We have already mentioned one way - getting worm eggs on hands and then somehow getting them from there to the digestive tract. This is typical of thread-worms. Contaminated food and drinks are entryway for roundworms. Tapeworm eggs are known to survive in raw or half-cooked meats and are also common in dog feces. Hookworms come from infected ground that you walk barefoot on.
Primary cause of worm infestations is poor personal hygiene and unhygienic living conditions, when it becomes easy for worm eggs to spread around and get into you.
So, do I have worms?
Once they get in the intestines, if they find adequate living conditions, worms will begin to feed on you and propagate in your intestines. A happy, thriving worm family manifests its presence in various ways, like alternating sessions of constipations and diarrhea that lead to loss of weight, cough and fever. Fever, vomiting, nausea, and irritability are other common symptoms. Severe rectal itching is is signature move of threadworms, while weight loss and inflammation of lungs and intestines are typical for roundworms.
Garlic is an ancient worm remedy. Its ingredients can enter into your body (and intestines) through your skin, so you can rub some garlic paste on if you do not wish to eat it; otherwise, three cloves at breakfast. Carrot is excellent for threadworms; try a cup of grated carrots and nothing else for breakfast for a few days. Pumpkin seed is excellent for tapeworms. Fast for a day, then take a tablespoon of peeled, crushed seeds and pour it with 250 ml of boiling water. Drink the mixture.
Papain, found in unripe papaya fruits, is effective against roundworms. Its seeds also have de-worming properties. Fresh bark of pomegranate root contains substances highly toxic to tapeworms. Flowers, leaves, bark and fruit of the Vasaka tree all have good de-worming properties. Acorin, found in calamus herbs, is one of the best de-worming agents available. You can also try a all-fruit diet for a couple of days, supported with whole-wheat bread and milk (no fats, oil, cream or butter).