Engelthaler D M, Hinnebusch B J, Rittner C M, Gage K L
Division of Vector Borne Infectious Diseases, National Center for Infectious Diseases, Centers for Disease Control and Prevention, Fort Collins, Colorado 80522, USA.
Am J Trop Med Hyg. 2000 May;62(5):552-60. doi: 10.4269/ajtmh.2000.62.552.
We used a quantitative competitive polymerase chain reaction assay to quantify Yersinia pestis loads in fleas and bacteremia levels in mice that were used as sources of infectious blood meals for feeding the fleas. Xenopsylla cheopis, the Oriental rat flea, achieved higher infection rates, developed greater bacterial loads, and became infectious more rapidly than Oropsylla montana, a ground squirrel flea. Both flea species required about 10(6) Y. pestis cells per flea to be able to transmit to mice. Most fleas that achieved these levels, however, were incapable of transmitting. Our results suggest that at the time of flea feeding, host blood must contain > or = 10(6) bacteria/ml to result in detectable Y. pestis infections in these fleas, and > or = 10(7) bacteria/mL to cause infection levels sufficient for both species to eventually become capable of transmitting Y. pestis to uninfected mice. Yersinia pestis colonies primarily developed in the midguts of O. montana, whereas infections in X. cheopis often developed simultaneously in the proventriculus and the midgut. These findings were visually confirmed by infecting fleas with a strain of Y. pestis that had been transformed with the green fluorescent protein gene.
我们使用定量竞争性聚合酶链反应分析法来量化跳蚤体内的鼠疫耶尔森菌载量以及小鼠体内的菌血症水平，这些小鼠被用作感染性血餐来源以供跳蚤吸食。印鼠客蚤，即东方鼠蚤，比地松鼠蚤蒙塔山蚤感染率更高，细菌载量更大，且更快具有传染性。两种跳蚤都需要每只跳蚤约10⁶个鼠疫耶尔森菌细胞才能传播给小鼠。然而，大多数达到这些水平的跳蚤都无法传播。我们的结果表明，在跳蚤吸食时，宿主血液中必须含有≥10⁶个细菌/毫升才能在这些跳蚤中导致可检测到的鼠疫耶尔森菌感染，而≥10⁷个细菌/毫升才能引起足以使两种跳蚤最终都能够将鼠疫耶尔森菌传播给未感染小鼠的感染水平。鼠疫耶尔森菌菌落主要在蒙塔山蚤的中肠中形成，而印鼠客蚤的感染通常在前胃和中肠同时发生。通过用绿色荧光蛋白基因转化的鼠疫耶尔森菌菌株感染跳蚤来直观地证实了这些发现。
