Cummings School of Veterinary Medicine, Tufts University, 200 Westboro Rd., North Grafton, MA 01536, USA.
Ticks Tick Borne Dis. 2010 Mar;1(1):66-8. doi: 10.1016/j.ttbdis.2010.01.001.
The American dog tick, Dermacentor variabilis, is fundamental to the perpetuation of Francisella tularensis tularensis on Martha's Vineyard, Massachusetts, U.S.A. Although infected ticks are relatively common on the island, human cases deriving from tick bite are rare. It may be that the quantum of bacteria within these naturally infected ticks is frequently too small to cause disease. Accordingly, we quantified the amount of F.t. tularensis bacteria in host-seeking ticks from the island. Contrary to our expectations, the majority of the ticks harbor large numbers of bacteria (median 3.3x10(8) genome equivalents/tick). Such a large quantum of infection might suggest that aerosolization of the ticks themselves might comprise the proximal determinant of risk for the inhalational tularemia that is common on Martha's Vineyard. However, the paradox of fewer ulceroglandular tularemia cases than would be expected given the abundance of potentially highly infectious ticks remains to be solved.
美国驯犬蜱，即达马森氏革蜱，是美国马萨诸塞州玛莎葡萄园岛土拉弗朗西斯菌土拉亚种持续存在的关键。尽管感染蜱虫在岛上较为常见，但源自蜱虫叮咬的人类病例却很罕见。这可能是因为这些自然感染的蜱虫体内的细菌数量经常太少而无法引起疾病。因此，我们对来自该岛的吸血蜱虫体内的 F.t. tularensis 细菌数量进行了定量分析。出乎意料的是，大多数蜱虫携带大量细菌（中位数为 3.3x10(8)基因组当量/蜱虫）。如此大量的感染可能表明，蜱虫本身的气溶胶化可能构成了玛莎葡萄园岛常见的吸入性土拉弗朗西斯菌病的近端决定因素。然而，鉴于大量可能具有高度传染性的蜱虫，溃疡腺鼠疫病例却比预期的要少，这一悖论仍有待解决。
