Laboratory of Bacteriology, Rocky Mountain Laboratories, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Hamilton, Montana United States of America.
PLoS Pathog. 2018 Jan 22;14(1):e1006859. doi: 10.1371/journal.ppat.1006859. eCollection 2018 Jan.
Fleas can transmit Yersinia pestis by two mechanisms, early-phase transmission (EPT) and biofilm-dependent transmission (BDT). Transmission efficiency varies among flea species and the results from different studies have not always been consistent. One complicating variable is the species of rodent blood used for the infectious blood meal. To gain insight into the mechanism of EPT and the effect that host blood has on it, fleas were fed bacteremic mouse, rat, guinea pig, or gerbil blood; and the location and characteristics of the infection in the digestive tract and transmissibility of Y. pestis were assessed 1 to 3 days after infection. Surprisingly, 10-28% of two rodent flea species fed bacteremic rat or guinea pig blood refluxed a portion of the infected blood meal into the esophagus within 24 h of feeding. We term this phenomenon post-infection esophageal reflux (PIER). In contrast, PIER was rarely observed in rodent fleas fed bacteremic mouse or gerbil blood. PIER correlated with the accumulation of a dense mixed aggregate of Y. pestis, red blood cell stroma, and oxyhemoglobin crystals that filled the proventriculus. At their next feeding, fleas with PIER were 3-25 times more likely to appear partially blocked, with fresh blood retained within the esophagus, than were fleas without PIER. Three days after feeding on bacteremic rat blood, groups of Oropsylla montana transmitted significantly more CFU than did groups infected using mouse blood, and this enhanced transmission was biofilm-dependent. Our data support a model in which EPT results from regurgitation of Y. pestis from a partially obstructed flea foregut and that EPT and BDT can sometimes temporally overlap. The relative insolubility of the hemoglobin of rats and Sciurids and the slower digestion of their blood appears to promote regurgitative transmission, which may be one reason why these rodents are particularly prominent in plague ecology.
跳蚤可以通过两种机制传播鼠疫耶尔森菌，即早期传播（EPT）和生物膜依赖传播（BDT）。不同跳蚤物种的传播效率不同，不同研究的结果并不总是一致。一个复杂的变量是用于感染性血液餐的啮齿动物血液的种类。为了深入了解 EPT 的机制以及宿主血液对其的影响，跳蚤被喂食带菌的小鼠、大鼠、豚鼠或沙鼠血液；并在感染后 1 至 3 天评估感染在消化道中的位置和特征以及鼠疫耶尔森菌的传染性。令人惊讶的是，两种啮齿动物跳蚤中，有 10-28%在喂食带菌大鼠或豚鼠血液后 24 小时内将部分感染的血液餐反流回食道。我们将这种现象称为感染后食道反流（PIER）。相比之下，PIER 在喂食带菌小鼠或沙鼠血液的啮齿动物跳蚤中很少观察到。PIER 与鼠疫耶尔森菌、红细胞基质和氧合血红蛋白晶体的密集混合聚集体的积累相关，这些聚集体充满前胃。在下一次进食时，发生 PIER 的跳蚤比未发生 PIER 的跳蚤更有可能出现部分堵塞，新鲜血液残留在食道内。感染带菌大鼠血液 3 天后，感染 Oropsylla montana 的跳蚤组比感染带菌小鼠血液的跳蚤组传播的 CFU 明显更多，并且这种增强的传播是生物膜依赖的。我们的数据支持这样一种模型，即 EPT 是由于部分阻塞的跳蚤前肠中鼠疫耶尔森菌的反流引起的，并且 EPT 和 BDT 有时可以重叠。大鼠和松鼠科动物血红蛋白的相对不溶性以及它们血液的消化速度较慢似乎促进了反流性传播，这可能是这些啮齿动物在鼠疫生态学中特别突出的原因之一。
