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.
Introduction. Giardia duodenalis is an intestinal protozoan with a high prevalence in children of developing countries. Molecular studies revealed a great genetic diversity of G. duodenalis, with assemblages A and B found mainly in humans. Despite its importance, the information on the molecular epidemiology of human giardiasis is still limited in Brazil.Objective. To characterize G. duodenalis molecular isolates in children from Salvador, Bahia, Brazil.Materials and methods. Giardia duodenalis positive fecal samples were obtained from 71 children from two day care centers and 39 users of a clinical analysis laboratory. Samples were analyzed by PCR-RFLP of the glutamate dehydrogenase (gdh) and beta-giardin genes and by the sequencing of beta-giardin.Results. Of the 110 G. duodenalis samples, 80 (72.7%) amplified one or both target genes. Of these, 62 (77.5 %) were identified as assemblage A and 18 (22.5%) as assemblage B. The subassemblage AII was identified in 58.8% (n=47) of isolates followed by the sub-assemblage AI (18.8%, n=15), BIV (11.2%, n=9), and BIII (5.0%, n=4). The AII sub-assemblage was the most frequent in children of both day care centers whereas AI was found only in the group attended at the clinical laboratory. Sub-assemblage AII predominated in children under two years.Conclusions. The higher frequency of AII sub-assemblage suggests that anthroponotic transmission is more common in Salvador, but that zoonotic transmission pathways are also present and a change in susceptibility to different molecular patterns of Giardia may occur during child growth.
MCAT and NMS conceived and designed the study. HCRJr, TCMR and APM were responsible for the recruitment of children and samples collection for the study. SSC and ASM performed the parasitological examination and coproantigen test for Cryptosporidium diagnosis. FTFP, RKNRS and JFM were responsible for the PCR/RFLP analysis. HFF and JNRP analyzed the Cryptosporidium DNA sequences. MCAT and FTFP carried out data analysis and wrote the manuscript. NMS, HCRJr, TCMR and APM re viewed and commented on the manuscript. All authors revised and approved the final version of the manuscript.
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