Influenza is a virus that infects the respiratory system. The symptoms include fever, coughing, runny nose, and fatigue. The virus has several strains that infect different species, such as humans, pigs, or birds. If a strain mutates to infect a different species, it can share genes with other strains and produce hybrids, such as the human, swine, avian strain currently spreading throughout the world.
Influenza Strains
Type A influenza, which infects humans, is subdivided based on the expression of certain surface proteins, called hemagglutinin (H) and neuraminidase (N). Hemagglutinin is the protein used to adhere to respiratory cells, affecting infectivity, and neuraminidase is the enzyme influenza uses to make it through the mucus in the respiratory system and is a drug target for treating influenza infection.
The 1918 strain of influenza, called the Spanish flu or “La Grippe”, was an H1N1 strain that killed an estimated 20-40 million people worldwide. It originated in the United States, but received more attention in Spain, where much mortality occurred. The strain infected mostly healthy young adults, and is considered the ideal study for pandemic influenza. The virus killed more people in a single year than the Bubonic Plague in 4 years. Death from the infection is thought to have been due to an over-reaction by the immune system, called a cytokine storm.
- 1957 Asian Flu
In 1957, a H2N2 influenza strain caused an outbreak in China that became a global pandemic. The strain affected mostly children and the elderly, killing approximately 2 million people worldwide. Immunity in young people was rare, and pneumonia was a common after effect of infection. Close contact was thought to have been the cause of spread among school children and army personnel. The first U.S. cases were seen during the summer months, a rare time for flu surges.
- 1968 Hong Kong Flu
Over the course of two years, a H3N2 influenza strain that originated in Hong Kong spread globally, killing roughly 1 million people. The virus took hold, more adversely affecting the elderly, during the winter months. Available antibiotics for secondary infections are believed to have influenced the mortality rate.
- 1977 Russian Flu
For those born after 1950, immunity to the H1N1 influenza strain due to exposure or vaccination was sparse, and 1977 found the younger population susceptible to an outbreak that originated in Russia. Termed a benign pandemic, the disease affected only children and a vaccine was produced for the next flu season.
- 2009 Mexican Flu
Though not yet officially a pandemic, health authority reports are indicating a growing concern that a H1N1 strain that has infected thousands and killed nearly 200 people in Mexico may become a pandemic. Several countries, including the United States, Canada, Spain, England, New Zealand, and Israel, have already confirmed cases, though they have not seen any deaths. Person to person transmission in two regions of the world is needed to term the outbreak a pandemic. Because this is a similar strain to the 1918 Spanish Flu, health authorities are on alert, but the infection does respond to treatment and medical advancements have occurred since that time.
Swine Flu Prevention
Health authorities are asking individuals to remain at home or seek medical care if they feel ill. The symptoms of this flu strain include vomiting and diarrhea in addition to respiratory symptoms. Wash hands with warm water and mild soap (not antibacterial), limit contact with other persons if feeling ill, and use tissues or a sleeve when sneezing to limit airborne spread.
Alicia Mae Prater - Alicia received her doctorate in Experimental Pathology in 2007. She has been a freelance writer and scientific editor since 2008.
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