Factors associated with chikungunya prevalence in northeastern Thailand in 2016–2017

Abstract

Background: Chikungunya (CHIK) fever is a self-limited acute febrile illness associated with polyarthritis. CHIK virus is transmitted by Aedes mosquitoes in which Aedes aegypti is regarded as the primary vector. Many factors can be attributed to the expansion of CHIKV infection, consisting of the increased number of travelers, spread of competent mosquitoes, adaptation of a new CHIKV strain with Aedes albopictus mosquitoes as well as the climate changes. Our previous research in the northeastern region of Thailand showed a risk of CHIKV outbreaks since the virus was circulating in human and mosquito populations. The aim of the current study was to investigate the effect of mosquito density, monthly climate variability and other factors on the prevalence of CHIKV infection in the same part of Thailand during 2016–2017. Methods and materials: Patients with a fever presenting at sub-district hospitals during a 2-year collection period were included in the study and their ages, gender, and location recorded. Climate variables as well as the disease's seasonal pattern were descriptively analyzed. Geo-referenced maps showing the distribution of observed chikungunya cases and mosquito density by sub-district in 2016 and 2017 were created using GIS and spatial statistics analysis (hot spot analysis). Results: The highest proportion of anti-CHIKV IgG (41.4%), indicating the long-term neutralizing antibodies, was in the 24–64 year-age group while active infection (anti-CHIKV IgM) was only present in the <15 age group. The recent circulation of CHIKV infection was evenly distributed among sub-districts based on participating hospitals and associated with the high density of the mosquito populations. Abundance of mosquitoes was affected by rainfall but not by the monthly temperature and humidity, which also related with the high proportion of CHIKV positive cases. Conclusion: Long-term anti-CHIKV antibodies were relatively abundant in older age-groups indicating silent circulation of CHIKV in the region and potential for outbreaks. The prevalence of CHIKV infections was seasonally distributed and associated with rainfall. The high density of mosquitoes increases the chance of CHIKV infections and transmission. Further analysis on vector indices and genetic characterization is needed for the public health prevention and mitigating the threat of CHIKV outbreaks.