Swine influenza (also called swine flu, hog flu, and pig flu) is an infection by any one of several types of swine influenza virus. Swine influenza virus (SIV) is any strain of the influenza family of viruses that is endemic in pigs. As of 2009, the known SIV strains include influenza C and the subtypes of influenza A known as H1N1, H1N2, H3N1, H3N2, and H2N3.
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. The meat of an infected animal poses no risk of infection when properly cooked.
During the mid-20th century, identification of influenza subtypes became possible, allowing accurate diagnosis of transmission to humans. Since then, only 50 such transmissions have been confirmed. These strains of swine flu rarely pass from human to human. Symptoms of zoonotic swine flu in humans are similar to those of influenza and of influenza-like illness in general, namely chills, fever, sore throat, muscle pains, severe headache, coughing, weakness and general discomfort.
Classification
Of the three genera of influenza viruses that cause human flu, two also cause influenza in pigs, with influenza A being common in pigs and influenza C being rare. Influenza B has not been reported in pigs. Within influenza A and influenza C, the strains found in pigs and humans are largely distinct, although due to reassortment there have been transfers of genes among strains crossing swine, avian, and human species boundaries.
Influenza C
Influenza C viruses infect both humans and pigs, but do not infect birds. Transmission between pigs and humans have occurred in the past. For example, influenza C caused small outbreaks of a mild form of influenza amongst children in Japan and California. Due to its limited host range and the lack of genetic diversity in influenza C, this form of influenza does not cause pandemics in humans.
Influenza A
Swine influenza is known to be caused by influenza A subtypes H1N1, H1N2, H2N3, H3N1, and H3N2. In pigs, three influenza A virus subtypes (H1N1, H1N2, and H3N2) are the most common strains worldwide. In the United States, the H1N1 subtype was exclusively prevalent among swine populations before 1998; however, since late August 1998, H3N2 subtypes have been isolated from pigs. As of 2004, H3N2 virus isolates in US swine and turkey stocks were triple reassortants, containing genes from human (HA, NA, and PB1), swine (NS, NP, and M), and avian (PB2 and PA) lineages.
Surveillance
Although there is no formal national surveillance system in the United States to determine what viruses are circulating in pigs, there is an informal surveillance network in the United States that is part of a world surveillance network.
Veterinary medical pathologist, Tracey McNamara, set up a national disease surveillance system in zoos because the zoos do active disease surveillance and many of the exotic animals housed there have broad susceptibilities. Many species fall below the radar of any federal agencies (including dogs, cats, pet prairie dogs, zoo animals, and urban wildlife), even though they may be important in the early detection of human disease outbreaks
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. The meat of an infected animal poses no risk of infection when properly cooked.
During the mid-20th century, identification of influenza subtypes became possible, allowing accurate diagnosis of transmission to humans. Since then, only 50 such transmissions have been confirmed. These strains of swine flu rarely pass from human to human. Symptoms of zoonotic swine flu in humans are similar to those of influenza and of influenza-like illness in general, namely chills, fever, sore throat, muscle pains, severe headache, coughing, weakness and general discomfort.
Classification
Of the three genera of influenza viruses that cause human flu, two also cause influenza in pigs, with influenza A being common in pigs and influenza C being rare. Influenza B has not been reported in pigs. Within influenza A and influenza C, the strains found in pigs and humans are largely distinct, although due to reassortment there have been transfers of genes among strains crossing swine, avian, and human species boundaries.
Influenza C
Influenza C viruses infect both humans and pigs, but do not infect birds. Transmission between pigs and humans have occurred in the past. For example, influenza C caused small outbreaks of a mild form of influenza amongst children in Japan and California. Due to its limited host range and the lack of genetic diversity in influenza C, this form of influenza does not cause pandemics in humans.
