东方蜜蜂微孢子虫对密林熊蜂的致病机理

Study on the pathogenic mechanism of Bombus patagiatus infected by Nosema ceranae

【研究目的】东方蜜蜂微孢子虫(Nosema ceranae)是一种细胞内专性寄生的微孢子虫,广泛寄生于东方蜜蜂(Apis cerana)和西方蜜蜂(Apis mellifera),不仅是危害蜜蜂的主要病原物之一,而且近年来国内外报道发现N.ceranae也感染重要经济昆虫-熊蜂(Bombus Latreille);【方法】采用传统生物学和电镜超微结构观察结合qPCR定量分析对N.ceranae在密林熊蜂上的致病机理进行了探讨;【结果】感染初期工蜂除取食减少和行动迟缓外无明显外观染病特征,感染后期工蜂萎靡,衰弱,飞翔无力。解剖后镜检发现中肠仅存少量孢子,但充满大量的细菌;熊蜂肠道组织切片发现N.ceranae主要经肠绒毛侵染中肠上皮细胞,核膨大并变形、线粒体体积变小甚至解体,内质网紊乱,但孢子只侵染寄主细胞质而不侵入细胞核,最终因线粒体解体,细胞破裂而导致死亡;qPCR定量分析得出在接种的3~4 d中肠和脂肪体中N.ceranae的感染量达到最高值,其他组织则基本未检测到;【结论】根据研究并结合前人工作,认为N.ceranae侵染熊蜂的病理过程是从中肠细胞的病理变化开始的,最后导致寄主细胞的碎裂、死亡,这一过程逐渐扩大至寄主的整个组织、器官,以致其功能丧失,严重的会导致熊蜂死亡。

【OBJECTIVE】Nosema ceranae(N. ceranae) are obligatory intracellular parasite that are commonly found in Apis cerana and Apis mellifera. N. ceranae are not only one of major pathogens in honey bees and recent studies also showed they were found in bumblebee(Bombus Latreille);【METHOD】Here we will explore the pathogenesis of N.ceranae in Bombus patagiatus using biological and ultra structure observation, and quantitative real-time PCR(qPCR)【RESULTS】In the initial infection, infected bees do not exhibit obvious external disease signs except that they eat less and move slowly; in the late period, infected bees showed dispirited, weak, and unable to fly. Through the observation of light microscope, few N. ceranae but a lot of bacteria were found in the midgut of bees. From the electron microscopy, N. ceranae mainly infect midgut of epithelial cells through intestinal villus; nuclear enlarges and are out of shape, mitochondria become smaller even disintegrating and endoplasmic reticulum become disorders. However, the spores only infect the cytoplasm of the host instead of invading the nuclear. At last, the disintegration of the mitochondria and the repture of the cell lead to the death. Quantitative analysis on RT-PCR shows that N. ceranae have reached the highest level in the midgut and fat body after being infected and other organizations are barely detected;【CONCLUSION】There isn't a common conclusion on the pathogenic mechanism of N. ceranae. According to our study and previous work, we have reached a primary conclusion that the pathological process infected by N. ceranae is started with the pathological changes of intestinal cells, which lead to the final death and fragmentation of the host cells. This process gradually expanded to the entire host tissues and organs, resulting in the loss of its function even its death.