Clinical symptoms of HPAI can vary but would typically follow a course of a sudden onset of illness accompanied by loss of appetite soon followed by a sudden rise in body temperature, lethargy, facial oedema with swollen and cyanotic combs and wattles and ending in death. Within a few days mortality will exceed 90%.

Newcastle disease is caused by entirely different viral pathogens. While the bird flu virus is orthomyxovirus, the Newcastle disease virus is paramyxovirus. Typically the first clinical signs to be seen with the Newcastle disease virus will have taken longer to appear and will include respiratory tract symptoms, diarrhea, lack of appetite and lethargy followed by neurotic symptoms in the later stages. With current rearing practices, chicken flocks that have been vaccinated with the Newcastle disease vaccine are unlikely to be susceptible to a typical Newcastle disease epidemic. The affected chicken population generally shows mild respiratory tract and neurotic symptoms and a decline in egg production together with low mortality.

(China.org.cn February 13, 2004)