(CNN)Here's a look at avian flu.
Avian influenza, also called avian flu or bird flu, is an illness that usually affects only birds.
There are many different strains of avian flu: 16 H subtypes and 9 N subtypes. Only those labeled H5, H7 and H10 have caused deaths in humans.
The most commonly seen and most deadly form of the virus is called "Influenza A (H5N1)," or the "H5N1 virus."
Most cases of human bird flu infections are due to contact with infected poultry or surfaces that are contaminated with infected bird excretions: saliva, nasal secretions or feces.
Symptoms of avian flu include fever, cough, sore throat and sometimes severe respiratory diseases and pneumonia.
The CDC recommends oral oseltamivir (brand name: Tamiflu), inhaled zanamivir (brand name: Relenza) and intravenous permavir (brand name: Rapivab) for the treatment of human illness associated with avian flu.
The mortality rate is close to 60% for infected humans.
Early 1900s -The avian flu is first identified in Italy.
1961 - The H5N1 strain is isolated in birds in South Africa.
December 1983 - Chickens in Pennsylvania and Virginia are exposed to the avian flu and more than five million birds are killed to stop the disease from spreading.
1997 - Eighteen people are infected by the H5N1 strain in Hong Kong, six die. These are the first documented cases of human infection. Hong Kong destroys its entire poultry population, 1.5 million birds.
1999 - Two children in Hong Kong are infected by the H9N2 strain.
February 2003 - Eighty-four people in the Netherlands are affected by the H7N7 strain of the virus, one dies.