Influenza A
Swine influenza is known to be caused by influenza A subtypes H1N1, H1N2, H2N3, H3N1, and H3N2. In pigs, three influenza A virus subtypes (H1N1, H1N2, and H3N2) are the most common strains worldwide. In the United States, the H1N1 subtype was exclusively prevalent among swine populations before 1998; however, since late August 1998, H3N2 subtypes have been isolated from pigs. As of 2004, H3N2 virus isolates in US swine and turkey stocks were triple reassortants, containing genes from human (HA, NA, and PB1), swine (NS, NP, and M), and avian (PB2 and PA) lineages.
Surveillance
Although there is no formal national surveillance system in the United States to determine what viruses are circulating in pigs, there is an informal surveillance network in the United States that is part of a world surveillance network.
Veterinary medical pathologist, Tracey McNamara, set up a national disease surveillance system in zoos because the zoos do active disease surveillance and many of the exotic animals housed there have broad susceptibilities. Many species fall below the radar of any federal agencies (including dogs, cats, pet prairie dogs, zoo animals, and urban wildlife), even though they may be important in the early detection of human disease outbreaks
As the swine influenza A (H1N1) virus is a new virus, no swine flu vaccine was immediately available to prevent infections.
And unfortunately, the seasonal flu vaccine that many of us receive will not provide any protection against the swine flu virus.
A vaccine has been developed, tested, and now FDA approved and will be available in October to help prevent infections from the 2009 H1N1 strain of the flu.
Swine Flu Vaccine
Can the swine flu vaccine be combined with the seasonal flu vaccine? No, as vaccine companies had to be done making seasonal flu vaccine before they could get started on the swine flu vaccine.
Once the swine flu is ready, who will get it?
CDC’s Advisory Committee on Immunization Practices (ACIP) recommends that swine flu vaccine should first go to:
Pregnant women
Household contacts and caregivers for children younger than 6 months of age
Healthcare and emergency medical services personnel
All children and young adults from 6 months through 24 years of age, and
Persons aged 25 through 64 years who have health conditions associated with higher risk of medical complications from influenza
That will take up about 159 million doses of swine flu vaccine. If supplies of swine flu vaccine are limited, priority should go to:
Pregnant women
Household contacts and caregivers for children younger than 6 months of age
Healthcare and emergency medical services personnel
Children 6 months through 4 years of age, and
Children 5 through 18 years of age who have chronic medical conditions
Next, as swine flu vaccine improves to the point that all priority groups have gotten vaccinated, everyone from the ages of 25 through 64 years will get vaccinated too. Lastly, people 65 or older, who have the least risk from the swine flu will be offered the swine flu vaccine.
Finding Swine Flu Shots
Although five companies are making H1N1 swine flu shots, including Sanofi Pasteur, Novartis, GSK, Medimmune and CSL, doctors won't be able to directly order swine flu vaccine from them. Instead, the federal government is purchasing all of the swine flu shots and then is distributing them via a centralized distribution program. Pediatricians and other health care providers should begin to preregister now if they want to receive swine flu vaccine to give their patients.
Parents might also want to ask their pediatrician if they are going to participate in the swine flu distribution program to make sure they have a place to get their kids a swine flu vaccine when they first become available in October.
Although the swine flu vaccine will be free, pediatricians will likely charge a small vaccine administration fee to their patients.
Swine Flu Vaccine Trials
The National Institute of Allergy and Infectious Diseases, part of the National Institutes of Health, has conducted swine flu clinical trials to make sure the new swine flu vaccines are safe and effective. They were conducted at eight university research hospitals and medical organizations across the United States, including Baylor College of Medicine in Houston, Children's Hospital Medical Center in Cincinnati, and Emory University in Atlanta.
The first clinical trials tested whether one or two doses are needed and will test both 15mcg and 30mcg doses of vaccine. Although the trials started in adults, they were also tested in children.
1976 Swine Flu Vaccine
Although it is true that we don't currently have a swine flu vaccine, there once was a swine flu vaccine that was made to target the swine flu H1N1 strain that was found at Fort Dix, New Jersey. Because of fears that this swine flu strain was similar to the flu strain that caused the 1918 Spanish Flu pandemic, a vaccination program immunized more than 40 million people in the United States between October 1976 to December 1976.
