Comparison of pathogenicity to Mycoplasma synoviae with different infection routs

Abstract:

[Background] The infection rate of Mycoplasma synoviae (MS) in chicken flocks has been increasing in China since 2010, and MS has been widely present in different flocks, including laying hens and/or breeders, white feather broilers and local breeds. The positive rate of MS antibody has exceeded 40%, which has seriously harmed Chinese chicken industry and caused serious economic losses. [Objective] The pathogenicity of MS to 56-day-old specific pathogen free (SPF) chickens with different infection routes was simultaneously compared. [Methods] The MS virulent FZ strain was used to infect 56-day-old SPF chickens by eye dropping, footpad injection, chest subcutaneous injection, single tracheal injection, and three consecutive tracheal injections. The clinical symptoms and anatomical pathological changes were observed from infection chickens, and MS antibody, re-isolation of pathogens from the trachea, and histopathological was determined at post-infection. [Results] The chicken infected MS FZ strain with different routes had different clinical symptoms and different morbidity. Footpad injection and chest subcutaneous injection could cause 100% of chickens exhibiting footpad swelling or chest cyst, while a single or three consecutive tracheal injection could cause 33%−50% of chickens exhibiting severe air sacculitis, the eye dropping infection had hardly caused clinical pathological changes; The footpad swelling showed proliferation of granulation tissue and a large amount of yellow cheese-like mass, and some blood-red liquid and yellow cheese-like mass were found in the chest cyst; Histopathological results showed that three consecutive tracheal injection were more likely to cause damage to the trachea, manifested mild inflammatory cell infiltration in the lamina propria/submucosa of the trachea, footpad swelling and chest cyst tissue had a lot of fibers tissue and blood vessel hyperplasia, accompanied by a large number of inflammatory cell infiltration. It was found that MS re-isolation from tracheal of birds challenged by eye dropping and tracheal injection could reach to 100%, and the MS were also isolated from the trachea by chest subcutaneous or footpad injection. MS antibody was easier to be detected from chickens challenged by footpads. [Conclusion] The pathogenicity of MS to SPF chickens with different infection routes was systematically compared, then the typical pathological lesions or virulence evaluation methods were presented after MS artificial infection, and a model of MS artificial infection to 56-day-old SPF chickens was successfully established. It is found that MS re-isolation from trachea was main indication for eye dropping and tracheal injection, and air sacculitis was auxiliary. In addition, footpad swelling or chest cyst was cardinal symptom to footpad and chest subcutaneous injection, respectively.