Understanding yellow fever-associated myocardial injury: an autopsy study

BACKGROUND

Yellow fever (YF) is a viral hemorrhagic fever, endemic in parts of South America and Africa. There is scarce evidence about the pathogenesis of the myocardial injury. The objective of this study is to evaluate the cardiac pathology in fatal cases of YF.

METHODS

This retrospective autopsy study included cases from the São Paulo (Brazil) epidemic of 2017-2019. We reviewed medical records and performed cardiac tissue histopathological evaluation, electron microscopy, immunohistochemical assays, RT-qPCR for YF virus (YFV)-RNA, and proteomics analysis on inflammatory and endothelial biomarkers.

FINDINGS

Seventy-three confirmed YF cases with a median age of 48 (34-60) years were included. We observed myocardial fibrosis in 68 (93.2%) patients; cardiomyocyte hypertrophy in 68 (93.2%); endothelial alterations in 67 (91.8%); fiber necrosis in 50 (68.5%); viral myocarditis in 9 (12.3%); and secondary myocarditis in 5 (6.8%). Four out of five patients with 17DD vaccine-associated viscerotropic disease presented with myocarditis. The cardiac conduction system showed edema, hemorrhages and endothelial fibrinoid necrosis. Immunohistochemistry detected CD68-positive inflammatory interstitial cells and YFV antigens in endothelial and inflammatory cells. YFV-RNA was detected positive in 95.7% of the cardiac samples. The proteomics analysis demonstrated that YF patients had higher levels of multiple inflammatory and endothelial biomarkers in comparison to cardiovascular controls, and higher levels of interferon gamma-induced protein 10 (IP-10) in comparison to sepsis (p = 0.01) and cardiovascular controls (p < 0.001) in Dunn test.

INTERPRETATION

Myocardial injury is frequent in severe YF, due to multifactorial mechanisms, including direct YFV-mediated damage, endothelial cell injury, and inflammatory response, with a possible prominent role for IP-10.

FUNDING

This study was funded by Fundação de Amparo à Pesquisa do Estado de São Paulo, Bill and Melinda Gates Foundation, Conselho Nacional de Desenvolvimento Científico e Tecnológico, Coordenação de Aperfeiçoamento de Pessoal de Nível Superior.

Testing the genomic stability of the Brazilian yellow fever vaccine strain using next-generation sequencing data

The live attenuated yellow fever (YF) vaccine was developed in the 1930s. Currently, the 17D and 17DD attenuated substrains are used for vaccine production. The 17D strain is used for vaccine production by several countries, while the 17DD strain is used exclusively in Brazil. The cell passages carried out through the seed-lot system of vaccine production influence the presence of quasispecies causing changes in the stability and immunogenicity of attenuated genotypes by increasing attenuation or virulence. Using next-generation sequencing, we carried out genomic characterization and genetic diversity analysis between vaccine lots of the Brazilian YF vaccine, produced by BioManguinhos–Fiocruz, and used during 11 years of vaccination in Brazil. We present 20 assembled and annotated genomes from the Brazilian 17DD vaccine strain, eight single nucleotide polymorphisms and the quasispecies spectrum reconstruction for the 17DD vaccine, through a pipeline here introduced. The V2IDA pipeline provided a relationship between low genetic diversity, maintained through the seed lot system, and the confirmation of genetic stability of lots of the Brazilian vaccine against YF. Our study sets precedents for use of V2IDA in genetic diversity analysis and in silico stability investigation of attenuated viral vaccines, facilitating genetic surveillance during the vaccine production process.

T Cell-Mediated Immunity towards Yellow Fever Virus and Useful Animal Models

The 17D line of yellow fever virus vaccines is among the most effective vaccines ever created. The humoral and cellular immunity elicited by 17D has been well characterized in humans. Neutralizing antibodies have long been known to provide protection against challenge with a wild-type virus. However, a well characterized T cell immune response that is robust, long-lived and polyfunctional is also elicited by 17D. It remains unclear whether this arm of immunity is protective following challenge with a wild-type virus. Here we introduce the 17D line of yellow fever virus vaccines, describe the current state of knowledge regarding the immunity directed towards the vaccines in humans and conclude with a discussion of animal models that are useful for evaluating T cell-mediated immune protection to yellow fever virus.