toxo

Question 1

toxo overview

Answer 1

-opportunistic
-causes toxoplasmosis
-final host is felines
-intermediate host is mammals
-transmitted fecal-oral

Question 2

3 forms of toxo

Answer 2

-tachyzoites
-tissue cysts (bradyzoit)
-oocysts

Question 3

tachyzoite stage

Answer 3

-rapidly growing stage in early infection
-acute phase lives in body fluids
-crescent-shaped (pear)
-asexual form
-multiples by endodyogeny
-can infect phagocytic & non-phagocytic cells
-anti-toxo Abs in serum bind to Ag on live trachyozoites
-killed by complement mediate lysis

Question 4

bradyzoites

Answer 4

-slow growing inside tissue cysts
-mark the chronic phase of infection
-resistant to low pH & digestive enzymes
-protective cyst wall dissolves & infects tissues
-released in intestine & highly infectious if consumed

Question 5

oocysts

Answer 5

-in cat feces
-gametocyte develop in the small intestine
-sexual cycle produces oocysts which is excreted in feces
-appear in cat poop 3-5 days after ingestion
-require oxygen
-sporulate in 1-5 days
-sporulated oocysts are infectious

Question 6

pathogenesis

Answer 6

-systemic disease (extra-interstitial phase)
-explosive replication of tachyzoites: massive direct destruction of cells & acute immune response
-affects brain, liver, lungs & striated muscles
-tissue cysts cause physical call damage & are source for latent disease

Question 7

toxo vaccine?

Answer 7

no

Question 8

detection of toxo (serology)

Answer 8

-antigen by ELISA
-antibody by: sabin dye test
-IgM ELISA
-IgG ELISA
-IgG avidity test
-ToRCH in newborns

Question 9

diagnosis of congenital toxo

Answer 9

-Ag in amniotic fluid
-PCR (research only)
-IgM Abs in fetal blood by ELISA
-fetal ultrasound around 20-24 weeks

Question 10

sabin dye test

Answer 10

-gold standard
-only in reference labs
-complement mediated neutralization test requiring live tachyzoites
-incubated with complement & serum
-alkaline methylene blue is added & reincubated

Question 11

diagnosis of toxo

Answer 11

-direct microscopy
-detection of tachyzoites in blood & tissue cyst in tissue biopsy
-staining methods: geimsa, PAS, silver stains, immunoperoxidase stain

Question 12

neural effects

Answer 12

in CT & MRIs congenitally infected children show periacqueductal inflammation & necrosis
-microcephaly: zika
hydrocephaly: toxo

Question 13

babies with congenital toxo manifest with:

Answer 13

-brain damage
-enlarged spleen & liver
-eye damage
-jaundice
-poor motor coordination
-unusually small head
-rash

Question 14

neonatal toxo infection can lead to:

Answer 14

-still birth
-chorioretinitis
-intracelluar calcification
-psychomotor disturbances
-hydrocephaly
-microcephaly
-blindness

Question 15

toxo implications on human health

Answer 15

-congenital toxoplasmosis
-post natal toxoplasmosis

Question 16

CMV IgM serology

Answer 16

-if (+) in cord/infant’s blood in 1st 3 weeks of life
-if (-), congenital infection not ruled out
-insensitive compared with urine culture for diagnosis of CMV

Question 17

rubella serology

Answer 17

-specific IgM remains detectable for 6-12 months
-persistence of IgG Abs in the infant’s serum beyond 3-6 months

Question 18

toxo serology

Answer 18

-specific IgG Abs detectable indefinitely 1-2 months post infection
-specific IgM testing often yields false pos or false neg
-IgM can persist for 6-24 months
-sendout confirmation testing

Question 19

syphilis serology

Answer 19

-quantitative non-treponemal serologic (RPR) titer > fourfold the mother’s titer

Question 20

rubella culture

Answer 20

virus isolation from nasal secretion

Question 21

CMV urine culture +/-

Answer 21

-shell vial assay or early antigen determination (EAD)
-inoculated culture cells in small vials are stained with fluorescein-conjugated monoclonal Ab to CMV Ag at 24-48 hours

Question 22

HSV viral culture

Answer 22

from vesicular swab, CSF, whole blood

Question 23

PCR CMV-DNA assay

Answer 23

-rapidly replacing viral culture- more sensitive & efficient for CMV detection (urine, saliva, serum, liver tissue)
-saliva PCR method of choice

Question 24

HSV viral PCR

Answer 24

DNA & rapid immunofluorescence assay (IFA)