Resumo

Human respiratory syncytial virus (HRSV) is one of the most important respiratory pathogens, since 64 million children between 0 and 5 years old are infected with this agent every year and can develop bronchiolitis and pneumonia, which can eventually cause death. Nowadays, prevention is possible through immunotherapy, but an effective vaccine is not yet available. Host immunity and viral genetic variability are important factors that can make vaccine production difficult. In this work, differences between biological clones of HRSV were detected in clinical samples in the absence and presence of serum collected from children in the convalescent phase of the illness and from their biological mothers. Three HRSV samples and respective sera were first characterized by immunofluorescence tests. Viral clones were selected by plaque assay in the absence and presence of serum. Partial nucleotide sequences of the G and F genes of HRSV biological clones were obtained and compared using bioinformatics programs. One non-synonymous mutation was found in the F gene (Ile5Asn) in one clone of an HRSV-B sample and one non-synonymous mutation was found in the G gene (Ser291Pro) in 4 clones of the same HRSV-B sample. Only one of these clones was obtained after treatment with the child´s serum. The alterations led respectively to an addition and a loss of glycosylation sites, conferring a possible advantage to the virus. In addition, some synonymous mutations were determined in two clones of the one of the HRSV-A samples. In conclusion, we found an intrapopulation variability of HRSV in the same patient. It is possible that minor sequences are selected by host antibodies contributing to the HRSV evolutionary process. This viral characteristic could hamper the development of an effective vaccine, and it could be a problem in the long-term use of immunotherapy against HRSV.