2009 Flu Pandemic

The 2009 flu pandemic is a global outbreak of a new strain of a influenza A virus subtype H1N1, officially named the “new H1N1”, first identified in April 2009, and commonly called “Swine flu.” It is thought to be a reassortment of four known strains of influenza A virus: one endemic in (normally infecting) humans, one endemic in birds, and two endemic in pigs (swine). Transmission of the new strain is human-to-human, with cooked pork products safe to eat as the virus cannot be transmitted by eating foods.

The outbreak began in Mexico, with evidence that Mexico was already in the midst of an epidemic for months before the outbreak was recognized. In early June, as the virus spread globally, the World Health Organization (WHO) declared the outbreak to be a pandemic, but also noted that most illnesses were of “moderate severity.” The virus has since spread to the Southern Hemisphere which entered its winter flu season, and to many less developed countries with limited healthcare systems. Because the virus was spreading with “unprecedented speed”, and many clinics were overwhelmed testing and treating patients, WHO stopped requiring countries to report all cases, but is still monitoring unusually large outbreaks.

The virus typically spreads from coughs and sneezes or by touching contaminated surfaces and then touching the nose or mouth. Symptoms, which can last up to a week, are similar to those of seasonal flu, and may include fever, sneezes, sore throat, coughs, headache, and muscle or joint pains. The U.S. Centers for Disease Control and Prevention (CDC) notes that most cases worldwide are usually mild, and most hospitalizations and deaths have been of persons that also had underlying conditions such as asthma, diabetes, obesity, heart disease, or a weakened immune system. The CDC’s Anne Schuchat states, “this is a virus that’s capable of causing a spectrum of illness that includes severe complications and death. . . It’s very important we take this virus seriously”. As the virus spreads easily between people, through the air or surface contact, those who get the flu are recommended to stay home from school or work and avoid crowds to avoid spreading the infection further.

In an attempt to slow the spread of the illness, a number of countries, especially in Asia, have quarantined airline passengers with flu symptoms, while some are also pre-screening passengers. WHO does not expect to have a full vaccine before the end of 2009, and vaccines available sooner may be limited and given first to healthcare workers, pregnant women, and other higher risk groups. Two or three injections will be required for maximum immunity from both the swine flu and seasonal flu. There is also concern if the new virus mutates further, it could become more virulent and less susceptible to any new vaccine.

Swine Flu

Swine influenza was first proposed to be a disease related to human influenza during the 1918 flu pandemic, when pigs became sick at the same time as humans. The first identification of an influenza virus as a cause of disease in pigs occurred about ten years later, in 1930. For the following 60 years, swine influenza strains were almost exclusively H1N1. Then, between 1997 and 2002, new strains of three different subtypes and five different genotypes emerged as causes of influenza among pigs in North America. In 1997-1998, H3N2 strains emerged. These strains, which include genes derived by reassortment from human, swine and avian viruses, have become a major cause of swine influenza in North America. Reassortment between H1N1 and H3N2 produced H1N2. In 1999 in Canada, a strain of H4N6 crossed the species barrier from birds to pigs, but was contained on a single farm.

The H1N1 form of swine flu is one of the descendants of the strain that caused the 1918 flu pandemic. As well as persisting in pigs, the descendants of the 1918 virus have also circulated in humans through the 20th century, contributing to the normal seasonal epidemics of influenza. However, direct transmission from pigs to humans is rare, with only 12 cases in the U.S. since 2005. Nevertheless, the retention of influenza strains in pigs after these strains have disappeared from the human population might make pigs a reservoir where influenza viruses could persist, later emerging to reinfect humans once human immunity to these strains has waned. Swine flu has been reported numerous times as a zoonosis in humans, usually with limited distribution, rarely with a widespread distribution. Swine influenza virus is common throughout pig populations worldwide. Transmission of the virus from pigs to humans is not common and does not always lead to human influenza, often resulting only in the production of antibodies in the blood. If transmission does cause human influenza, it is called zoonotic swine flu. People with regular exposure to pigs are at increased risk of swine flu infection.