脊尾白虾“僵尸病”的初探

为确定2018年冬季以来江苏省沿海地区养殖脊尾白虾患“僵尸病”的病原及流行病学特点,实验采用LB培养基和PDA培养基从病虾血淋巴中分离得到直径为1~3 mm、边缘整齐、米黄色隆起菌落;人工回感实验结果显示,回感后的脊尾白虾表现出与自然患病脊尾白虾相同的症状,并在回感脊尾白虾体内也分离出了相同的菌株,符合科赫氏法则。对该菌株进行形态观察结合18S rRNA序列对比及系统发育分析,发现分离菌株MQ2101具有酵母的典型形态,且与二尖梅奇酵母相似度达99.82%,结果表明菌株MQ2101为二尖梅奇酵母。致病性结果初步分析显示,MQ2101对脊尾白虾的半致死浓度 (LD₅₀)为1.39×10⁷ CFU/尾。病理学观察发现,患病脊尾白虾鳃、肌肉和肝胰腺均发生不同程度的病变,其中肝胰腺病变最为严重,肝小管呈现空泡化,管腔体积变大;在鳃和肝胰腺组织中均存在大量定殖的菌体。流行病学调查结果显示,每年2—5月发病迅速,发病率为5%~30%,死亡率为3%~10%。本研究确定了二尖梅奇酵母为江苏沿海地区脊尾白虾“僵尸病”的病原,其对脊尾白虾具有较强致病性,主要侵染组织为肝胰腺和鳃。以上研究结果为脊尾白虾“僵尸病”的防控提供了相关科学依据。

A preliminary study on the "zombie disease" of Exopalaemon carinicauda

In recent years, an epidemic disease called "zombie disease" by local farmers has appeared in the ridgetail white prawn (Exopalaemon carinicauda) breeding area of Jiangsu Province. The main symptoms of the disease include reddish body color, whitish muscles and milky liquid under the carapace. The diseased prawns usually show slow movement and reduce food intake and died quickly after leaving the water. In order to determine the pathogen and epidemiological characteristics of the "zombie disease"in farmed E. carinicauda in the coastal area of Jiangsu Province since the winter of 2018, LB medium and PDA medium were used to isolate colonies with a diameter of 1-3 mm, neat edges, and beige-colored elevation from the hemolymph of diseased shrimp, which was named MQ2101. This strain was identified as Metschnikowia bicuspidata by means of morphologic structure observation, 18S rRNA gene analysis and constructing phylogenetic tree. Furthermore, the pathogenicity of the strain MQ2101 was confirmed by the infection experiment in healthy E. carinicauda. The results showed the infected E. carinicauda died with the similar symptoms to naturally morbid E. carinicauda and the same bacterium could be isolated from the infected E. carinicauda. The LD₅₀ of strain MQ2101 to E. carinicauda was 1.39×10⁷ CFU/ind. Histopathology and transmission electron microscopic observation showed that there were different degrees of lesions in gills, muscle and hepatopancreas, of which hepatopancreas lesions were the most serious, with hepatic tubules vacuolated and lumen volume enlarged. Moreover, a large number of colonized bacteria were found in gill and hepatopancreas. Epidemiological findings showed the disease frequently occured in the cool season (February to May), mainly erupted in prawn and crab mixed ponds, with a incidence rate of 5%-30% and a mortality rate of 3%-10%, the morbidity was increasing year by year. In the present study, M. bicuspidata was identified as the pathogen of "zombie disease" in E. carinicauda in coastal areas of Jiangsu Province, which is highly pathogenic to E. carinicauda and mainly infects the hepatopancreas and gills. It was the first time that revealed M. bicuspidata infection in E. carinicauda and the pathological changes caused by the infection. The above findings provide a scientific basis for the prevention and control of "zombie disease" in the culture of prawns.