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Life Cycle

 
     
   
  http://cal.vet.upenn.edu/dxendopar/parasitepages/cestodes/t_multiceps.html  
 
 

In a typical cycle, the egg of T. multiceps, T. serialis, T.brauni, and T.glomerata in dog feces is ingested by sheep (or other intermediate hosts such as humans).  The oncosphere (tapeworm embryo) hatches in the small intestine and the larval tapeworm burrows through the intestinal wall migrating through vessels and tissues until it reaches the central nervous system (CNS).  There the larva develops, forming a fluid-filled, bladder-like cyst within which multiple protoscoleces (tapeworm larvae) develop.  Such a structure is called a “coenurus”- hence the name of the disease.  The species of Taenia that cause coenurosis typically have a remarkable affinity for the CNS.  The mechanism(s) by which migrating larvae identify neural tissue and preferentially locate in the CNS is unknown.  In the CNS the coenurus enlarges slowly (reaching infective stage in about 6-8 months), causing a fatal disease in sheep called “blind staggers.”  When the dog eats the sheep and ingests the coenurus, the scolices attach to the small intestinal wall and the worms begin to form proglottids, (a section of the tape worm that contains both female and male reproductive organs).  Gravid proglottids, proglottids containing the eggs, detach from the end of the worm and pass out in the feces.  The sheep (or other intermediate hosts) eat these eggs and the cycle repeats.

Occasionally, humans become “accidental intermediate hosts” for the larvae of these tapeworms by ingesting the eggs via an oral fecal route.  This usually happens by eating contaminated fruits and vegetables.  Hence humans are “accidental intermediate hosts.” Although only about 100 cases have been reported, the larvae apparently retain their affinity for neural tissue in humans because most of these cases involve the CNS.  In order of importance, coenuri were found in brain, subcutaneous or intermuscular tissues, eye, or spinal cord.