Epidemiological Evidence for Lineage-specific Differences in the Risk of Inapparent Chikungunya Virus Infection.

UC BERKELEY AUTHOR: Bustos Carrillo, Burger-Calderon, Eva Harris

DATE OF PUBLICATION: November 2018

REGION: North America

REFERENCE:  Bustos Carrillo F, Collado D, Sanchez N, Ojeda S, Lopez Mercado B, Burger-Calderon R, Gresh L, Gordon A, Balmaseda A, Kuan G, Harris E. DOI: 10.1128/JVI.01622-18.

SUMMARY/ABSTRACT: In late 2013, chikungunya virus (CHIKV) was introduced into the Americas, leading to widespread epidemics. A large epidemic caused by the Asian chikungunya virus (CHIKV) lineage occurred in Managua, Nicaragua, in 2015. Literature reviews commonly state that the proportion of inapparent CHIKV infections ranges from 3 to 28%. This study estimates the symptomatic-to-asymptomatic ratio of CHIKV infections and identifies risk factors of infection. In October-November 2015, 60 symptomatic CHIKV-infected children were enrolled as index cases and prospectively followed, alongside 236 household contacts, in an index cluster study. Samples were collected upon enrollment and on days 14 or 35 and tested by rRT-PCR, IgM-ELISA, and Inhibition ELISA to detect pre- and post-enrollment CHIKV infections. Of 236 household contacts, 55 (23%) had experienced previous or very recent infections, 41 (17%) had active infections at enrollment, and 21 (9%) experienced incident infections. Vehicle ownership (multivariate-adjusted risk ratio (aRR): 1.58) increased the risk of CHIKV infection whereas ≥4 municipal trash collections/week (aRR: 0.38) and having an external water faucet (aRR: 0.52) protected against CHIKV infection. Among 63 active and incident infections, 31 (49%, 95% CI: 36%, 62%) were asymptomatic, yielding a symptomatic-to-asymptomatic ratio of 1:0.97 (95% CI: 1:0.56, 1:1.60). Although our estimate is outside the 3-28% range reported previously, Bayesian and simulation analyses, informed by a systematic literature search, suggested that the proportion of inapparent CHIKV infections is lineage-dependent and that more inapparent infections are associated with the Asian lineage than the ECSA lineage. Overall, these data substantially improve knowledge regarding chikungunya epidemics.ImportanceChikungunya virus (CHIKV) is an understudied threat to human health. During the 2015 chikungunya epidemic in Managua, Nicaragua, we estimated the ratio of symptomatic-to-asymptomatic CHIKV infections, which is important for understanding transmission dynamics and public health impact. This index cluster study identified persons at risk of infection and followed them, enabling capture of asymptomatic infections. We estimated that 31 (49%) of 63 at-risk participants had asymptomatic CHIKV infections, which is significantly outside the 3-28% range reported in literature reviews. However, recent seroprevalence studies, including two large pediatric cohort studies in the same setting, had also found percentages of inapparent infections outside the 3-28% range. Bayesian and simulation analyses, informed by a systematic literature search, revealed that the percentage of inapparent infections in epidemic settings varies by the phylogenetic lineage of CHIKV. Our study quantifies and provides the first epidemiological evidence that chikungunya epidemic characteristics are strongly influenced by CHIKV lineage.

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