pathology of infectious diseases IV - lecture notes - julia

Question 1

what is entamoeba histolytica?

Answer 1

• parasitic ameoba that can infect GI tract
• creates ulcers - characteristic lesion due to necrosis
• protozoan
• has both infectous form (stable cyst that contaminates food and water) and invasive trophozoite form in GI tract

Question 2

what allows entamoeba histoytica to adhere?

Answer 2

has a surface lectin that allows adherance to colonic epithelium, invasion, and confers complement resistance

Question 3

how does entamoeba histolytica cause disease?

Answer 3

• kills PMNs
• liquefies tissues
• causes “sterile abscesses” - ameobas are in there so not really sterile, but no bacteria
• causes collitis with “flask-shaped ulcers”, liver abscess with liquefied necrotic material

Question 4

what would an ulcer due to entameoba histolytica look like?

Answer 4

flask-like

Question 5

what are pseudopods?

Answer 5

• pathogenic amebi that move in one direction put out separate area that engulfs cells that they come up against
• bottom right darker area in picture

Question 6

what is the pathologic consequence of acute amebic colitis?

Answer 6

• ruptured bowel
• organisms can get into lymph and blood stream and get to other organs

Question 7

where in an amebic liver abscess would you find the amebi?

Answer 7

• around the edge, where they’re eating the still living tissue
• if you put a needle into the center of the abscess, won’t get any bacteria or ameba

Question 8

what is clostridium difficile?

Answer 8

• toxin-producing, gram positive, spore-forming anaerobic bacillus

Question 9

how does clostridium difficile spread?

Answer 9

• normal component of bowel flora
• when give antibiotics, can overgrow
• also widespread in nature
• spores stable in environment

Question 10

how does clostridium difficile cause disease?

Answer 10

• releases cytotoxins A and B
• these kill cells

Question 11

what is the pathologic effect of clostridium difficile?

Answer 11

• fever
• gi pain
• diarrhea
• pseudomembrane formation

Question 12

how is C. dif diagnosed?

Answer 12

• look for toxin itself or the genetic material responsible for the toxin - most strains produce both kinds of toxins

Question 13

what does a pseudomembrane formation consist of?

Answer 13

• fibrin
• inflammatory cells
• bacteria
• dead cells

Question 14

what does a pseudomembrane look like histologically?

Answer 14

pile of cellular debris that contains bacteria, dead cells, fibrin - not a true cellular membrane

Question 15

what causes cryptococcal meingitis?

Answer 15

cryptococcus neoformans = encapsulated yeast

Question 16

where is cryptococcus neoformans found? how is it spread?

Answer 16

• found worldwide in high nitrogen soils
• aerosol spread

Question 17

what does cryptococcus neoformans cause?

Answer 17

• common respiratory infection (primary infection always always respiratory)
• immunosuppresed tend to disseminate to meninges, bone, skin
• can cause chronic meningitis, hydorcephalus

Question 18

how does cryptococcus neoformans cause disease?

Answer 18

• has polysaccharide capsule
• no toxin
• little acute inflammatory diagnosis
• but eventually causes loose granulomas

Question 19

how is cryptococcal meningitis diagnosed?

Answer 19

• polysaccharide capsule used for diagnosis - gets broken down in body and gets into CSF with meningitis or can be in serum of patients
• stain for mellanin cause it uses tryptophan to make a mellanin-like pigment
• silver impregnation technique

Question 20

how is malaria transmitted?

Answer 20

• mosquito
• species feed with body at 45 degree angle to surface

Question 21

what causes malaria?

Answer 21

various species of plasmodium

Question 22

how does malaria infect the body?

Answer 22

• infecious forms (sporozites) are in mosquito
• bite injects form that infects hepatocytes
• parasite forms that infects erythrocytes matures in the liver
• break out
• infects RBCs

Question 23

how does malaria cause disease?

Answer 23

• infected RBCs lyse => acute anemia and toxicity due to hemoglobin that’s been released
• release infectous merozoites
• these attach to and invade new RBCs
• => periodic fevers correlated to RBC infection and lysis cycle
• a few gametocytes, infectious for mosquitoes, are eventually formed
• binding of infected RBC to endothelium via integrin and thrombospondin receptors - parasite changes membrane of RBCs so it doesn’t stay in circulation
• => clogging of tiny capillaries and huge cytokine response

Question 24

what are the clinical features of malaria?

Answer 24

• fever (can be periodic - more likely to be periodic in patients living in endemic areas)
• high parasitemia
• severe anemia
• cerebral dysfunction
• renal failure due to toxicity of Hb and sludging in capillaries
• => pulmonary edema and death
• cerebral malaria can evolve very rapidly and be fatal

Question 25

what are the patterns of morphologic change caused by malaria? (what would you expect to see in the spleen, liver, brain)

Answer 25

• enlargement of spleen and liver because they pick up remnants of RBCs so in chronic malaria will have enlargement
• cerebral malaria will have small vessels clogged with parasitized RBCs, can have hemorrhage around these vessels
• little inflammatory infilatrate
• brain can swell = cerebral edema

picture = spleen on left, liver on right

Question 26

how is malaria diagnosed?

Answer 26

• examination of blood films
  
  • look at the RBCs