The influenza virus is a highly contagious virus that infects the epithelial cells of the respiratory tracts, notes Microbiology and Immunology Online, a website provided by the University of South Carolina School of Medicine. The influenza virus causes symptoms such as a high fever, body aches, sore throat, fatigue and a non-productive cough. The three main types of influenza virus are influenza A, influenza B and influenza C.
Influenza A
According to the Merck Manuals, the influenza A virus is the most prevalent type of flu virus, causing about 95 percent of all influenza cases. Influenza A is separated into 16 different subtypes, based on viral surface proteins, hemagglutinin and neuraminidase. Influenza A is responsible for winter epidemics of the flu causing common flu symptoms, including a high fever, headaches, a runny nose, cold chills and, in severe cases, pneumonia and death, notes the Ohio State University Medical Center.
Influenza B
According to MayoClinic.com, influenza B virus causes smaller, localized outbreaks with milder symptoms. Influenza B virus cannot cause pandemics, but it can cause an epidemic, meaning it can affect several members of a community at the same time. Influenza B virus is are not categorized into subtypes based on surface proteins like influenza A; however, there are different strains of the influenza B virus. Symptoms of influenza B virus include a headache, fever, sore throat and pain.
Influenza C
According to the Center for Disease Control and Prevention, influenza C virus is the least pathogenic of all three types, causing mild respiratory illness and symptoms resembling the common cold. Influenza C virus is not linked to pandemic or epidemic outbreaks; thus, their proteins are not used in the production of yearly vaccines. Influenza C viruses are not classified according to subtypes because they are fairly stable and thus are not prone to antigenic drift or antigenic shift.
