BackgroundDengue is a febrile illness transmitted by mosquitoes, causing disease across the tropical and sub-tropical world. Antibody prevalence data and serotype distributions describe population-level risk and inform public health decision-making.Methodology/Principal findingsIn this cross-sectional study we used data from a pediatric dengue seroprevalence study to describe historical dengue serotype circulation, according to age and geographic location. A sub-sample of 780 dengue IgG-positive sera, collected from 30 sites across urban Indonesia in 2014, were tested by the plaque reduction neutralization test (PRNT) to measure the prevalence and concentration of serotype-specific neutralizing antibodies according to subject age and geography. PRNT results were obtained from 776 subjects with mean age of 9.6 years. 765 (98.6%) neutralized one or more dengue serotype at a threshold of >10 (1/dil). Multitypic profiles were observed in 50.9% of the samples; a proportion which increased to 63.1% in subjects aged 15–18 years. Amongst monotypic samples, the highest proportion was reactive against DENV-2, followed by DENV-1, and DENV-3, with some variation across the country. DENV-4 was the least common serotype. The highest anti-dengue antibody titers were recorded against DENV-2, and increased with age to a geometric mean of 516.5 [1/dil] in the oldest age group.Conclusions/SignificanceWe found that all four dengue serotypes have been widely circulating in most of urban Indonesia, and more than half of children had already been exposed to >1 dengue serotype, demonstrating intense transmission often associated with more severe clinical episodes. These data will help inform policymakers and highlight the importance of dengue surveillance, prevention and control.

Japanese encephalitis virus (JEV) is a zoonotic, mosquito-borne flavivirus, distributed across Asia. Infections are mostly mild/asymptomatic but symptoms include neurological disorders, sequelae and fatalities. Data to inform control strategies are limited by incomplete case reporting. We used JEV serological data from a multi-country Asian dengue vaccine study in children aged 2-14 years to describe JEV endemicity by plaque reduction neutralization test (PRNT50). 1479 unvaccinated subjects were included. A minimal estimate of pediatric JEV seroprevalence in dengue-naïve individuals was 8.1% in Indonesia, 5.8% in Malaysia, 10.8% in Philippines and 30.7% in Vietnam, translating to annual infection risks varying from 0.8% (in Malaysia) to 5.2% (in Vietnam). JEV seroprevalence and annual infection estimates were much higher in children with history of dengue infection, indicating cross-neutralization within the JEV PRNT50 assay. These data confirm JEV transmission across predominantly urban areas and support a greater emphasis on JEV case-finding, diagnosis and prevention.

Understanding the heterogeneous nature of dengue transmission is important for prioritizing and guiding the implementation of prevention strategies. However, passive surveillance data in endemic countries are rarely adequately informative. We analyzed data from a cluster-sample, cross-sectional seroprevalence study in 1–18 year-olds to investigate geographic differences in dengue seroprevalence and force of infection in Indonesia. We used catalytic models to estimate the force of infection in each of the 30 randomly selected sub-districts. Based on these estimates, we determined the proportion of sub-districts expected to reach seroprevalence levels of 50%, 70% and 90% by year of age. We used population averaged generalized estimating equation models to investigate individual- and cluster-level determinants of dengue seropositivity. Dengue force of infection varied substantially across Indonesia, ranging from 4.3% to 30.0% between sub-districts. By age nine, 60% of sub-districts are expected to have a seroprevalence ≥70%, rising to 83% by age 11. Higher odds of seropositivity were associated with higher population density (OR = 1.54 per 10-fold rise in population density, 95% CI: 1.03–2.32) and with City (relative to Regency) administrative status (OR = 1.92, 95% CI: 1.32–2.79). Our findings highlight the substantial variation in dengue endemicity within Indonesia and the importance of understanding spatial heterogeneity in dengue transmission intensity for optimal dengue prevention strategies including future implementation of dengue vaccination programmes.

Background: Bluetongue is a vector-borne disease of ruminants caused by bluetongue virus (BTV) belonging to Reoviridae. So far, 28 serotypes of BTV have been reported, and distribution of various serotypes is not uniform among different geographical areas. The virus is endemic in tropical areas where vector population is abundant and these areas act as source population for virus spread to the neighbouring temperate sink areas. Australasia is one of the stable source-sink episystems with circulation of different serotypes. During this study, genetic relations of the serotypes circulating in the Australasian region were analysed and the serotypes that are unique to this episystem and those which entered this episystem during recent past were identified.Methods & Materials: Data about BTV serotypes circulating and genome sequence were collected from public databases. Phylogenetic analysis was done using MEGA and BEAST.Results: Majority of the BTV serotypes circulating in Australasia are either unique (BTV-20, -21 and -23) to the region or distinct (BTV-1, -2, -3, -4, -9 and 16) from their counterparts in other sourcesink episystems and belong to Eastern topotype. Apart from these, serotypes of western origin are also found to be circulating , and some (BTV-2 and -10) are indistinguishable from the live attenuated vaccines being used in Africa (BTV-2) and USA (BTV-10). However, these two serotypes are not reported outside India.Conclusion: We could conclude that BTV-20, -21 and -23 are unique to Australasian region and eastern topotype viruses of serotypes BTV-1, -2, -3, -4, -9 and -16 have probably diverged from their western counterparts hundreds of years ago and evolved since then. Among the serotypes of western origin, BTV-5, 7, -12 and -24 seem to have entered this area in the recent past and got established in more than one country whereas vaccine strains of BTV-2 and -10 did not. Identification of circulating serotypes of BTV in this region is important for evaluating virus movement and for vaccine design.

There are errors in Table 3 due to an incorrect calculation. The force of infection is μ, the mean number of primary infections per year or average rate at which susceptible individuals are infected, not p, the probability of a person living in the area being infected in one year. Please see the corrected Table 3 here.