They are like roaches in the house and fleas on your pets. They will come back and you will have to eliminate them again, and again, and again.
I've heard that it takes 9 cycles of taking anti-parasiticals for 10 days on and 10 days off, to get them completely out of your system. Some say 10 days on, 5 days off. Others say 90 days on, 30 days off. I guess it depends on what kind of parasites you have in your system, which products you are using and who's advising you. Listen to your body and it will guide you.
Adult females lay thousands of eggs, which (I've been told) don't hatch out until their "Mama" is dead. Apparently the eggs are sensitive to the adult females hormones, or something, and they remain dormant until the female that laid them is dead, then they hatch out. I am not sure if all this information is correct. It is just what I've heard.
If you completely change your lifestyle to minimize recontamination, you can probably just do routine maintenence for a few days each month and keep them at a minimum. People here say the best time to go after them is around the full moon, because that is when they are most active.
It is my understanding that parasites and eggs are everywhere. They are in the air we breath, fruits, vegetables, water, meat, dairy, pets, soil, etc etc. Some people have strong immune systems, and parasites don't flourish in their bodies. Those of us with compromised immune systems and chronic illnesses are more vulnerable and sensitive to serious infection, and prone to serious reinfection. The more you do to strengthen your immune system, and avoid recontamination the better.
If you don't change your diet and lifestyle, decontaminate your pets, drink pure water, get more exercise, etc, etc, you will probably have to take anti-parasiticals most of the time. They say parasites will become resistant to remedies if you take them continuously, so it is important to rotate the herbs you take.