尽管人类癌症很要命，但至少它不会传染。然而对于蛤蜊、淡菜及其它的海生蚌类来说，情况就不一样了。最近在《自然》杂志上发表的一项新研究称，这些动物会患上一种癌症，与白血病类似，且这种癌症看起来会通过水体传播，而且不仅是在同一物种的成员之间，甚至是两个不同物种之间传播。基因分析揭示出，不同个体淡菜(上图)癌细胞的相似度要远高于这些淡菜健康细胞的相似度，这说明这种癌症并不是宿主淡菜自身组织发展出来的，而可能是来自于一个共同的外部病源。科研人员在鸟蛤中也发现了类似的情况，但有证据证明，两种明显的癌细胞体系随着时间分别进化。金地毯贝壳蛤是其中最有意思的一个：宿主细胞和癌细胞之间的不同显示出癌细胞是来自外部的病源，但是这些癌细胞看起来如此不同，更像是另外一个蛤蜊物种帘蛤 (Venerupis corrugata)的宿主细胞。研究团队得出结论说，癌变最开始发生于V.corrugata中，但是在某个时刻跨物种传播到了Polititapes aureus。这个结论表明，至少对于蚌类来说，癌细胞表现得像一种新的传染中介，在很多方面和传统的病原体相似，会持续进化出新的基因变化让它们得以生存并繁殖。这类可传染的癌症在几种哺乳动物中也被发现过，这些动物包括袋獾和某些犬类。研究作者提出，这些关于蚌类的新发现显示，有些动物对病状更敏感，但是人类处在安全区，至少目前为止是这样。

原文摘要：As bad as cancer is in humans, at least it’s not contagious. The same can’t be said for clams, mussels, and other marine bivalves. According to a new study, published online today in Nature,these creatures can suffer from a form of cancer similar to leukemia that appears to be transmitted through the water and can pass not only between members of one species, but even between two different ones. Genetic analyses revealed that, even in different mussels (pictured above), cancer cells were much more similar to each other than to healthy host cells, suggesting that the cancer hadn’t originally developed in host mussel tissue, but may have come from a common outside source. The cockles revealed a similar story, but showed evidence of two distinct lineages of cancer cells that evolved separately over time. The golden carpet shell clams told the most interesting tale of all: Again, dissimilarities between the host cells and the cancerous cells gave the appearance that the cancer cells were from an outside source, but this time the differences were so pronounced that the cancer cells looked much more like host cells from an entirely different species of clam—the pullet carpet shell (Venerupis corrugata). The team concludes that the cancer mutations initially arose in V. corrugata, but crossed species to Polititapes aureus at some point. For the bivalves at least, the results suggest that cancer acts like a new type of infectious agent, similar in many ways to traditional pathogens that continually evolve new genetic tweaks that allow them to survive and reproduce. This type of transmissible cancer has also been discovered in several mammals including Tasmanian devils and certain breeds of dogs. The new results in bivalves, the authors suggest, show that some animals are more susceptible to phenomenon, but humans are in the clear—at least, so far.