"So, naturalists observe, a flea has smaller fleas that on him prey; and these have smaller still to bite ’em; and so proceed ad infinitum."
- Jonathan Swift

March 11, 2010

March 11 – Sputnik virus

As noted by the Jonathan Swift quote at the top of this blog, many parasite themselves are infected with parasites. These obligate parasites of other parasites are called "hyperparasites". Parasitoid wasps that infect and enslave caterpillars can themselves be impregnated by hyperparasitoid wasps, parasitic crustaceans like Sacculina are parasitized by bizarre hyperparasitic isopods, some parasitic flukes are infected by protozoan and bacterial parasites. Viruses cannot replicate on their own and must inject their genetic material into the cell of their host, hijacking its cellular machinery for its own replication, thus making them obligate intracellular parasites. In 2008, it was found that some viruses themselves can become infected by other viruses. In this case, the host is the virus you met yesterday, a strain of mimivirus, and the parasite belongs to a previously unknown group of virus that have been termed "virophages". Bernard La Scola and colleagues discovered that these hyperparasitic viruses, which they named "Sputnik". Each of these Sputnik measuring 50 nm in size, and just as more traditional virus hijack the machinery of their host cells for replication, the Sputnik commandeers the "viral factories" of the mimivirus to churn out more virophages at the host's expense. In a case of "you are what you eat" (in this case "you are what you infect"), the virophage's own genome is littered with genes from its own host, some of which are genes that the mimivirus itself had also acquired from the cells it infects, making the virophage a strange genetic chimaera.

Contributed by Tommy Leung.
Image from this source.


  1. I just want to say that I am really enjoying this blog. I've long been interested in (and spooked by) parasites and their many bizarre lifestyles, and your columns have become part of my daily routine. Cheers.

  2. I would love to learn more about the copepods that attack Sacculina.