The nature of a virus allows it to mutate without warning. It works rather like a safe-breaker, trying to crack the code that each body uses to create new cells. It can replicate with dazzling speed once it has deciphered any one individual’s genetic code. The avian influenza virus concentrates on the lungs of its host, and quickly spreads to all parts of the respiratory system. Saliva, sputum, nasal discharge and even tears may be rich in pathogen counts, and spread infection amongst other birds in a flock or a pen. A virus is opportunistic and will not hesitate to try and colonize other life forms in the vicinity. Most humans and animals have sophisticated defense mechanisms that counter threat from any virus. A virus has the ability to live stealthily in a body with powerful defenses and wait for a chance to cross over to another that may be weakened by poor diet and other diseases.
Ease of infection transfer, the ability of individuals to harbor a virus without apparent symptoms and speed of replication are the three primary factors that lead to a sudden and explosive outbreak in a community. Poor hygiene and living habits exacerbate the problem, and make containment in an emergency very difficult. Quarantine is not practical on a large scale. Asian authorities have resorted to mass slaughter of suspect birds and other animals until now, but the prospects of large numbers of human carriers and victims are disturbing for people everywhere. Aircraft and the global economy are legacies of our times that enable and cause large-scale and continuous transfer of people between areas infected with bird flu virus, and other parts of the world. People arriving at ports of entry and showing signs of fever and severe respiratory distress can be screened and isolated, but there could be plane loads of carriers who appear healthy, and who arrive ever hour of the day, and spread the virus. Most wild birds that use North America for transit during autumn and spring live in the Arctic and South America, but species from the heart of Asia are also found amongst them. Bird migration is a natural wonder deserving the most assiduous conservation, but it is a threat and potential source of infection where their reserves and haunts are near human dwellings, poultries, dairies and hog farms and ranches.