Aubree Gordon

Global burden of respiratory infections due to seasonal influenza in young children: a systematic review and meta-analysis

BACKGROUND The global burden of disease attributable to seasonal influenza virus in children is unknown. We aimed to estimate the global incidence of and mortality from lower respiratory infections associated with influenza in children younger than 5 years. METHODS We estimated the incidence of influenza episodes, influenza-associated acute lower respiratory infections (ALRI), and influenza-associated severe ALRI in children younger than 5 years, stratified by age, with data from a systematic review of studies published between Jan 1, 1995, and Oct 31, 2010, and 16 unpublished population-based studies. We applied these incidence estimates to global population estimates for 2008 to calculate estimates for that year. We estimated possible bounds for influenza-associated ALRI mortality by combining incidence estimates with case fatality ratios from hospital-based reports and identifying studies with population-based data for influenza seasonality and monthly ALRI mortality. FINDINGS We identified 43 suitable studies, with data for around 8 million children. We estimated that, in 2008, 90 million (95% CI 49-162 million) new cases of influenza (data from nine studies), 20 million (13-32 million) cases of influenza-associated ALRI (13% of all cases of paediatric ALRI; data from six studies), and 1 million (1-2 million) cases of influenza-associated severe ALRI (7% of cases of all severe paediatric ALRI; data from 39 studies) occurred worldwide in children younger than 5 years. We estimated there were 28,000-111,500 deaths in children younger than 5 years attributable to influenza-associated ALRI in 2008, with 99% of these deaths occurring in developing countries. Incidence and mortality varied substantially from year to year in any one setting. INTERPRETATION Influenza is a common pathogen identified in children with ALRI and results in a substantial burden on health services worldwide. Sufficient data to precisely estimate the role of influenza in childhood mortality from ALRI are not available. FUNDING WHO; Bill & Melinda Gates Foundation.

Dynamics of Dengue Disease Severity Determined by the Interplay Between Viral Genetics and Serotype-Specific Immunity

The complex interactions between serotype-specific immunity and viral genetics drive dengue disease outcomes in endemic populations. Dissecting Dengue Dynamics In some parts of the world, mosquito bites cause more than a maddening itch. These tiny insect vessels can host dengue viruses (DENVs), which the mosquitoes transmit to human beings. DENVs cause disease states that range in severity from asymptomatic infection to the potentially fatal dengue hemorrhagic fever (DHF) and dengue shock syndrome (DSS). Infection with one DENV serotype offers a person lifelong protection against that serotype and temporary immune protection from severe dengue disease caused by a different DENV serotype. But once this immune-protected period passes, the individual becomes at increased risk for more severe disease. “What line separates the rumble of the wheels from the howl of the wolves?”1 Now, OhAinle et al. dissect the complex interactions between DENV immunity and viral genetics that drive dengue disease outcomes in endemic Nicaraguan populations. To address this worldwide public health problem, the authors carried out two independent clinical studies of dengue epidemics in Managua, Nicaragua, from 2004/5 to 2008/9. In these populations, patients displayed a striking increase in severe dengue disease outcomes caused by DENV-2 infection across several epidemic seasons. The increase in severe cases in later seasons could be attributed, in part, to waning DENV-1 immunity. However, OhAinle et al. also determined that the increased risk of severe DENV-2–related disease correlated with substitution, in patients, of the Asian/American DENV-2 NI-1 clade with a new virus clade, NI-2B. The authors then molecularly characterized the various viral genomes, assessed the viruses’ fitness levels in vitro, and measured the extent of viremia in patient blood samples; experimental results supported the emergence of a fitter virus in later epidemic seasons. OhAinle et al. also found that the NI-1 clade displayed enhanced virulence specifically in children who had been immune to DENV-1; in contrast, DENV-3 immunity correlated with more severe disease resulting from NI-2B infections. These data highlight the complex interplay between viral genetics and population dynamics that increase the risk of severe dengue disease. This study offers insights into viral evolution and the effects of a patient’s immunological background on viral fitness and virulence. A detailed understanding of DENV epidemiology and pathogenesis should aid in the design of a much-needed dengue vaccine. 1From Invisible Cities by Italo Calvino The rapid spread of dengue is a worldwide public health problem. In two clinical studies of dengue in Managua, Nicaragua, we observed an abrupt increase in disease severity across several epidemic seasons of dengue virus serotype 2 (DENV-2) transmission. Waning DENV-1 immunity appeared to increase the risk of severe disease in subsequent DENV-2 infections after a period of cross-protection. The increase in severity coincided with replacement of the Asian/American DENV-2 NI-1 clade with a new virus clade, NI-2B. In vitro analyses of viral isolates from the two clades and analysis of viremia in patient blood samples support the emergence of a fitter virus in later, relative to earlier, epidemic seasons. In addition, the NI-1 clade of viruses was more virulent specifically in children who were immune to DENV-1, whereas DENV-3 immunity was associated with more severe disease among NI-2B infections. Our data demonstrate that the complex interaction between viral genetics and population dynamics of serotype-specific immunity contributes to the risk of severe dengue disease. Furthermore, this work provides insights into viral evolution and the interaction between viral and immunological determinants of viral fitness and virulence.

