Anti-Plasmodium vivax merozoite surface protein 3 ϒ (PvMSP3 ϒ) antibodies upon natural infection.

Merozoite surface protein 3 of Plasmodium vivax (PvMSP3) contains a repertoire of protein members with unique sequence organization. While the biological functions of these proteins await elucidation, PvMSP3 has been suggested to be potential vaccine targets. To date, studies on natural immune responses to this protein family have been confined to two members, PvMSP3α and PvMSP3ß. This study analyzed natural IgG antibody responses to PvMSP3γ recombinant proteins derived from two variants: one containing insert blocks (CT1230nF) and the other without insert domain (NR25nF). The former variant was also expressed as two subfragment proteins: one encompassing variable domain I and insert block A (CT1230N) and the other spanning from insert block B to conserved block III (CT1230C). Serum samples were obtained from 246 symptomatic vivax malaria patients in Tak (n = 50) and Ubon Ratchathani (n = 196) Provinces. In total, 176 (71.5%) patients could mount antibodies to at least one recombinant PvMSP3γ antigen. IgG antibodies directed against antigens CT1230nF, CT1230N, CT1230C and NR25nF occurred in 96.6%, 61.4%, 71.6% and 68.2% of samples, respectively, suggesting the widespread occurrence of B-cell epitopes across PvMSP3γ. The rates of seropositivity seemed to correlate with the number of previous malaria episodes. Isotype analysis of anti-PvMSP3γ antibodies has shown predominant cytophilic subclass responses, accounting for 75.4-81.7% for IgG1 and 63.6-77.5% for IgG3. Comparing with previous studies in the same cohort, the numbers of serum samples reactive to antigens derived from P. vivax merozoite surface protein 9 (PvMSP9) and thrombospondin-related anonymous protein (PvTRAP) were higher than those to PvMSP3γ, being 92.7% and 87.0% versus 71.5%, respectively. Three (1.22%) serum samples were nonresponsive to all these malarial proteins. Nevertheless, the relevance of naturally acquired antibodies to PvMSP3γ in host protection requires further studies.

Usefulness of a new immunochromatographic assay using fluorescent silica nanoparticles for serodiagnosis of Thai patients with amebiasis.

A fluorescence immunochromatography (FIC) kit was developed recently using fluorescent silica nanoparticles coated with a recombinant C-terminal fragment of the surface lectin intermediate subunit (C-Igl) of Entamoeba histolytica to establish rapid serodiagnosis of amebiasis. We further evaluated the system using serum samples from 52 Thai patients with amebiasis. Of the patients, 50 (96%) tested positive using FIC. The samples were also tested using enzyme-linked immunosorbent assay (ELISA) with C-Igl as the antigen. Two samples were negative on ELISA but positive on FIC. The correlation coefficient between the fluorescence intensity using FIC and the optical density value using ELISA was 0.5390, indicating a moderate correlation between the two tests. Serum samples from 20 patients with malaria and 22 patients with Clostridioides difficile infection were also tested using FIC. The false-positive rates were 4/20 (20%) and 1/22 (4%) in patients with malaria and C. difficile infection, respectively. Combining the data from the present study with our previous study, the sensitivity and specificity of FIC were determined to be 98.5% and 95.2%, respectively. The results of the 50 samples were studied using a fluorescence scope and a fluorescence intensity reader, and the findings were compared. Disagreements were found in only two samples showing near-borderline fluorescence intensity, indicating that the use of scope was adequate for judging the results. These results demonstrate that FIC is a simple and rapid test for the serodiagnosis of amebiasis.

Analysis of D-A locus of tRNA-linked short tandem repeats reveals transmission of Entamoeba histolytica and E. dispar among students in the Thai-Myanmar border region of northwest Thailand.

Intestinal parasitic infections, including those caused by Entamoeba species, are a persistent problem in rural areas of Thailand. The aims of this study were to identify pathogenic Entamoeba species and to analyze their genotypic diversity. Stool samples were collected from 1,233 students of three schools located in the Thai-Myanmar border region of Tak Province, Thailand. The prevalence of Entamoeba infection was measured by polymerase chain reaction (PCR) using species-specific primers. Thirty-one (2.5%) positive cases were detected for E. histolytica, 55 (4.5%) for E. dispar, and 271 (22.0%) for E. coli. Positive samples for E. histolytica and E. dispar were exclusively obtained from a few school classes, whereas E. coli was detected in all grades. No infections caused by E. moshkovskii, E. nuttalli, E. chattoni, and E. polecki were detected in the students studied. The D-A locus of tRNA-linked short tandem repeats was analyzed in samples of E. histolytica (n = 13) and E. dispar (n = 47) to investigate their diversity and potential modes of transmission. Five genotypes of E. histolytica and 13 genotypes of E. dispar were identified. Sequences of the D-A were divergent, but several unique genotypes were significantly prevalent in limited classes, indicating that intra-classroom transmission has occurred. As it was unlikely that infection would have been limited within school classes if the mode of transmission of E. histolytica and E. dispar had been through the intake of contaminated drinking water or food, these results suggest a direct or indirect person-to-person transmission mode within school classes. Positive rates for three Entamoeba species were 2-fold higher in students who had siblings in the schools than in those without siblings, suggesting that transmission occurred even at home due to heavy contacts among siblings.

Development of a sensitive immunochromatographic kit using fluorescent silica nanoparticles for rapid serodiagnosis of amebiasis.

We have previously shown that the C-terminal region of the intermediate subunit of Entamoeba histolytica galactose- and N-acetyl-D-galactosamine-inhibitable lectin (C-Igl) is a useful antigen for serodiagnosis of amebiasis. An immunochromatographic kit was developed using fluorescent silica nanoparticles coated with C-Igl prepared in Escherichia coli. Samples for examination were added to the freeze-dried particles and then applied to the immunochromatographic device, in which a test line on the membrane was also coated with C-Igl. Fluorescent intensity was measured using a hand-held reader. In an evaluation of the kit using a human monoclonal antibody, the minimum amount of C-Igl specific antibody showing positive results was 100 pg. In the evaluation of serum samples with different antibody titers in indirect immunofluorescent antibody tests in the kit, 20 µL of serum was sufficient to obtain positive results at 30 min. Serum samples from symptomatic patients with amebic colitis and amebic liver abscess and those from asymptomatic E. histolytica-cyst carriers showed positive results in the kit. Based on evaluation using sera from healthy controls and patients with other infectious diseases, the sensitivity and specificity of the kit were 100 and 97.6%, respectively. Therefore, we conclude that the newly developed kit is useful for rapid serodiagnosis of amebiasis.