Correlations between schistosoma mansoni-specific immunoglobulins (igg1, igg2, igg3, igm), infection intensity and age among school pupils in Asembo area, western Kenya.

Abstract

ABSTRACT Schistosoma mansoni is a blood parasite that is common among school going pupils living near water bodies. It causes a disease known as schistosomiasis or bilhaziasis. Infected pupils stand higher risks of developing anaemia, absenteeism from school, retarded physical and mental growth and development, hence poor academic achievement. Human hosts respond to the infection by producing various immunoglobulins like IgA, IgD, IgE, IgG1, IgG2, IgG3, IgG4 and IgM. Some of these immunoglobulins like IgG1, IgG3 and IgE confer protective immunity to the host against the infection, while others like IgG2, IgG4 and IgM lead to susceptibility of the host to the infection. Although studies have been conducted in Asembo area indicating a prevalence rate of S. mansoni infection at 35-80% among school children, infection intensity of the parasite, levels of protective and susceptibility immunoglobulins, and correlations between these antibodies in relation to the infection intensity and age among the infected children have not been established. This study sought to investigate the infection intensity, levels of IgG1, IgG2,, IgG3 and IgM immunoglobulins, and how these antibodies correlate with intensity of infection and age among school children suffering from S. mansoni in Asembo, which is an endemic area for the infection. The study followed a cross-sectional design and involved use of 350 stool and venous blood samples obtained from S. mansoni-infected children aged between 5-20 years, attending primary and secondary schools in Asembo area. The study area has a total of 31,293 school-going children. The participants were recruited using simple random sampling technique. The stool samples were used for determination of infection intensities by means of Kato Katz technique. The blood samples were used to obtain plasma for determination of immunoglobulin levels by means of indirect Enzyme Linked Immunosorbent Assay (ELISA) method, using soluble worm antigen preparations (SWAP) and soluble egg antigens (SEA) of the parasite. Multivariate analysis of variance (ANOVA) was conducted to determine if mean levels of immunoglobulins and infection intensities were significantly different between the age groups. Tukey’s Honest Significant Difference test was used to obtain the least significant differences in the levels of the immunoglobulins and infection intensities. Spearman’s Rank Correlation Coefficient was used to determine the correlations between concentrations of the IgG1, IgG2, IgG3 and IgM immunoglobulins versus infection intensity and age of the infected school pupils. Regression analysis was done to assess the strength of associations between levels of the immunoglobulins, infection intensity and age. Levels of the immunoglobulins were dependent variables while intensity of infection and age were independent variables. The levels of anti-SWAP IgG1, IgG3 and anti-SEA IgG1 peaked at the age bracket of 17-20 years. The levels of anti-SWAP IgG2, IgM and anti-SEA IgM were highest at the age bracket of 5-8 years. The anti-SEA IgG3 levels peaked at the age bracket of 9-12 years. Intensity of infection was highest at 184.06 eggs per gram at the age bracket of 13-16 years. Positive correlations existed between anti-SWAP IgG1 and infection intensity ( = 0.321, p=0.001), anti-SWAP IgG2 and infection intensity ( =0.187, p=0.001), anti-SEA IgG1 and intensity of infection ( =0.168, p=0.002) and anti-SEA IgG3 and infection intensity ( =0.155, p=0.005). Negative correlations were found between anti-SWAP IgM and infection intensity ( =0.115, p=0.039). No correlations existed between anti-SWAP IgG3 and infection intensity ( =0.011, p=0.838) and anti-SEA IgM and infection intensity ( =0.097, p=0.082). Positive correlations were established between anti-SWAP IgG1 and age ( =0.472, p=0.001), anti-SWAP IgG3 and age ( =0.223, p=0.001), and anti-SEA IgG1 and age ( =0.286, p=0.001). There were negative correlations between anti-SWAP IgG2 and age ( =-0.476, p=0.001), anti-SWAP IgM and age ( =-0.436, p=0.001) and anti-SEA IgM and age ( =0.315, p=0.001). There were no correlations between anti-SEA IgG3 and age ( =0.073, p=0.193). The and P values were considered to be statistically significant at >0.1 or >-0.1, and P<0.05 respectively. It was concluded that as the school children grow older, there is an increase in levels of protective immunoglobulins like IgG1 and IgG3 while on the other hand there is a decrease in levels of blocking immunoglobulins like IgG2 and IgM. The findings of this study are expected to enhance the understanding of the immunological relationship between the human host and S. mansoni parasite during the infection, hence provide research scientists with additional knowledge aimed at developing a vaccine against schistosomiasis. The study recommends investigations into the correlations between total IgG levels versus infection intensity and age of infected school pupils, and use of more sensitive protocols for assaying anti-SEA IgG2 levels.