RESUMEN
Susceptibility of influenza A viruses to baloxavir can be affected by changes at amino acid residue 38 in the polymerase acidic (PA) protein. Information on replicative fitness of PA-I38-substituted viruses remains sparse. We demonstrated that substitutions I38L/M/S/T not only had a differential effect on baloxavir susceptibility (9- to 116-fold) but also on in vitro replicative fitness. Although I38L conferred undiminished growth, other substitutions led to mild attenuation. In a ferret model, control viruses outcompeted those carrying I38M or I38T substitutions, although their advantage was limited. These findings offer insights into the attributes of baloxavir-resistant viruses needed for informed risk assessment.
Asunto(s)
Antivirales/uso terapéutico , Farmacorresistencia Viral/genética , Subtipo H1N1 del Virus de la Influenza A/genética , Subtipo H3N2 del Virus de la Influenza A/genética , Infecciones por Orthomyxoviridae/tratamiento farmacológico , Oxazinas/uso terapéutico , Piridinas/uso terapéutico , Tiepinas/uso terapéutico , Triazinas/uso terapéutico , Replicación Viral/genética , Sustitución de Aminoácidos , Animales , Dibenzotiepinas , Modelos Animales de Enfermedad , Perros , Hurones , Secuenciación de Nucleótidos de Alto Rendimiento , Células de Riñón Canino Madin Darby , Masculino , Pruebas de Sensibilidad Microbiana , Morfolinas , Infecciones por Orthomyxoviridae/virología , Piridonas , ARN Polimerasa Dependiente del ARN/genética , Estaciones del Año , Resultado del Tratamiento , Proteínas Virales/genéticaRESUMEN
BACKGROUND: Patients contracting influenza A(H7N9) infection often developed severe disease causing respiratory failure. Neuraminidase (NA) inhibitors (NAIs) are the primary option for treatment, but information on drug-resistance markers for influenza A(H7N9) is limited. METHODS: Four NA variants of A/Taiwan/1/2013(H7N9) virus containing a single substitution (NA-E119V, NA-I222K, NA-I222R, or NA-R292K) recovered from an oseltamivir-treated patient were tested for NAI susceptibility in vitro; their replicative fitness was evaluated in cell culture, mice, and ferrets. RESULTS: NA-R292K led to highly reduced inhibition by oseltamivir and peramivir, while NA-E119V, NA-I222K, and NA-I222R caused reduced inhibition by oseltamivir. Mice infected with any virus showed severe clinical signs with high mortality rates. NA-I222K virus was the most virulent in mice, whereas virus lacking NA change (NA-WT) and NA-R292K virus seemed the least virulent. Sequence analysis suggests that PB2-S714N increased virulence of NA-I222K virus in mice; NS1-K126R, alone or in combination with PB2-V227M, produced contrasting effects in NA-WT and NA-R292K viruses. In ferrets, all viruses replicated to high titers in the upper respiratory tract but produced only mild illness. NA-R292K virus, showed reduced replicative fitness in this animal model. CONCLUSIONS: Our data highlight challenges in assessment of the replicative fitness of H7N9 NA variants that emerged in NAI-treated patients.