pathology of infectious diseases IV - lecture notes - julia Flashcards
what is entamoeba histolytica?
- 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
what allows entamoeba histoytica to adhere?
has a surface lectin that allows adherance to colonic epithelium, invasion, and confers complement resistance
how does entamoeba histolytica cause disease?
- 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
what would an ulcer due to entameoba histolytica look like?
flask-like
what are pseudopods?
- 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
what is the pathologic consequence of acute amebic colitis?
- ruptured bowel
- organisms can get into lymph and blood stream and get to other organs
where in an amebic liver abscess would you find the amebi?
- 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
what is clostridium difficile?
- toxin-producing, gram positive, spore-forming anaerobic bacillus
how does clostridium difficile spread?
- normal component of bowel flora
- when give antibiotics, can overgrow
- also widespread in nature
- spores stable in environment
how does clostridium difficile cause disease?
- releases cytotoxins A and B
- these kill cells
what is the pathologic effect of clostridium difficile?
- fever
- gi pain
- diarrhea
- pseudomembrane formation
how is C. dif diagnosed?
- look for toxin itself or the genetic material responsible for the toxin - most strains produce both kinds of toxins
what does a pseudomembrane formation consist of?
- fibrin
- inflammatory cells
- bacteria
- dead cells
what does a pseudomembrane look like histologically?
pile of cellular debris that contains bacteria, dead cells, fibrin - not a true cellular membrane
what causes cryptococcal meingitis?
cryptococcus neoformans = encapsulated yeast
where is cryptococcus neoformans found? how is it spread?
- found worldwide in high nitrogen soils
- aerosol spread
what does cryptococcus neoformans cause?
- common respiratory infection (primary infection always always respiratory)
- immunosuppresed tend to disseminate to meninges, bone, skin
- can cause chronic meningitis, hydorcephalus
how does cryptococcus neoformans cause disease?
- has polysaccharide capsule
- no toxin
- little acute inflammatory diagnosis
- but eventually causes loose granulomas
how is cryptococcal meningitis diagnosed?
- 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
how is malaria transmitted?
- mosquito
- species feed with body at 45 degree angle to surface
what causes malaria?
various species of plasmodium
how does malaria infect the body?
- 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
how does malaria cause disease?
- 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
what are the clinical features of malaria?
- 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
what are the patterns of morphologic change caused by malaria? (what would you expect to see in the spleen, liver, brain)
- 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
how is malaria diagnosed?
- examination of blood films
- look at the RBCs
