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January 17, 2016 Archives

Dragonflies are ancient: with damsel flies, they were among the earliest flying insects. An analysis based on molecular data and fossil evidence suggests a date of 480mya for the first insects, around the same time that land plants evolved, and includes a rather impressive family tree for the taxon; the earliest dragonfly fossils are around 325my old.

Back when I was doing my Hons year at uni, a friend was studying feeding in nymphal dragonflies, which was quite something to watch! (The feeding, not the friend.) If you look at them head-on - there's a good view in this video - they've got a well-developed set of mandibles. But the thing to watch out for, if you're something dinner-sized, is the big, extensible labium (analogous to a lower jaw) - this shoots out at great speed to catch passing water boatmen, mosquito larvae, or other suitable prey.

So, they're active predators, and this means that they need excellent vision. Like all insects, dragonfly eyes are based on units called ommatidia. However, dragonfly eyes are hugeMost of the animal's head is covered by the two compound eyes, each of which is made up of roughly 28,000 of those ommatidia. Much of their brain must be given over to processing that information, given the speed at which they move and the accuracy of their attacks (apparently up to 95% of attempts on prey are successful).

And since I mentioned speed, here's a video from the BBC on just how quickly dragonflies react to the sight of potential prey.

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I had another head-desk moment today, on reading a bit more of Judy Wilyman's PhD thesis (a bit at a time is quite enough). The document has quite a bit to say about smallpox. I've already noted the ill-considered statement that the vaccine has never been subject to clinical trials - a statement unaccompanied by any "now, I wonder why not?" explanation.

Incidentally, in commenting on that post, Tsu Do Nimh pointed out that there have been quite a few natural experiments that allow a comparison of morbidity and mortality between the vaccinated and non-vaccinated, beginning back in 18th-century Boston. In this instance the practice of variolation (using pus or scab material from someone recently infected) was used to protect people from smallpox; it was not as effective as modern vaccines and there were concerns that people still became ill and died. However, the comparative statistics are compelling. There were 3 outbreaks of smallpox in Boston, in 1721, 1764, & 1792, During those outbreaks the deaths per thousand cases of smallpox among the non-variolated ranged from 146 to 298. For the variolated group, deaths/1000 cases ranged from 9 to 20.

Wilyman must have missed this somehow.

But it gets worse. 

It's quite evident that Wilyman would prefer to attribute declines in rates of infection from diseases such as measles, polio & smallpox solely to 'environmental' factors, such as isolation of patients, along with better hygiene and nutrition. No-one would deny that these are important, but it's also worth noting that 1950s America (ie the US) had high standards of both hygiene and nutrition - and fairly high rates of morbidity and mortality from measles. Nonetheless, she claims (p128 of the thesis proper) for smallpox that 

isolation of the cases alone could have stopped the circulation of the virus and eradicated this disease
Why? Because, in her view
smallpox is only transferrable by direct skin-to-skin contact.
Now, while it's true that the main route of transmission is face-to-face contact (and not skin-to-skin - the World Health Organisation notes that the virus can travel in saliva droplets on the breath of an infected person), that's by no means the only route. As the Centres for Disease Control point out
Smallpox can also be spread through direct contact with infected bodily fluids or contaminated objects such as bedding or clothing. Rarely, smallpox has been spread by virus carried in the air in enclosed settings such as buildings, buses, and trains.

That information was extremely easy to find. It's surprising, to say the least, that the usual rigorous literature review required for a PhD thesis did not turn up the same information. And that the examiners didn't notice its absence.

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Recent Comments

  • Alison Campbell: Thanks, Beth - another one for my reading list. read more
  • Beth: That book "Smallpox and its Eradication" is very informative and read more
  • Beth: She didn't actually say that the efficacy should have been read more
  • Alison Campbell: Thanks, Beth; my thoughts exactly. I was horrified to see read more
  • Beth: Here were my comments about the smallpox passage: p. 105 read more
  • Alison Campbell: ooooh you are awful, herr doktor! read more
  • herr doktor bimler: incomplete molecular structure This sounds like something from a bad read more
  • Alison Campbell: I wouldn't mind if he kept his strange beliefs to read more
  • Grant: Yeah. Feeding instructions needed. On one hand hilarious anyone thinks read more
  • herr doktor bimler: The milk goes in the puss. Not the other way read more