The multifaceted zoonotic risk of H9N2 avian influenza

Authors: PUSCH, ELIZABETH - Orise Fellow; Suarez, David

Submitted to: Veterinary Sciences
Publication Type: Review Article
Publication Acceptance Date: 9/14/2018
Publication Date: 9/21/2018
Citation: Pusch, E., Suarez, D.L. 2018. The multifaceted zoonotic risk of H9N2 avian influenza. Veterinary Sciences. 5(4):82. https://doi.org/10.3390/vetsci5040082.
DOI: https://doi.org/10.3390/vetsci5040082

Interpretive Summary: Avian influenza viruses are naturally found in wild birds, primarily ducks and gulls, but the virus can be transmitted to domestic poultry including chickens. One particular subtype, H9N2 avian influenza, has jumped from wild birds to chickens on at least 4 separate occasions. The virus has been allowed to get established in chickens and it is now a chicken adapted virus that is widely present in some foreign countries. Although the H9N2 subtype of avian influenza is considered a low pathogenic virus because it doesn't cause severe disease in experimental studies, in the field severe disease and occasional mortality is seen because of co-infections with other diseases. The H9N2 virus can also on rare occasions infect humans. Fortunately the disease in humans is mild, but there is concern that the virus could become more widespread and more pathogenic, potentially leading to a human pandemic. This review discusses the potential zoonosis of H9N2 and why it is important to control the disease in chickens.

Technical Abstract: Poultry-adapted H9N2 avian influenza viruses (AIVs) are commonly found in many countries in Asia, the Middle East, Africa, and Europe, and although classified as low pathogenic viruses, they are an economically important disease. Besides the importance of the disease in the poultry industry, some H9N2 AIVs are also known to be zoonotic. The disease in humans appears to cause primarily a mild upper respiratory disease and doesn’t cause or only rarely causes the severe pneumonia often seen with other zoonotic AIVs like H5N1 or H7N9. Serologic studies in humans, particularly in occupationally exposed workers, show a large number of people with antibodies to H9N2, suggesting infection is commonly occurring. Of the four defined H9N2 poultry lineages, only two lineages, the G1 and the Y280 lineages, are associated with human infections. Almost all of the viruses from humans have a leucine at position 226 (H3 numbering) of the hemagglutinin associated with a higher affinity of binding with a2,6 sialic acid, the host cell receptor most commonly found on glycoproteins in the human upper respiratory tract. For unknown reasons there has also been a shift in recent years of poultry viruses in the G1 and Y280 lineages to also having leucine instead of glutamine, the amino acid found in most avian viruses, at position 226. The G1 and Y280 poultry lineages because of their known ability to infect humans, the high prevalence of the virus in poultry in endemic countries, the lack of antibody in most humans, and the shift of poultry viruses to more human-like receptor binding makes these viruses a human pandemic threat. Increased efforts for control of the virus, including through effective vaccine use in poultry, is warranted for both poultry and public health goals.