森林革蜱、草原革蜱感染和经期传播莱姆病螺旋体的实验研究

Failure to transmit Lyme spirochetes transstadially in Dermacentor silvarum and D. nuttalli (Acari: Ixodidae)

以实验室培育的非感染森林革蜱Dermacentorsilvarum、草原革蜱D .nuttalli刺叮人工感染 2 1天后的阳性KM鼠 ,利用分离培养和PCR方法检测蜱对螺旋体的保持能力以及体内螺旋体对敏感动物的感染能力。结果如下 :非感染幼蜱均可以通过吸血获得莱姆病螺旋体 ,饱血森林革蜱和草原革蜱幼蜱PCR阳性率均为 5 0 0 %而分离阳性率都为 2 0 0 %。饱血脱落后 ,这些幼蜱只能在饱血后 2天内分离到莱姆病螺旋体。PCR检测阳性也只能持续到 4天 ,均不能跨越蜕皮阶段。蜕化为若蜱后 ,若蜱以及分别受到这些若蜱刺叮的KM鼠均未发现阳性感染。非感染若蜱吸食感染的KM鼠后 ,饱血森林革蜱和草原革蜱获得了莱姆病螺旋体 ,PCR检测阳性率分别为 5 0 0 %和 2 0 0 %。分离阳性率分别达到 33 3%和 6 0 0 %。这些若蜱分别于饱血后 2天和 3天可以分离到莱姆病螺旋体 ,PCR扩增阳性也只能分别持续到饱血后 4天和 6天 ,均不能跨越蜕皮阶段 ;蜕化为成蜱后 ,成蜱以及受到它们攻击的KM鼠均未获阳性检测结果。同种蜱不同地理株在感染和保持莱姆病螺旋体的能力上也没有差异。森林革蜱、草原革蜱的幼蜱和若蜱虽可以吸血感染但均不具备经期传播莱姆病螺旋体BorreliagariniiCHNM4的能力 。

To determine the principal vectors of Lyme disease in North China, the capability of Dermacentor silvarum and D.nuttalli to transmit Lyme spirochetes transstadially was estimated under laboratory conditions.Spirochete\|free larval ticks were found to acquire Borrelia garinii if allowed to feed on infected KM mice. PCR tests indicated that 50% of such larvae subsequently became infected by B.garinii . However, cultivation revealed that only about 20 0% of these larva harbored live spirochetes. Spirochetes were detectable in D. silvarum and D. nuttalli larvae up to 8 days after ingestion but remained alive for only 2 days after ingestion. All engorged larvae no longer contained live spirochetes by the time they reached the nymph stage. PCR and cultivation indicated that both newly emerged nymphs and KM mice parasitised by these nymphs were negative for B. garinii. Spirochete\|free nymph ticks could also acquire B. garinii by feeding on infected KM mice. PCR indicated that 50% of such nymphs became infected. Cultivation of spirochetes from engorged nymphs indicated infection rates of 33 3% and 60 0% respectively. Spirochetes were detectible for between 4 and 6 days but remained alive for only 2-3 days after ingestion. None of the engorged nymphs contained live spirochetes by the time they reached the adult stage. After molting, neither newly emerged adults or KM mice parasitized by them were found to be infected. The same tick species collected from different sites were similarly incapable of maintaining live Lyme spirochetes. We conclude that D. silvarum and D. nuttalli are unable to transmit infectious B. garinii to subsequent developmental stages. The presence of spirochetes in D. silvarum and D. nuttalli may be tied to co\|feeding with Ixodes persulcatus.