1). This reversion offers the most plausible Crizotinib FDA explanation for the increased transmissibility and pathogenicity in contact birds in the N1142K group. The reversion mutation also explains the greater weight loss, morbidity, and mortality in the contact birds than in the infected birds in this group. No other reversion mutations were sequenced from swabs of contact ducks infected with the other viruses, including the H241Q virus. FIG. 3. Weight change in mallards infected with mutant and wild-type H5N1 influenza viruses. (A) Groups of ducks were inoculated with 106 EID50 of recombinant virus. (B) Contact ducks were introduced into each group’s cage 1 day p.i. Ducks were weighed daily … TABLE 3.

Morbidity and mortality caused by the recombinant H5N1 influenza viruses in mallardsa To assess replication and transmission potential, titers of virus shed from the trachea and cloaca were measured (Table (Table4).4). Inoculated birds in all groups shed virus on day 3; therefore, it is clear that all of the viruses were capable of initial infection and replication. However, even at this early time point, the viruses containing HA protein mutation Y231H or K582I productively infected fewer ducks than wild-type and H241Q viruses. Wild-type and H241Q viruses were shed at similar levels on days 3 and 5. On day 7, wild-type virus was not shed, whereas the H241Q virus continued to be shed. All contact birds in the wild-type and HA241Q groups were shedding virus by day 3 p.i. (100% transmission). All contact birds in the H241Q group succumbed to infection, whereas only half of the contact birds in the wild-type group died.

The Y231H virus was not detected in any contact birds throughout the experiment, showing that the mutation results in attenuated transmission compared to that of the wild-type virus. Five days p.i., the K582I virus was detected in one inoculated bird and one contact bird, showing that its fitness and transmissibility were lower than that of the wild-type virus. The N1142K virus showed inconsistent shedding in inoculated birds. Inoculated birds shed virus on day 3 but not on day 5, yet some birds again shed virus on days 7 and 10. This result suggests that transmission to contact birds was mediated by the reverted K1142N virus, which was then transmitted back to inoculated ducks before being detected on days 7 and 10. On day 3 p.i.

, tracheal shedding was generally observed more often and at higher titers than cloacal shedding, consistent Batimastat with previous work (48). The H241Q and K582I mutations did not appear to increase cloacal virus shedding; thus, small decreases in the pH of activation (and inactivation) of the HA protein may be insufficient to enhance virus replication in the low-pH environment of the duck digestive tract (49). TABLE 4.