Phenotyping of peripheral blood mononuclear cells during acute dengue illness demonstrates infection and increased activation of monocytes in severe cases compared to classic dengue fever.

In vitro studies have attempted to identify dengue virus (DEN) target cells in peripheral blood; however, extensive phenotyping of peripheral blood mononuclear cells (PBMCs) from dengue patients has not been reported. PBMCs collected from hospitalized children suspected of acute dengue were analyzed for DEN prM, CD32, CD86, CD14, CD11c, CD16, CD209, CCR7, CD4, and CD8 by flow cytometry to detect DEN antigen in PBMCs and to phenotype DEN-positive cells. DEN prM was detected primarily in activated monocytes (CD14(+), CD32(+), CD86(+), CD11c(+)). A subset of samples analyzed for DEN nonstructural protein 3 (NS3) confirmed that approximately half of DEN antigen-positive cells contained replicating virus. A higher percentage of PBMCs from DHF patients expressed prM, CD86, CD32, and CD11c than did those from DF patients. Increased activation of monocytes and greater numbers of DEN-infected cells were associated with more severe dengue, implicating a role for monocyte activation in dengue immunopathogenesis.

Trends in Patterns of Dengue Transmission over 4 Years in a Pediatric Cohort Study in Nicaragua

BACKGROUND Dengue is the most prevalent mosquito-borne viral disease in humans and a major urban public health problem worldwide. METHODS A prospective cohort study of approximately 3800 children initially aged 2-9 years was established in Managua, Nicaragua, in 2004 to study the natural history of dengue transmission in an urban pediatric population. Blood samples from healthy subjects were collected annually prior to the dengue season, and identification of dengue cases occurred via enhanced passive surveillance at the study health center. RESULTS Over the first four years of the study, seroprevalence of anti-dengue virus (DENV) antibodies increased from 22%-40% in the 2-year-old cohort and 90%-95% in the 9-year-old cohort. The incidence of symptomatic dengue cases and the ratio of inapparent to symptomatic DENV infection varied substantially from year to year. The switch in dominant transmission from DENV-1 to DENV-2 was accompanied by an increase in disease severity but, paradoxically, a decrease in transmission. Phylogeographic analysis of full-length DENV-2 sequences revealed strong geographic clustering of dengue cases. CONCLUSIONS This large-scale cohort study of dengue in the Americas demonstrates year-to-year variation of dengue within a pediatric population, revealing expected patterns in transmission while highlighting the impact of interventions, climate, and viral evolution.

