|JADHAO, SAMADHAN - Foreign Agricultural Service (FAS, USDA)
Submitted to: Avian Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/6/2009
Publication Date: 3/1/2010
Citation: Jadhao, S., Suarez, D.L. 2010. New approach to delist highly pathogenic avian influenza viruses from BSL3+ select agents to BSL2 non-select status for diagnostics and vaccines. Avian Diseases. 54:302-306.
Interpretive Summary: Highly pathogenic avian influenza is a serious disease in poultry, including chickens ducks and turkeys, because it is highly infectious and can cause high mortality. Control of outbreaks may be by rapid detection and quarantine of infected flocks, but if the virus becomes widespread then vaccination for control is often used. Ideally a vaccine should include a virus that is close to the field strain as possible to get the best protection, but with highly pathogenic avian influenza this is hard to do because working with these viruses requires specially contained laboratory or production facilities. This project was designed to take a highly pathogenic virus and weaken the virus so that it could safely be used in a laboratory with a lower level of containment. We used a highly pathogenic virus from Vietnam and changed it to be non-pathogenic, and showed it was non-pathogenic by laboratory and animal studies. This virus, once regulatory approval is given, can be used in many vaccine or diagnostic laboratories which will help in routine work and development.
Technical Abstract: Highly pathogenic avian influenza viruses (AIV) are Select Agents in the United States and are required to be handled in bio-containment level 3 enhanced (BSL3+) facilities. Using a reverse genetics system, we attenuated a highly pathogenic virus with the goal of making it low pathogenic and having it delisted as a Select Agent so that it could be handled in a bio-containment level 2 facility for diagnostic or vaccine production applications. We utilized two approaches to attenuate the target AIV by mutating the highly pathogenic hemagglutinin (HA) cleavage site to be low pathogenic and by replacing the full length non-structured (NS) gene segment with a naturally truncated 124 amino acid NS1 coding gene from A/turkey/Oregon/73 (H7N3) virus(tkOR71 trNS1). To delist an AIV so that it can be handled in a BSL2 facility, the amino acid sequence of the HA cleavage site of the rescued virus must be confirmed to be compatible with a low pathogenic AIV, it should not plaque in cell culture without supplementation of exogenous trypsin, and intravenous pathotyping in 4-6 week old specific pathogen free chickens must confirm that the virus is low pathogenic. The candidate A/duck/Vietnam/Baclieu/09/07 (rH5N1/PR8/trNS1) virus with five PR8 internal genes, tkOR71 trNS1 gene and A/chicken/Indonesia/7/03 N1 NA gene was constructed. The virus was shown to not plaque in cell culture without addition of trypsin. The virus was low pathogenic in the standard intravenous pathotyping test (IVPI=0) and also caused no disease in a separate intranasal inoculation test in four-week old specific pathogen free chickens demonstrating the virus is suitable for deselection.