Generation of a Highly Pathogenic Avian Influenza A Virus from an Avirulent Field Isolate by Passaging in Chickens

Abstract

Highly virulent avian influenza viruses can arise from avirulent strains maintained in poultry, but evidence to support their generation from viruses in wild birds is lacking. The most likely mechanism for the acquisition of virulence by benign avian viruses is the introduction of mutations by error-prone RNA polymerase, followed by the selection of virulent viruses. To investigate whether this mechanism could apply to wild waterfowl, we studied an avirulent wild-swan virus that replicates poorly in chickens. After 24 consecutive passages by air sac inoculation, followed by five passages in chicken brain, the avirulent virus became highly pathogenic in chickens, producing a 100% mortality rate. Sequence analysis at the hemmaglutinin cleavage site of the original isolate revealed a typical avirulence type of sequence, R-E-T-R, which progressed incrementally to a typical virulence type of sequence, R-R-K-K-R, during repeated passages in chickens. These results demonstrate that avirulent viruses maintained in wild waterfowl in nature and bearing the consensus avirulence type sequence R-E-T-R have the potential to become highly pathogenic while circulating in chickens.

Immunization with live nonpathogenic H5N3 duck influenza virus protects chickens against highly pathogenic H5N1 virus

“…1). Our observations match with previous reports of inefficient replication and transmission of aquatic bird viruses in chickens (Ito et al, 2001 andCilloni et al, 2010).…”

“…For example, all attempts to propagate the LPAI H5N3 virus A/whistling swan/Shimane/499/83 by intranasal, intratracheal, and intracerebral inoculation into 1-day-old chickens were unsuccessful. This virus acquired partial virulence in 2-dayold chickens only after 11 passages through air sacs (Ito et al, 2001). Introduction of four basic amino acid residues at the HA cleavage site and ten subsequent consecutive passages in air sacs of chickens were needed for acquisition of intravenous pathogenicity of a non-pathogenic H9N2 virus in chickens (Soda et al, 2011).…”

Genetic characterization of H5N2 influenza viruses isolated from wild birds in Japan suggests multiple reassortment

“…However, the presence of H5N2 viruses in migratory wild birds in Japan represents a continued risk for poultry, as H5N2 LPAIV may acquire high pathogenicity by consecutive passages in chickens [21,56]. In this study, the NP genes of the H5N2 viruses isolated in 2011 (11UO samples) were from the same lineage as H3N8 viruses isolated from domestic ducks in Vietnam.…”

The Development of Pathogenicity of Avian Influenza Virus Isolated from Indonesia

“…Such a kind of condition permits the virus to spread in a variety of organs, leading to systemic infection. Whereas most a virulent strains have a single arginine or monobasic cleavage site that will be cleaved only by trypsin secreted from cells in the respiratory and intestinal tract, so the virus only produced localized infection (Harimoto and Kawaoka, 2001;Ito et al, 2001).…”