东方蜜蜂微孢子虫对密林熊蜂的致病机理

Pathogenic Mechanism of Bombus patagiatus Infected by Nosema ceranae

【目的】明确东方蜜蜂微孢子虫(Nosema ceranae)对密林熊蜂(Bombus patagiatus)的侵染性及致病机理。【方法】采用传统生物学和电镜超微结构观察的方法,结合qPCR定量分析对东方蜜蜂微孢子虫在密林熊蜂上的致病机理进行探讨。【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,但充满大量细菌;熊蜂肠道组织切片发现东方蜜蜂微孢子虫侵染中肠上皮细胞后导致核膨大并变形、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,最终导致线粒体解体,细胞破裂;qPCR定量分析得出接种后3—4 d中肠和脂肪体中微孢子虫的感染量达到最高值,其它组织则基本未检测到。【结论】东方蜜蜂微孢子虫可侵染异源寄主熊蜂,致病机理为微孢子虫引起寄主中肠上皮细胞内溶物发生病变,并导致整个中肠上皮细胞的破裂和凋亡。

[Objective] The objective of this study is to define the infectivity and pathogenic mechanism ofNosema ceranae to Bombus patagiatus. [Method] Traditional biology and ultrastructure under electronic microscope methods were used, and combined with the quantitative real-time PCR （qPCR） to explore the pathogenesis ofN. ceranae to B. patagiatus. [Result] In the initial infection, the infected bees did not exhibit obvious external disease signs except decreased feeding and motor retardation. In the late period, the infected bees exhibited dispirited, weak and unable to fly. Through observation with light microscope, few N. ceranae but a lot of bacteria were found in the midgut of bees. N. ceranae mainly infected midgut of epithelial cells, the nuclear enlarged and out of shape, mitochondria become smaller even disintegrating and endoplasmic reticulum become disorders. However, the spores only infected the cytoplasm of the host instead of invading the nuclear, which lead to the disintegration of the mitochondria and cytoclasis. Quantitative analysis on RT-PCR showed that N. ceranae reached the highest level in the midgut and fat body 3-4 d after being infected and other organizations were barely detected. [Conclusion] N. ceranae can cross-species infect B. patagiatus and the pathological process starts with the pathological changes of intestinal cells, which lead to the cytoclasis and apoptosis.