California Polytechnic State University, Biological Sciences Department, 1 Grand Ave., San Luis Obispo, CA 93407, USA.
Vet Parasitol. 2010 May 11;169(3-4):296-303. doi: 10.1016/j.vetpar.2010.01.002. Epub 2010 Jan 7.
From bottlenose dolphins, to walruses, to sea otters, the parasitic protozoan Toxoplasma gondii is infecting marine mammals around the world. Whereas the terrestrial transmission pathways of T. gondii are well-described, the transmission pathway by which marine mammals are being infected is unknown. We hypothesize that migratory filter feeders, specifically northern anchovies (Engraulis mordax) and Pacific sardines (Sardinops sagax), are serving as biotic vectors for T. gondii within the marine environment. By filtering oocysts from seawater, these fishes could be transporting the oocysts from nearshore to pelagic environments. In this study, we experimentally exposed northern anchovies and Pacific sardines to T. gondii oocysts under laboratory conditions. Following exposure, the fishes' alimentary canals were harvested and assayed for the presence of T. gondii by PCR. Fish exposed to as few as 1197 oocysts/L seawater tested positive for T. gondii by PCR. In total, the PCR assay detected T. gondii DNA in 66% (40/61) of the exposed fishes. Oocyst infectivity was confirmed by mouse bioassay: 30% (7/23) of mice developed toxoplasmosis when fed fish exposed to 100,000 oocysts/L. This study demonstrates that both northern anchovies and Pacific sardines can filter T. gondii oocysts out of seawater under experimental conditions. Our experiments with anchovies demonstrated that the oocysts persisted in the fish for at least 8h post-exposure and our experiments with sardines demonstrated that the oocysts remained infectious inside the fish's alimentary canals.
从宽吻海豚、海象到海獭，寄生虫原虫刚地弓形虫正在感染世界各地的海洋哺乳动物。虽然刚地弓形虫的陆地传播途径已经得到很好的描述，但海洋哺乳动物被感染的传播途径尚不清楚。我们假设洄游滤食性鱼类，特别是北方凤尾鱼（Engraulis mordax）和太平洋沙丁鱼（Sardinops sagax），在海洋环境中充当刚地弓形虫的生物载体。这些鱼类通过从海水中过滤出卵囊，可以将卵囊从近岸带到远洋环境中。在这项研究中，我们在实验室条件下用刚地弓形虫卵囊实验性地暴露北方凤尾鱼和太平洋沙丁鱼。暴露后，采集鱼类的消化道，并用 PCR 检测刚地弓形虫的存在。在暴露于低至 1197 个卵囊/L 海水中的鱼类中，通过 PCR 检测出刚地弓形虫呈阳性。总共，PCR 检测法在 66%（40/61）暴露的鱼类中检测到刚地弓形虫 DNA。卵囊感染力通过小鼠生物测定得到证实：当用暴露于 100,000 个卵囊/L 的鱼喂养时，30%（7/23）的小鼠患上了弓形体病。这项研究表明，北方凤尾鱼和太平洋沙丁鱼在实验条件下都可以从海水中过滤出刚地弓形虫卵囊。我们用凤尾鱼进行的实验表明，卵囊在暴露后至少在鱼体内持续 8 小时，我们用沙丁鱼进行的实验表明，卵囊在鱼的消化道内保持感染性。
