Wild Brazilian yellow fever virus infection in Syrian hamsters (Mesocricetus auratus): Clinical and histopathological analyses

The Yellow Fever virus (YFV) wild-type strains studied until now have little or no ability to evade the Syrian hamster interferon antiviral response. Thus, evaluating the susceptibility of this model to new YFV isolates is paramount to aid in the understanding of their viscerotropic phenotype. To this end, Syrian hamsters were inoculated intraperitoneally with two Brazilian wild-type YFV isolates originated from dying or dead howler monkeys obtained during outbreaks in the states of Rio Grande do Sul in 2008 (PR4408) and Rio de Janeiro in 2019 (RJ155). The results were compared with a YFV experimental vaccine strain (17DD_exp). The main findings observed for animals infected with the PR4408 strain were progressive weight loss and persistent viremia (at least up to day seven post-infection), associated with viral RNA detection in the liver, and hepatic, splenic, and pancreatic histological alterations consistent with YF. The infection was eliminated seven days post-infection in animals inoculated with the RJ155 strain. No changes were observed for animals infected with 17DD_exp virus. The findings indicate that both Brazilian isolates are able to infect Syrian hamsters, resulting in histopathological changes compatible with the YF pathology observed in humans. Furthermore, the PR4408 strain exhibited increased virulence in this mammalian model, despite causing a non-fatal infection.