Nowcasting the Spread of Chikungunya Virus in the Americas

Abstract

BackgroundIn December 2013, the first locally-acquired chikungunya virus (CHIKV) infections in the Americas were reported in the Caribbean. As of May 16, 55,992 cases had been reported and the outbreak was still spreading. Identification of newly affected locations is paramount to intervention activities, but challenging due to limitations of current data on the outbreak and on CHIKV transmission. We developed models to make probabilistic predictions of spread based on current data considering these limitations.Methods and FindingsBranching process models capturing travel patterns, local infection prevalence, climate dependent transmission factors, and associated uncertainty estimates were developed to predict probable locations for the arrival of CHIKV-infected travelers and for the initiation of local transmission. Many international cities and areas close to where transmission has already occurred were likely to have received infected travelers. Of the ten locations predicted to be the most likely locations for introduced CHIKV transmission in the first four months of the outbreak, eight had reported local cases by the end of April. Eight additional locations were likely to have had introduction leading to local transmission in April, but with substantial uncertainty.ConclusionsBranching process models can characterize the risk of CHIKV introduction and spread during the ongoing outbreak. Local transmission of CHIKV is currently likely in several Caribbean locations and possible, though uncertain, for other locations in the continental United States, Central America, and South America. This modeling framework may also be useful for other outbreaks where the risk of pathogen spread over heterogeneous transportation networks must be rapidly assessed on the basis of limited information.

Spread of Zika virus in the Americas

“…Exposed mosquitoes transition to the infectious class at a rate V , which is inversely proportional to the mean extrinsic latent period in the mosquito population (2). Susceptible, exposed, and infectious mosquitoes all die at a rate that is inversely proportional to the mosquito lifespan, µ V (70). The mosquito-to-human force of infection follows the usual mass-action law in each subpopulation whose linear extension varies from a few miles to about 50 miles depending on the population density and specific area of the world.…”

Noncapped Alphavirus Genomic RNAs and Their Role during Infection

“…Moreover, the ultimate outcome of alphaviral infection differs between vertebrate and invertebrate hosts, as infection of a vertebrate host results in acute cytolytic infection whereas infection of invertebrate hosts often results in persistent infection with minimal cell death (5-11). The widespread geographic distribution of competent vector mosquito species leading to contact with immunologically naive human populations has resulted in several significant outbreaks of alphaviral disease (12)(13)(14). Perhaps most notable is the ongoing reemergence of chikungunya virus, which caused significant morbidity during the height of the 2006 epidemic, with as many as 40,000 new cases per week (13).…”

Preventing Zika virus infection during pregnancy by timing conception seasonally

“…There were 22 no abnormalities in ZIKV-negative women [2]. Lastly, the complete ZIKV genome was 23 recovered from the brain of a fetus with microcephaly aborted by an expectant mother 24 infected during the 13 th week of gestation [7], and the CDC reported on two newborns 25 from Brazil with microcephaly who died shortly after birth and two miscarriages, all 26 tested positive for ZIKV [8]. In addition to the epidemiological evidence, newly 27 developed mouse models of ZIKV have demonstrated that ZIKV strains from French…”

“…No official stance on delaying pregnancy has been 57 taken for unexposed women. Problematically, the public is receiving a mixed message, arboviruses vectored by Aedes aegypti (i.e., chikungunya virus, CHIKV) [22][23][24][25][26].…”