I am going to travel to the US from Moscow, making a 2-hour stopover in London, then from the US I will travel to Ecuador in less than 24 hours of waiting. Is there any current restriction to enter the country (USA) due to current Covid events?

If you travel from a place that is with a high rate of contagion, you must quarantine in the US, but if not, you have to fill out an online form to enter the US, and then to enter Ecuador you have to travel with you the results of the covid test, carried out by isopado, that test has to be less than a week. The blood test won't do.

They are supposed to bring the test results with them oseha test performed covid I do not know what mask and social distance always hand sanitacer I think this is the return

You should only keep a quarantine for fourteen days and have contact with people as little as possible during that 14 days.