(CNN) -- Here's a look at what you need to know about avian flu.
Avian influenza, also called avian flu or bird flu, is an illness that usually affects only birds. A new strain jumped to baby seals in 2011. While there have been deaths from certain strains of avian flu, person-to-person infections are rare.
The official name for the most commonly seen and most deadly form of the virus is called "Influenza A (H5N1)," or the "H5N1 virus."
In March 2013, a strain of bird flu previously not seen in humans - H7N9 - was detected in China.
People have killed hundreds of millions of birds around the world in an attempt to control the spread of the avian flu that has now reached three continents: Asia, Europe and Africa.
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.
Diagnosis/Treatment: 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 and feces.
Symptoms of avian flu include fever, cough, sore throat, and sometimes severe respiratory diseases and pneumonia.
The FDA has approved four drugs to combat influenza - amantadine, rimantadine, oseltamivir (brand name: Tamiflu), and zanamivir (brand name: Relenza).
H5N1 is resistant to two of the FDA approved drugs used to combat influenza - amantadine and rimantadine.
The mortality rate is nearly 60 percent for infected humans.
Confirmed human cases of Avian Flu (H5N1 strain) Since December 26, 2003: Azerbaijan - 8 cases, 5 deaths Bangladesh - 7 cases, 1 death Cambodia - 47 cases, 33 deaths Canada - 1 case, 1 death China - 45 cases, 30 deaths Djibouti - 1 cases, 0 deaths Egypt - 173 cases, 63 deaths Indonesia - 195 cases, 163 deaths Iraq - 3 cases, 2 deaths Laos - 2 cases, 2 deaths Myanmar - 1 case, 0 deaths Nigeria - 1 case, 1 death Pakistan - 3 cases, 1 death Thailand - 25 cases, 17 deaths Turkey - 12 cases, 4 deaths Vietnam - 125 cases, 62 deaths Total - 649 cases, 385 deaths
Timeline: Early 1900s -The avian flu is first identified in Italy.
1961 - The H5N1 strain is first 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.
May 1997 - 18 people are infected by the H5N1 strain in Hong Kong, and six die. These are the first documented cases of human infection. Hong Kong destroys its entire poultry population (1.5 million birds) in three days.
1999 - Two children in Hong Kong are infected by the H9N2 strain.
February 2003 - 84 people in the Netherlands are affected by the H7N7 strain of the virus, and one dies.
January 25, 2004 - China bans imports of Thai chicken products. Nine million chickens are slaughtered in Thailand in an effort to stop the spread of the disease.
February 2, 2004 - The World Health Organization is investigating possible human-to-human transmission among a family in Vietnam. Three family members have died of the illness, and one has recovered. One member had no contact with infected poultry while the others did.
February 7, 2004 - 12,000 chickens are slaughtered in Kent County, Delaware, after they are found to be infected with a H7 virus.
February 23, 2004 - A flock of 6,600 broiler chickens in Gonzalez County, Texas, is destroyed after being diagnosed with an "extremely infectious and fatal" form of bird flu, the H5N2 strain.
February 5, 2005 - The Cambodian Health Ministry and WHO confirm the first human death in Cambodia (the H1N1 strain, on January 30).
October 7, 2005 - The avian flu reaches Europe. Romanian officials quarantine a village of about 30 people after three dead ducks there test positive for bird flu.
November 12, 2005 - A one-year-old boy in Thailand tests positive for the lethal H5N1 strain of avian influenza.
November 16, 2005 - WHO confirms two human cases of bird flu in China, including a female poultry worker who died from the H5N1 strain.
November 17, 2005 - Two deaths are confirmed in Indonesia from the H5N1 strain of avian influenza.
January 1, 2006 - A Turkish teenager dies of the H5N1 strain of avian influenza in Istanbul, and later that week, two of his sisters follow.
January 17, 2006 - A 15-year-old girl from Northern Iraq dies after contracting bird flu.
February 20, 2006 - The French Health Ministry confirms that a duck in central France had the H5N1 strain of avian flu.
February 20, 2006 - Vietnam becomes the first country to successfully contain the disease. A country is considered disease-free when no new cases are reported in 21 days.
March 12, 2006 - Officials in Cameroon confirm cases of the H5N1 strain. The avian flu has now reached four African countries.
March 13, 2006 - The avian flu is confirmed by officials in Myanmar (Burma).
May 11, 2006 - Djibouti announces its first cases of H5N1 - several birds and one human.
December 20, 2011 - The U.S. Department of Health and Human Services releases a statement saying that the government is urging scientific journals to omit details from research they intend to publish on the transfer of H5N1 among mammals. There is concern that the information could be misused by terrorists.
July 31, 2012 - Scientists announce that H3N8, a new strain of avian flu, caused the death of more than 160 baby seals in New England in 2011.
March 2013 - The official Chinese news agency Xinhua reports that two people in China have died after falling ill with a strain of bird flu, H7N9, not detected before in humans.
November 6, 2013 - There have been 139 confirmed cases of H7N9 including 45 confirmed deaths.
December 2, 2013 - A woman in Hong Kong is hospitalized with H7N9 after coming in contact with live poultry in the mainland China city of Shenshen.
December 6, 2013 - A 73-year-old woman infected with H10N8 dies in China, the first human fatality from this strain.
January 8, 2014 - Canadian health officials confirm that a resident from Alberta has died from H5N1 avian flu, the first case of the virus in North America. It is also the first case of H5N1 infection ever imported by a traveler into a country where the virus is not present in poultry.
January 2014 - Over the course of the month WHO is notified by the National Health and Family Planning Commission of China (NHFPC) of 116 confirmed cases of H7N9, including seven deaths.