Most outbreaks are caused by LPAI viruses. The LPAI signs vary greatly and depend on many factors, including the age and species infected, the virulence of the virus, concurrent infections, and husbandry. In most outbreaks, signs are predominantly those of a respiratory disease with coughing, sneezing, rales, lacrimation, sinusitis, and depression. In egg layers decreased egg production and quality are seen.
In young growing turkeys the disease may be subclinical or severe, particularly where secondary infection with live pasteurella vaccine, E. coli, or bordetella occurs. Outbreaks in egg laying turkeys often reduce production markedly and frequently are associated with abnormal eggshell pigmentation and quality.
Morbidity and mortality are highly variable, depending upon the same factors that determine clinical signs noted above.
HPAI is a severe form of influenza usually seen in chickens. Viruses of high pathogenicity may cause fatal infections preceded by few signs. Onset is sudden, the course is short, affected birds are quite ill, and mortality may approach 100%. Signs may relate to the respiratory, enteric, or nervous systems. There may be diarrhea, edema of the head and face, or nervous disorders.
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