Differential susceptibility of geographically distinct <i>Ixodes ricinus</i> populations to tick-borne encephalitis virus and louping ill virus

Tick-borne encephalitis virus (TBEV) is an emerging pathogen in the Netherlands. Multiple divergent viral strains are circulating and the focal distribution of TBEV remains poorly understood. This may, however, be explained by differences in the susceptibility of tick populations for specific viruses and viral strains, and by viral strains having higher infection success in their local tick population. We investigated this hypothesis by exposing Dutch <i>Ixodes ricinus</i> ticks to two different TBEV strains: TBEV-NL from the Netherlands and TBEV-Neudoerfl from Austria. In addition, we exposed ticks to louping Ill virus (LIV), which is endemic to large parts of the United Kingdom and Ireland, but has not been reported in the Netherlands. Ticks were collected from two locations in the Netherlands: one location without evidence of TBEV circulation and one location endemic for the TBEV-NL strain. Ticks were infected in a biosafety level 3 laboratory using an artificial membrane feeding system. Ticks collected from the region without evidence of TBEV circulation had lower infection rates for TBEV-NL as compared to TBEV-Neudoerfl. <i>Vice versa</i>, ticks collected from the TBEV-NL endemic region had higher infection rates for TBEV-NL compared to TBEV-Neudoerfl. In addition, LIV infection rates were much lower in Dutch ticks compared to TBEV, which may explain why LIV is not present in the Netherlands. Our findings show that ticks from two distinct geographical populations differ in their susceptibility to TBEV strains, which could be the result of differences in the genetic background of the tick populations.蜱传脑炎病毒（Tick-borne encephalitis virus, TBEV）在荷兰已成为一种新发病原体。当前存在多种进化分歧显著的病毒毒株在当地流行，而该病毒的局部分布特征仍未得到充分解析。不过，这一现象或可通过以下两方面得到解释：其一，不同蜱种群对特定病毒及毒株的易感性存在差异；其二，部分毒株在本地蜱种群中具备更高的感染定植成功率。我们针对该假说开展研究，将荷兰蓖麻硬蜱（Ixodes ricinus）分别暴露于两种TBEV毒株：源自荷兰的TBEV-NL以及源自奥地利的TBEV-Neudoerfl。此外，我们还将蜱暴露于羊跳跃病病毒（Louping Ill virus, LIV）——该病毒在英国及爱尔兰大部分地区呈地方性流行，但尚未在荷兰有过报道。本次研究的蜱样本采集自荷兰两处地点：一处未检测到TBEV流行迹象，另一处为TBEV-NL毒株的地方性流行区域。所有感染实验均在生物安全3级实验室中，通过人工膜饲系统完成。实验结果显示：相较于TBEV-Neudoerfl，采集自无TBEV流行区域的蜱对TBEV-NL的感染率更低；反之，采集自TBEV-NL地方性流行区域的蜱对TBEV-NL的感染率则高于TBEV-Neudoerfl。此外，荷兰蜱对LIV的感染率远低于其对TBEV的感染率，这或可解释为何LIV未在荷兰出现。本研究结果表明，两个不同地理种群的蜱对TBEV毒株的易感性存在显著差异，这一差异可能源于不同蜱种群的遗传背景不同。