Molecular determinants of Yellow Fever Virus pathogenicity in Syrian Golden Hamsters: one mutation away from virulence

Abstract

ABSTRACTYellow fever virus (Flavivirusgenus) is an arthropod-borne pathogen which can infect humans, causing a severe viscerotropic disease with a high mortality rate. Adapted viral strains allow the reproduction of yellow fever disease in hamsters with features similar to the human disease. Here, we used the Infectious Subgenomic Amplicons reverse genetics method to produce an equivalent to the hamster-virulent strain, Yellow FeverAp7, by introducing a set of 4 synonymous and 6 non-synonymous mutations into a single subgenomic amplicon, derived from the sequence of theAsibistrain. The resulting strain, Yellow FeverAp7M, induced a disease similar to that described forAp7in terms of symptoms, weight evolution, viral loads in the liver and lethality. Using the same methodology, we produced mutant strains derived from eitherAp7MorAsibiviruses and investigated the role of each ofAp7Mnon-synonymous mutations in itsin vivophenotype. This allowed identifying key components of the virulence mechanism in hamsters. InAp7Mvirus, the reversion of either E/Q27H or E/D155A mutations, led to an important reduction of both virulence andin vivoreplicative fitness. In addition, the introduction of the single D155AAp7Mmutation within the E protein of theAsibivirus was sufficient to drastically modify its phenotype in hamsters towards both a greater replication efficiency and virulence. Finally, inspection of theAsibistrain E protein structure combined toin vivotesting revealed the importance of an exposed α-helix in domain I, containing residues 154 and 155, forAp7Mvirulence in hamsters.