Barnacle geese: I am wondering if the MDW is not similar:
Barnacle Geese are so called because people were either not able or to or couldn't see the Geese Nesting, I understand they prefer isolated and remote locations, I believe that the myth of them hatching from "Barnacles" was a direct result of people not observing or understanding their nesting behaviours.
How is the MDW similar?
Well my current feeling is that the MDW is based on large parasitic worms, firstly because their morphology seems to closely resemble the descriptions I have read of the MDW but also now because of their life cycle: I understand that they are microscopic (or very tiny at least) when they are eggs and hatchlings but grow to a much greater size once they colonise the intestine.
I also understand that they depend on fresh water to find a host (as in the animal drinks water containing the eggs) and give that the Gobi desert is on of the most arid places on Earth, I suspect that its oases were ideal homes for such parasitic creatures, because of the amount of animals that would drink from them, given that the oases must have been frequented by Herdsman and their animals.
(the situation in the Gobi desert and the tradition of animal Herding in Mongolia may explain why the problem was particularly acute in there: hence the name Mongolian death worm) I should also mention that some infestations of parasitic worms can be so severe that they are Fatal.
You would have a situation of constant infection and recontamination and without a full understanding (because they did not have powerful microscopes) the Herdsmen would only be able to guess at the source of the parasitic worms they found upon butchering their animals (or worms that emerged when the animal was still alive). I believe that is where the "striking from distance" idea came from, as in it was as good an explanation as any because they did not posses they necessary tools to provide a better explanation.
If we use cholera as an example it was not until relatively recently that it was understood, this and similar diseases in England were avoided by people drinking beer (Made with boiled water killing the "nasties") and I understand in the orient the same was true with Tea (boiling water again)
I just looked on wikipedia about Mongolian tea and found this:
"An old tradition among many Mongols was to not drink water straight"*
Which I believe was similar in reason to the way Beer was preferred to water in England.
*((source))
Suutei tsai - Wikipedia