Prospective birth cohort in a hyperendemic dengue area in Northeast Brazil: methods and preliminary results

Mannose-binding lectin levels and MBL2 gene polymorphisms are associated to dengue infection in Brazilian children at the early ages

BACKGROUND

The mannose-binding lectin (MBL) plays an important role in innate immunity. Genetically determined variations in serum levels of MBL may influence the susceptibility and clinical outcome of dengue infection in early life.

METHODS

We investigated MBL2 gene polymorphisms and serum levels of MBL (total and functional) in children with asymptomatic (n=17) and symptomatic (n=29), primary dengue infections, and age-matched uninfected children (n=84) enrolled in a Brazilian dengue birth cohort. Polymorphisms of the MBL2 gene were assessed by RT-PCR, while ELISA were used to quantify serum levels of MBL.

RESULTS

We found that the X allele and YX genotype in the MBL2 were more frequent in dengue cases than controls. Likewise, the LXPA haplotype was exclusively found in dengue cases, thus probably related to dengue infection in our setting. Moreover, we found a higher frequency of the O allele and AO genotype in control group. Serum levels of total and functional MBL were higher in dengue naïve infants than dengue cases.

CONCLUSIONS

MBL2 variants related to lower production of serum MBL were associated to dengue infection in infants, while intermediate to high levels of total and functional serum MBL were associated with protection. These findings highlight the role of MBL2 variants and serum levels of MBL in the susceptibility to dengue disease at early ages.

A populational-based birth cohort study in a low-income urban area in Rio de Janeiro, Brazil: implementation and description of the characteristics of the study

A comprehensive cohort study including an entomological surveillance component can contribute to our knowledge of clinical aspects and transmission patterns of arbovirosis. This article describes the implementation of a populational-based birth cohort study that included an entomological surveillance component, and its associated challenges in a low-income community of Rio de Janeiro, Brazil. The participants were recruited in two periods: from 2012 to 2014, and from 2015 to 2017. The children had scheduled pediatric consultations and in case of fever. Epidemiological, clinical data and biological samples were collected at pediatric visits. Active febrile surveillance was performed by telephone calls, social networking, message apps, and household visits. A total of 387 newborns and 332 new children were included during the first and second recruitment periods, respectively. By July 2017, there were 451 children on follow-up. During the study, 2,759 pediatric visits were performed: 1,783 asymptomatic and 976 febrile/rash consultations. The number of febrile or rash consultations increased 3.5-fold after the use of media tools for surveillance. No temporal pattern, seasonality or peak of febrile cases was observed during the study period. A total of 10,105 adult mosquitoes (including 3,523 Aedes spp. and 6,582 Culex quinquefasciatus) and 46,047 Aedes eggs were collected from households, schools, and key sites. Although challenging, this structured sentinel populational-based birth cohort is relevant to the knowledge of risks and awareness of emerging pathogens.

Incidence and risk factors for Dengue virus (DENV) infection in the first 2 years of life in a Brazilian prospective birth cohort

This study assessed the incidence and risk factors for dengue virus (DENV) infection among children in a prospective birth cohort conducted in the city of Recife, a hyperendemic dengue area in Northeast Brazil. Healthy pregnant women (n = 415) residing in Recife who agreed to have their children followed were enrolled. Children were followed during their first 24 months of age (May/2011-June/2014), before the 2015 Zika virus outbreak. DENV infection was detected by reverse-transcriptase polymerase chain reaction and/or serology (anti-DENV IgM/IgG). The incidence rates per 1000 person-years (py) and its association with risk factors by age bands (0-12, >12-30 months) were estimated through Poisson regression models. Forty-nine dengue infections were detected; none progressed to severe forms. The incidence rates were 107·6/1000py (95% CI 76·8-150·6) and 93·3/1000py (95% CI 56·1-154·4) in the first and second years of age, respectively. Male children (risk ratios (RR) = 2·33; 95% CI 1·09-4·98) and those born to DENV-naïve mothers (RR = 2·42; 95% CI 1·01-5·80) were at greater risk of infection in the first year of age. In the second year, children born to Caucasian/Asian descent skin colour mothers had a threefold higher risk of infection (RR = 3·34; 95% CI: 1·08-10·33). These data show the high exposure of children to DENV infection in our setting and highlight the role of biological factors in this population's susceptibility to infection.

Dengue Virus-Specific Antibodies Enhance Brazilian Zika Virus Infection

Anti-Flavivirus antibodies are highly cross-reactive and may facilitate Zika virus (ZIKV) infection through the antibody-dependent enhancement (ADE) mechanism. We demonstrate that dengue-specific antibodies enhance the infection of a primary Brazilian ZIKV isolate in a FcγRII-expressing K562 cell line. In addition, we demonstrate that serum samples from dengue-immune pregnant women enhanced ZIKV infection. These findings highlight the need for epidemiological studies and animal models to further confirm the role of ADE in the development of congenital and neurological complications associated with ZIKV infections.

Placental Transfer of Dengue Virus (DENV)-Specific Antibodies and Kinetics of DENV Infection-Enhancing Activity in Brazilian Infants

BACKGROUND

Maternal-fetal transferred dengue virus (DENV)-specific antibodies have been implicated in the immunopathogenesis of dengue during infancy.

METHODS

A prospective birth cohort was established in a dengue-endemic area in the Northeast Region of Brazil. DENV-specific immunoglobulin G (IgG) and DENV-1-4 serotype-specific neutralizing antibody (NAb) levels were assessed in 376 paired maternal and umbilical cord blood samples. The kinetics of enhancing activity by maternally acquired DENV antibodies was determined in serum samples from children enrolled in the cohort.

RESULTS

Mothers were mostly immune to DENV-3 alone (53.7%) or combined with DENV-4 (30.6%). Levels of DENV-specific IgG, DENV-3 NAbs, and DENV-4 NAbs were significantly higher in newborns than in their respective mothers. Mothers immune to a single serotype transferred greater levels of DENV-specific IgG (P = .02) and DENV-3 NAbs (P = .04) than mothers immune to multiple DENV serotypes. Maternally acquired DENV-3 NAbs disappeared in >90% of the children by the age of 4 months. The peak enhancing activity was detected by the age of 2 months (P < .0001) and rapidly declined by the age of 4 months (P = .0035).

CONCLUSIONS

Unlike Asian infants, the enhancing activity of DENV infection by maternally transferred DENV antibodies occurs at earlier ages in Brazilian children. These findings might explain the low occurrence of severe dengue among infants in our setting.