Swine influenza or Swine flu is a respiratory disease commonly found in pigs which is caused by type A influenza virus - it causes high levels of illness in pigs but low death rates and while swine flu viruses may circulate among swine throughout the year, most outbreaks occur during the autumn and winter months similar to flu outbreaks in humans.
As with all influenza viruses, swine flu viruses change constantly and pigs can be infected by avian influenza and human influenza viruses as well as swine influenza viruses.
However when influenza viruses from different species infect pigs, the viruses can reassort (the mixing of the genetic material) and new viruses that are a mix of swine, human and/or avian influenza viruses can emerge and this has in fact happened before and different variations of swine flu viruses have emerged.
The Centers for Disease Control and Prevention (CDC) in the United States says there are currently four main influenza type A virus subtypes that have been isolated in pigs - H1N1, H1N2, H3N2, and H3N1, but most of the recently isolated influenza viruses from pigs have been H1N1 viruses. The current swine flu H3N2 viruses are closely related to human H3N2 viruses.
Swine flu viruses do not usually affect humans and the few cases which have occurred have been in persons in close contact with pigs and there have also been only a few cases of human to human spread of swine flu.
Swine flu is spread through coughing or sneezing of people infected with the influenza virus - people may become infected by touching something with flu viruses on it and then touching their mouth or nose.
The symptoms of swine flu in people are similar to the symptoms of regular human seasonal influenza and include fever, lethargy, lack of appetite and coughing - some people also have a runny nose, sore throat, nausea, vomiting and diarrhea.
Swine flu viruses are not transmitted by food and you can not get swine influenza from eating properly handled and cooked pork and pork products.
Swine flu is diagnosed by a respiratory specimen collected within the first 4 to 5 days of illness, when an infected person is most likely to be shedding the virus but some people, especially children, may shed the virus for 10 days or longer - the specimen is sent to a laboratory testing.
There are a number of antiviral drugs used to treat influenza and the CDC recommends the use of oseltamivir or zanamivir for the treatment and/or prevention of infection with swine influenza viruses.
Experts say H1N1 swine flu viruses are antigenically very different from human H1N1 viruses and, therefore, vaccines for human seasonal flu would not provide protection from H1N1 swine flu viruses.
Swine flu is spread among pigs by close contact and symptoms can include sudden onset of fever, depression, coughing, discharge from the nose or eyes, sneezing, breathing difficulties, eye redness or inflammation, and lack of appetite.
H1N1 and H3N2 swine flu viruses are endemic among pig populations in the United States and other countries and is something that the industry deals with on a routine basis.
While there are vaccines available for pigs to prevent swine influenza, there is as yet no vaccine to protect humans from swine flu.
According to the World Health Organisation (WHO) as of the 28th of April, 2009, there were 64 confirmed cases in the U.S., 26 in Mexico, including seven deaths, 6 in Canada, 3 in New Zealand, 2 in the United Kingdom, 2 in Israel and 2 in Spain.
The WHO has raised the worldwide pandemic alert level to Phase 4 (out of a possible 6) - a Phase 4 alert is characterized by confirmed person-to-person spread of a new influenza virus able to cause "community-level" outbreaks."
In order to stay healthy and reduce their likelihood of becoming infected or of spreading the virus, people are advised to cover the nose and mouth with a tissue when they cough or sneeze and dispose of the tissue immediately, wash their hands often with soap and water, especially after a cough or sneeze and avoid touching the eyes, nose or mouth and avoid close contact with sick people.
Infected people should stay home from work or school and limit contact with others to keep from infecting them.
The CDC has recommend that all nonessential travel to Mexico should be avoided all nonessential travel to Mexico and the WHO currently has not advised any restriction on regular travel or closure of borders but says people who are ill should delay any international travel and seek medical attention, in line with guidance from national authorities.