In humans, influenza viruses are primarily transmitted through respiratory droplets produced from coughing and sneezing. IDV can infect humans but is not known to cause illness. IAV and IBV circulate in humans and cause seasonal epidemics, and ICV causes a mild infection, primarily in children. Influenza B virus (IBV) and Influenza C virus (ICV) primarily infect humans, and Influenza D virus (IDV) is found in cattle and pigs. Aquatic birds are the primary source of Influenza A virus (IAV), which is also widespread in various mammals, including humans and pigs. There are four types of influenza virus, termed influenza viruses A, B, C, and D. Other complications of infection include acute respiratory distress syndrome, meningitis, encephalitis, and worsening of pre-existing health problems such as asthma and cardiovascular disease. Influenza may progress to pneumonia, which can be caused by the virus or by a subsequent bacterial infection. Diarrhea and vomiting can occur, particularly in children. These symptoms typically begin 1–2 days and less typically 3-4 days after exposure to the virus and last for about 2–8 days. Symptoms range from mild to severe and often include fever, runny nose, sore throat, muscle pain, headache, coughing, and fatigue. Influenza, commonly known as " the flu", is an infectious disease caused by influenza viruses.
Influenza virus, magnified approximately 100,000 timesįever, runny nose, sore throat, muscle pain, headache, coughing, fatigue