Standardization of a new model of H9N2/escherichia coli challenge in broilers in Lebanon

Barbour EK, Mastori FA, Abdel Nour AM, Shaib HA, Jaber LS, Yaghi RH, Sabra A, Sleiman FT, Sawaya RK, Niedzwiecki A, Tayeb IT, Kassaify ZG, Rath M, Harakeh S, Barbour KE
Veterinaria Italiana 2009; 45(2): 317 – 322.

Abstract:
Primary infection by low pathogenic avian influenza (LPAI) predisposes poultry for secondary infection by Escherichia coli, leading to significant economic losses. Future research in control of this ailment requires the establishment of a successfully controlled challenge by avian influenza virus (AIV)/E.coli. Six groups of broilers (6 birds/group) were included for the standardization of the controlled challenge by AIV/E.coli.

Birds in groups 1-5 received an intratracheal challenge of 0.5 ml of low haemagglutinating units of H9N2 virus at 20 d of age. At the age of 23 d, birds in group 1 received an intrathoracic (right air sac) E. coli challenge equivalent to 1.6 x 109 colony-forming units (cfu)/0.5 ml/bird, while birds in groups 2-5 received E. coli by the same route and in the following respective decreasing order of viable cells: 1.6 x 106, 1.6 x 105, 1.6 x 104 and 1.6 x 103 cfu. Birds in control group 6 were deprived of H9N2 and E.coli challenge. Results showed significant early mortality in group1 that was challenged with the highest number of E. coli, in comparison to groups 2-6 (p<0.05); however, the average weight at 28d of age was similar in surviving birds of groups 2-6 (p<0.05). The frequencies of four signs at 2 d and at 5 d post E. coli challenge (conjunctivitis, diarrhea, ocular exudates and rales) in the surviving birds of groups 2-5 were more often higher than those observed in control group 6 (p<0.05). These four signs and five gross lesions (abdominal airsacculitis, left thoracic airsacculitis, pericarditis, right thoracic airsacculitis and tracheitis) had a decreasing pattern of frequency, related to a decrease in the E.coli count used in the challenge.

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