In 1918, a worldwide epidemic of influenza A resulted in the deaths of 40-50 million people. This strain of influenza A, known as H1N1-referring to the genotypes of the viral surface proteins, hemagglutinin (H) and neuraminidase (N)-was shown to be derived from an avian virus that adapted to infect and grow in human cells. Interestingly, by 1957, the H1N1 strains of Influenza A had completely disappeared from the human population, to be replaced by new strains (H2N2) that contained three gene segments from avian origin. The most likely explanation for the disappearance of the early twentieth century form of H1N1 Influenza A virus is:
A) The replacement by a more pathogenic strain of Influenza A in 1957
B) The slow accumulation of mutations in the 1918 Influenza A virus that impaired its infectivity in humans
C) The changes in human living conditions leading to spread of Influenza A from pigs into humans, rather than from birds
D) High levels of existing immunity in the human population to the H1N1 surface antigens
E) The greater mobility of the human population due to the rapid increase in airplane travel

Question

Quizplus · Accepted Answer

The replacement by a more pathogenic strain of Influenza A in 1957 is the most likely explanation for the disappearance of the early twentieth century form of H1N1 Influenza A virus. This is because the new H2N2 strain, which contained gene segments from avian origin, effectively outcompeted the H1N1 strain, leading to its disappearance from the human population.

In 1918, a Worldwide Epidemic of Influenza a Resulted in the Deaths