Another reason not to eat raw or undercooked fish
Diphyllobothrium latum is the largest of the humanopathogenic tapeworms and can be found in the northern hemisphere, Chile and Uganda. The highest incidence is apparently in areas around rivers where humans consume raw fish (which is something I've never fully understood anyway, but that's not of interest here).
The eggs are being passed into the water via the faecal route and after maturing into a copepod they wait to be picked up by a suitable intermediate host, most of the time a sweetwater fish (i.e. a minnow). There they develop into larvae and migrate into the fish flesh. These small sweetwater fish are notr really part of the human diet, but they are certainly on the menu of trout and pike, and the larvae use the opportunity to infect these bigger fish.
When eaten by humans, the larvae develop into mature worms and attach themselves to the small intestine of the human host and start to grow. A fully grown Diphyllobothrium latum can measure up to 10m and can stay up to 10 years in the host. My budgies never lastet that long.
Symptoms are usually rare, but anaemia, abdominal discomfort, diarrhoea and very rarely intestinal obstruction are associated with D.L., and eggs are easily found microscopically in the patient's stool.
Treatment is with good old Praziquantel and seems to work ok, but I'd rather not have the little monster in my tummy at all.
I always knew there was a reason I don't like Sushi..
http://www.dpd.cdc.gov/dpdx/HTML/diphyllobothriasis.htm
http://www.cdfound.to.it/HTML/dip1.htm
http://cal.vet.upenn.edu/dxendopar/parasitepages/cestodes/d_latum.html