[A dengue epidemic in Ipupiara and Prado, Bahia. A seroepidemiologic survey]

Entry of dengue virus serotypes and their geographic distribution in Brazilian federative units: a systematic review

OBJECTIVE

To describe the entry of Dengue virus (DENV) serotypes in Brazil and its federative units.

METHODS

A systematic review of studies published between 1980 and 2018 in databases and in the gray literature was performed using descriptors related to the years of entry of the DENV serotypes. Additionally, experts and official sources of information (Brazilian Ministry of Health) were consulted.

RESULTS

From 100 publications selected for the systematic review, 26 addressed the entry of DENV serotypes in the North region of the country, 33 in the Northeast, 24 in the Southeast, 14 in the Central-West, and five in the South. DENV-1 and DENV-4 were introduced in the North region in 1981. DENV-2 was introduced in the Southeast in 1990. DENV-3 was introduced in the North in 1999.

CONCLUSION

The rapid expansion of dengue throughout the Brazilian territory was verified from the second half of the 1980s, with the gradual entry of the four serotypes, which resulted in the emergence of epidemics of arbovirus, which are currently verified in the country. Considering the epidemiology of the disease, more information should be disseminated and published in the wide-ranging scientific literature for a better understanding of the spread and circulation of DENV serotypes.

Individual, household and environmental factors associated with arboviruses in rural human populations, Brazil

Landscape change is one of the foremost drivers of the emergence of infectious diseases. Exploring demographic, household and environmental conditions under which infectious diseases occur may inform strategies to prevent disease emergence in human populations. We collected blood samples from 523 humans and explore factors for arbovirus emergence in Bahia, Brazil. The overall arbovirus seroprevalence was 65.2%, with the genus Flavivirus most prevalent (64.4%). Based on monotypic reactions, the population had contact with five arbovirus: Dengue 3, Ilheus, Oropouche, Caraparu and Eastern equine encephalitis virus. To our knowledge, this is the first study reporting exposure to Oropouche, Caraparu and Eastern equine encephalitis virus in human populations in Bahia, Northeast of Brazil. The best model fit demonstrated that household and environmental variables were more predictive of the risk of arbovirus exposure than demographic variables. The presence of forest and free-living monkeys in the areas close to the communities had a protective effect for the human population (i.e. lower seroprevalence). The dilution effect is considered as one explanation for this finding. These results highlight the important ecological role of wildlife-friendly agriculture.

Immune status alters the probability of apparent illness due to dengue virus infection: Evidence from a pooled analysis across multiple cohort and cluster studies

Dengue is an important vector-borne pathogen found across much of the world. Many factors complicate our understanding of the relationship between infection with one of the four dengue virus serotypes, and the observed incidence of disease. One of the factors is a large proportion of infections appear to result in no or few symptoms, while others result in severe infections. Estimates of the proportion of infections that result in no symptoms (inapparent) vary widely from 8% to 100%, depending on study and setting. To investigate the sources of variation of these estimates, we used a flexible framework to combine data from multiple cohort studies and cluster studies (follow-up around index cases). Building on previous observations that the immune status of individuals affects their probability of apparent disease, we estimated the probability of apparent disease among individuals with different exposure histories. In cohort studies mostly assessing infection in children, we estimated the proportion of infections that are apparent as 0.18 (95% Credible Interval, CI: 0.16, 0.20) for primary infections, 0.13 (95% CI: 0.05, 0.17) for individuals infected in the year following a first infection (cross-immune period), and 0.41 (95% CI: 0.36, 0.45) for those experiencing secondary infections after this first year. Estimates of the proportion of infections that are apparent from cluster studies were slightly higher than those from cohort studies for both primary and secondary infections, 0.22 (95% CI: 0.15, 0.29) and 0.57 (95% CI: 0.49, 0.68) respectively. We attempted to estimate the apparent proportion by serotype, but current published data were too limited to distinguish the presence or absence of serotype-specific differences. These estimates are critical for understanding dengue epidemiology. Most dengue data come from passive surveillance systems which not only miss most infections because they are asymptomatic and often underreported, but will also vary in sensitivity over time due to the interaction between previous incidence and the symptomatic proportion, as shown here. Nonetheless the underlying incidence of infection is critical to understanding susceptibility of the population and estimating the true burden of disease, key factors for effectively targeting interventions. The estimates shown here help clarify the link between past infection, observed disease, and current transmission intensity.

Dengue disease severity is known to vary widely from the very severe to asymptomatic. There is a wide range of estimates of how many infections result in each of these outcomes. It is known that after a first infection the outcome of a second infection with a different serotype varies over time, but this has not been taken into account in these previous estimates. In this paper, we use modelling methods, combined with information from published dengue research in which individuals are followed over time, to estimate the proportion of infections that result in symptoms at different times after infection. We estimated the proportion of infections that are symptomatic for first infections as 0.18 (95% Credible Interval, CI: 0.16, 0.20), 0.13 (95% CI: 0.05, 0.17) for individuals infected in the year following a first infection and 0.41 (95% CI: 0.36, 0.45) for those experiencing secondary infections after this first year. The estimates here will help understand how cases relate to underlying transmission, which is vital for understanding how much of the population are susceptible to infection and for effectively targeting interventions.

