[Zer0 (OP)]

Are They inside of Us?
If so, then Why does the Body not Attack or Kill them?
They are like Foreign/Alien bodies, then Why no Immune Attack?
How was the Symbiotic Mutually Beneficial Relationship formed?
For What Reasons?
Who signed the Agreement/Contract?

[evan_au]

Are They (nematodes) inside of Us?

Maybe - unless you have taken a dose of ivermectin recently and/or live in a country with a purified water supply and well-cooked food.

This group is called helminths; nematodes are just one group of the 300 or so species of parasitic worm that infects humans.
https://en.wikipedia.org/wiki/Parasitic_worm

If so, then Why does the Body not Attack or Kill them?

Many of them produces chemical signals which turn down the host immune system, avoiding rejection.

This has been put to good use by people with chronic inflammation conditions, who intentionally infect themselves with helminths; some claim good results with their debilitating inflammation condition.
- Helminth infection sometimes proves fatal in countries with inadequate sanitation, nutrition and healthcare
- In Western societies, overnutrition is a bigger threat, so a low dose of parasitic worms are not much of a threat (provided you choose the species wisely, and have a regular blood test to ensure they aren't taking too much out of your system).

[Zer0 (OP)]

WoW!

How Independent i feel, but how Dependent i am on Others.

Wonder if a Human body could Survive without Endosymbiosis?

[set fair]

Has helminth treatment been tried for hospitalised covid patients when the danger to life is the overreaction of the immune system?

[paul cotter]

I don't think that would help. The main problem with covid is the so called cytokine storm where excessive quantities of proinflamatory interleukins are released. Helminths and other parasites generally trigger the eosinophil cohort of leukocytes, part of the innate immune system.