Al-Kappany Y M, Abu-Elwafa S A, Hilali M, Rosenthal B M, Dunams D B, Dubey J P
Parasitology Department, Faculty of Veterinary Medicine, Mansoura University, 35516 Mansoura, Egypt.
J Parasitol. 2013 Dec;99(6):997-1001. doi: 10.1645/13-274.1. Epub 2013 Jun 12.
Cats serve as definitive hosts for zoonotic Toxoplasma gondii , a protozoan that threatens human reproductive health, but they also excrete sporocysts of related protozoan that pose no known human health risk. Here we provide the first definitive evidence for natural infection with the enzootic parasite Sarcocystis muris, one such enzootic parasite. Sporulated Sarcocystis sp. sporocysts were found in rectal contents of an adult feral cat ( Felis catus ) in Giza, Egypt. After these sporocysts were orally inoculated into 2 Swiss Webster mice, sarcocysts were found to have developed in skeletal muscles 114 days later. As observed through transmission electron microscopy, the cyst wall corresponded to Type 1, and the parasitophorous vacuolar membrane had tiny outpocketing of blebs (<200 nm thick) that were not invaginated into the interior of the cyst; these structures were identical to the sarcocyst wall described for a Costa Rican isolate of S. muris that has served as an experimental model for nearly 4 decades. Two parasite-free cats fed sarcocyst-infected muscles developed patent infections; fully sporulated sporocysts (10-11 × 7.0 μm) were found in the lamina propria of small intestines of cats killed 6 and 7 days postinoculation (PI). Interferon gamma gene knockout (KO) mice were orally inoculated with sporocysts from experimentally infected cats, and their tissues were examined histologically; sarcocysts were found in 5 KO mice killed 87, 115, 196, 196, 196 days PI, but no stages were seen in 5 KO mice 10, 14, 14, 18, and 39 days PI. Bradyzoites were released from intramuscular sarcocysts of a KO mouse killed 115 days PI and orally inoculated into 5 KO mice. No stage of Sarcocystis was found in any organ (including intestinal lamina propria) of KO mice killed 4, 8, 81, 190, and 190 days PI, confirming that the definitive host is required to complete the life cycle even in the case of immunodeficient mice. This is the first confirmation of S. muris infection in a naturally infected cat anywhere.
猫是人畜共患的刚地弓形虫的终末宿主，这种原生动物会威胁人类生殖健康，但它们也会排出相关原生动物的孢子囊，而这些孢子囊对人类健康并无已知风险。在此，我们首次提供了自然感染动物源性寄生虫鼠肉孢子虫的确切证据，鼠肉孢子虫就是这样一种动物源性寄生虫。在埃及吉萨的一只成年野猫（家猫）的直肠内容物中发现了已孢子化的肉孢子虫属孢子囊。将这些孢子囊经口接种到2只瑞士韦伯斯特小鼠体内后，114天后在其骨骼肌中发现了肉孢子囊。通过透射电子显微镜观察，囊壁对应于1型，寄生泡膜有微小的泡状突起（厚度<200纳米），且未内陷到囊腔内；这些结构与近40年来用作实验模型的哥斯达黎加分离株鼠肉孢子虫所描述的肉孢子囊壁相同。两只未感染寄生虫的猫喂食了感染肉孢子囊的肌肉后发生了显性感染；在接种后6天和7天处死的猫的小肠固有层中发现了完全孢子化的孢子囊（10 - 11×7.0微米）。将来自实验感染猫的孢子囊经口接种到干扰素γ基因敲除（KO）小鼠体内，并对其组织进行组织学检查；在接种后87、115、196、196、196天处死的5只KO小鼠中发现了肉孢子囊，但在接种后10、14、14、,18和39天处死的5只KO小鼠中未发现任何阶段。从接种后115天处死的一只KO小鼠的肌内肉孢子囊中释放出缓殖子，并经口接种到5只KO小鼠体内。在接种后4、8、81、190和190天处死的KO小鼠的任何器官（包括小肠固有层）中均未发现肉孢子虫的任何阶段，这证实即使在免疫缺陷小鼠的情况下，也需要终末宿主来完成生命周期。这是在任何地方自然感染的猫中首次确认感染鼠肉孢子虫。
