Ann Lab Med 2020; 40(5): 382-389  https://doi.org/10.3343/alm.2020.40.5.382
Specific IgG and IgA Antibody Reactivities in Sera of Children by Enzyme-Linked Immunoassay and Comparison With Giardia duodenalis Diagnosis in Feces
Flávia Thamiris Figueiredo Pacheco, Ph.D.1,2, Silvia Souza de Carvalho, M.S.1, Samara Alves Santos, M.S.1, Gisele Maria Trindade das Chagas, B.Pharm.1, Mariana Conceição Santos, B.Pharm.1, Jéssica Gleide Souza Santos, B.Pharm.1, Hugo da Costa-Ribeiro Júnior, Ph.D.2, Tereza Cristina Medrado Ribeiro, Ph.D.2, Ângela Peixoto de Mattos, Ph.D.2, Maria Aparecida Gomes, Ph.D.3, Neci Matos Soares, Ph.D.1, and Márcia Cristina Aquino Teixeira, Ph.D.1
1Department of Clinical and Toxicological Analysis, Pharmacy College and 2Hospital Professor Edgard Santos, Federal University of Bahia, Salvador, Brazil; 3Department of Parasitology, Institute of Biological Sciences, Federal University of Minas Gerais, Belo Horizonte, Brazil
Corresponding author: Márcia Cristina Aquino Teixeira, Ph.D.
Department of Clinical and Toxicological Analysis, Pharmacy College, Federal University of Bahia, Salvador, Bahia 40170-115, Brazil
Tel: +55-71-3283-6954
Fax: +55-71-3283-6949
E-mail: marciat@ufba.br
Received: September 15, 2019; Revised: January 5, 2020; Accepted: March 31, 2020; Published online: September 1, 2020.
© Korean Society for Laboratory Medicine. All rights reserved.

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Abstract
Background: Giardia duodenalis is conventionally diagnosed in fecal samples using parasitological methods. However, sensitivity is poor when only a single sample is analyzed, due to intermittent excretion of cysts in feces. Alternatively, the serum antibodies to G. duodenalis can be used for parasite diagnosis and epidemiological studies to determine previous exposure. We compared the rate of G. duodenalis infection between serum anti-Giardia IgG and IgA antibodies and fecal examination in Brazilian children.
Methods: Fecal and serum samples were tested from 287 children at a clinical laboratory and from 187 children at daycare centers. Fecal samples were processed using conventional parasitological methods and coproantigen detection for Giardia diagnosis. Serum samples were tested using an in-house ELISA for detection of anti-Giardia IgG and IgA.
Results: G. duodenalis was found in 8.2% (N=39) of the 474 children analyzed. The sensitivity and specificity of ELISA were 80.0% and 90.0% for IgG and 80.0% and 83.3% for IgA, respectively. The total positivity rate of anti-Giardia IgG and IgA in the sera was 13.9% (N=66) and 23.6% (N=112). The agreement between the positivity of specific antibodies and the detection of G. duodenalis in feces was moderate for ELISA-IgG, kappa index (95% CI)=0.543 (0.422–0.664), and mild for ELISA-IgA, kappa index (95% CI)=0.283 (0.162–0.404). Among the children infected with other enteroparasites, 11.6% (N=10) and 24.4% (N=21) showed reactivity to anti-Giardia IgG and to IgA, respectively. This cross-reactivity was more frequent in samples from children infected with Endolimax nana and Entamoeba coli.
Conclusions: The higher frequency of specific antibody reactivity compared with G. duodenalis diagnosis in feces could reflect continuous exposure of children to G. duodenalis infection, resulting in long-lasting immunological memory and/or cross-reactivity with other intestinal amoebas.
Keywords: Giardia duodenalis, Infection, Children, Diagnosis, Antibodies, ELISA, Cross-Reactivity



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