Reemergence of yellow fever virus in southeastern Brazil, 2017–2018: What sparked the spread?

Abstract

Background The 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 findings Using 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/Significance The 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.

Genomic epidemiology unveils the dynamics and spatial corridor behind the Yellow Fever virus outbreak in Southern Brazil

“…By 2017, a record primary forest deforestation was measured along the Doce river valley in the state of Minas Gerais ( 34 ). Coinciding with this, as reported by Rosser and colleagues ( 35 ), the reemergence of YFV in the state of Minas Gerais was observed during a severe drought period. This may have contributed to the spread of YFVat rural-urban boundaries, creating environmental pressures that sparked its reemergence close to Brazil’s southeastern cities.…”

Mechanisms of Yellow Fever Transmission: Gleaning the Overlooked Records of Importance and Identifying Problems, Puzzles, Serious Issues, Surprises and Research Questions

“…The third topic concerns the impacts of drought on YF outbreak. Recently, it was proposed that drought in the sylvan environments in Brazil triggered a chain reaction leading to the emergence of a large outbreak in 2016–2019 [ 298 ]. This interesting conclusion deserves further research, because in the past, increased YF activity coincided with the arrival of rainy seasons that rapidly increased the populations of sylvan vectors.…”

Exploring potential risk pathways with high risk groups for urban Rift Valley fever virus introduction, transmission, and persistence in two urban centers of Kenya

“…With insight from previous RVFV disease introductions and other urban arbovirus outbreaks [ 8 , 10 , 14 , 25 ], this qualitative study foreshadows how some key high risk populations in urban centers may identify and respond to an urban introduced RVFV viremic animal. For recognizing the likely first urban livestock cases, slaughterhouses are a key entry point for RVFV as animals enter in high volume from a wide geographical range.…”

“…However, this has not been proven as RVFV can be transmitted by a wide range of arthropod vectors and opportunity for direct transmission independent of personal livestock ownership has been suggested [3][4][5][6]. Other arboviruses have caused devastating outbreaks in urban areas in response to altered climatic conditions and vector preferences, but there has never been a documented urban outbreak of RVF [7][8][9][10]. Limited insight on the unique and diverse challenges faced by urban areas may have resulted in these areas being omitted from mitigation efforts, field studies, and scenario planning [11].…”