H9N2 avian influenza transmission and antigenicity

Authors: Suarez, David

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 8/1/2017
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Low pathogenic H9N2 avian influenza has become endemic in parts of Asia, the Middle East and North Africa causing respiratory disease with occasional mortality. The use of vaccination has become common to try and control the clinical disease, but vaccination has not been shown to be an effective eradication tool. The H9N2 subtype is not from a single source, and like with other avian influenza viruses can be separated into American and Eurasian lineages. However, the endemic viruses are all of Eurasian origin. However, the endemic viruses appear to have originated from three unique viral lineages, often referred as the G1, Beijing, and Y439 lineages. The G1 lineage is primarily found in the Middle East, the Y439 virus in South Korea, and the Beijing lineage is found in China and surrounding countries. Since their first detection in the 1990’s the viral lineages have evolved into many unique sublineages which is similar in complexity to the clades and subclades of H5 highly pathogenic avian influenza viruses. Characterization of some recent viruses from China demonstrate that they are highly poultry adapted, and easily infect and transmit in chickens. For example the chicken infectious dose 50 of a 2014 Chinese virus was less than log 10^2, with transmission occurring in all contact control birds. Conversely, historical North American H9N2 viruses have a high infectious dose 50 and do not transmit efficiently in contact control birds. Other representative strains are also being characterized to determine if any specific lineage is more infectious and transmissible than other viral lineages. The highly infectious and transmissible nature of the H9N2 viruses has also been compared to the recent H7N9 viruses from China. Although the H9N2 and H7N9 viruses share closely related internal genes, the H7N9 viruses are much less transmissible and require a higher infectious dose 50. Studies with reverse genetics technology has shown the H9 hemagglutinin gene is the key gene that controls the ability of the virus to easily transmit even when all the other genes are the same between the two viruses. Antigenic analysis, as measured by hemagglutination inhibition tests, is being used to determine antigenic variability. Because the difficulty to obtain representative strains from all the different sublineages, a viral vectored adenovirus system is being used to express the hemagglutinin gene to produce reference antisera to provide antigenic maps of current viral variants as reported in public databases. A combination of the genetic sequence information, antigenic variation, and biological characterization will provide an improved understanding of these important pathogens. Specifically, the data can be used to better understand when vaccines should be updated to provide better field protection. This data can also be useful to propose a unified nomenclature system for H9N2 viruses.