Pathogenicity of Gallibacterium anatis was studied in hens and cockerels in a natural infection model. Specified pathogen free (SPF) chickens were hatched and used in two experiments. In case of females, 30-week-old hens were infected intranasally with G. anatis whereas control birds were left uninfected. Birds were killed at 3, 7, 10, 28 and 38 days post infection (dpi) for necropsy. Laying performance of the two groups was compared until five weeks post infection (wpi). Following infection, egg production declined in the infected group at one wpi and was lowest at 3 wpi (47.2 % vs 86.7 % in control). Furthermore, the bacteria got access to the ovary at 3 dpi persisting until 38 dpi. Pathological lesions (egg peritonitis, pericarditis, degeneration of ovary and oviduct, rupture of follicles) were noticed in infected birds which further correlate with decreased egg production. Recovery of G. anatis from egg yolk at 10 dpi indicated the potential vertical transmission of the pathogen.
In the second trial, 35-weeks-old cockerels were infected and necropsy was done as in hens. Also semen quality was assessed in infected and control birds. In consequence, the pathogen invaded testis and epididymis at 7 dpi (until 38 dpi) causing histopathological lesions in epididymis. Additionally, the pathogen was reisolated from semen collected at 18-29 dpi. Upon semen analysis, density (1.00±0.95 billions of sperm/ml of semen at 4 wpi), motility (total 72.28±19.98% and progressive 50.55±23.30% at 1 wpi) and viability (71.88±7.04% at 1 wpi) of spermatozoa were significantly reduced than in control birds. Long term persistency of G. anatis in gonadal organs and deterioration of semen quality might further affect on breeding performance of cockerels.
In conclusion, for the first time clinical symptoms and lesions with G. anatis have been reproduced in adult chickens in controlled experimental set up following intranasal infection.