Human Enterovirus 109: a Novel Interspecies Recombinant Enterovirus Isolated from a Case of Acute Pediatric Respiratory Illness in Nicaragua†

ABSTRACT Enteroviruses (Picornaviridae family) are a common cause of human illness worldwide and are associated with diverse clinical syndromes, including asymptomatic infection, respiratory illness, gastroenteritis, and meningitis. In this study, we report the identification and complete genome sequence of a novel enterovirus isolated from a case of acute respiratory illness in a Nicaraguan child. Unbiased deep sequencing of nucleic acids from a nose and throat swab sample enabled rapid recovery of the full-genome sequence. Phylogenetic analysis revealed that human enterovirus 109 (EV109) is most closely related to serotypes of human enterovirus species C (HEV-C) in all genomic regions except the 5′ untranslated region (5′ UTR). Bootstrap analysis indicates that the 5′ UTR of EV109 is likely the product of an interspecies recombination event between ancestral members of the HEV-A and HEV-C groups. Overall, the EV109 coding region shares 67 to 72% nucleotide sequence identity with its nearest relatives. EV109 isolates were detected in 5/310 (1.6%) of nose and throat swab samples collected from children in a pediatric cohort study of influenza-like illness in Managua, Nicaragua, between June 2007 and June 2008. Further experimentation is required to more fully characterize the pathogenic role, disease associations, and global distribution of EV109.

Symptomatic versus inapparent outcome in repeat dengue virus infections is influenced by the time interval between infections and study year.

Four dengue virus serotypes (DENV1-4) circulate globally, causing more human illness than any other arthropod-borne virus. Dengue can present as a range of clinical manifestations from undifferentiated fever to Dengue Fever to severe, life-threatening syndromes. However, most DENV infections are inapparent. Yet, little is known about determinants of inapparent versus symptomatic DENV infection outcome. Here, we analyzed over 2,000 DENV infections from 2004 to 2011 in a prospective pediatric cohort study in Managua, Nicaragua. Symptomatic cases were captured at the study health center, and paired healthy annual samples were examined on a yearly basis using serological methods to identify inapparent DENV infections. Overall, inapparent and symptomatic DENV infections were equally distributed by sex. The mean age of infection was 1.2 years higher for symptomatic DENV infections as compared to inapparent infections. Although inapparent versus symptomatic outcome did not differ by infection number (first, second or third/post-second DENV infections), substantial variation in the proportion of symptomatic DENV infections among all DENV infections was observed across study years. In participants with repeat DENV infections, the time interval between a first inapparent DENV infection and a second inapparent infection was significantly shorter than the interval between a first inapparent and a second symptomatic infection. This difference was not observed in subsequent infections. This result was confirmed using two different serological techniques that measure total anti-DENV antibodies and serotype-specific neutralizing antibodies, respectively. Taken together, these findings show that, in this study, age, study year and time interval between consecutive DENV infections influence inapparent versus symptomatic infection outcome, while sex and infection number had no significant effect. Moreover, these results suggest that the window of cross-protection induced by a first infection with DENV against a second symptomatic infection is approximately 2 years. These findings are important for modeling dengue epidemics and development of vaccines.

The Nicaraguan Pediatric Dengue Cohort Study: Study Design, Methods, Use of Information Technology, and Extension to Other Infectious Diseases

Dengue is a mosquito-borne viral disease that is a major public health problem worldwide. In 2004, the Pediatric Dengue Cohort Study was established in Managua, Nicaragua, to study the natural history and transmission of dengue in children. Here, the authors describe the study design, methods, and results from 2004 to 2008. Initially, 3,721 children 2–9 years of age were recruited through door-to-door visits. Each year, new children aged 2 years are enrolled in the study to maintain the age structure. Children are provided with medical care through the study, and data from each medical visit are recorded on systematic study forms. All participants presenting with suspected dengue or undifferentiated fever are tested for dengue by virologic, serologic, and molecular biologic assays. Yearly blood samples are collected to detect inapparent dengue virus infections. Numerous information and communications technologies are used to manage study data, track samples, and maintain quality control, including personal data assistants, barcodes, global information systems, and fingerprint scans. Close collaboration with the Nicaraguan Ministry of Health and use of almost entirely local staff are essential components for success. This study is providing critical data on the epidemiology and transmission of dengue in the Americas needed for future vaccine trials.

