RESUMO
BACKGROUND: Yellow fever virus (YFV) is a vector-borne flavivirus endemic to Africa and Latin America. Ninety per cent of the global burden occurs in Africa where it is primarily transmitted by Aedes spp, with Aedes aegypti the main vector for urban yellow fever (YF). Mosquito life cycle and viral replication in the mosquito are heavily dependent on climate, particularly temperature and rainfall. We aimed to assess whether seasonal variations in climatic factors are associated with the seasonality of YF reports. METHODOLOGY/PRINCIPAL FINDINGS: We constructed a temperature suitability index for YFV transmission, capturing the temperature dependence of mosquito behaviour and viral replication within the mosquito. We then fitted a series of multilevel logistic regression models to a dataset of YF reports across Africa, considering location and seasonality of occurrence for seasonal models, against the temperature suitability index, rainfall and the Enhanced Vegetation Index (EVI) as covariates alongside further demographic indicators. Model fit was assessed by the Area Under the Curve (AUC), and models were ranked by Akaike's Information Criterion which was used to weight model outputs to create combined model predictions. The seasonal model accurately captured both the geographic and temporal heterogeneities in YF transmission (AUC = 0.81), and did not perform significantly worse than the annual model which only captured the geographic distribution. The interaction between temperature suitability and rainfall accounted for much of the occurrence of YF, which offers a statistical explanation for the spatio-temporal variability in transmission. CONCLUSIONS/SIGNIFICANCE: The description of seasonality offers an explanation for heterogeneities in the West-East YF burden across Africa. Annual climatic variables may indicate a transmission suitability not always reflected in seasonal interactions. This finding, in conjunction with forecasted data, could highlight areas of increased transmission and provide insights into the occurrence of large outbreaks, such as those seen in Angola, the Democratic Republic of the Congo and Brazil.
Assuntos
Clima , Meio Ambiente , Estações do Ano , Febre Amarela/transmissão , Vírus da Febre Amarela/fisiologia , Aedes/fisiologia , Aedes/virologia , Angola/epidemiologia , Animais , Brasil/epidemiologia , República Democrática do Congo/epidemiologia , Surtos de Doenças , Humanos , Mosquitos Vetores/fisiologia , Mosquitos Vetores/virologia , Temperatura , Replicação Viral , Febre Amarela/epidemiologia , Febre Amarela/virologia , Vírus da Febre Amarela/isolamento & purificaçãoRESUMO
OBJECTIVES: We aimed to determine whether the presentation of Chikungunya virus (CHIKV) infection differs between older and younger adults with regard to clinical form during the acute phase defined by the World Health Organization: acute clinical, atypical, and severe acute. DESIGN: Cross-sectional, retrospective. SETTING: University Hospital of Martinique. PARTICIPANTS: Individuals aged 65 and older (n = 267, mean age 80.4 ± 87.9) who attended the emergency department with a positive biological diagnosis of CHIKV (reverse transcriptase polymerase chain reaction) between January and December 2014 and a randomly selected sample of individuals younger than 65 (n = 109, mean age 46.2 ± 12.7). RESULTS: Typical presentation was present in 8.2% of older adults and 59.6% of younger individuals (P < .001), atypical presentation in 29.6% of older adults and 5.6% of younger individuals (P < .001), and severe presentation in 19.5% of older adults and 17.4% of younger individuals (P = .65). One hundred fourteen (42.7%) of the older group and 19 (17.4%) of the younger group could not be classified in any category (absence of fever, absence of joint pain, or both) (P < .001). CONCLUSION: Only 8.2% of the older adults presenting in the acute phase of CHIKV have typical forms, suggesting that the most-frequent clinical presentation of CHIKV in older adults differs from that in younger individuals.
Assuntos
Febre de Chikungunya/diagnóstico , Febre de Chikungunya/epidemiologia , Vírus Chikungunya/isolamento & purificação , Distribuição por Idade , Fatores Etários , Idoso , Idoso de 80 Anos ou mais , Artralgia/virologia , Estudos Transversais , Feminino , Febre de Causa Desconhecida/virologia , Humanos , Masculino , Pessoa de Meia-Idade , Estudos Retrospectivos , Reação em Cadeia da Polimerase Via Transcriptase Reversa , Fatores de RiscoRESUMO
Abstract. Current regulations stipulate a yellow fever (YF) booster every 10 years. We conducted a systematic review of the protective efficacy and duration of immunity of YF vaccine in residents of disease-endemic areas and in travelers to assess the need for a booster in these two settings and in selected populations (human immunodeficiency virus-infected persons, infants, children, pregnant women, and severely malnourished persons). Thirty-six studies and 22 reports were included. We identified 12 studies of immunogenicity, 8 of duration of immunity, 8 of vaccine response in infants and children, 7 of human-immunodeficiency virus-infected persons, 2 of pregnant women, and 1 of severely malnourished children. Based on currently available data, a single dose of YF vaccine is highly immunogenic and confers sustained life-long protective immunity against YF. Therefore, a booster dose of YF vaccine is not needed. Special considerations for selected populations are detailed.