Epidemiology of dengue, chikungunya and zika in a naïve population in St. Kitts, West Indies

Arboviruses such as dengue (DENV), chikungunya (CHIKV) and Zika (ZIKV) are of increasing global health concern and have caused recent rapid outbreaks in the Americas. However, studies focusing on behavioural risk that would assist with the understanding of transmission factors are scarce. This prospective study followed immunologically naïve adults in an arbovirus endemic environment to investigate disease detection, transmission and associated risk factors. University students from non-endemic areas studying in St. Kitts and Nevis were recruited as volunteers in three cohorts of sentinels between September 2014 and May 2015 (n = 224). Plasma was collected at enrolment and every 4 months subsequently until September 2016 and assayed for anti-DENV and anti-CHIKV IgM and IgG ELISA antibodies. Additionally, specimens collected from suspected cases of acute arboviral infection within the wider island population and mosquitoes captured in neighbourhoods were analysed for DENV, CHIKV and ZIKV by RT-PCR. Epidemiological data gathered at each sampling were investigated using mixed effect models, generalised estimating equations, Bayesian techniques and Cox proportional hazards survival analysis. Evidence of dengue infection was found in all (100%) the suspected cases born in St. Kitts but proof of recent infection was elusive. Chikungunya prevalence in sentinels was 12.7% (95% PI: 8.2-18.4%), whereas prevalence in suspected cases born in St. Kitts was 69.6% (95% CI: 47.1-86.8%). Zika prevalence was 39.1% (95% CI: 25.1- 54.6%) and evidence of infection and vertical transmission were also found in Ae. aegypti mosquitoes. Climatic variables were significantly associated with transmission followed by socio-economic conditions, frequency of mosquito bites and exposure to Ae. aegypti. Data suggested that arbovirus transmission in St. Kitts are epidemic and expire when climatic conditions become unfavourable for mosquito transmission or herd immunity reaches a critical threshold. These findings increase the understanding of arboviral transmission in small islands and can assist in more efficient outbreak response.