cns consists of the brain and the spinal cord -...

� CNS consists of the brain and the spinal cord

&infections can be caused by:› 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.

� 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.› Gram-positive

› Anaerobic

› Rod shaped

› Produces a terminal spore

› Toxin produced by C. tetani is neurogenic

� Etiologic agent is Clostridium botulinum.› 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:› 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

� Complications from infectious endocarditis:

› 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.

� 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,contactwith 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› Gram-negative› Requires specialized medium for growth› Involves ticks, mice, and deer› Humans are incidentally involved

� Acute Lyme disease characterized by:› Fever› Migratory bull’s-eye rash› Muscular and joint pain› Often meningeal irritation› Deer are host for the final stages

� 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 Rickettsiarickettsii.

› 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.

© Dr. M. A. Ansary / Science Photo Library

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.

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:› 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.

• 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

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_method

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cns consists of the brain and the spinal cord -...

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