NB protein does not affect influenza B virus replication in vitro and is not required for replication in or transmission between ferrets

Abstract

The influenza B virus encodes a unique protein, NB, a membrane protein whose function in the replication cycle is not, as yet, understood. We engineered a recombinant influenza B virus lacking NB expression, with no concomitant difference in expression or activity of viral neuraminidase (NA) protein, an important caveat since NA is encoded on the same segment and initiated from a start codon just 4 nt downstream of NB. Replication of the virus lacking NB was not different to wild-type virus with full-length NB in clonal immortalized or complex primary cell cultures. In the mouse model, virus lacking NB induced slightly lower IFN-a levels in infected lungs, but this did not affect virus titres or weight loss. In ferrets infected with a mixture of viruses that did or did not express NB, there was no fitness advantage for the virus that retained NB. Moreover, virus lacking NB protein was transmitted following respiratory droplet exposure of sentinel animals. These data suggest no role for NB in supporting replication or transmission in vivo in this animal model. The role of NB and the nature of selection to retain it in all natural influenza B viruses remain unclear.

Influenza A virus is transmissible via aerosolized fomites

“…Guinea pigs do not transmit pre-2009 H1N1 viruses efficiently 45,46 , while ferrets do 47 . Ferrets have been shown to transmit fewer strains of influenza B virus by airborne routes 48 than guinea pigs 49,50 . But both influenza A (H1N1) and B viruses have transmitted well enough among people to become endemic in humans.…”

Characterization of Influenza B Virus Variants with Reduced Neuraminidase Inhibitor Susceptibility

“…It is important to note that our study contributes to the very limited number of animal studies that have reported influenza B virus transmission to date. One previous study demonstrated successful influenza B transmission between guinea pigs in contact and noncontact models ( 38 ), while only two studies (with mixed results) have previously reported on influenza B virus transmission in the ferret model ( 39 , 40 ). Of these two studies, one study reported successful aerosol and contact transmission of a mouse-adapted influenza B virus, but it could not demonstrate transmission by either model using a nonmouse-adapted isolate ( 39 ).…”

“…Of these two studies, one study reported successful aerosol and contact transmission of a mouse-adapted influenza B virus, but it could not demonstrate transmission by either model using a nonmouse-adapted isolate ( 39 ). The second study using a modified influenza B virus lacking the NB protein showed that one out of the four recipient ferrets was successfully infected by aerosol transmission ( 40 ). Our results show successful contact transmission of both the influenza B wild-type viruses tested (4 out of 4 ferrets) and transmission of influenza B variants in the ferret model with circulating human influenza viruses.…”

Characterization of influenza B virus variants with reduced neuraminidase inhibitor susceptibility

“…It is important to note that our study contributes to the very limited number of animal studies that have reported influenza B virus transmission to date. One previous study demonstrated successful influenza B transmission between guinea pigs in contact and non-contact models (38), while only two studies (with mixed results) have previously reported on influenza B transmission in the ferret model (39, 40). Of these two, one study reported successful aerosol and contact transmission of a mouse-adapted influenza B virus, but could not demonstrate transmission by either model using a non-mouse adapted isolate (39).…”

“…Of these two, one study reported successful aerosol and contact transmission of a mouse-adapted influenza B virus, but could not demonstrate transmission by either model using a non-mouse adapted isolate (39). The second study using a modified influenza B virus lacking the NB protein showed that one out of the four recipient ferrets were successfully infected by aerosol transmission (40). Our results show successful contact transmission of both the influenza B wild-type viruses tested (4 out of 4 ferrets) and transmission of influenza B variants in the ferret model with circulating human influenza viruses.…”