Sex bias in infectious disease epidemiology: patterns and processes

BACKGROUND

Infectious disease incidence is often male-biased. Two main hypotheses have been proposed to explain this observation. The physiological hypothesis (PH) emphasizes differences in sex hormones and genetic architecture, while the behavioral hypothesis (BH) stresses gender-related differences in exposure. Surprisingly, the population-level predictions of these hypotheses are yet to be thoroughly tested in humans.

METHODS AND FINDINGS

For ten major pathogens, we tested PH and BH predictions about incidence and exposure-prevalence patterns. Compulsory-notification records (Brazil, 2006-2009) were used to estimate age-stratified ♂:♀ incidence rate ratios for the general population and across selected sociological contrasts. Exposure-prevalence odds ratios were derived from 82 published surveys. We estimated summary effect-size measures using random-effects models; our analyses encompass ∼0.5 million cases of disease or exposure. We found that, after puberty, disease incidence is male-biased in cutaneous and visceral leishmaniasis, schistosomiasis, pulmonary tuberculosis, leptospirosis, meningococcal meningitis, and hepatitis A. Severe dengue is female-biased, and no clear pattern is evident for typhoid fever. In leprosy, milder tuberculoid forms are female-biased, whereas more severe lepromatous forms are male-biased. For most diseases, male bias emerges also during infancy, when behavior is unbiased but sex steroid levels transiently rise. Behavioral factors likely modulate male-female differences in some diseases (the leishmaniases, tuberculosis, leptospirosis, or schistosomiasis) and age classes; however, average exposure-prevalence is significantly sex-biased only for Schistosoma and Leptospira.

CONCLUSIONS

Our results closely match some key PH predictions and contradict some crucial BH predictions, suggesting that gender-specific behavior plays an overall secondary role in generating sex bias. Physiological differences, including the crosstalk between sex hormones and immune effectors, thus emerge as the main candidate drivers of gender differences in infectious disease susceptibility.

Indicadores socioambientais para vigilância da dengue em nível local

Este artigo caracteriza uma localidade quanto às condições de saneamento e processos de degradação ambiental que possam estar relacionados à transmissão da dengue, além de discutir a construção de novos indicadores socioambientais visando à vigilância epidemiológica. A área de estudo foi a Ilha da Conceição, no município de Niterói, RJ. Informantes-chave foram entrevistados para obter informações que pudessem ser utilizadas nas construções de novos indicadores. Ao se compararem os dados do IBGE com os fornecidos pelos informantes, foram encontradas algumas diferenças. Os dados dos informantes são mais condizentes com a realidade local, propiciando, de acordo com a área, a observação de diferentes modus operandi de coleta de lixo e limpeza pública. Os casos concentraram-se nos setores favela plana e favela morro. Concluiu-se que os indicadores referentes à frequência de abastecimento de água e coleta de lixo se mostram importantes para serem analisados em estudos de nível local associados com a incidência da dengue.

[Progression of dengue virus circulation in the State of Bahia, Brazil, 1994-2000]

INTRODUCTION

The strength of the re-emergence of dengue virus and the severity of these infections put this disease in the priority agenda of the institutions responsible for protecting the health of populations. Important for understanding the epidemiology of dengue nowadays refers to the knowledge of the patterns of spatial-temporal diffusion, though there is few research addressing this issue. This study describes the process of dissemination of dengue in the state of Bahia, from 1994 to 2000.

METHODS

This ecological study space-time, with the units of analysis, county, epidemiological week, month, trimester and year. There has been construction of the trend line and has been mapping the sequential occurrence of dengue in the municipality for the period.

RESULTS

There were 164,050 reported cases of dengue and the introduction of this virus in Bahia, unlike other states, occurred on a small city, though there is intermittency in spatial and temporal records of cases at the beginning of this epidemic. The virus circulated in all climatic zones fact what highlight its high transmission power. The highest intensity of detection of cases and territorial expansion was in the littoral (zone humid and half-humid) ideal area for the survive of the vector.

CONCLUSIONS

Hypothetically, the intermittent space-time pattern initially observed, could have allowed the control of the progression of the epidemic, if structured action to vectorial combat was carried out.

Spatial point analysis based on dengue surveys at household level in central Brazil

Background

Dengue virus (DENV) affects nonimunne human populations in tropical and subtropical regions. In the Americas, dengue has drastically increased in the last two decades and Brazil is considered one of the most affected countries. The high frequency of asymptomatic infection makes difficult to estimate prevalence of infection using registered cases and to locate high risk intra-urban area at population level. The goal of this spatial point analysis was to identify potential high-risk intra-urban areas of dengue, using data collected at household level from surveys.

