Avian Influenza is known to affect especially wild and domestic birds as well as pigs but rare cases of human infection are updated. Since 2004 though, more than 200 confirmed cases of the avian virus in humans have been detected and analyzed by the World Health Organization. The infection with the A influenza virus is thought to have been done by direct contact with sick birds or their secretions. Scientists are still searching for the method how low and highly pathogenic viral strains might affect humans.

Health organizations all over the world continuously monitor human cases of avian flu outbreaks although no actual man to man transmission of the disease has been registered. The bird flu virus represents a real danger for humans as it is able to perform mutations by combining with human types of Influenza; this would lead to disastrous epidemics if the disease could spread between humans. Since 1997 all suspicions of avian flu in humans have been closely observed.

The first cases of bird to human transmission occurred in Hong Kong in 1997 resulting in 6 deaths after 18 persons have been infected. About 1.5 million birds have been destroyed to annihilate the infection source. The H5N1 type of influenza showed no direct transmission from human to human.

In 1999 in China two more cases of infection were noted when two children became ill though the real source has not been discovered. Both patients recovered after the infection with the low pathogenic virus H9N2.

In the State of Virginia in 2002 one person showed serological marks of infection, after poultry farm was contaminated with the H7N2.

Another situation of H5N1 infestation occurred in 2003 in Hong Kong when two members of one family became ill and one of them died. They are believed to have contacted the virus during a visit in China but the exact source has not been established. A second family member died of a respiratory condition but no further testing was made.

2003 in Netherlands, several cases of infection appeared in some poultry farms; pigs and humans were also involved in the disease. 89 workers got infected With H7N7 and showed symptoms of fever, muscle aches, conjunctivitis and cough. One person died of respiratory distress syndrome and complications.

In 2003 one child was found to suffer from the low pathogenic H9N2 in Hong Kong but he recovered completely. The same year in New York a patient with respiratory symptoms was detected after tests to suffer from H7N2 and he safely recovered in a few weeks.

In 2004 in Canada the H7N3 virus type infected a few poultry workers in a farm epidemics but all showed easy eye infections. H5N1 occurred in 2004 in Vietnam and Thailand when a possible human to human transmission appeared. Further cases of human infestation with H5N1 occurred in Cambodia, China, Indonesia, Egypt, Iraq and Turkey in 2005 after human contact with sick dead swans. In the same countries several other cases appeared in 2006.