Ask a Scientist : “What is a Parasite” Featuring the Tapeworm
This is a continuation of the lecture on parasites by Dr. Jim McKerrow from the Department of Pathology at the University California San Francisco. Jim presented his parasites, or rather his lecture on them, at the StrEAT Park in the Mission District in San Francisco.
The diners absorbed details of the the tapeworm over their Mexican food and beer from the various food trucks in the food park. Warmed by the overhead gas lamps in the tent, we learned how we can become infected with tapeworms from eating undercooked pork or beef.
These parasitic helminths, Taenia saginata (beef Tapeworm), or Taenia solium (pork tapeworm), reside in the intestines of its definitive host by hooking their four heads (or scolex) into the walls of the intestines and absorbing nutrients intended for the host. It can reside there for up to 25 years.
This not so little flat worm reaches lengths of up to 6 meters… The strange sexual beast contains both reproductive organs. Each segment or proglottid making up the length of the worm contain ovaries and testes. There may be up to a 1000 proglottids making up the length of this flat worm. Remember; this creature is approximately 6 meters long. That’s a lot of balls. This parasite can create many more tapeworms as each mature poglottid breaks down and releases eggs which end up in feces of the definitive host.
The eggs make their way into the next host (intermediate host) when it consumes infected food from the feces, or eggs from the feces. The eggs hatch in the intestines and the larvae make their way to the liver, lungs and or, brain and develop a cyst. One cyst produces many scoleces (heads) or larvae. When these cysts are consumed by the unsuspecting human or animal, the scoleces (singl. Scolex) will embed into the intestinal wall of its host and the cycle continues.
Introduction to Microbiology, 9th Edition, Tortora, Gerard.J, Funke, Berdall R., Christine L. Case. Publisher: Pearson Benjamin Cummings. 2007 print.
CDC Taeniasis (Tapeworms)
Ask a Scientist website
Dr. Jim McKerrow page at UCSF