Hand, foot, and mouth disease (HFMD) caused by enteroviruses remains a public health threat, particularly in the Asia-Pacific region during the past two decades. Moreover, the introduction of multiple subgenotypes and the emergence of recombinant viruses is of epidemiological importance. Based on either the full genome or VP1 sequences, 32 enteroviruses (30 from HFMD patients, 1 from an encephalitic patient, and 1 from an asymptomatic contact case) isolated in Thailand between 2006 and 2014 were identified as 25 enterovirus 71 (EV71) isolates (comprising 20 B5, 1 C2, 2 C4a, and 2 C4b subgenotypes) and 7 coxsackievirus A16 (CA16) isolates (comprising 6 B1a and 1 B1b subgenotypes). The EV71 subgenotype C4b was introduced into Thailand for the first time in 2006 and was replaced by subgenotype C4a strains in 2009. Phylogenetic, similarity plot and bootscan analyses of the complete viral genomes identified 12 recombinant viruses among the 32 viral isolates. Only one EV71-B5 isolate out of 20 was a recombinant virus with one region of intratypic or intertypic recombination, while all four EV71-C4 isolates were recombinant viruses having undergone double recombination, and all seven CA16 isolates were recombinant viruses. The recombination breakpoints of these recombinants are located solely within the P2 and P3 regions. Surveillance for circulating strains and subgenotype replacement are important with respect to molecular epidemiology and the selection of the upcoming EV71 vaccine. In addition, the clinical importance of recombinant viruses needs to be further explored.

BackgroundHand, foot and mouth disease (HFMD) is endemic among population of young children in Thailand. The disease is mostly caused by enterovirus 71 (EV71) and coxsackievirus A16 (CA16).MethodsThis study conducted serosurveillance for neutralizing (NT) antibodies to EV71 subgenotypes B5 and C4a, and to CA16 subgenotypes B1a and B1b, in 579 subjects of various ages using a microneutralization assay in human rhabdomyosarcoma (RD) cells. These test viruses were the major circulating subgenotypes associated with HFMD in Thailand during the study period.ResultsWe found that the levels of seropositivity against all 4 study viruses were lowest in the age group of 6–11 months, i.e., 5.5% had antibody to both EV71 subgenotypes, while 14.5% and 16.4% had antibody to CA16 subgenotypes B1a and B1b, respectively. The percentages of subjects with antibodies to these 4 viruses gradually increased with age, but were still less than 50% in children younger than 3 years. These laboratory data were consistent with the epidemiological data collected by the Ministry of Public Health which showed repeatedly that the highest number of HFMD cases was in children aged 1 year. Analyses of amino acid sequences of the test viruses showed 97% identity between the two subgenotypes of EV71, and 99% between the two subgenotypes of CA16. Nevertheless, the levels of seropositivity and antibody titer against the two subgenotypes of EV71 and of CA16 were not significantly different.ConclusionsThis study clearly demonstrated NT antibody activity across EV71-B5 and EV71-C4a subgenotypes, and also across CA16-B1a and CA16-B1b subgenotypes. Moreover, there were no significant differences by gender in the seropositive rates and antibody levels to any of the 4 virus subgenotypes.Electronic supplementary materialThe online version of this article (10.1186/s12985-018-1074-8) contains supplementary material, which is available to authorized users.

This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made. Abstract Background: Ethnicity and environmental factors can influence the percentages of lymphocyte subpopulations. This study aimed to assess the percentages of lymphocyte subpopulations according to age in Thai children. Methods: This was a cross-sectional study. The percentages of lymphocyte subpopulations were measured in umbilical cord blood and peripheral blood of healthy Thai children aged 1 month-15 years. The participants were stratified into five age groups: (a) cord blood; (b) age < 2 years; (c) age 2-5 years; (d) age 5-10 years; and (e) age 10-15 years. Results: Of 182 total samples, 32, 39, 41, 28, and 42 were from cord blood, children aged <2 years, children aged 2-5 years, children aged 5-10 years, and children aged 10-15 years, respectively. The percentages of most lymphocyte subpopulations including CD8 + T cells, CD19 + cells, γδ T cells, double-negative T cells, NK cells, and NK T cells increased significantly with age. Only the CD4+ T-cell percentage decreased in older children. Moderate correlations were observed between age and the percentages of CD4+ T cells, γδ T cells, NK cells, NK T cells, and double-negative T cells. Weak correlations were observed between age and the percentages of CD8+ T cells and CD19+ cells. Conclusion:Our study demonstrated age-related changes in the percentages of lymphocyte subpopulations in Thai children, which differed from those described in other countries. Therefore, the establishment of age-specific reference values for lymphocyte subsets in each country is recommended. K E Y W O R D S flow cytometry, immunology, lymphocyte subsets, reference values, T cells How to cite this article: Lerkvaleekul B, Apiwattanakul N, Klinmalai C, Hongeng S, Vilaiyuk S. Age-related changes in lymphocyte subpopulations in healthy Thai children. J Clin Lab