nodes to blood


› From there can spread to the lungs
› Referred to as pneumonic plague

Bacteria multiply very rapidly in lymph nodes
› Produces a bubo

From bubo, bacteria spread rapidly into the
blood.
© CDC
Infection of wild animals that can be transmitted
to humans.
 Infected animals may not show any signs.
 Caused by Francisella tularensis

› Grows only on specialized medium
› Takes up to 10 days of incubation
› Ingestion of contaminated meat or water



Brucella enters the host through cuts in the skin,contact
with mucous membranes, inhalation; I ngestion
Zoonotic infection which involves infection of the
reproductive tract.
Transmission to humans is by:
› Occupational contact
› Ingesting contaminated animal products

Chronic illness in humans
› Can last for weeks or months
› Causes fever, night sweats, and weight loss
› Cyclic pattern of symptoms – undulant fever



Transmitted to humans by Ixodes tick.
Caused by the spirochete Borrelia burgdorferi
›
›
›
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Gram-negative
Requires specialized medium for growth
Involves ticks, mice, and deer
Humans are incidentally involved
Acute Lyme disease characterized by:
›
›
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Fever
Migratory bull’s-eye rash
Muscular and joint pain
Often meningeal irritation
Deer are host for the final stages
© CDC/James Gathany

Rickettsia are coccobacilli that have
characteristics of both bacteria and viruses.
› Divide by binary fission, Very small
› Gram-negative but stain very poorly
 Better resolved with Giemsa stain
› Have a peptidoglycan cell wall with a Gram-negative
outer layer
› Are obligate intracellular parasites

Most common infection is Rocky Mountain
Spotted Fever (RMSF) caused by Rickettsia
rickettsii.
› Seen throughout the world

Most have animal reservoirs
› Transmitted by arthropod vectors
› Spread through the vector’s life cycle
› Occurs in association with exposure to wooded areas
infested with ticks.

Vectors are ticks.
› Different vectors in different geographic locations
Epidemic typhus is a classic example of a
rickettsial infection.
 Most prevalent in U.S. is RMSF.
 Both characterized by fever, rash, and muscle
aches.
 Both may be fatal as a result of vascular collapse
 Rickettsia pathogens do not harm the tick
 Rash is the most characteristic feature.

Several forms of typhus, but the two most
important are:
 Epidemic Typhus- Caused by Rickettsia
prowazekii.
 Transmitted by human louse Pediculus humanus
corporis.
 Historically seen in times of war or famine.

› Crowding and infrequent bathing are common


Endemic typhus is caused by Rickettsia typhi.
Primary infection rodent to rodent
› Human infection incidental

Transmitted to humans by the rat flea
› Headache, muscle aches, and fever
› Maculopapular rash forms
Viruses can be found in the blood – viremia.
 Some viruses use blood cells as their hosts.
 CYTOMEGALOVIRUS- is a herpes viral genus
of the Herpesviruses group
 ARBOVIRUSES- a group of viruses that are
transmitted by arthropod vectors & infections in
blood are classified as fever infections.
 Dengue fever & Yellow fever: arbovirus attacks
the liver and vector for both are mosquitoes.
EPSTEIN-BARR VIRUS- human
herpesvirus, a cancer-causing virus of
the herpes family, which includes
herpes simplex virus1 and 2, and is
one of the most common viruses in
humans.
© Dr. M. A. Ansary / Science Photo Library
FILOVIRUSES- Ebola and Marburg
 Ebola is very contagious.
› Transmission is person-to-person
› 10% of population in rural Central Africa carry Ebola
antibodies.

Marburg virus has also been seen in nosocomial
settings.
› 25% mortality rate
Ebola & Marburg both cause hemorrhaging in the
skin, mucous membranes, and internal organs.
› Liver cells, lymphoid tissue, kidneys, gonads are all
destroyed & can also cause brain damage

Reasons for such rapid hemorrhaging are still not
clear.
› Evidence that Marburg replicates in vascular
endothelial cells
› Causes necrosis and bleeding

Ebola causes symptoms in as little as 4-6 days.
› Mortality rate is extremely high: 60-80%.
› There is no treatment.

There are several important and dangerous
parasitic infections of the blood:
›
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›
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Malaria
Trypanosomiasis
Filariasis
Toxoplasmosis
Schistosomiasis


American form of trypanosomiasis.
Caused by the flagellate protozoan Trypanosoma
cruzi.

Caused by thread-like filarial nematodes
(roundworms) family known as "filariae

Tissue changes seen in elephantiasis are often
irreversible.
› Enlarging of the extremities may be ameliorated
through the use of pressure bandages.

Control of the vector helps prevent infection.
© CDC
•
Toxoplasmosis is a parasitic disease caused by the
protozoan Toxoplasma gondii
• The parasite infects most genera of warm-blooded
animals, including humans, but the primary host is
the felid (cat) family
• Animals are infected by eating infected meat, by
ingestion of feces of a cat that has itself recently
been infected, or by transmission from mother to
fetus.
• (Refer website /text bk for images)
Schistosomiasis
Schistosomiasis also known as bilharzia, bilharziosis or
snail fever) is a parasitic disease caused by several
species of tremotodes ("flukes")
› a parasitic worm of the genus Schistosoma
› Refer internet/textbo ok for images
Skin and eyes are in contact with potentially
pathogenic organisms all the time.
Many infections can occur on the skin.
› The skin is always exposed to pathogens.
› Soft tissue below the skin is a breeding ground for
infections.
Eyes are open to the outside world.
› Infections here extremely dangerous.
 Proximity to the nervous system
 Potential for loss of vision
© Necrotizing faciitis, Steve Burdette. In www.antimicrobe.org; Empiric, 2008. Esun Technologies, Pittsburgh, PA
Salient sign is blistering and
peeling off of large sheets of
skin.
Caused by two exotoxins
secreted by certain strains of
S. aureus – exfoliatins.
Normally restricted to
infants
Can occur in adults,
especially in late stages
of toxic shock syndrome
•Gangrene caused by Clostridium
perfringens.
• Tissue necrosis resulting from an
obstructed blood supply.
•Bacteria responsible for the
infection release gases.
•Usually associated with deep tissue
wounds.
•Movement of the affected area
causes snap, crackle, and popping
sounds , a foul smell
•Infection is accompanied by high
fever, massive tissue destruction,
shock, and blackened skin.
•If not treated, gas gangrene is
lethal.
•Topical eye drops and ointments containing
erythromycin or gentamicin are effective against acute
bacterial conjunctivitis.
•Fluoroquinolones can be used for eye infections caused
by Pseudomonas.
•Quinolones such as ciprofloxacin useful for all types of
eye infection.

Microbiology, A clinical Approach -
Danielle Moszyk-Strelkauskas-Garland
Science 2010

http://en.wikipedia.org/wiki/Scientific_met
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