Diphyllobothrium latum is also known as the broad fish tapeworm. There are many different host species, mainly those carnivores which eat fish, and this includes man. These worms can reach to a length of 10 meters and can shed in the region of one million eggs per day. The eggs are ovoid with an operculum (cap) at one end and a knob at the other and measure 60 x 40 microns in size. When they are released into the intestine they are only partially embryonated and require from 8 days to several weeks for the infective coracidium to develop. When the eaten by the definitive host it passes through the stomach and the scolex becomes embedded in the mucosa of the small intestine and develops rapidly producing eggs within 10-14 days. People generally become infected when uncooked fish are eaten and it is particularly prevalent in those cultures which eat a lot of freshwater fish and prepare it by methods other than cooking.
In many cases human infections go largely unnoticed, because of the nonspecific symptoms such as intestinal discomfort, nausea, and diarrhea. However, in some cases pernicious anaemia develops which is related to the malabsorbtion of vitamin B12.
There are a large number of possible drugs available to treat this disease, the two main ones used are Niclosamide and praziquantel, both of which are highly effective.
Effective control measures include cooking fish properly or freezing the fish down below -12 C for a minimum of 24 hrs.
The photomicrograph above shows the operculated eggs of Diphylobothrium latum with the pointer pointing at the cap. A wet preparation of a concentrated faecal sample was made. x800. Fecal material and bacteria can be seen in the background.