Methods

Two household surveys took place in the city of Goiania (~1.1 million population), Central Brazil in the year 2001 and 2002. First survey screened 1,586 asymptomatic individuals older than 5 years of age. Second survey 2,906 asymptomatic volunteers, same age-groups, were selected by multistage sampling (census tracts; blocks; households) using available digital maps. Sera from participants were tested by dengue virus-specific IgM/IgG by EIA. A Generalized Additive Model (GAM) was used to detect the spatial varying risk over the region. Initially without any fixed covariates, to depict the overall risk map, followed by a model including the main covariates and the year, where the resulting maps show the risk associated with living place, controlled for the individual risk factors. This method has the advantage to generate smoothed risk factors maps, adjusted by socio-demographic covariates.

Results

The prevalence of antibody against dengue infection was 37.3% (95%CI [35.5–39.1]) in the year 2002; 7.8% increase in one-year interval. The spatial variation in risk of dengue infection significantly changed when comparing 2001 with 2002, (ORadjusted = 1.35; p < 0.001), while controlling for potential confounders using GAM model. Also increasing age and low education levels were associated with dengue infection.

Conclusion

This study showed spatial heterogeneity in the risk areas of dengue when using a spatial multivariate approach in a short time interval. Data from household surveys pointed out that low prevalence areas in 2001 surveys shifted to high-risk area in consecutive year. This mapping of dengue risks should give insights for control interventions in urban areas.

The dynamics of dengue virus serotype 3 introduction and dispersion in the state of Bahia, Brazil

By 2002, dengue virus serotype 1 (DENV-1) and DENV-2 had circulated for more than a decade in Brazil. In 2002, the introduction of DENV-3 in the state of Bahia produced a massive epidemic and the first cases of dengue hemorrhagic fever. Based on the standardized frequency, timing and location of viral isolations by the state's Central Laboratory, DENV-3 probably entered Bahia through its capital, Salvador, and then rapidly disseminated to other cities, following the main roads. A linear regression model that included traffic flow, distance from the capital and DENV-1 circulation (r2 = 0.24, p = 0.001) supported this hypothesis. This pattern was not seen for serotypes already in circulation and was not seen for DENV-3 in the following year. Human population density was another important factor in the intensity of viral circulation. Neither DENV-1 nor DENV-2 fit this model for 2001 or 2003. Since the vector has limited flight range and vector densities fail to correlate with intensity of viral circulation, this distribution represents the movement of infected people and to some extent mosquitoes. This pattern may mimic person-to-person spread of a new infection.

[Dengue: sero-epidemiological survey and virological surveillance in Campinas, São Paulo, Brazil]

The epidemiology of dengue in the municipality of Campinas, São Paulo, Brazil, was studied in 1998 using a randomized sero-epidemiological survey. Epidemiological surveillance data from 1996-2003 were also analyzed, with an emphasis on virological surveillance. 1,260 individuals participated in the survey and had blood samples drawn by finger stick on filter paper. Blood samples were tested by EIA-ICC, an enzyme immunoassay using infected cells as antigen. Dengue antibody prevalence (14.79%) was lower than in other surveys in other States of Brazil, but higher than in two other serological surveys in São Paulo State. Dengue antibody prevalence was far higher than the reported case incidence during the 1996, 1997, and 1998 epidemics. Antibody prevalence and reported case incidence in different health districts were disproportional. The article concludes by recommending further research on the significance of transmission rates during epidemics and more intensive virological surveillance, especially in years with few reported cases.

[Epidemiology of dengue in Salvador-Bahia, 1995-1999]

Since 1981, Brazil has registered dengue epidemic and simultaneous circulation of the DEN-1 and DEN-2 serotypes in over 2,700 municipalities. In Salvador- Bahia, located in the Northeastern region of the Country, two epidemic outbreaks occurred in the years of 1995 and 1996, with further endemic spread of the disease. This study analyses the incidence of the virosis within this municipal area, from 1995 to 1999, considering, among other variables, its distribution in the Sanitary Districts and density of Aedes aegypti. Registers of notified cases and the city's Vectorial Control Program were used as data source. The incidence rate of notified cases of dengue in 1995 and 1996, which were 691.4 and 393.5 per 100,000 inhabitants, respectively, decreased to 65 per 100,000 inhabitants in 1998. In the poorer Sanitary Districts, this index reached figures of over 800 per 100,000 inhabitants. The Premise Index for Aedes aegypti reached 54.1% in one of the Districts. Bearing in mind the relevance of the re-emergence of dengue in the world, the authors discuss the possible factors which condition the virus introduction, its epidemiological presentation over the course of four years, and the effectiveness of the vectorial combat (eradication) program.