Tapeworms

Right now, you're probably picturing a long, white, segmented, flat worm burrowing into the side of someone's intestines. Some of you probably picture hapless campers eating undercooked fish, or yuppies who don't know any better eating Sushi. Others among you may, perhaps, think that the worms are obtained from eating undercooked beef or pork. Some of you probably even imagine these worms burrowing into someone's brain. None of you are wrong- but then, you're not exactly right, either.

You see, there's not just one tapeworm that can get into people, each with their own special life cycle and possible pathogenic effects. Some of the most common tapeworms found in people are: Bovine tapeworm, Porcine Tapeworm, Fish tapeworm, and Dog tapeworm. The Bovine tapeworm is actually benign in Humans (though quite pathogenic for cattle), except in rare cases where bowel obstruction may occur- the worm, "knowing" that it's in a human, sits in your upper small intestine and simply takes a very small portion of your meals to sustain itself. You won't lose weight, contrary to popular myth, and you will likely never know if you are infested. Occasionally, a worm segment will detach and be shed from your body, ideally shedding the egg-filled segment in a grassy area where the eggs will subsequently be consumed by a cow. Once in the cow, conformational changes in the eggs occur as they pass through each of the cow's four stomachs (which is what prevents them hatching in a human) which cause them to hatch. The juvenile worms then proceed out through the intestinal wall and burrow into the cow's various bodily tissues, including muscle, organ, and brain. Once there, the worms remain dormant until the cow is slaughtered and consumed- in this case, by a human who failed to cook the meat thoroughly enough to kill the juvenile worm- completing the life cycle.[1]

As creepy as Bovine tapeworms are, they're the most benign of the various tapeworms. The next worm we'll look at is the fish tapeworm. As with the cow tapeworm, the fish tapeworm infests its host through ingestion of the juvenile stage in undercooked meat. Disease from the fish tapeworm is rare, but it can cause bowel obstruction and, in very rare cases, liver and gall bladder disease. Also, this is the largest among the tapeworms that can infest humans, growing up to thirty feet in length. Sushi lovers need not despair! The fish tapeworm has only ever been found in freshwater fish, and can be readily killed by freezing the meat. Just cook your freshwater fish, and you'll be fine. [2]

The dog tapeworm is a special cycle, where infestation of humans is a complete accident, as far as we can tell. Taenia Hydatigena, which sheds an infectious stage in canine stool, can be ingested by various mammals- typically sheep- and people. Once consumed, the worm leaves the intestine, and forms a large cyst in the abdominal cavity, where it produces more larvae and hides from the intermediate host's immune system while it's waiting for the host- and therefor, the cyst- to be eaten by a dog. If the cyst is ruptured prematurely, such as by abdominal trauma, many thousands of larvae can be released into the abdominal cavity. In Humans, the immune system can recognize the worm from the initial, infectious encounter, which can lead to the sudden onset of anaphylaxis and death subsequent to the worms' release into the abdominal cavity. Failing the rupture of the cyst, you could live a full and healthy life with this worm and be none the wiser. [3]

The Piece de Resistance here is the porcine tapeworm- Taenia Solium. The intent of the porcine tapeworm's life cycle is suspected to be much like that of the bovine worm's, in that the worm exists as a cyst-encased juvenile stage in the various tissues of a pig's body, waiting for consumption by a human. Once consumed, the juvenile develops into a fully fledged worm in the intestines of a human, and sheds eggs to be consumed by pigs. The really scary part about this worm is one of the few things that we'll go over here that's genuinely terrifying- the worm's eggs cannot tell the difference between a human gut tract and a porcine gut tract. If you were to eat bovine tapeworm eggs, no disease would develop. If, however, you were to consume porcine tapeworm eggs because, say, a restaurant chef who is infested didn't wash their hands after they had a stool, the eggs would hatch, and you would develop Cysticercosis (the juvenile stage of the worm in your various tissues). One famous form of this is Neurocysticercosis, where you actually develop juvenile stage worm cysts in your brain, potentially with pathogenic effects, including seizures, headaches, confusion, excess fluid on the brain, difficulty maintaining balance, and death (severity dependent on the number of cysts). What makes it scary is that its epidemiology is subtle and hard to avoid- it's not somebody sneezing, pouring blood out of every pore, or eating undercooked meat; it's as easy as someone else not washing their hands.[4][5][6]

So what can you do? WASH YOUR FILTHY MEAT HOOKS. Washing your hands regularly and after you use the bathroom is how you can help prevent the spread of almost every transmissible disease. There are medications you can take that will treat tapeworm infestation, so see your practitioner if you suspect that you're infected. Make sure that you cook all your meat thoroughly before consumption. As always, you can help by sharing what you've learned here (and sharing the facebook post it rode in on), doing your own research, and supporting those who support science! If you have any questions, comments, or concerns, feel free to leave them on the blog here, or ask me on the facebook post.






[1]http://bioweb.uwlax.edu/bio203/s2009/temanson_caro/Life%20Cycle.htm
[2]http://www.cdc.gov/parasites/diphyllobothrium/
[3]http://www.vetsonline.com/publications/veterinary-times/archives/n-43-46/cysticercosisa-a-controlling-tapeworm-in-dogs-and-sheep.html
[4]http://www.cdc.gov/parasites/taeniasis/biology.html
[5]http://www.cdc.gov/parasites/cysticercosis/disease.html
[6]http://www.cdc.gov/parasites/cysticercosis/