Swine Flu:

Swine influenza is a highly contagious respiratory disease in pigs caused by one of several swine influenza A viruses. 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). The current epidemic is caused by the H1N1 serovar of Influenza A.

Human cases of swine influenza A (H1N1) have been reported worldwide in 2009. Cases of influenza-like illness were first reported in Mexico on March 18; the outbreak was subsequently confirmed as swine influenza A [4]. As of 1600 GMT, 3 May 2009, 18 countries have officially reported 898 cases of influenza A (H1N1) infection. Mexico has reported 506 confirmed human cases of infection, including 19 deaths [5]. The United States Government has reported 226 laboratory confirmed human cases from 30 states, including one death [6]. The following countries have reported laboratory confirmed cases with no deaths - Austria (1), Canada (85), China, Hong Kong Special Administrative Region (1), Costa Rica (1), Denmark (1), France (2), Germany (8), Ireland (1), Israel (3), Italy (1), Netherlands (1), New Zealand (4), Republic of Korea (1), Spain (40), Switzerland (1) and the United Kingdom (15). So far no cases have been reported from India.

Swine Influenza - A Pandemic

By April 29, 2009 - Swine flu had pushed the World Health Organization to raise its pandemic alert level to phase 5, which means that a pandemic is imminent. The WHO's pandemic alert phases are as follows [7] (Fig. 1):

Phase 1  :	A virus in animals has caused no known infections in humans.
Phase 2  :	An animal flu virus has caused infection in humans.
Phase 3  :	Sporadic cases or small clusters of disease occur in humans. Human-to-human transmission, if any, is insufficient to cause community-level outbreaks.
Phase 4  :	The risk for a pandemic is greatly increased but not certain. The disease-causing virus is able to cause community-level outbreaks.
Phase 5  :	Still not a pandemic, but spread of disease between humans is occurring in more than one country of one WHO region.
Phase 6  :	This is the pandemic level. Community-level outbreaks are in at least one additional country in a different WHO region from phase 5. A global pandemic is under way.

Figure 1. Pandemic Influenza Phases [7].

An influenza pandemic occurs when a new influenza virus appears against which the human population has no immunity, resulting in epidemics worldwide with enormous numbers of deaths and illness. With the increase in global transport, as well as urbanization and overcrowded conditions, epidemics due the new influenza virus are likely to quickly take hold around the world. Outbreaks of influenza in animals, especially when happening simultaneously with annual outbreaks of seasonal influenza in humans, increase the chances of a pandemic, through the merging of animal and human influenza viruses. During the last few years, the world has faced several threats with pandemic potential, making the occurrence of the next pandemic a matter of time. Current epidemiological models project that a pandemic could result in 2 to 7.4 million deaths globally [8].

The most recent pandemics included the 1889 pandemic, the 1918-1919 Spanish pandemic (influenza virus subtype H1), the 1957 pandemic (subtype H2N2), the 1968-1969 pandemic (Hong Kong subtype H3N2), and, to a lesser extent, the Russian pandemic in 1977 (subtype H1N1) [9]. The 1918 Spanish influenza pandemic infected one third of the world's population (an estimated 500 million people) and caused approximately 50 million deaths [10].