Laboratories of The Rockefeller Institute for Medical Research.
J Exp Med. 1919 Oct 1;30(4):401-10. doi: 10.1084/jem.30.4.401.
The foregoing experiments show that symptoms and lesions closely resembling those of yellow fever in man may be induced in guinea pigs by the bite of female stegomyias that have previously sucked the blood of a yellow fever patient or of an animal experimentally infected with Leptospira icteroides. With mosquitoes infected directly from a yellow fever patient the infectivity seems to become manifest after a longer period of incubation than with those infected with the animal blood. In the former, at least 12 days are said to be necessary before they become infectious, and this hypothesis seems to be borne out by the present experiment. On the other hand, the mosquitoes which were engorged with the infected blood of the guinea pig were found to be capable of transmitting the disease within 8 days after the feeding. This discrepancy may be explained by the fact that the number of leptospira existing in experimentally infected guinea pigs is far greater than that in human blood. The frequency with which positive transmission by the stegomyia was obtained in both instances was very small indeed, in view of the number of mosquitoes employed. It appears that even under natural circumstances the percentage of mosquitoes that eventually become infected with the yellow fever microbe by sucking the blood may be very small. It has already been shown by previous investigators that to transmit yellow fever from a patient to a non-immune person requires from 0.1 to 2 cc. of blood at the height of disease. According to my estimate a female stegomyia may take up 0.01 cc. or even less. Apparently a mosquito occasionally becomes infectious by taking up the one or two organisms which happen to be circulating in the peripheral blood of man, and it is these occasionally infected few which carry the disease. It is not difficult to realize the extent of ever increasing danger from a constant supply of the microbic virus which an endemic center or an epidemic of yellow fever can provide. One infected mosquito may mean many patients, and the life of such a mosquito is usually longer than that of the persons whom it fatally infects. Finally, it is of interest to note that the development and maintenance of Leptospira icteroides are indispensably associated with the blood constituent, the serum, and this is amply supplied by the bloodsucking insect. The organism is one of the most fragile of all the pathogenic parasites and cannot survive the concurrence of other less fastidious organisms such as bacteria. The comparatively aseptic body cavity of the stegomyia furnishes a secure shelter for the parasite, which undoubtedly penetrates the zone of safety as soon as it is taken into the stomach of the insect. Unlike many other parasites this organism is capable of penetrating the intact skin or a bacteriaproof filter, and hence it is probably an easy matter for it to pierce the tissue of the visceral organs of the mosquito. Whether or not Leptospira icteroides can survive and multiply only in the body of Stegomyia calopus and not in other varieties or genera is yet to be determined. Another interesting fact with regard to the extrinsic life of this organism is that it can multiply steadily at a temperature from 18-37 degrees C. The optimum temperature, at which it remains viable for many months, is 26 degrees . The climate in most of the tropical countries offers optimum conditions both for Leptospira icteroides and for the mosquito which carries and nourishes it.
上述实验表明，通过先前吸食过黄热病患者或经实验感染了黄疸钩端螺旋体的动物血液的雌性埃及伊蚊叮咬，可在豚鼠身上诱发与人的黄热病极为相似的症状和病变。通过直接感染黄热病患者的蚊子传播的传染性似乎比通过动物血液感染的蚊子潜伏期更长。至少需要 12 天，才能使前者具有传染性，这一假设似乎得到了本实验的证实。另一方面，被感染的豚鼠血液喂饱的蚊子在进食后 8 天内就可以传播疾病。这种差异可能是因为实验感染的豚鼠中存在的钩端螺旋体数量远远超过人血中的数量。鉴于所用蚊子的数量，无论哪种情况，通过埃及伊蚊进行的阳性传播的频率都非常低。即使在自然情况下，通过吸食血液而最终感染黄热病微生物的蚊子的比例也可能非常低。先前的研究人员已经表明，要将黄热病从患者传播给未感染者，在疾病高峰期需要 0.1 至 2 毫升的血液。根据我的估计，一只雌性埃及伊蚊可能会吸食 0.01 毫升甚至更少的血液。显然，蚊子偶尔会通过吸食人外周血液中循环的一两个生物体而变得具有传染性，而正是这些偶尔感染的少数蚊子携带了这种疾病。从一个地方性中心或黄热病流行提供的不断供应的微生物病毒中，可以意识到不断增加的危险程度是不难实现的。一只受感染的蚊子可能意味着许多患者，而这种蚊子的寿命通常比它致命感染的人还要长。最后，值得注意的是，黄疸钩端螺旋体的发展和维持与血液成分——血清密不可分，而吸血昆虫则充分提供了这种成分。该生物体是所有致病性寄生虫中最脆弱的之一，不能在其他不太挑剔的生物体（如细菌）共存的情况下存活。埃及伊蚊相对无菌的体腔为寄生虫提供了安全的庇护所，寄生虫无疑一旦进入昆虫的胃中就会穿透安全区。与许多其他寄生虫不同，该生物体能够穿透完整的皮肤或无菌过滤器，因此它很容易穿透蚊子内脏器官的组织。黄疸钩端螺旋体是否只能在 Stegomyia calopus 体内存活和繁殖，而不能在其他品种或属中存活和繁殖，还有待确定。关于该生物体外生活的另一个有趣事实是，它可以在 18-37 摄氏度的温度下稳定繁殖。最适温度为 26 摄氏度，可使它存活数月。大多数热带国家的气候都为黄疸钩端螺旋体和携带并滋养它的蚊子提供了最佳条件。
