Department of Clinical Sciences, College of Veterinary Medicine, North Carolina State University, Raleigh, NC 27607, USA.
Department of Veterinary Pathobiology, College of Veterinary Medicine, Oklahoma State University, Stillwater, OK 74078, USA.
Ticks Tick Borne Dis. 2022 Jan;13(1):101847. doi: 10.1016/j.ttbdis.2021.101847. Epub 2021 Oct 10.
Cytauxzoon felis is a tick-borne hemoprotozoan parasite that causes life-threatening disease in domestic cats in the United States. Currently, the platforms for C. felis research are limited to natural or experimental infection of domestic cats. This study aims to develop an alternative model by infecting Amblyomma americanum ticks with C. felis via direct injection. Amblyomma americanum adults were injected with C. felis-infected feline erythrocytes through two routes: directly into the digestive tract through the anal pore (IA injection), or percutaneously into the tick hemocoel (IH injection). RNAscope® in situ hybridization (ISH) was used to visualize the parasites within the ticks at different time points after injection. Four months after injection, ticks were divided into 3 infestation groups based on injection methods and inoculum type and fed on 3 naïve cats to assess the ticks' ability to transmit C. felis. Prior to the transmission challenge, selected ticks from each infestation group were tested for C. felis RNA via reverse transcription-PCR (RT-PCR). In both IA- and IH-injected ticks, ISH signals were observed in ticks up to 3 weeks after injection. The number of hybridization signals notably decreased over time, and no signals were detected by 4 months after injection. Prior to the transmission challenge, 37-57% of the sampled ticks were positive for C. felis RNA via RT-PCR. While the majority of injected ticks successfully attached and fed to repletion on all 3 cats during the transmission challenge, none of the cats became infected with C. felis. These results suggest that injected C. felis remained alive in ticks but was unable to progress to infective sporozoites after injection. It is unclear why this infection technique had been successful for other closely related tick-borne hemoprotozoa and not for C. felis. This outcome may be associated with uncharacterized differences in the C. felis life cycle, the lack of the feeding or molting in our model or absence of gametocytes in the inoculum. Nonetheless, our study demonstrated the potential of using ticks as an alternative model to study C. felis. Future improvement of a tick model for C. felis should consider other tick species for the injection model or utilize infection methods that more closely emulate the natural infection process.
猫泰勒虫是一种蜱传血原虫寄生虫，可导致美国家养猫致命性疾病。目前，猫泰勒虫研究的平台仅限于对家养猫进行自然或实验感染。本研究旨在通过直接向美洲钝眼蜱体内注射猫泰勒虫来建立一种替代模型。通过两种途径将感染猫泰勒虫的猫红细胞直接注入美洲钝眼蜱的消化道（IA 注射）或经皮注入蜱的血腔（IH 注射）：将美洲钝眼蜱成虫。注射后不同时间点，使用 RNAscope®原位杂交（ISH）技术观察寄生虫在蜱体内的存在情况。注射后 4 个月，根据注射方法和接种物类型将蜱分为 3 个侵染组，并将其接种于 3 只幼稚猫，以评估蜱传播猫泰勒虫的能力。在进行传播挑战之前，从每个侵染组中选择蜱，通过逆转录-PCR（RT-PCR）检测猫泰勒虫 RNA。在 IA 和 IH 注射的蜱中，注射后 3 周内均观察到 ISH 信号。随着时间的推移，杂交信号数量显著减少，注射后 4 个月未检测到信号。在进行传播挑战之前，通过 RT-PCR，37-57%的采样蜱呈猫泰勒虫 RNA 阳性。虽然在传播挑战期间，大多数注射的蜱都成功附着并在 3 只猫上饱食，但没有猫感染猫泰勒虫。这些结果表明，注射的猫泰勒虫在蜱中仍然存活，但在注射后无法发育成感染性孢子。目前尚不清楚为什么这种感染技术对其他密切相关的蜱传血原虫有效，而对猫泰勒虫无效。这种结果可能与猫泰勒虫生命周期中未被描述的差异、我们模型中缺乏摄食或蜕皮或接种物中缺乏配子体有关。尽管如此，我们的研究表明，使用蜱作为替代模型研究猫泰勒虫是可行的。未来改善猫泰勒虫的蜱模型应考虑其他蜱种用于注射模型，或采用更接近自然感染过程的感染方法。
