Different influenza viruses

H7N9

What: The influenza A (H7N9) virus is a strain of influenza viruses that normally infect birds. Both the source of infection and the mode of transmission are uncertain.

Symptoms: Most patients with this infection have severe pneumonia. Symptoms include fever, cough and shortness of breath.

How many: As of Tuesday, there have been 28 cases of the H7N9 virus, including nine deaths.

H1N1

What: H1N1, commonly known as swine flu, is an influenza virus that spreads from human to human. It originated from animals and its most well-known strains are endemic in pigs. It was declared pandemic by the World Health Organisation (WHO) from June 10, 2009, to Aug 10, 2010.

Symptoms: Symptoms include high fever, cough, muscle pains, sore throat, fatigue, vomiting or diarrhoea.

How many: As of May 30, 2010, there were reported laboratory confirmed cases of pandemic influenza in 214 countries and territories of the swine flu strain of H1N1, including more than 18,138 deaths.

H5N1

What: H5N1 is a type of influenza virus that infects birds. It is commonly called avian influenza (or bird flu). Human cases occur occasionally, human-to-human transmission is difficult. When infected, the human mortality rate is about 60 per cent.

Symptoms: Initial symptoms include high fever, diarrhoea, vomiting, chest pain and bleeding from the nose and gums. Difficulty in breathing develops around five days following the first symptoms.

How many: As of March 12 this year, there have been 622 confirmed cases and 371 deaths since 2003 .


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