The immunization program was stopped early because the swine flu pandemic didn't occur, and the swine flu vaccine was thought to cause many side effects, including Guillain-Barre syndrome.
How many cases of Guillain-Barre syndrome were there? About 40, or 1 per million people vaccinated. Even that was considered too high though in light of the fact that there didn't seem to be any cases of swine flu that season.
And unfortunately, the seasonal flu vaccine that many of us receive will not provide any protection against the swine flu virus.
A vaccine has been developed, tested, and now FDA approved and will be available in October to help prevent infections from the 2009 H1N1 strain of the flu.
Swine Flu Vaccine
Can the swine flu vaccine be combined with the seasonal flu vaccine? No, as vaccine companies had to be done making seasonal flu vaccine before they could get started on the swine flu vaccine.
Once the swine flu is ready, who will get it?
CDC’s Advisory Committee on Immunization Practices (ACIP) recommends that swine flu vaccine should first go to:
Pregnant women
Household contacts and caregivers for children younger than 6 months of age
Healthcare and emergency medical services personnel
All children and young adults from 6 months through 24 years of age, and
Persons aged 25 through 64 years who have health conditions associated with higher risk of medical complications from influenza
That will take up about 159 million doses of swine flu vaccine. If supplies of swine flu vaccine are limited, priority should go to:
Pregnant women
Household contacts and caregivers for children younger than 6 months of age
Healthcare and emergency medical services personnel
Children 6 months through 4 years of age, and
Children 5 through 18 years of age who have chronic medical conditions
Next, as swine flu vaccine improves to the point that all priority groups have gotten vaccinated, everyone from the ages of 25 through 64 years will get vaccinated too. Lastly, people 65 or older, who have the least risk from the swine flu will be offered the swine flu vaccine.
Finding Swine Flu Shots
Although five companies are making H1N1 swine flu shots, including Sanofi Pasteur, Novartis, GSK, Medimmune and CSL, doctors won't be able to directly order swine flu vaccine from them. Instead, the federal government is purchasing all of the swine flu shots and then is distributing them via a centralized distribution program. Pediatricians and other health care providers should begin to preregister now if they want to receive swine flu vaccine to give their patients.
Parents might also want to ask their pediatrician if they are going to participate in the swine flu distribution program to make sure they have a place to get their kids a swine flu vaccine when they first become available in October.
Although the swine flu vaccine will be free, pediatricians will likely charge a small vaccine administration fee to their patients.
Swine Flu Vaccine Trials
The National Institute of Allergy and Infectious Diseases, part of the National Institutes of Health, has conducted swine flu clinical trials to make sure the new swine flu vaccines are safe and effective. They were conducted at eight university research hospitals and medical organizations across the United States, including Baylor College of Medicine in Houston, Children's Hospital Medical Center in Cincinnati, and Emory University in Atlanta.
The first clinical trials tested whether one or two doses are needed and will test both 15mcg and 30mcg doses of vaccine. Although the trials started in adults, they were also tested in children.
1976 Swine Flu Vaccine
Although it is true that we don't currently have a swine flu vaccine, there once was a swine flu vaccine that was made to target the swine flu H1N1 strain that was found at Fort Dix, New Jersey. Because of fears that this swine flu strain was similar to the flu strain that caused the 1918 Spanish Flu pandemic, a vaccination program immunized more than 40 million people in the United States between October 1976 to December 1976.
The immunization program was stopped early because the swine flu pandemic didn't occur, and the swine flu vaccine was thought to cause many side effects, including Guillain-Barre syndrome.
How many cases of Guillain-Barre syndrome were there? About 40, or 1 per million people vaccinated. Even that was considered too high though in light of the fact that there didn't seem to be any cases of swine flu that season.
