North American authorities recognize two "pathotypes" of bird flu or Avian Influenza (AI): low or mildly pathogenic(LPAI or MPAI) and highly pathogenic (HPAI). A strain is not categorized as highly pathogenic until it kills 75% of birds infected.
HPAI strains typically are detected as a result of poultry deaths... The designation of high pathogenicity generally is based on what happens to healthy chickens when they're exposed to the virus. If the virus kills at least 6 out of 8 chickens in a challenge trial, it is deemed highly pathogenic.
Mild bird flus are known to mutate into highly pathogenic forms. However, only an HPAI diagnosis triggers government intervention in North America. US scientists have recommended eradication programs for mild forms of H5 and H7 bird flu, but the experts have been ignored and their recommendations dismissed for "economic" reasons.
History has proven that prevention of HPAI is based on successful control of H5 or H7 LPAI.
Meat and eggs from poultry with "low path" bird flu are sold legally as food in the USA, Canada and other countries. The evidence suggests that humans infected with "low path" bird flu end up with chronic disease - and serve as "mixing vessels" to create more virulent and deadly mutations.
...H5N1 bird flu pathology is found in connective tissue of the blood vessels, lungs, gut, heart, brain and other organs, and is known to infect "apidose" or fat cells. The symptoms generally depend on the severity of the infection, its length, and the locations of infection in the body.
With LPAI outbreaks in poultry there is mild to moderate inflammation of the trachea, sinuses, air sacs and conjunctiva. In laying birds there often is ovarian atresia and involution of the oviduct. Various degrees of congestive, hemorrhagic, transudative, and necrotic lesions have been described.
Chronic infection with low path bird flu is not recognized in humans. However, the chronic disease pandemic sweeping the globe has the same pathology as H5N1 bird flu: the proliferation of abnormal myofibroblasts in connective tissue and smooth muscle cells throughout the body with aberrant wound healing and "tissue remodelling."
And the human chronic disease pandemic just keeps getting worse...
ATSNN. Bird Flu and Beyond: Chronic Disease to Kill 400 Million
ATSNN: Bird Flu, and the "Neglected Epidemic"