Swine Flu

Introduction

Swine influenza is a highly contagious respiratory disease in pigs caused by one of several swine influenza A viruses. In addition, influenza C viruses may also cause illness in swine. Current strategies to control swine influenza virus (SIV) in animals typically include one of several commercially available bivalent swine influenza virus vaccines.

Transmission of swine influenza viruses to humans is uncommon. However, the swine influenza virus can be transmitted to humans via contact with infected pigs or environments contaminated with swine influenza viruses. Once a human becomes infected, he or she can then spread the virus to other humans, presumably in the same way as seasonal influenza is spread (ie, via coughing or sneezing).

History

The ability to trace outbreaks of swine flu in humans dates back to investigation of the 1918 Spanish influenza pandemic, which infected one third of the world’s population (an estimated 500 million people) and caused approximately 50 million deaths. In 1918, the cause of human influenza and its links to avian and swine influenza was not understood. The answers did not begin to emerge until the 1930s, when related influenza viruses (now known as H1N1 viruses) were isolated from pigs and then humans.¹

In humans, the severity of swine influenza can vary from mild to severe. From 2005 until January 2009, 12 human cases of swine flu were reported in the United States. None were fatal. In 1988, however, a previously healthy 32-year-old pregnant woman in Wisconsin died of pneumonia as a complication of swine influenza.

A 1976 outbreak of swine influenza in Fort Dix, New Jersey, involved more than 200 cases, some of them severe, and one death.² The first discovered case involved a soldier at Fort Dix who complained of feeling weak and tired. He died the next day.