Submitted to: Virology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/9/1995
Publication Date: N/A
Interpretive Summary: This report describes the characterization of an H5N2 subtype strain of avian influenza (AI) virus isolated from emus. It was shown that this strain could give rise to a derivative, deadly to poultry, in very short course in the laboratory. The deadly derivative had an additional sequence of amino acids found in the surface envelope protein (hemagglutinin) not found in the original mild parent virus. This inserted information was most likely responsible for causing the shift to the deadly type because it allowed full processing of the envelope protein in cells outside the respiratory and digestive tracts of infected birds. This allowed replication of the virus in other tissues and organs such as the brain and heart, resulting in a severe, deadly infection. One importance of the finding lies in the fact that this deadly, laboratory generated variant is identical to H5N2 isolates recently found in poultry. . This provides us then with an excellent laboratory model for studying how AI viruses become deadly in nature. Secondly, the report is significant because it is the first to molecularly describe an AI isolate from a ratite (emu, ostriches, rheas, cassowaries).
Technical Abstract: Recent isolations of avian influenza (AI) viruses from ratite species have raised questions concerning their origin, transmission to commercial poultry, and potential for virulence. One isolate of low pathogenicity, A/Emu/TX/39924/93 (H5N2), was subjected to a procedure which rapidly selects and/or amplifies highly pathogenic (HP) strains. The resulting highly virulent derivative had an altered hemagglutinin (HA) protein containing an arg-lys insertion near the cleavage site. The remainder of the HA sequence differed by seven amino acids from the parent. One of these specified a potential N-linked glycosylation signal at amino acid #11-13 in the derivative, not present in the parent. The HA precursor of the derivative, but not the parent was readily cleaved during replication in cell culture without addition of trypsin and in experimentally infected chickens, the virus produced lesions typical of HPAI. A reverse transcriptase-polymerase chain reaction (RT-PCR) primer set was designed to amplify only if the inserted six nucleotides were present. The set yielded product only from highly virulent, derivative samples and not the parent. Thus, there was either an undetectable level of the HP variant in the parent stock or the insertion occurred rapidly during the selection process.