滑液囊支原体不同感染途径的致病力比较

Comparison of pathogenicity to Mycoplasma synoviae with different infection routs

摘要:

[背景] 自2010年以来，我国鸡群中滑液囊支原体（Mycoplasma synoviae，MS）的感染率不断增高，目前MS已广泛存在于我国不同的鸡群中，包括蛋鸡、种鸡、白羽肉鸡和地方品种鸡等，其血清阳性率已超过40%，严重危害我国养鸡业，并造成了严重的经济损失。[目的] 系统比较MS以不同感染途径对56日龄无特定病原（Specific Pathogen Free，SPF）鸡的致病力。[方法] 采用MS强毒FZ株以点眼、爪垫注射、胸部皮下注射、单次气管注射、连续3次气管注射等不同途径感染56日龄SPF鸡，观察感染后临床症状和解剖病理变化，检测感染后的MS抗体，并且对气管组织进行病原再分离和组织病理学观察。[结果] MS的FZ株以不同途径感染SPF鸡后临床表现和发病率差异较大，爪垫注射和胸部皮下注射可导致100%的鸡发生爪垫肿大或胸部囊肿，而单次或连续3次气管注射可引起33%-50%的鸡发生严重气囊炎，点眼感染途径基本不能引起临床病理变化；爪垫肿大主要为肉芽组织增生和出现大量的黄色干酪样块状物质，胸部囊肿在囊肿部位有大量的血红色样液体和黄色干酪样块状物质；组织病理学结果显示连续3次气管注射方式感染更易对气管造成损伤，表现为气管黏膜固有层/黏膜下层发生轻微至轻度灶性炎细胞浸润，而爪垫肿大和胸部囊肿组织有大量的纤维组织和血管增生，同时伴有大量炎性细胞浸润；点眼和气管注射途径的气管MS病原再分离率可达100%，而胸部皮下注射或脚垫注射也可从气管中分离到MS病原；爪垫注射途径更易引起MS抗体转阳。[结论] 系统比较了MS以不同感染途径对56日龄SPF鸡的致病性，并筛选出了相应的评价指征，成功建立了MS人工感染8周龄SPF鸡的发病模型，其中点眼感染途径和气管注射途径以气管病原再分离作为主要指征，辅以气囊炎进行评价，而胸部皮下注射和爪垫注射途径分别以胸部囊肿和爪垫肿胀作为主要病理指征进行评价。

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.