Mosquitoes and soft ticks cannot transmit Lyme disease spirochetes
Mosquitoes and soft ticks cannot transmit Lyme disease spirochetes
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蚊子和软蜱不能传播莱姆病螺旋体
DOI：
10.1007/s00436-001-0584-1
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发表时间：
2002
影响因子：
2
通讯作者：
D. Richter
中科院分区：
文献类型：
--
作者：
F. Matuschka;D. Richter
研究人员经常假设，在吸血节肢动物中发现病原体提供了确凿的证据，证明这些节肢动物参与了该病原体的地方流行周期。这一假设可能导致这样的结论，即软蜱和蚊子是莱姆病病原体，广义上的布氏疏螺旋体的媒介。这种推理过分简化了任何这种传输周期的要求。作为病原体宿主的能力是媒介传播感染传播周期的最基本要求;某种最低程度的媒介能力是必不可少的。在莱姆病的情况下，感受态载体必须能够从宿主获得病原体，允许其发育，支持其增殖，然后必须能够将病原体递送至储存宿主（Matuschka和Spielman 1986）。作为莱姆病的媒介，蚊子或软蜱必须能够获得不止螺旋体。事实上，莱姆病螺旋体的存在已在大西洋两岸除硬蜱以外的各种吸血节肢动物中得到证实（Magnarelli et al 1986; Halouzka et al. 1998; Hubalek et al. 1998）。然而，我们缺乏证据表明这些节肢动物可以将病原体传播到传播周期的另一个层次。据我们所知，只有少数研究者研究了昆虫可能作为莱姆病病原体的有效载体的可能性（Magnarelli等，1986，1987; Magnarelli和安德森，1988）。当这些昆虫通过膜摄入螺旋体感染的血液后，在其头部发现螺旋体时，提示这些病原体通过伊蚊进行机械传播。在另一个实验中，允许野外收集的伊蚊以有能力但不含螺旋体的储库宿主为食。尽管后来在十分之一的蚊子身上检测到了螺旋体，但它们所吞噬的宿主都没有感染。蚊子不能将螺旋体传播给第二层宿主。没有记录表明，以鸽子为食的阿尔加斯蜱传播莱姆病螺旋体的企图。然而，对这些鸟类进行的广泛血清流行病学研究和对其数千种寄生虫进行的微生物观察表明，鸽子及其蜱在莱姆病病原体的地方性传播周期中不起作用（Fabbi等人，1995年; Thormahlen等人，1997年; Dautel等人，1999年）。在自然界中，很少有鸽子蜱以莱姆病螺旋体的宿主为食。更小的是，这种蜱虫随后可能以人为食的机会。莱姆病的病原体非常适合其蜱虫和脊椎动物宿主。它们螺旋状的形状使它们能够更有效地穿过宿主相对粘稠的皮肤，而不是血液（Kimsey和Spielman 1990）。因此，螺旋体血症是罕见的，持续时间短。硬蜱病媒蜱，如欧洲的木蜱（Ixodes ricinus）和北美的鹿蜱（Ixodes dammini），将它们相对较短的口器插入宿主的皮肤，首先以淋巴液为食，然后以在由此产生的喂养池中收集的血液为食。它们的长期进食期在2至8天之间，允许螺旋体被困在皮肤中形成的进食腔中。另一方面，Argasid蜱主要以血液为食，而且它们的速度要快得多，蚊子和成虫通常在不超过10分钟内充血。蚊子从毛细血管中进食，而且比Argas蜱更快，在大约90秒内充满。因此，硬蜱比硬蜱或蚊子更容易摄取莱姆病螺旋体。Parasitol Res（2002）88：283-284 DOI 10.1007/s00436-001-0584-1
Investigators frequently assume that the discovery of a pathogen in a blood-feeding arthropod provides conclusive proof that these arthropods participate in the enzootic cycle of that pathogen. This assumption may lead to the conclusion that soft ticks and mosquitoes are vectors of the agent of Lyme disease, Borrelia bugdorferi sensu lato. This reasoning oversimplifies the requirements of any such transmission cycle. The ability to serve as a host to a pathogen is the most elementary requirement of the transmission cycle of a vector-borne infection; some minimal degree of vector competence is essential. In the case of Lyme disease, a competent vector must be able to acquire the pathogen from a host, permit its development, support its multiplication and must then be able to deliver the pathogen to a reservoir host (Matuschka and Spielman 1986). To serve as a vector of the agent of Lyme disease, it follows that a mosquito or a soft tick must be capable of more than spirochete acquisition. Indeed, the presence of Lyme disease spirochetes has been demonstrated in various blood-feeding arthropods other than ixodid ticks on both sides of the Atlantic (Magnarelli et al 1986; Halouzka et al. 1998; Hubalek et al. 1998). We lack evidence, however, that such arthropods can transmit the pathogen to another level in the cycle of transmission. To our knowledge, only a few investigators have examined the possibility that insects may serve as competent vectors for the agent of Lyme disease (Magnarelli et al. 1986, 1987; Magnarelli and Anderson 1988). Mechanical transmission of these pathogens by Aedes mosquitoes was suggested when spirochetes were found in the heads of such insects after they had ingested spirochete-infected blood through a membrane. In another experiment, field-collected Aedes mosquitoes were permitted to feed on competent but spirochete-free reservoir hosts. Although spirochetes were later detected in a tenth of these mosquitoes, none of the hosts on which they engorged acquired an infection. Mosquitoes fail to transmit spirochetes to a second level of hosts. No attempts to transmit Lyme disease spirochetes with the Argas ticks that feed on pigeons have been recorded. Extensive seroepidemiologic studies on these birds and microbiological observations on thousands of their argasid parasites, however, suggest that pigeons and their ticks play no role in the enzootic transmission cycle of the agent of Lyme disease (Fabbi et al. 1995; Thormahlen et al. 1997; Dautel et al. 1999). In nature, few pigeon ticks feed on hosts competent for Lyme disease spirochetes. Even smaller is the chance that such ticks might subsequently feed on a person. The agent of Lyme disease is exquisitely adapted to its tick and vertebrate hosts. Their cork-screw like form permits them to move more effectively through the relatively viscous skin of their host than through its blood (Kimsey and Spielman 1990). As a result, spirochetemia is rare and of short duration. Ixodid vector ticks, such as the wood tick (Ixodes ricinus) in Europe and the deer tick (Ixodes dammini) in North America, insert their relatively short mouthparts into their host’s skin and feed first on lymphatic fluid and then on the blood that collects in the resulting feeding pool. Their prolonged feeding period, between 2 and 8 days, permits spirochetes to become trapped in the feeding cavity that is formed in the skin. Argasid ticks, on the other hand, feed mainly on blood, and they do so much more rapidly, with nymphs and adults generally engorging in no more than 10 min. Mosquitoes feed from capillaries and do so even more rapidly than Argas ticks, becoming replete within about 90 s. Ixodid ticks, therefore, are far more likely than an argasid tick or a mosquito to ingest Lyme disease spirochetes. Parasitol Res (2002) 88: 283–284 DOI 10.1007/s00436-001-0584-1