Abstract
BackgroundThe 2017–2018 yellow fever virus (YFV) outbreak in southeastern Brazil marked a reemergence of YFV in urban states that had been YFV-free for nearly a century. Unlike earlier urban YFV transmission, this epidemic was driven by forest mosquitoes. The objective of this study was to evaluate environmental drivers of this outbreak.Methodology/Principal findingsUsing surveillance data from the Brazilian Ministry of Health on human and non-human primate (NHP) cases of YFV, we traced the spatiotemporal progression of the outbreak. We then assessed the epidemic timing in relation to drought using a monthly Standardized Precipitation Evapotranspiration Index (SPEI) and evaluated demographic risk factors for rural or outdoor exposure amongst YFV cases. Finally, we developed a mechanistic framework to map the relationship between drought and YFV. Both human and NHP cases were first identified in a hot, dry, rural area in northern Minas Gerais before spreading southeast into the more cool, wet urban states. Outbreaks coincided with drought in all four southeastern states of Brazil and an extreme drought in Minas Gerais. Confirmed YFV cases had an increased odds of being male (OR 2.6; 95% CI 2.2–3.0), working age (OR: 1.8; 95% CI: 1.5–2.1), and reporting any recent travel (OR: 2.8; 95% CI: 2.3–3.3). Based on this data as well as mosquito and non-human primate biology, we created the “Mono-DrY” mechanistic framework showing how an unusual drought in this region could have amplified YFV transmission at the rural-urban interface and sparked the spread of this epidemic.Conclusions/SignificanceThe 2017–2018 YFV epidemic in Brazil originated in hot, dry rural areas of Minas Gerais before expanding south into urban centers. An unusually severe drought in this region may have created environmental pressures that sparked the reemergence of YFV in Brazil’s southeastern cities.
Highlights
Between December 2016 and July 2019, a yellow fever virus (YFV) outbreak occurred in southeastern Brazil, resulting in over 2,000 confirmed human cases [1,2]
In 2017–2018, cities in southeastern Brazil experienced an unusual outbreak of yellow fever virus
In the early 20th century, these cities had large outbreaks of yellow fever, spread by Aedes mosquitoes. Until this recent outbreak, they had been free of yellow fever for nearly a century. While this outbreak was spread by Haemagogus forest mosquitoes, the reemergence of yellow fever in densely populated urban areas raises serious concerns about it reestablishing ongoing transmission in cities, spread by urban Aedes mosquitoes
Summary
Between December 2016 and July 2019, a yellow fever virus (YFV) outbreak occurred in southeastern Brazil, resulting in over 2,000 confirmed human cases [1,2]. The height of this epidemic occurred during the summer seasons of 2017 and 2018. Mosquitoes, which live and breed in forest canopies, feed primarily on non-human primates (NHPs) and only sporadically feed on humans [4,5,6] This results in low human transmission levels with periodic small outbreaks occurring in rural northern and western forest states of Brazil. The objective of this study was to evaluate environmental drivers of this outbreak
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