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Swine influenza is an acute, highly contagious, respiratory disease that results from infection with type A influenza virus. Field isolates of variable virulence exist, and clinical manifestation may be determined by secondary organisms. Pigs are the principal hosts of classic swine influenza virus. (Human infections have been reported, but porcine strains of influenza A do not appear to easily spread in the human population. However, deaths have occurred in immunocompromised people.) In 2009 a pandemic strain of H1N1 influenza A virus spread globally. It infected people, swine, and poultry, as well as a small number of dogs, cats, and other animals. The disease in swine occurs commonly in the midwestern USA (and occasionally in other states), Mexico, Canada, South America, Europe (including the UK, Sweden, and Italy), Kenya, China, Japan, Taiwan, and other parts of eastern Asia.

Having a single one of these symptoms does not mean you have pandemic swine flu, but, you don't need to have all of these symptoms to suspect infection, either. The symptoms of swine flu in people are similar to the symptoms of regular human seasonal influenza. Watch for some combination of the following symptoms:

1. Fever of 101°F (41°C) or higher

2. Coughing

3. Headache

4. Sneezing

5. Body Aches

6. Fatigue

7. Dizziness

8. Chest pain

9. Abdominal pain

10. Shortness of breath

11. Malaise

12. Runny Nose

13. Sore throat

14. Vomiting

15. Diarrhea

16. Rigors (chills or shivers)

Caution: If you suspect that you might have a flu infection, consult a physician as soon as possible. Don't wait! It is important for people who have chronic health conditions, women who are pregnant, and people with other high risk factors to pay special attention to warning signs. Influenza can make the symptoms, of other chronic medical conditions, worse

Swine flu and regular flu are both types of illness caused by different strains of the influenza virus. Regular flu is generally of types A, B or C, whereas swine flu is a strain (H1N1 virus) that is said to have originated in pigs.

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 because of reassortment there have been transfers of genes among strains crossing swine, avian, and human species boundaries.

Influenza C

Influenza 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. Because of 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, four influenza A virus subtypes (H1N1, H1N2,H3N2 and H7N9) 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. In August 2012, the Center for Disease Control and Prevention confirmed 145 human cases (113 in Indiana, 30 in Ohio, one in Hawaii and one in Illinois) of H3N2v since July 2012. The death of a 61-year-old Madison County, Ohio woman is the first in the nation associated with a new swine flu strain. She contracted the illness after having contact with hogs at the Ross County Fair.

Surveillance

Although there is no formal national surveillance system in the United States to determine what viruses are circulating in pigs, an informal surveillance network in the United States is part of a world surveillance network.