Under anesthesia, parasitic worms are sometimes fooled into believing the host is dead and make a quick exit.
Onchocerca volvulus in the early stages. You don't want to see the later stages.
Stillwater's Lily Lake, linked to parasite that killed boy, ripe for illness - TwinCities.com
Use that Frontline stuff on your cat or dog once a month. It's expensive but it works.
Keep your cats indoors. Do not change their litterboxes without gloves if you have cuts or open sores on your hands:
Cat poop parasite controls minds early -- and permanently, study finds - NBC News
Cook your meat! None of this: "I like my steaks so rare, they're squirming on the plate" idiocy. Cook that s-hit! After handling raw beef, wash your hands with soap and water at least a couple of times before touching ANYTHING.
Never eat any meat raw not even hotdogs or bacon--it can be deadly if eaten raw. Do not eat raw dough or raw eggs. It's especially important to watch that kids don't do this stupid stuff for kicks. The parasites are already in the food and must be killed via thorough cooking. Also make sure kids wash their hands with soap and water after defecating (adults too, I've seen some that don't).
I carry napkins and tissue paper in my pockets everywhere I go because I will not open a public restroom door with my bare hands. Also, use your foot to flush a public toilet--don't touch the handle. All it takes a little fecal matter to get on your hands then you touch your lips or rub your eyes. That's all it takes.
Waterborne Diseases | A-Z List
Take a shower with soap and water immediately before going into a public pool (and make sure you wash your a-sshole!) and take another immediately after getting out. If a public pool does not have these showers and make them mandatory for all swimmers, DO NOT swim in that pool!
CDC Online Newsroom | Press Release | CDC study finds fecal contamination in pools
You have been warned.