Some Ethnic Groups More Susceptible to H7N9 Bird Flu

Researchers recently found that Indigenous Alaskan and Australian people are more susceptible to the novel – and deadly – H7N9 influenza virus than people of other ethnic origins because they have limited immunity against influenza A viruses.

H7N9 virus Image: WHO

H7N9 virus
Image: WHO

Usually, your immune system springs into action as soon as an invader such as a virus is detected. Viral protein segments – called peptides – are presented on human leukocyte antigens (HLAs) protruding from the surface of cells for detection by cytotoxic T cells, which can then destroy the infected cells. Some HLA types are more common among certain ethnicities.

While we all lack immunity against the H7N9 influenza virus, which first emerged in February 2013 from birds in China, previous studies had shown that memory cytotoxic T cells yielded from prior exposure to influenza A viruses – either seasonal or pandemic – may confer some protection against the current H7N9 influenza virus. Researchers investigated these findings further by identifying the extent to which these memory cytotoxic T cells can respond against H7N9 and by estimating the variation in the immune response across different ethnic groups.

To find out, they first compared the peptides from the H7N9 virus that matched those from other influenza A viruses such as the H1N1 pandemic of 1918, the H1N1 “swine flu” pandemic of 2009, and seasonal H1N1 influenza A viruses from 1933, 1983, and 2006. They located 32 peptides from H7N9 that are also found in these influenza viruses and may potentially elicit an immune response.

Next, they obtained blood samples from healthy individuals and exposed them to the H7N9 peptides for 10 days after which they determined their level of cytotoxic T cell activity. By comparing HLA types that can present these peptides between ethnic groups, they estimated the cytotoxic T cell response among them.

Their analysis revealed that some ethnic groups possessed HLA versions could that could elicit strong cytotoxic T cell responses not only against H7N9 but against any human influenza A virus while other ethnicities had versions that offered limited protection. Caucasians (includes people from Europe, North Africa, and Southwestern Asia) had the highest HLA coverage against the H7N9 peptides at 57 percent; Orientals and Africans were second at around 38 percent; Indigenous Australians and Alaskans came last showing only a 16 percent immune activity against the H7N9 peptides.

This lack of immunity among Indigenous Alaskans and Australians is primarily due to their relatively isolated populations without any prior exposure to influenza A viruses. Thus, if they are infected with H7N9, their symptoms may be prolonged and more severe. These findings seem to support past observations: Up to 20 percent of Indigenous Australians died in 1919 during the influenza pandemic compared with less than 1 percent of Caucasian Australians. And more recently in the 2009 H1N1 influenza pandemic, 16 percent of the patients that required hospitalization came from these groups.

In light of these results, the researchers suggest that vaccines based on cytotoxic T cells may protect these communities to some extent. But vaccination will not be required yet; so far all cases of H7N9 have been restricted to China and were traced back to direct exposure to infected poultry.

Reference

Quiñones-Parra S., Grant, E., Loh, L., Nguyen T.H.O, Campbell, K.A., Tong S.Y.C., Miller, A.,…Kedzierska, K. (2014). Preexisting CD8+ T-cell immunity to the H7N9 influenza A virus varies across ethnicities, PNAS; published ahead of print January 6, 2014, DOI:10.1073/pnas.1322229111

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