Effect of species, breed and route of virus inoculation on the pathogenicity of H5N1 highly pathogenic influenza (HPAI) viruses in domestic ducks

Abstract

H5N1 highly pathogenic avian influenza (HPAI) viruses continue to be a threat to poultry in many regions of the world. Domestic ducks have been recognized as one of the primary factors in the spread of H5N1 HPAI. In this study we examined the pathogenicity of H5N1 HPAI viruses in different species and breeds of domestic ducks and the effect of route of virus inoculation on the outcome of infection. We determined that the pathogenicity of H5N1 HPAI viruses varies between the two common farmed duck species, with Muscovy ducks (Cairina moschata) presenting more severe disease than various breeds of Anas platyrhynchos var. domestica ducks including Pekin, Mallard-type, Black Runners, Rouen, and Khaki Campbell ducks. We also found that Pekin and Muscovy ducks inoculated with two H5N1 HPAI viruses of different virulence, given by any one of three routes (intranasal, intracloacal, or intraocular), became infected with the viruses. Regardless of the route of inoculation, the outcome of infection was similar for each species but depended on the virulence of the virus used. Muscovy ducks showed more severe clinical signs and higher mortality than the Pekin ducks. In conclusion, domestic ducks are susceptible to H5N1 HPAI virus infection by different routes of exposure, but the presentation of the disease varied by virus strain and duck species. This information helps support the planning and implementation of H5N1 HPAI surveillance and control measures in countries with large domestic duck populations.

Figure 1

Study 1: survival rate of ducks after inoculation with the Mongolia/09 H5N1 HPAI virus. Two-week-old ducks were inoculated with 10⁶ EID₅₀ of the virus and mortality was monitored for 9 days. The length of survival was statistically shorter for Muscovy ducks (Cairina moschata) compared to the five breeds of Anas platyrhynchos var. domestica, as determined by the log rank test (p < 0.05).

Figure 2

Study 1: virus shedding. Ducks were intranasally inoculated with the Mongolia/09 H5N1 HPAI virus. Oropharyngeal and cloacal swabs were taken from all birds remaining at 3 dpi. For Muscovy ducks, no shedding data was available because all died by 2 dpi. Groups with asterisk are significantly different (p < 0.05).

Figure 3

Study 2: survival rates of Muscovy (Cairina moschata) and Pekin (Anas platyrhynchos var. domestica) ducks inoculated by the intranasal (IN), intracloacal (IC), or intraocular (IO) routes with the Egypt/07 or Egypt/08 H5N1 HPAI viruses. Survival rates were not statistically different between the ducks receiving virus by the same route of inoculation as determined by the log rank test (p < 0.05). Survival rates were not different between all Muscovy ducks regardless of the virus, with the exception of ducks inoculated with Egypt/07 via IO and ducks inoculated with Egypt/08 via IC. Survival rates were different between Pekin ducks inoculated with Egypt/07 compared with Egypt/08.

Figure 4

Study 2: virus shedding. Ducks were inoculated by the intranasal (IN), intracloacal (IC), or intraocular (IO) route with Egypt/07 or Egypt/08 H5N1 HPAI virus. Oropharyngeal and cloacal swabs were taken from all remaining birds at 3 dpi. Groups with asterisk (*) are significantly different (p < 0.05).