RESUMO
The nature and role of re-infection and partial immunity are likely to be important determinants of the transmission dynamics of human respiratory syncytial virus (hRSV). We propose a single model structure that captures four possible host responses to infection and subsequent reinfection: partial susceptibility, altered infection duration, reduced infectiousness and temporary immunity (which might be partial). The magnitude of these responses is determined by four homotopy parameters, and by setting some of these parameters to extreme values we generate a set of eight nested, deterministic transmission models. In order to investigate hRSV transmission dynamics, we applied these models to incidence data from eight international locations. Seasonality is included as cyclic variation in transmission. Parameters associated with the natural history of the infection were assumed to be independent of geographic location, while others, such as those associated with seasonality, were assumed location specific. Models incorporating either of the two extreme assumptions for immunity (none or solid and lifelong) were unable to reproduce the observed dynamics. Model fits with either waning or partial immunity to disease or both were visually comparable. The best fitting structure was a lifelong partial immunity to both disease and infection. Observed patterns were reproduced by stochastic simulations using the parameter values estimated from the deterministic models.
Assuntos
Transmissão de Doença Infecciosa , Modelos Imunológicos , Infecções por Vírus Respiratório Sincicial/transmissão , Vírus Sincicial Respiratório Humano/fisiologia , Humanos , Incidência , Lactente , Infecções por Vírus Respiratório Sincicial/epidemiologia , Infecções por Vírus Respiratório Sincicial/imunologiaRESUMO
BACKGROUND: In contrast to influenza A, minor influenza B viruses can co-circulate with the dominant strain during an epidemic allowing the re-emergence of old strains and reassortment between those different strains. The 2001-2002 influenza season in the northern hemisphere was distinguished by the re-emergence of the Victoria-lineage viruses, which replaced the Yamagata-lineage, after being restricted to East Asia throughout the 1990s. OBJECTIVES: To describe the antigenic and genetic characteristics of influenza B viruses detected in South and South East Brazil and determine their lineages. STUDY DESIGN: Influenza samples collected during epidemics between 1999 and 2002 were analyzed by indirect immunofluorescence assay (IFA). Positive results were confirmed through multiplex PCR and isolation in cell culture. Isolated viruses were antigenically characterized by hemagglutination inhibition. Fourteen hemagglutinin (HA) gene sequences obtained in this work were used for phylogenetic analysis. RESULTS: Brazilian isolates from 2002 were associated with the Victoria-lineage, diverging from the vaccine used throughout that influenza season in Brazil. CONCLUSIONS: These results indicate the reappearance of Sichuan/7/97-like samples in South and South East Brazilian Regions simultaneously. They indicate the need for neuraminidase gene evaluation and demonstrate the importance of influenza laboratory surveillance to establish which strains should be included in the influenza vaccine.
Assuntos
Surtos de Doenças , Vírus da Influenza B , Influenza Humana/epidemiologia , Brasil/epidemiologia , Técnica Indireta de Fluorescência para Anticorpo , Testes de Inibição da Hemaglutinação , Humanos , Vírus da Influenza B/classificação , Vírus da Influenza B/genética , Vírus da Influenza B/imunologia , Vírus da Influenza B/isolamento & purificação , Influenza Humana/virologia , Dados de Sequência Molecular , Filogenia , Reação em Cadeia da Polimerase , Análise de Sequência de DNARESUMO
We analyzed the respiratory syncytial virus (RSV) groups and their epidemiological pattern that were detected over the course of seven years in southern Brazil. The two RSV groups co-circulated each year, but frequencies of groups A and B varied both between and within yearly outbreaks. In 1991, group A predominated over group B (p=0.0016). RSV outbreaks analyzed showed a temperature-dependent pattern and no association with rainfall, similarly to other countries from southern South America. Knowledge of the variants is important in terms of both diagnosis and definition of a vaccine composition.
Assuntos
Infecções por Vírus Respiratório Sincicial/epidemiologia , Vírus Sincicial Respiratório Humano/isolamento & purificação , Brasil/epidemiologia , Pré-Escolar , Surtos de Doenças , Humanos , Lactente , Nasofaringe/virologia , Vírus Sincicial Respiratório Humano/classificação , Estações do Ano , TemperaturaRESUMO
The grouping characteristics of 29 respiratory syncytial virus (RSV) present in nasopharyngeal cells collected from hospitalized children with bronchiolitis during the 1990 RSV season in Porto Alegre, RS, were analysed. Twenty-two were grouped as belonging to group A and 7 to group B. Cyanosis, oxygen therapy, cough, length of hospitalization and atelectasis were observed to be more frequently found within group B infected children. Other clinical signs and symptoms were similarly found in both groups.
