Reassortant influenza A viruses in wild duck populations: effects on viral shedding and persistence in water

Abstract

Wild ducks of the genus Anas represent the natural hosts for a large genetic diversity of influenza A viruses. In these hosts, co-infections with different virus genotypes are frequent and result in high rates of genetic reassortment. Recent genomic data have provided information regarding the pattern and frequency of these reassortant viruses in duck populations; however, potential consequences on viral shedding and maintenance in the environment have not been investigated. On the basis of full-genome sequencing, we identified five virus genotypes, in a wild duck population in northwestern Minnesota (USA), that naturally arose from genetic reassortments. We investigated the effects of influenza A virus genotype on the viral shedding pattern in Mallards (Anas platyrhynchos) and the duration of infectivity in water, under different temperature regimens. Overall, we found that variation in the viral genome composition of these isolates had limited effects on duration, extent and pattern of viral shedding, as well as on the reduction of infectivity in water over time. These results support that, in wild ducks, functionally equivalent gene segments could be maintained in virus populations with no fitness costs when genetic reassortments occur.

Figure 1.

(a,b) Total and restricted viral shedding duration in the cloaca and (c,d) in the oropharynx, based on virus isolation. Each bar represents the mean duration, in days (with s.e. of the mean), for each tested virus genotype.

Figure 2.

(a) Cloacal and (b) oropharyngeal viral shedding load over time. Each colour line represents a LOESS curve (with s.e. of the mean) fitted to the values of a virus genotype (green, H3N8; red, H4N8; light blue, H6N1; purple, H6N2; dark blue, H6N8; black, H3N8-C).

Figure 3.

The virus infectivity in water over time as a function of temperature regimens. Colour lines represent the least-squares regression lines for each temperature regimen (solid lines, constant temperature; dashed lines, variable temperature).