They will come from the food you eat and the dirt and filth where you live. Some will look exactly like angle worms 5 times enlarged. Although there are other symptoms, positive proof that you are infested is when a worm crawls out of your nose. That undoubtedly will shake you up a bit. It always does.
Personal hygiene is the best preventive measure against parasitic infestations.
You may not be really clean from the day you go down until you get out, but there are things you must try to do. Wash your body and clothes as often and as well as you can. An above all, pick lice off at least daily. Kerosene is more effective but gasoline will do. Either will make you a bit sick, but will make the worms a lot sicker.