The virus isolated from patients in the United States was found to be made up of genetic elements from four different flu viruses in 2009 flu pandemic. It were swine influenza virus typically found in Asia and Europe, North American swine influenza, North American avian influenza, and human influenza. The reassortment of human influenza and swine influenza viruses is the result caused from the new strain. In the Preliminary genetic characterization it has been found that, the hemagglutinin (HA) gene was similar to that of swine flu viruses present in U.S. pigs since 1999 but there are genes that resembles versions present in European swine flu. The mixtures of swine flu, bird flu, and human flu viruses are themselves from the six genes from American swine flu.

The symptom of the H1n1 flu:
- Fever
- Lethargy
- Runny nose
- Cough
- Sore throat
- Lack of appetite
- Vomiting and diarrhoea in some cases.

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