How many types of Flu viruses are there?

Dr Rob: There are three main types of flu virus: influenza A, B and C. Influenza A tends to cause the most severe illness in humans and is typically associated with epidemics. Wild birds are the natural host for influenza A but occasionally the virus can spread to domestic animals, which are often kept in close quarters and in low hygiene conditions. This makes it easier for humans to catch the virus, sometimes leading to flu outbreaks and new strains of the virus.