Clinical Attack Rate and Presentation of Pandemic H1N1 Influenza versus Seasonal Influenza A and B in a Pediatric Cohort in Nicaragua

BACKGROUND. Little is known about the clinical presentation and epidemiology of influenza A H1N1pdm in children in developing countries. We assessed the severity of influenza A H1N1pdm in children in Nicaragua by comparing H1N1pdm cases to seasonal influenza cases in an ongoing cohort study. METHODS. The Nicaraguan Influenza Cohort Study was established in June 2007 to study the burden and seasonality of pediatric influenza in a tropical developing country. During the period from June 2007 through November 2009, a total of 4391 children aged 2-14 years participated in the cohort. We examined the attack rate of clinical influenza and assessed symptoms at first presentation in febrile patients with H1N1pdm versus those with seasonal influenza A or B. RESULTS. The estimated clinical attack rate of H1N1pdm in the cohort was 20.1%, compared to 11.7% and 15.1% for seasonal influenza A and 11.9% and 24.2% for seasonal influenza A and B in 2007 and 2008, respectively. Symptoms significantly associated with H1N1pdm cases versus seasonal influenza A cases were sore throat (adjusted odds ratio [OR], 1.7; 95% confidence interval [CI], 1.2-2.5), wheezing (OR, 5.1; 95% CI, 1.3-19.0), rhonchi (OR, 4.6; 95% CI, 1.4-15.0), crepitations (OR, 16.2; 95% CI, 2.1-128.7), pneumonia (OR, 8.0; 95% CI, 1.7-37.3), nausea (OR, 2.8; 95% CI, 1.5-5.1), and loss of appetite (OR, 2.1; 95% CI, 1.4-3.1). In addition, 3 concurrent influenza and dengue virus coinfections were identified. CONCLUSIONS. Children with influenza A H1N1pdm presented with significantly more symptoms of lower respiratory infection and gastrointestinal symptoms than children with seasonal influenza. The clinical influenza attack rate was high in both pandemic and seasonal years.

Antibody-dependent enhancement of severe dengue disease in humans

Too much or too little—better than some Dengue fever is caused by a mosquito-transmitted flavivirus resembling Zika virus. Both viruses can cause severe diseases in humans with catastrophic sequelae. It has been suspected in humans, and shown in animal models, that the hosts immune responses can make disease worse. Katzelnick et al. examined data from a long-term study of Nicaraguan children exposed to dengue virus (see the Perspective by Feinberg and Ahmed). They confirmed that antibody-dependent enhancement of disease occurs at a specific range of antibody concentrations. Low levels of antibody did not enhance disease, intermediate levels exacerbated disease, and high antibody titers protected against severe disease. These findings have major implications for vaccines against flaviviruses. Indeed, recent vaccine trials have shown evidence of severe disease in some recipients who were previously exposed to virus. Science, this issue p. 929; see also p. 865 A long-term Nicaraguan pediatric cohort reveals that a narrow range of preexisting antibody titers increases the risk of severe dengue disease. For dengue viruses 1 to 4 (DENV1-4), a specific range of antibody titer has been shown to enhance viral replication in vitro and severe disease in animal models. Although suspected, such antibody-dependent enhancement of severe disease has not been shown to occur in humans. Using multiple statistical approaches to study a long-term pediatric cohort in Nicaragua, we show that risk of severe dengue disease is highest within a narrow range of preexisting anti-DENV antibody titers. By contrast, we observe protection from all symptomatic dengue disease at high antibody titers. Thus, immune correlates of severe dengue must be evaluated separately from correlates of protection against symptomatic disease. These results have implications for studies of dengue pathogenesis and for vaccine development, because enhancement, not just lack of protection, is of concern.

Ultrasound measurement of gallbladder wall thickening as a diagnostic test and prognostic indicator for severe dengue in pediatric patients

Gallbladder wall thickening measured by ultrasound was significantly associated with severe dengue, as well as with hallmark features of thrombocytopenia and elevated hematocrit/hemoconcentration, in children with suspected dengue in Nicaragua. We demonstrate that gallbladder wall thickening serves as a clinically relevant diagnostic test and prognostic indicator of severe dengue in pediatric populations.