MICROBIOLOGY

• Taenia saginata (beef tapeworm), Taenia solium (pork tapeworm), Taenia asiatica (pork tapeworm), and Taenia hydatigena (canid tapeworm) are intestinal cestodes.
  
  • All Taenia species can cause tapeworm infection of the human intestine (Taeniasis) by ingesting larvae in undercooked meat.
  • T. saginata does NOT cause cysticercosis.
    • T. solium is the primary cause of human cysticercosis by ingesting proglottids or eggs through fecal-oral transmission; T. hydatigena can also cause human cysticercosis.
• Epidemiology:
  • T. saginata is the most common and widely distributed human tapeworm, infecting 60 million people worldwide.
  • Endemic throughout Latin America, Africa, Central Asia and the Middle East; less common in Europe and Southeast Asia; uncommon in Australia and the U.S., but epidemiology may shift with increased global migration.
• Life cycle:
  • Eggs or gravid proglottids are passed in the stool.
  • Cattle ingest contaminated vegetation, and oncospheres hatch in the intestine.
  • Organisms invade the intestinal wall, migrate to striated muscles, and develop into cysticerci.
  • Humans ingest raw or undercooked infected meat, and gastric juices activate larvae, leading to the evagination of scolex and attachment to the jejunum.
  • Over 2-3 months, cysticercus develops into an adult tapeworm; it may grow up to 10 meters long and live up to 25 years.
• Adults may have 1,000-2,000 proglottids containing tens of thousands of eggs and a distinctive scolex with 4 disks.
• Eggs are spherical, thick-walled, and radially striated, measuring 30-35 microns in diameter.