Approximately 80% of barnacles in Burrard Inlet, British Columbia, Canada, are infected with metacercariae, a life stage of the trematode Maritrema gratiosum, but the origin of these infestations is unknown. Trematode parasites have a three‐host life cycle and six distinct life stages. Adults usually infect shorebirds, which release the parasites’ eggs in their feces; these eggs subsequently metamorphose into miracidia, which then infect snails. At this point, the miracidia develop into sporocysts that asexually produce thousands of free‐swimming larvae (cercariae), which emerge from the snails. The cercariae then locate and infect the next host (a bivalve, a barnacle or other type of crustacean, or a fish) and form a metacercaria, protected by a spherical cyst, in their soft tissue (note: all three images show M gratiosum metacercariae embedded in barnacle tissue). In the final stage of the life cycle, a shorebird eats an infected host and the metacercariae hatch into the next generation of adults.

Given the high proportion of infected barnacles in Burrard Inlet, and the density of metacercariae (typically in the hundreds) contained within them, it is a mystery as to why there are no records of snails infected with M gratiosum at this location. Likewise, surveys at other sites of heavy barnacle infections have failed to detect substantial numbers of infected snails. One answer to this puzzle may be that the cercariae are transported over long distances by tidal currents and the infected snails (the sources of the cercariae) are relatively far away. Alternatively, these metacercariae may persist and remain viable for months or even years, such that even a relatively small number of infected snails could produce enough cercariae to infect millions of barnacles over time. Given that cercariae are known to transmit many diseases to humans (eg schistosomiasis), our barnacle mystery provides a great opportunity to study the dispersal patterns of a disease‐causing agent.

加拿大不列颠哥伦比亚省Burrard Inlet的藤壶中大约80％感染了尾cer，这是Mari线虫的一生。，但是这些侵扰的来源尚不清楚。吸虫的寄生虫具有三个宿主的生命周期和六个不同的生命阶段。成虫通常会感染shore鸟，它们会在粪便中释放出寄生虫的卵。这些卵随后变质为水acid病，然后感染蜗牛。在这一点上，水mir症发展成孢子囊，无性地产生了成千上万的自由生长的幼虫（尾c），这些幼虫从蜗牛中出来。然后，尾c定位并感染下一个宿主（双壳类，藤壶或其他类型的甲壳类动物或鱼类），并在其软组织中形成一个由球形囊肿保护的meta尾note（注意：所有三个图像均显示了M graatiosumcer藤在藤壶组织中的嵌入）。在生命周期的最后阶段，shore鸟吞噬了被感染的宿主，the尾ch孵化了下一代。

鉴于Burrard湾中被感染的藤壶的比例很高，并且其中包含的尾the的密度（通常为数百个），为什么没有关于蜗牛被M Graatiosum感染的记录仍是一个谜。在这个位置。同样，在其他重度藤壶感染场所的调查也未能发现大量被感染的蜗牛。这个难题的一个答案可能是尾通过潮流被长距离运输，而被感染的蜗牛（尾c的来源）则相对较远。或者，这些尾cer可以持续存在并存活数月甚至数年，使得即使相对少量的被感染的蜗牛也可以产生足够的尾c以随着时间的推移感染数百万只藤壶。鉴于已知尾c可将多种疾病传播给人类（例如血吸虫病），我们的藤壶之谜为研究致病因素的传播方式提供了一个绝好的机会。