Microbiology: A Systems Approach 4th Edition by Marjorie Kelly Cowan

Exercise 5

Flu: The Real Deal
Influenza: The word strikes fear in the hearts of many. These tiny viral particles, composed of no more than a bit of genetic material and a protein coat, can hijack your cells, produce more viruses, and spread to other cells and other people, often with disastrous consequences. Not only do people dread the symptoms of fever, cough, sore throat, stuffy nose, head and body aches, and fatigue, but pandemics of influenza have swept across the globe in waves, killing millions. Since 1918, there have been four major pandemics: "The Spanish flu" occurred in 1918 and sickened 20%-40% of the world's population, killing nearly 50 million people. In 1957, "the Asian flu" killed 1-2 million people. Nearly a decade later, "the Hong Kong flu" spread throughout the world, with deaths estimated around 1 million, with the highest death rates among individuals 65 and over. It wasn't until 2009 that another flu pandemic began in Mexico, spreading to the United States and affecting nearly 74 countries-it was dubbed "the swine flu." Despite 80 million people vaccinated against the disease, the CDC estimates that 43-89 million people became ill with the virus and it caused tens of thousands of deaths.
Each of these pandemics was caused by a different strain of influenza. Strains of influenza virus are identified by characteristics of the hemagglutinin (H) and neuraminidase (N) capsid proteins. The influenza virus, with its segmented RNA genome, is able to mutate rapidly. Mutations can result in changes to the capsid proteins that allow the virus to evade the immune system. Sixteen different types of H antigens and nine different types of N antigens have been identified; each viral strain is identified by the numbered type of each H and N antigen found on its capsid. For example, the Spanish flu pandemic was caused by the H1N1 strain, the Asian flu pandemic was caused by the H2N2 strain, and the Hong Kong flu was caused by the H3N2 strain. The 2009 swine flu pandemic was caused by a novel strain of H1N1.
What other animals can develop influenza infections
What are the possible consequences of influenza virus transmission between animals and humans
Strains of influenza can infect birds, pigs, horses, and dogs, as well as humans. Although transmission of influenza strains from animals to humans is rare, scientists have determined that it does in fact occur. Genomic analysis of past pandemic strains has revealed the presence of avian (bird) influenza genes in these human influenza viruses. Swine influenza virus is not usually transmitted to humans, but certain variant strains have been found to infect humans that live or work in close contact with pigs. Because pigs can contract both human and avian influenza, there is a higher probability of several viruses circulating in the same organism at one time. This can result in the production of a novel variant strain, as occurred during the 2009 swine flu pandemic. Analysis of this strain revealed the presence of two types of swine influenza genes in addition to avian and human influenza viral sequences, and it became known to scientists as a "quadruple reassortant" virus.

Today, two main types of avian influenza are infecting humans: low pathogenic avian influenza A (LPAI) viruses and highly pathogenic influenza A (HPAI) viruses. The Centers for Disease Control and Prevention (CDC) reports that there have been approximately 600 cases of HPAI in humans throughout the world since 2003. These illnesses are due to infection with the H5N1 strain of influenza, which exhibits a nearly 60% mortality rate in affected individuals. The CDC and the World Health Organization (WHO) have been carefully monitoring this strain of influenza because it has the potential to cause another pandemic.
What is being done to prevent a pandemic caused by H5N1 influenza