Original Scientific Article
Evaluation of the effect of co-infection by Mycoplasma gallisepticum (MG) and E. coli O78 on the pathogenicity of avian influenza (H9N2) in the SPF chicks
Nahed Yehia * ,
Dalia M. Omar ,
Nermin M. Monir ,
Dalia Said ,
Ahmed S. Helmy ,
Fatma Amer ,
Kawkab A. Ahmed ,
Nermeen A. Marden ,
Mona A.A. AbdelRahman

Mac Vet Rev 2026; 49 (1): i - x

10.2478/macvetrev-2025-0033

Received: 19 April 2025

Received in revised form: 17 August 2025

Accepted: 18 August 2025

Available Online First: 29 December 2025

Published on: 15 March 2026

Correspondence: Nahed Yehia, nermeen.marden@gmail.com
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Abstract

Co-infection significantly influences disease severity. This study investigated the impact of co-infections with Escherichia coli (E. coli) O78 and Mycoplasma gallisepticum (MG), alone and in combination, on the pathogenicity of low- pathogenic avian influenza H9N2 in specific pathogen-free (SPF) chickens. Seventy one-day-old SPF chicks were divided into seven equal groups (G), where G1 is the control one, G2-G4 were infected with H9, MG, and E. coli, respectively, and G5-G7 were co-infected with MG-H9, E. coli-H9, and MG-E. coli-H9, respectively. The study monitored clinical symptoms, mortality rates, H9N2 hemagglutination inhibition antibody titers, viral shedding through qRT-PCR, and histopathological changes in experimentally infected groups. The findings revealed that the group co-infected with all three pathogens had the highest significant mortality rate (70%), with severe clinical symptoms, moderate histopathological changes in the trachea and lungs, along with the highest significant hemagglutination inhibition antibody titers (6.40±0.52, 7.30±0.67 log2) at 7 and 14 days post-infection, respectively. This group also demonstrated the highest viral shedding (3.53±0.01, 4.53±0.09, 3.60±0.05 log10 EID50/ml) at 2, 4, and 7 days post-infection, respectively, with significant differences, and the longest duration of H9N2 shedding (10 days post-infection). In summary, co-infection enhanced the pathogenicity of H9N2; furthermore, co-infection with E. coli O78 increased H9N2 pathogenicity more than co-infection with M. gallisepticum, and the combination of both bacteria resulted in the highest pathogenicity of the H9N2 virus.

Keywords: H9N2 co-infection, Mycoplasma gallisepticum, E. coli O78, SPF chicks

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Copyright

©2025 Yehia N. This is an open-access article published under the terms of the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Conflict of Interest Statement

The authors declared that they have no financial or non-financial conflict of interest regarding authorship and publication of this article.

Citation Information

Macedonian Veterinary Review. Volume 49, Issue 1, Pages i-x, e-ISSN 1857-7415, p-ISSN 1409-7621, DOI:  https://doi.org/10.2478/macvetrev-2025-0033

The all content of the Macedonian Veterinary Review, except where otherwise noted, is licensed under a Creative Commons Attribution License.