Viruses express tissue tropism and host specificity. In particular, the avian influenza strain H5N1 has rare incidences in humans due to the reduced distribution of alpha-2,3 sialic acids in the lower respiratory tract. As a consequence, when the H5N1 strain does infect a human, the disease is very severe due to the risk of pneumonia. In contrast, human influenza strains (H1N1, among others) attach to alpha-2,6 sialic acids, which are readily expressed in the upper and lower respiratory tract. Which of the following would not be true if a mutation were to allow the H5N1 strain to attach to alpha-2,6 sialic acids?

Choose one:

A. The avian influenza strain could be transmitted easily from human to human.

B. An epidemic would likely ensue due to the lack of immunity to the new avian influenza strain.

C. The avian influenza strain could be transmitted directly from birds to humans.

D. The avian influenza strain would only infect the lower respiratory tract of humans.

Hint: Alpha-2,6 sialic acid is expressed throughout the human respiratory tract.

Of the mentioned statements, the incorrect one is option D.

Explanation:

The normal H5N1 strain or the bird flu virus when get attached with the alpha 2,3-sialic acid results in the infection of the lower respiratory tract in humans. The condition occurs very rarely. In comparison, the H1N1 or the human influenza strain gets attached with alpha-2,6 sialic acids and easily results in the infection of the upper and lower respiratory tract.  

However, if the mutation takes place in the H5N1 strain, it can bind with the alpha-2,6 sialic acid and can result in the overall infection of the human respiratory tract. Now due to the occurrence of mutations in the H5N1 strain, bird flu can get transmit easily from birds to humans and from one human to another human. Also due to lack of immunity because of the emergence of new strain, the condition can become lethal as, like normal flu, the mutated strain can also result in the infection of the entire respiratory tract.  

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