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TWiP 72 letters

Robin writes:

plethora (n.)

1540s, a medical word for "excess of body fluid," from Late Latin plethora, from Greek plethore "fullness," from plethein "be full" (see pleio-). Figurative meaning "too-muchness, overfullness in any respect" is first recorded 1700. Related: Plethoric.

Are birds infected?

"No" "Only warm blooded animals".

"Warm-blooded animals" includes birds.

David writes:

Dear guys,

Question, who is Spencer Wells, arose in final minutes of TWIP show I just heard, near mention of tragocytosis (sp?) and a couple of enjoyed PBS series.

Spencer Wells also had a PBS (I think) bit of his production. Must be something <ten years ago now, but charmed me so that it seems fresher than that. I've always wished to see him back with more. Wish I knew the title.

He is a geneticist, and I guess was on the cutting edge of reconstructing the origins of human dispersal. He clarified the first spread of sapiens along the South Asian corridor, ultimately to Australia. Your context was "tropical species which went where it didn't need clothes."
His bearing seemed a little (American) aristocratic, but not in an offensive way. I thought his discussion was especially smart, and I felt exceptionally well informed by the show. Is it conceivable that it was a bit too far above intellectual middlebrow to satisfy the viewing demographic? I don't know, and shouldn't even speculate, and must add that I too have enjoyed the other PBS productions you guys named. Besides, human origins has always been a favorite hobbyhorse of mine.

Anyway, the genetics-based reconstruction of human population origins has moved by leaps and bounds since, as you know, yet I haven't encountered any but snippets of detail in public productions. I wish Spencer would come back with a new show on the subject.

That's who I think he is.


PS So what is tragocytosis?

Rachel writes:

Dear TWiP Team:

In listening to TWiP episode 71 whilst gently tending my cell culture garden, I noted an inaccuracy in your classification/description of birds. In the context of the host range of Strongyloides, Vincent asks, "Are birds infected?" To which Dickson replies, "No... warm blooded animals," implying that birds are not warm blooded animals. This is a mistake that I have noted being made in previous episodes of the TWiX family of podcasts as well. Most birds are, indeed, warm blooded animals, more precisely homeothermic endotherms, as are most mammals.

A one-time point in need of clarification the same part of the conversation, which seemed to be about Strongyloides in general, not S. stercoralis specifically, is that, while it is true that S. stercoralis only seems to infect mammals, there is at least one species which does infect birds, S. avium.

Thanks for the interesting podcasts.

Rachel Tell

Rachel Tell, DVM, PhD
Postdoctoral Research Fellow
University of Iowa

Colin writes:

hi, is there a parasite known to kill all virus it encounters.
is there a virus known to kill all parasites?

Has any virus been found to have parasites yet? and if so do they have virus? and so on and on?

I know these questions may seem a little perhaps different, but what do you guys think?

Kind Regards,

James writes:

I’m not a veterinarian or a fish farmer. But I trained as a marine scientist, including a large part of my studies at the Institute of Aquaculture, and worked on the production of a vaccine. A bit of feedback concerning show TWiP 70 (which was great as always!).

Apologies if anything has been discussed across TWiX, feel free to center on interesting bits (if any).

Zoonotic or non-zoonotic invasive bodies

Just as significant, if not greater risk of invasive aquatic species likely to be through ballast water in shipping. This has already had significant impact across the atlantic. Carcinus maenas (Green crab / european crab) has been well studied and decimated your soft shelled crabs in parts of America. They hitchhiked as larvae in the ballast, which when expelled at shore to raise the height of the ship to enter so do the larvae. Conversely America then sent signal Crayfish over by the same means to pay Europe back!

This is why in Australia in addition to strict animal import rules (i.e. never, almost), ships are order to remove ballast much further out at sea in order to protect the barrier reef. As well as severe consequences for shipping firms, ship captains flaunting this will have severe consequences (non-nationals face banning from the country and it’s territorial waters- a career ender).

‘Aquaculture’ vs Rearing

Unlike True Eels, the Monopterus albus does not require migration to, for example in European species, the Sargasso Sea in order to complete it’s life cycle. However, I suspect (although I cannot find any exact confirmation) that M. albus has still yet to have it’s full life cycle closed in aquaculture. Hence the phrase ‘farm raised’ or ‘reared’ being used. In my quick search the only specific confirmation to captive either way to breeding of M albus was a negative one (, with a few US government agencies refering to ‘escapes from aquaculture farms’. But these could refer to those that escaped from a farm of another species, e.g. fish. Sorry I can’t be more specific most of my documentation is in storage in Scotland.

In Anguilla it actually still requires the capture of live elevers (young), and ongrowing in capture. They cannot be ‘bred’. Despite this is similar to the maturation of Salmon, which can have it’s life cycle closed, the closing of the Anguilla sp life cycle has still eluded scientists. I did find one reference to use of hormone treatments for M. albus, but I am sceptical barring further documentation.

DD, brisked over there being fresh and salt water eels. Anguilla anguilla (European eels), that are part of the true eels (Anguilla) and are normally fresh living but migrate to sea for spawning. European eels migrate all the way to the Sargasso sea! (satelite tracking of eels: Larvae return via the gulf stream.

The same is true for the American eel (Anguilla rostrata which also travels to sea for spawning, although the journey is less dramtic as it’s european cousin.

The whole of the Anguilla is often described as freshwater due to the greatest part of its life being freshwater.
Eels have strict protection in the UK. It means criminals try to harvest elevens at night. Leading to police waiting in the dark for them!


You mentioned polyculture. It has been known, on developing areas for pigs to be cultured in wooden sheds. On the lower level, chickens are cultured. Both floor have gaps between floorboards for the excrement to fall through to the lower level. Below the fish? It is built over rivers, so below the chickens are small fish cages!

This also kind of side arches into DD's new podcast (first episode was great) but i will save that for a separate email.

Didn’t catch many eels (100)- I can beat that!

There was a now infamous article of contamination in fish feed and effects on human health due to PCB’s. It rose to stardom due to the BBC being reprimanded for its use as part of a ‘documentary’ that was highly biased. It involved a sample of less than ten fish (five I think). It was a farmed versus wild comparison assuming feed would result in the changes on the chemical. Of the fish sampled some were from America, some UK. The ONE ‘farmed fish’ that was ordered, it turned out wasn’t even farmed (never specified when ordered). It got published and was being reviewed as part of EU policy. The blunder only got found out through coincidence of a scientist being on the EU review board also being at the Institute supplying the fish, knowing they only used wild samples of that species (and later confirmed this).

great to hear all your collective podcasts
(too warm at about 18oC)

Rachel writes:

Hello TWIP team-

I would like you to know that there are veterinarians listening to This Week in Parasitism. I am a veterinarian, immunologist, and steady TWIx listener. I have recommended all three TWIx podcasts to many colleagues, veterinary and otherwise, over the last year since I came across them for the first time. I find TWIP, in particular, is interesting to the me due, in no small part, to my veterinary training. We spent a lot of time on eukaryotic parasites, especially those with zoonotic potential.

Additional Episode 70 notes: I would really like it if you would spend more time explicitly on the non-human side of zoonoses, as you brush up against it during many episodes but rarely spend much time on it. Also, add me, along with letter-writer Heather, to the list of people who would love an episode here and there devoted to aquatic or aquaculture themes (my background is largely in the immunology & diseases of fish).

Keep up the good work, I like having TWIx in my rotation of cell-culture listening.

Rachel Tell

Rachel Tell, DVM, PhD
Postdoctoral Research Fellow
University of Iowa


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