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Bird and pig flu mutations could mean human outbreaks

Kathleen Blanchard's picture
Bird and pig flu mutates in ways that could cause human outbreaks.

MIT researchers say there are concerns that flu viruses circulating among pigs and birds could strike humans in a big way. According to their estimates, the strains that have the ability to grab genes from different pools could lead to a pandemic.

Could the 1968 flu pandemic repeat itself?

One of the concerns, the scientists say is that there are many strains of H3N2 circulating in birds and pigs that share the same genes as the 1968 flu pandemic.

Ram Sasisekharan, the Alfred H. Caspary Professor of Biological Engineering at MIT said in a press release it is unlikely that current flu vaccines would provide protection. He suggests being prepared by incorporating some of the H3N2 strains into our current vaccines.

H3 flu viruses are the type that circulate each year, can infect animals and humans and of which there are many subtypes.

H3N2 flu kills approximately 36,000 people in the U.S. annually, but has become less dangerous because the human body recognizes it.

But when a new strain mixes in, viruses can become more deadly.

A recent example is H1N1 flu in 2009 that was very similar to the pandemic flu virus that killed 50 to 100 million people in 1918.

Sasisekharan said they wanted to see if the same thing could happen with H3N2 because there seems to be a lot more mixing between humans and pigs.

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The researchers explain when new strains of flu invade humans the immune system fails to launch a defense because it only recognizes the more common strains.

For the study, researchers compared 1968 H3N2 strains that caused a pandemic with approximately1,100 H3 strains currently circulating in pigs and birds, focusing on the HA protein gene coding.

They specifically wanted to see how the immune system would react by calculating a value known as the “antigenic index” for each strain – the percentage of genetic regions that are identical to the 1968 H3 strain.

They also looked at the viruses’ ability to attach to the respiratory tract in humans.

The results showed there are 81 H3 viruses circulating since 2000 have the potential to cause widespread flu outbreak - 549 came from birds and 32 were isolated from pigs.

“One of the amazing things about the influenza virus is its ability to grab genes from different pools,” Sasisekharan said in a press release. “There could be viral genes that mix among pigs, or between birds and pigs.

Six of the flu viruses in pigs already have the potential to adapt to humans. When they exposed the viruses to current flu vaccine antibodies, there was no response.

The MIT researchers are studying the H5 or Avian (bird) flu virus in a similar fashion to find out more about its ability to cause pandemics in humans. The suggestion to public health organizations from the researchers is to be prepared for bigger threats from flu viruses that are constantly mutating, making current flu vaccines ineffective.

Image credit: Wikimedia commons