Enterovirus infections in young infants: are children still protected by maternal antibodies?

Enterovirus infections are frequent in childhood and may be involved in development of several chronic diseases including type 1 diabetes. Maternal antibodies have a protective effect in young infants. It has been proposed that this protection is now vanishing due to decreasing circulation of enteroviruses in Western countries. We aimed to analyse the occurrence of enterovirus infections in 55 infants and to assess the protection provided by maternal antibodies to these children and the development of enterovirus antibodies in a prospective cohort study. In addition, the presence of enteroviruses was detected in faeces using RT-PCR and their serotype identified using VP1 region sequencing. Our results showed that before polio vaccination 12 of 194 faecal samples were positive for enterovirus RNA (coxsackieviruses A4, A5, A16 or echoviruses 13 and 16). After vaccination Sabin 1, 2 and 3 poliovirus strains predominated in stool samples. From birth to 6 months of age polio IgG and IgA increased in most of children whereas the levels of other enterovirus antibodies started to increase from 6 months to 24 months age. The frequency of maternal neutralizing antibodies was generally quite high but still 3 out of 8 infants had no maternal antibodies against the enterovirus serotype which they had in stool sample. This study shows that enterovirus infections are relatively frequent already before the age of 3 months. Considerable proportion of infants lack maternal antibodies against the virus causing their infection. The significance of this phenomenon needs to be evaluated in larger studies.