Variable effect of vaccination against highly pathogenic avian influenza (H7N7) virus on disease and transmission in pheasants and teals

Highly pathogenic avian influenza viruses can affect many bird species, with disease symptoms ranging from severe morbidity and high mortality to mild transient illness. Much is known about infections in chickens, but for other captive birds the relations between disease symptoms, excretion patterns, and transmission, as well as the effect of vaccination on these relations are not clear. We report results from experimental transmission studies with a highly pathogenic H7N7 virus and two commonly kept bird species (ringed teals and golden pheasants). The results show that depending on the host species the virus can spread in unvaccinated birds with or without disease symptoms. Vaccination reduces disease symptoms markedly, but need not always reduce virus transmission. We discuss the implications for the control of highly pathogenic avian influenza.