Trichobilharzia szidati (causing Swimmer's itch

Parasite of the day ^ | March 15, 2016 | Tommy Leung

[AdmSmith]

If you have ever gone for a swim in a lake and later found your arms and legs covered in red itchy welts resembling mosquito bites, it is quite likely that you have encounter parasites related to the one being featured today. Trichobilharzia szidati is an avian blood fluke, and it has relatives living all over the world in both freshwater and marine environments. While they usually infect waterbirds like duck, they are not very good at telling birds apart from humans. To them, any warm-blooded terrestrial vertebrate animal is fair game, which is rather unfortunate for both humans and flukes alike - more so for them than us. As a result of this encounter, we end up covered in intensely itchy spots, but getting under the skin of a human means immediate death for such flukes.

So why is that the case? Blood flukes are masterful molecular mimics - they are able to disguise themselves with proteins that resembles the host's own molecules, allowing them to stealthily sneak pass the host's immune system. But Trichobilharzia szidati and similar avian blood flukes have evolved to bypass the immune system of birds, and when it encounters a mammalian immune systems like ours - all bets are off. Our immune system takes immediate action against this intruder with extreme prejudice, which results in an inflammatory reaction that manifest itself as "duck itch" or "swimmer's itch".

[AdmSmith]

In a large fish pond with a relatively low infection prevalence such as 5%, the infected snails would be contributing about a 500 kilograms of biomass per year in the form of T. szidati cercariae. But in some location where almost half the snails are infected at any given period, the yearly output of all these snails can add to to 4.65 tons of parasite larvae, which weighs as much as an Asian elephant.

[AdmSmith]

As an alternative to politics here are some other parasites ;-)

[DannyTN]

Here's a fluke parasite...

[AdmSmith]

... with relatives living all over the world in both freshwater and marine environments.

LOL!