"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

April 19, 2010

April 19 - Placentanema gigantissma


The parasite featured today is the longest known parasitic nematode, appropriately, its host is also one of the largest known living animal - the sperm whale (Physeter macrocephalus). The name of this parasite is Placentanema gigantissma, and it is indeed a gigantic worm. The female worm can reach up to 8.4 m long, while the smaller male reach "only" 3.75 m in length.

Its scientific name also indicates its peculiar microhabitat - this nematode has only ever been found in the uterus and placenta of female sperm whales. Even though they are relatively common, very little is known about this species. How this parasite transmit from host to host is currently unknown, though it is likely that this is facilitated by the expulsion of the placenta (with the female worm within) at birth, and eggs are released as the female worm decomposes. It has been suggested that larval worms infect the female whale prior to sexual maturity and remain dormant until the whale becomes pregnant.

The photo is of the host, in this case a young sperm whale.
For further details, see p. 839 of Diseases of Marine Animals Vol 4 Part 2 (free to download from here)

Contributed by Tommy Leung.


7 comments:

  1. Is it possible the parasite is transmitted in utero from mother to daughter?

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  2. No one knows at the moment - as you can imagine, this worm is probably one of the most difficult organism to study on this planet - living in such an odd environment.

    We only know that it exists - everything else including it life-cycle, ecology, how common/rare it might before, host-parasite interactions are completely unknown

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  3. how did they discover it?

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    1. I'm guessing they discovered it while looking in the placenta of a dead sperm whale.

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  4. Was just reading in the "Diseases of Marine Animals" book that they think that it might be transmitted after the placenta is expelled after birth, with eggs or larvae released into the water from the decomposing female. How it gets into the next sperm whale is anyone's guess!

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    1. I think it'll be really interesting to know if it has any intermediate/paratenic host (especially if they are scavengers that might feed on the decomposing placenta!). But then, it might also be a vertically-transmitted parasite...

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  5. Well I would imagine I would need som type of intermediate host

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