Article: Evaluation of new ELISA to detect Chagas Flashcards
Background Chagas disease
-Only occurs in Americas, caused by Trypanosoma cruzi
-Kissing bugs bite an individual, and rub their feces on their faces at night ew xD Then the person shoves it on the open cuts/eyes/mouth.
Bugs often live in cracks and holes of houses
-16-20 million people infected, 50.000 deaths yearly, 90 mil people at risk
-Often people might be asymptomatic carriers, and can transmit it via blood transfusion. Congenital transmission is also possible.
-In recent years, immigration to USA and Canada increased, hispanic population is equalized to African American population (around %12 each)
Establishing infections is chronic and untreatable: so this increase in immigrants can bring possible blood transfection risk
The transmission risk is between 2-48% probably changing because of how long the donor is infected, or whether the assays are accurate.
1/25.000 blood donors are infected in USA, where immigration is high (Miami, LA) = 1/8000
Parasite remains viable for 20 days in refrigerator, and might even survive cryopreservation
Materials Methods (patient info also)
Specificity evaluation: 10.192 blood donors in Texas
Sensitivity evaluation: 180 positive, 50 Bolivia, 50 Ecuador, 100 collected from different Latin America countries
ELISA was regular Ag ELISA lol
In order to confirm the positive cases: they additionally did RIPA assay (immunoprecipitation apparently, you lyse cells, check bands)
RIPA was the current gold standard
T.cruzi Ag ELISA results
Specificity:
Among 10.192: 3 was clearly positive, also confirmed by RIPA
-S/CO ratio (signal to cut off ratio= shows how positive the sample is) in negative samples was = 0.050, in positive samples it is 4.6
(Between 1-0= negative)
Apparently 2/3 samples, the ones that were weaker (1.26,2.49 ratio) belonged to same person, the other one had 6.13 = strong positive
-Test was %100 specific, also the cutoff was proper. Because the gray area (0.5 to 1) was all RIPA negative.
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Sensitivity: (180 positive)
5/178 were negative, IFA test was also done for these samples which was negative, but RIPA of 4 was positive. Mean of all positive samples: 4.56
Two of those 4 were in gray zone: in 0.93/0.83, but they repeated the test then it was all slightly above 1 each time.
Sensitivity: %97.7
Discussion:
Testing method was really successful, high spec. and sensitivity
But 3/10.000 donor points out that = still people w asymptomatic Chagas are donating blood
They say 4/177 patients that cannot be pinpointed by ELISA was probably indeed positive (RIPA was right) although apparently there’s high RIPA cross-reactivity between chagas and visceral leishmania
So the cutoff of 1: they had to retest 2 ELISA negative ones because they were around 0.9-0.8 actually but were originally positive. Average of
