The flu, also called influenza, is a medical illness characterized by infection of the respiratory tract. Similar to, but typically more severe than, the common cold, influenza symptoms include fever, cough, malaise, fatigue, sore throat, headache, nausea, vomiting and diarrhea. Generally speaking, the flu is caused by a number of viruses, collectively known as influenza viruses. There are three separate influenza viral types, called A, B and C.
Cause of Seasonal Flu
Seasonal flu, or conventional flu, is that flu which occurs each year during the colder months known as flu season. Seasonal flu is caused by infection with the influenza A or B viruses. As described by the Centers for Disease Control and Prevention, or CDC, there are many subtypes of the influenza A & B viruses, and these in turn can mutate or change frequently. Because of this great and ever-changing variety, each year scientists research to predict which viral types and strains are most likely to circulate in the general population causing the flu. Based on these scientific estimates, a novel yearly vaccine is created to combat the seasonal flu.
Cause of Swine Flu
Swine flu is a flu disease caused by a variant of the influenza A virus, commonly referred to as the swine flu virus. The official name of the swine flu virus is H1N1 influenza A virus. The CDC explains that the name "swine flu virus" comes from the fact that in addition to having human genes, H1N1 also has components of a virus that normally circulates in pigs. This novel flu strain was first discovered in April, 2009. Shortly following its discovery, H1N1 influenza was declared a pandemic by the World Health Organization, which at the time documented 30,000 confirmed cases of H1N1 influenza in 74 countries.
Cause of Bird Flu
Bird flu, also called avian influenza, is caused by a collection of avian influenza A viruses. Bird flu is typically an infection in birds, but certain of these viruses have been known to affect humans as well. Perhaps the most well known of these viruses is the H5N1 influenza A virus, which has been responsible for a number of bird flu outbreaks in the human population. In the May 1, 2002 issue of "Clinical Infectious Disease", Dr. Paul Chan describes the well-known outbreak of bird flu virus in Hong Kong in 1997, which resulted in 18 infections and six deaths. Although infection in humans is rare and appears to be limited to those in close contact with diseased poultry, the virus can be highly pathogenic.
References
- Centers for Disease Control and Prevention: Types of Influenza Viruses
- World Health Organization: What is the Pandemic (H1N1) 2009 Virus?
- World Health Organization: World Now at the Start of 2009 Influenza Pandemic
- Centers for Disease Control and Prevention: 2009 H1N1 Flu ("Swine Flu") and You
- Centers for Disease Control and Prevention: Key Facts About Avian Influenza (Bird Flu) and Avian Influenza A (H5N1) Virus
