Influenza (the flu) is responsible for approximately 250,000 to 500,000 deaths
annually, but periodically its toll has been much higher. For example, the
1918 flu pandemic killed approximately 30 million people worldwide and is
considered the worst spread of a deadly illness in recorded history. With
highly virulent flu strains emerging periodically, it is little wonder that
the scientific community is actively studying influenza biology. In \(2007,\)
the National Institute of Allergy and Infectious Diseases completed sequencing
of 2035 human and avian influenza virus strains. Influenza strains undergo
recombination as described in this chapter, and they have a high mutation rate
owing to the error-prone replication of their genome (which consists of RNA
rather than DNA). In addition, they are capable of chromosome reassortment in
which various combinations of their eight chromosomes (or portions thereof)
can be packaged into progeny viruses when two or more strains infect the same
cell. The end result is that we can make vaccines, but they must change
annually, and even then, we can only guess at what specific viral strains will
be prevalent in any given year. Based on the above information, consider the
following questions:
(a) Of what evolutionary value to influenza viruses are high mutation and
recombination rates coupled with chromosome reassortment?
(b) Why can't humans combat influenza just as they do mumps, measles, or
chicken pox?
(c) Why are vaccines available for many viral diseases but not influenza?
