Development of aMycoplasma gallisepticuminfection model in turkeys

Abstract

Mycoplasma gallisepticum causes chronic respiratory disease in chickens and is also highly pathogenic in turkeys. Several live attenuated M. gallisepticum vaccines are available for prevention of disease in chickens but they are considered to be either not safe or not efficacious in turkeys. The studies presented here aimed to develop a suitable infection model in turkeys, a prerequisite for development of a vaccine against M. gallisepticum for turkeys. Two wild-type Australian M. gallisepticum strains, Ap3AS and 100809/31, were used and their capacity to induce lesions was evaluated in 5-week-old to 6-week-old turkeys exposed to aerosols of these strains. Gross air sac lesion scores in the group exposed to Ap3AS were significantly greater than those in the group exposed to 100809/31 (P < 0.05). Histological tracheal lesion scores and tracheal mucosal thicknesses were significantly greater in birds exposed to either strain than in the unexposed birds (P < 0.05), but no significant differences were observed between the two infected groups. In a subsequent experiment, 6-week-old to 7-week-old turkeys were exposed to different doses of M. gallisepticum Ap3AS. Serology and M. gallisepticum re-isolation performed 14 days after infection showed that all birds exposed to Ap3AS were positive by rapid serum agglutination and by culture. Gross air sac lesion scores in the groups exposed to the highest dose, 8.17 × 10 8 colour-changing units Ap3AS/ml, as well as a 10-fold lower dose were significantly more severe than in the uninfected control group. Lesion scores and tracheal mucosal thicknesses were significantly greater in birds exposed to Ap3AS than in the unexposed birds (P < 0.05). However, no significant differences were seen in tracheal mucosal thicknesses or lesion scores between the groups exposed to the different doses of Ap3AS. This study has established a reliable challenge model for M. gallisepticum infection in turkeys, which will be useful for evaluation of potential M. gallisepticum vaccine candidates for this species.

Immune responses to vaccination and infection with Mycoplasma gallisepticum in turkeys

“…The strain comparison and Ap3AS dose-response studies have been described previously (Wijesurendra et al, 2015). For the strain comparison study, a total of 30 five-to-six-week-old commercial turkeys (Hybrid Bronze) were obtained from a mycoplasma-free commercial turkey breeder farm, randomly allocated into three groups of 10 birds each and housed in three positive-pressure fibreglass isolators.…”

“…The methods used for experimental infection in the strain comparison and Ap3AS dose-response studies have been described previously (Wijesurendra et al, 2015). Briefly, in the strain comparison study, the turkeys in the negative control group were exposed to an aerosol of MB (Whithear et al, 1996).…”

“…Typically infection of the infraorbital sinuses, as well as the lower respiratory tract, is seen in turkeys, and thus the disease is classically described as infectious sinusitis (Jerstad et al, 1959). A number of studies have examined the lesions induced by this pathogen in the respiratory tract of chickens or turkeys, and have described diffuse infiltration of the tracheal mucosa with mononuclear cells and varying numbers of small to large focal aggregations of lymphocytes, resulting in moderate to extensive thickening of the tracheal mucosa accompanied by epithelial degeneration and metaplasia with or without luminal exudation (Nunoya et al, 1987;Papazisi et al, 2002;Kleven et al, 2004;Sanei et al, 2007;Shil et al, 2011;Wijesurendra et al, 2015). Airsacculitis is also a prominent gross feature of the disease and the gross appearance of airsacculitis has been used extensively to assess the severity of disease caused by infection with M. gallisepticum in chickens and turkeys (Lin & Kleven, 1982;Ferguson et al, 2004;Kleven et al, 2004;Sanei et al, 2007).…”

“…Airsacculitis is also a prominent gross feature of the disease and the gross appearance of airsacculitis has been used extensively to assess the severity of disease caused by infection with M. gallisepticum in chickens and turkeys (Lin & Kleven, 1982;Ferguson et al, 2004;Kleven et al, 2004;Sanei et al, 2007). Recently the histopathological changes in the infraorbital sinuses and the air sacs of turkeys infected with an aerosol of a culture of M. gallisepticum have been characterized and these studies revealed the presence of focal lymphocytic aggregations within the sinus mucosa and air sacs (Wijesurendra et al, 2015).…”

“…In a previous study, we examined the lesions induced in turkeys after infection with two different strains of M. gallisepticum, and compared the lesions induced by different doses of the more virulent of these strains, Ap3AS (Wijesurendra et al, 2015). The main aim of this study was to develop methods for investigating in greater depth the lymphocytic responses and the humoral immune responses against M. gallisepticum in these previous trials, and also to apply these methods to the examination of the responses seen after vaccination with the attenuated M. gallisepticum GapA + ts-11 strain and subsequent challenge with virulent M. gallisepticum.…”