Influenza, also known as the flu, is a respiratory infection. The flu virus infects the cells in the upper respiratory tract, including the nose, throat and lungs. It can cause moderate to severe complications in all age groups. These include chills and fever, muscular aches and pains, sore throat, nausea and vomiting. In the United States, influenza causes more than 200,000 hospitalizations and 36,000 deaths every year, according to the National Foundation for Infectious Diseases.
Seasonal Influenza
Seasonal influenza can be distinguished by sudden or rapid onset of high fever, muscle pains, severe malaise, headache, rhinitis and non-productive cough. Other complications can include sinus congestion, nasal discharge, headache, burning or itching of the eyes and increased light sensitivity. According to the Immunization Action Coalition, humans can be infected with two basic influenza virus types, A and B. These viruses differ by their unique genetic material. People are less likely to develop serious clinical illness from the flu if they have been previously exposed to infection with another related strain, either through infection or by immunization with vaccines.
Swine Flu or Swine Influenza
Swine flu is an acute and highly contagious respiratory illness of pigs caused by H1N1 influenza virus sub-type. Some common symptoms are nasal secretions, coughs, decreased appetite and listless behavior. According to the National Library of Medicine, swine flu does not normally infect humans, but people can develop the swine flu infection, especially when they have had close contacts with pigs.
Avian Influenza
Avian influenza is a contagious disease of birds caused by influenza A H5N1 viruses. Wild birds act as hosts to bird flu viruses by carrying them in their intestines. According to the Centers for Disease Control and Prevention, avian influenza viruses do not usually infect humans, but several cases of human infection have been reported from direct or close contact with infected birds--commonly domesticated chickens, ducks or turkeys--or through contact with surfaces, such as dirt and cages, that have been contaminated with the virus.
