Abstract
Background:
Low pathogenic H9N2 avian influenza (LPAI H9N2) caused by the influenza A virus which belongs to the family Orthomyxoviridae. It caused mild respiratory symptoms and a drop in egg production in poultry. Outbreaks of AI-H9N2 occurred in poultry since the 1990s in many countries in USA, Europe, and Asia. Recently, outbreaks of H9N2 in commercial chicken were recorded in Morocco, Tunisia, Libya, and Egypt. Furthermore, numerous studies demonstrated that co-infection with AI H9N2 and other pathogens results in severe respiratory illness with high mortality in broiler chickens. Outbreaks of respiratory disease with variations in mortality rate were recorded in broiler flocks growing on southwest of Tripoli in Libya.
Aim:
The present study was conducted to explain the variation of mortality rate on broiler flocks growing on the southwest area of Tripoli by detection of AI H9N2 antibodies and antigens.
Methods:
A total of 453 sera samples, 60 tracheal swabs, and 60 cloacal swabs were collected from unvaccinated broiler flocks against avian influenza. Specific avian influenza type A antibodies were detected by using the Elisa test, and specific AI-H9N2 antibodies were detected by using the HI test, whereas, specific AI-H9N2 antigens were detected in tracheal and cloacal swabs by using One-Step RT-PCR (M gene) technique.
Results:
Respiratory disease with significant variations in mortality rate were recorded in broiler flocks growing on southwest of Tripoli in Libya; the broiler mortality rate was 62.2% in Twisha region farms compared to 11% in other farms. Avian influenza type A antibodies were detected at a high level in Twisha region farms, and other farms (95.2%, and 76.7%, respectively). The positive samples for AI type A were tested for AI H9N2 using HI test. The percentage of AI-H9N2 antibodies was quite similar in all studied flocks suffering with high and low mortality rates (53.4%, and 46.8%, respectively). Additionally, AI-H9N2 antigens were detected only in tracheal swabs in Twisha farm 3, Al-Maamoura, and Ber Al-Tota districts.
Conclusion:
This study confirmed the endemic of AI- H9N2 in broiler flocks on southwest of Tripoli-Libya. Also, it clarified that AI-H9N2 was no responsibility on the high mortality rate by itself in broiler flocks. Moreover, this study supported the presence of other subtypes of avian influenza in studied area.

Key words: H9N2, Broiler, Variation, Mortality rate