A serological framework to investigate acute primary and post-primary dengue cases reporting across the Philippines.

BACKGROUND: In dengue-endemic countries, targeting limited control interventions to populations at risk of severe disease could enable increased efficiency. Individuals who have had their first (primary) dengue infection are at risk of developing more severe secondary disease, thus could be targeted for disease prevention. Currently, there is no reliable algorithm for determining primary and post-primary (infection with more than one flavivirus) status from a single serum sample. In this study, we developed and validated an immune status algorithm using single acute serum samples from reporting patients and investigated dengue immuno-epidemiological patterns across the Philippines. METHODS: During 2015/2016, a cross-sectional sample of 10,137 dengue case reports provided serum for molecular (anti-DENV PCR) and serological (anti-DENV IgM/G capture ELISA) assay. Using mixture modelling, we re-assessed IgM/G seroprevalence and estimated functional, disease day-specific, IgG:IgM ratios that categorised the reporting population as negative, historical, primary and post-primary for dengue. We validated our algorithm against WHO gold standard criteria and investigated cross-reactivity with Zika by assaying a random subset for anti-ZIKV IgM and IgG. Lastly, using our algorithm, we explored immuno-epidemiological patterns of dengue across the Philippines. RESULTS: Our modelled IgM and IgG seroprevalence thresholds were lower than kit-provided thresholds. Individuals anti-DENV PCR+ or IgM+ were classified as active dengue infections (83.1%, 6998/8425). IgG- and IgG+ active dengue infections on disease days 1 and 2 were categorised as primary and post-primary, respectively, while those on disease days 3 to 5 with IgG:IgM ratios below and above 0.45 were classified as primary and post-primary, respectively. A significant proportion of post-primary dengue infections had elevated anti-ZIKV IgG inferring previous Zika exposure. Our algorithm achieved 90.5% serological agreement with WHO standard practice. Post-primary dengue infections were more likely to be older and present with severe symptoms. Finally, we identified a spatio-temporal cluster of primary dengue case reporting in northern Luzon during 2016. CONCLUSIONS: Our dengue immune status algorithm can equip surveillance operations with the means to target dengue control efforts. The algorithm accurately identified primary dengue infections who are at risk of future severe disease.

Serological Evidence of Widespread Zika Transmission across the Philippines.

Zika virus (ZIKV) exposure across flavivirus-endemic countries, including the Philippines, remains largely unknown despite sporadic case reporting and environmental suitability for transmission. Using laboratory surveillance data from 2016, 997 serum samples were randomly selected from suspected dengue (DENV) case reports across the Philippines and assayed for serological markers of short-term (IgM) and long-term (IgG) ZIKV exposure. Using mixture models, we re-evaluated ZIKV IgM/G seroprevalence thresholds and used catalytic models to quantify the force of infection (attack rate, AR) from age-accumulated ZIKV exposure. While we observed extensive ZIKV/DENV IgG cross-reactivity, not all individuals with active DENV presented with elevated ZIKV IgG, and a proportion of dengue-negative cases (DENV IgG-) were ZIKV IgG-positive (14.3%, 9/63). We identified evidence of long-term, yet not short-term, ZIKV exposure across Philippine regions (ZIKV IgG+: 31.5%, 314/997) which was geographically uncorrelated with DENV exposure. In contrast to the DENV AR (12.7% (95%CI: 9.1-17.4%)), the ZIKV AR was lower (5.7% (95%CI: 3-11%)) across the country. Our results provide evidence of widespread ZIKV exposure across the Philippines and suggest the need for studies to identify ZIKV infection risk factors over time to better prepare for potential future outbreaks.

Prevalence of Pediculus capitis in schoolchildren in Battambang, Cambodia.

BACKGROUND/PURPOSE: Pediculus capitis is the most common human ectoparasite. When it feeds on the blood through the scalp of its host, the anticoagulant in its saliva causes scalp inflammation and itching, and consequent scratching by the host causes further inflammation from bacterial infection. P. capitis infestation is currently a common parasitic dermatosis and a critical public health concern in underdeveloped countries. METHODS: Through naked eye inspection of P. capitis on or in the hair from 323 school children in Cambodia. RESULTS: A total of 143 children (44.3%) were found to have P. capitis infestation. Univariate analysis revealed that girls had a significantly higher infection rate than boys. Overall, young aged schoolchildren (10 yrs old ≤) showed significantly higher infection rate than old aged schoolchildren (>10 yrs old). Groups stratified by time revealed that schoolchildren studied at the afternoon classes than morning classes in Tuol Prum Muoy Primary School had a significantly higher risk in acquisition of P. capitis infestation. Multivariate analysis results indicated that relative to the boys, the girls were at a significantly higher risk of contracting P. capitis infection. When stratified by inspection time with the Tuol Prum Muoy Primary School morning classes as the reference, the Tuol Prum Muoy Primary School afternoon classes exhibited a significantly higher risk of P. capitis infection. CONCLUSION: Primary school children in Cambodia have a high P. capitis infection rate and thus require effective treatment and prevention measures to treat symptoms and lower the infection rate.

Prevalence and Risk Factors for Intestinal Parasitic Infection in Schoolchildren in Battambang, Cambodia.

Most intestinal parasitic infections (IPIs), commonly endemic in tropical resource-poor developing countries, are neglected tropical diseases. Parasitic infections and malnutrition are most commonly found in children. We determined the prevalence of IPIs and the risk factors in Battambang Province, northwestern Cambodia, from August to September 2015. This study collected 308 valid questionnaires and specimens from Dontri (173, 56.2%) and Kon Kaêk (135, 43.8%) primary schools. All stool samples were examined using Chang's Feces Examination Apparatus through the merthiolate-iodine-formaldehyde technique. Headache (259, 84.1%), recurrent cough (249, 80.8%), and abdominal pain (235, 76.3%) were the most common symptoms as detected from questionnaire investigation. A total of 155 students were positive for any parasite type; a single parasite type was observed in 97 students (31.5%), two types in 40 students (13.0%), three types in 14 students (4.6%), and four types in four students (1.3%). Nine gastrointestinal parasite species (three helminths and six protozoa) were identified in the stool samples. The most common parasites in schoolchildren were Giardia intestinalis (31.5%) and Entamoeba histolytica/dispar (17.5%). This is the first IPIs study, and more than half of the schoolchildren were infected with parasite species in Moung Russey District of Battambang Province. We found nine parasite species, including helminths and protozoa, and pathogenic protozoa were the main source of IPIs. Improving the detection method, sanitation facilities, and personal hygiene as well as utilizing combined drugs are all important measures to greatly reduce IPIs in Cambodian schoolchildren.