The 2009 outbreak of Influenza A virus subtype H1N1 is an epidemic of a new strain of influenza virus identified in April 2009, commonly referred to as "swine flu" by the media. The source of the outbreak in humans is still unknown. Cases were first discovered in the U.S. and officials soon suspected a link between those incidents and an earlier outbreak of late-season flu cases in Mexico. Within days hundreds of suspected cases, some of them fatal, were discovered in Mexico, with yet more cases found in the U.S. and several other countries in the Northern Hemisphere. Soon thereafter, the U.N.'s World Health Organization (WHO), along with the U.S. Centers for Disease Control and Prevention (CDC), expressed concern that the A(H1N1) could become a worldwide flu pandemic, and WHO then raised its pandemic disease alert level to "Phase 5" out of the six maximum, as a "signal that a pandemic is at the imminent level".
Although virologists have noted that the outbreak has proven relatively mild and less fatal than historic pandemics, other health officials, including CDC Director Richard Besser, worry about what might happen later in the year, stating that "we are not seeing any sign of this petering out. We are still on the upswing of the epidemic curve. The number of cases is expected to rise as the new flu spreads across the country." In addition, the new virus strain could mutate over the coming months, leading to a new and potentially more dangerous flu outbreak later in the year.
The new strain is an apparent reassortment of four strains of influenza A virus subtype H1N1.Analysis by the CDC identified the four component strains as one endemic in humans, one endemic in birds, and two endemic in pigs (swine).However, other scientists have stated that analysis of the 2009 swine flu (A/H1N1) viral genome suggests that all RNA segments are of swine origin, and "this preliminary analysis suggests at least two swine ancestors to the current H1N1, one of them related to the triple reassortant viruses isolated in North America in 1998." One swine influenza ancestor strain was widespread in the United States, the other in Eurasia. Both the place and the species in which the virus originated are unknown. Analysis has suggested that the H1N1 strain responsible for the current outbreak first evolved around September 2008 and circulated in the human population for several months before the first cases were detected. The new strain was first diagnosed in two children by the CDC, first on April 14 in San Diego County, California and a few days later in nearby Imperial County, California. Neither child had been in contact with pigs. Spread within Mexico Further information: 2009 swine flu outbreak in Mexico The outbreak was first detected in Mexico City, where surveillance began picking up a surge in cases of influenza-like illness (ILI) starting March 18. The surge was assumed by Mexican authorities to be "late-season flu" (which usually coincides with a mild Influenzavirus B peak) until April 21, when a U.S. Centers for Disease Control and Prevention alert concerning two isolated cases of a novel swine flu was reported in the media. Some samples were sent to the U.S.-based CDC on April 18. The Mexican cases were confirmed by the CDC and the World Health Organization to be a new strain of H1N1. Cases were also reported in the states of San Luis Potosí, Hidalgo, Querétaro and Mexico State.Mexican Health Minister José Ángel Córdova on April 24, said "We’re dealing with a new flu virus that constitutes a respiratory epidemic that so far is controllable." Mexican news media speculate that the outbreak may have started in February near a Smithfield Foods pig plant amid complaints about its intensive farming practices, although no pigs in Mexico have tested positive for the virus. Smithfield Foods retorted that that it had found no clinical signs or symptoms of the presence of swine influenza in the company's swine herd, or its employees at its joint ventures in Mexico, and routinely administers influenza virus vaccination to their swine herds and that it conducts monthly testing for the presence of swine influenza. The first death from swine flu occurred on April 13, when a diabetic woman from Oaxaca died from respiratory complications. The Mexican fatalities are alleged to be mainly young adults of 25 to 45, a common trait of pandemic flu. Although by late April there had been reports of 152 "probable deaths" in Mexico, the WHO had received reports of only 7 confirmed deaths as of April 29 and explicitly denied the larger figure. Later, Mexico's Health Secretary declared that around 100 early suspected deaths from swine flu could not be confirmed because samples were not taken.The WHO Rapid Pandemic Assessment Collaboration has estimated that 23,000 individuals may have been infected in Mexico in 14 to 73 generations of flu propagation prior to late April. Southern Hemisphere The outbreak comes at the beginning of the flu season for the Southern Hemisphere, including Australia, Oceania, southern Africa, and most of South America. July is usually the height of flu season in this part of the world.In a May 18th article, CDC’s Dr. Richard Besser was quoted as saying in reference to the Southern Hemisphere: “We’ll be looking at the virus to see [if it] has mutated into something more severe.”
The new strain has spread widely beyond Mexico and the U.S., with confirmed cases in forty-one countries and suspected cases in fifty. Many countries have advised their inhabitants not to travel to infected areas. Areas including Australia, Hong Kong, Iceland, India, Indonesia, Malaysia, Philippines, Singapore, South Korea and Thailand are monitoring visitors returning from flu-affected areas to identify people with fever and respiratory symptoms. Many countries have also issued warnings to visitors of flu-affected areas to contact a doctor immediately if they had flu-like symptoms. Mexico's schools, universities, and all public events were closed from April 24 to May 6, 2009. By May 3, 2009, more than 400 school closures in the U.S., which included entire school districts in Texas, affected 250,000 students due to confirmed or probable cases in students or staff. Most cases outside North America are recent travellers to Mexico or the US. Intra-national infections have been reported only from Mexico, the USA, Canada,the UK,Spain, Germany,Italy, Belgium and Panama.
Although the FAO, WHO, and OIE have reaffirmed that "Influenza viruses are not known to be transmissible to people through eating processed pork or other food products derived from pigs," and although influenza A viruses are inactivated by heating, nevertheless some countries banned import and sale of pork products "as a precaution against swine flu".
Several countries, including Serbia, China and Russia banned the import of pork products from North America in general as a response to the outbreak, despite assurances from the WHO that the disease is not spread through pork. On April 29, the Egyptian Government decided to kill all 300,000 pigs in Egypt, despite a lack of evidence that the pigs had, or were even suspected of having, the virus.This led to clashes between pig owners and the police in Cairo.On May 5, Afghanistan's only pig, which resides at the Kabul zoo, was quarantined amid flu fears. On May 10, in Alberta, Canada, 500 pigs were culled on a farm which housed pigs confirmed to have H1N1. Authorities state it was to better quarantine those pigs that had H1N1, and maintain that the culling was not a direct action against the virus. In Alberta, Canada, provincial and federal officials announced on May 2 that a 2,200-head pig herd in central Alberta was under quarantine after preliminary findings indicated some of the animals were infected with swine flu in a case of reverse zoonosis; it was presumed that a carpenter who had recently visited Mexico infected the swine while installing a roof vent on their barn. The farm was quarantined and 500 infected pigs were destroyed even though they were recovering.Alberta agriculture minister George Groeneveld said that health officials expected no problems with export of pork from Canada to the United States, and that there was "absolutely no evidence" that the flu virus can be transmitted through eating pork.
