Microbiology and Parasitology

• Cestodes


  Parasitic flatworms classified under the subkingdom Metazoa, phylum Platyhelminthes
• Cestodes


  • Do not possess a digestive system nor a nervous system
  • Absorb nutrients and eliminate waste products through their outer surface called the tegument
  • Commonly known as tapeworms
  • Flat and consist of three distinct regions: head, neck, and body (proglottids)
  • Head contains an organ of attachment called the scolex
• Cestodes are considered as primitive worms
• Scolex


  • Consists of either hooks, suckers, or sucking grooves
  • May have a fleshy extension called a rostellum to which hooks may be attached
• Body


  • Divided into multiple segments (proglottids)
  • A series of proglottids is called a strobila
• Cestodes


  • Are hermaphroditic (self-fertilizing)
  • Each proglottid contains both male and female reproductive organs
  • Each proglottid is capable of laying eggs (gravid segment)
• Neck


  • Serves as the region of growth and connects the head to the body
  • The worm grows by adding new proglottids from the neck
  • The oldest proglottids are found at the most distal part of the body
• Cestode life cycle


  1. Egg

  2. Larva

  3. Adult worm
• Egg


  • Contains an embryo called the oncosphere
  • Equipped with small hooks (hooklets) that enable the parasite to pierce the intestinal wall
  • Excreted in host feces and transmitted to intermediate hosts (cattle, pig, fish)
• Infection in humans


  1. Ingestion of undercooked or raw flesh of intermediate host containing infective larvae

  2. Ingested larvae transformed into adult worms in host intestines

  3. Adult worm undergoes self-impregnation

  4. Gravid segment ruptures to release eggs in host intestines

  5. Eggs passed out in host feces
• Taenia saginata (Beef Tapeworm)


  • Intermediate host is cattle
  • Eggs enter cattle blood vessels and develop into cysticerci (larvae) in skeletal muscles
  • Humans are the definitive host
• • Eggs of T. saginata are indistinguishable from T. solium (pork tapeworm)
  • Differentiated by scolex and proglottid structures
• T. saginata scolex


  Does not contain a rostellum
• T. saginata proglottid


  Rectangular in appearance with 15-30 uterine branches
• T. solium proglottid


  Square in appearance with 7-15 uterine branches
• T. saginata infection is common in areas where beef is routinely eaten, especially undercooked
• Adult T. saginata worms do not produce significant damage in the small intestines
• Taeniasis


  • Majority of patients are asymptomatic
  • High worm burden may cause diarrhea, abdominal pain, loss of appetite, weight loss, and body malaise
  • Gravid proglottids may reach anus causing itchiness (pruritus ani)
• Examination of fecal specimen is the procedure of choice for diagnosis
• Praziquantel is the drug of choice against the adult worm
• Prevention and control


  • Proper waste disposal and sanitation
  • Adequate cooking of beef
  • Freezing of beef meat for 10 days to kill encysted larvae
  • Prompt treatment of infected persons
• Taeniasis


  A disease
• Taeniasis


  • Majority of patients are asymptomatic
  • Those with high worm burden may complain of diarrhea, abdominal pain, loss of appetite with resultant weight loss, and body malaise
  • The gravid proglottids may reach the anus where egg-laying may occur resulting in itchiness in the anal region (pruritus Ani)
• Taenia Solium - pork tapeworm
• Taenia solium


  Pork Tapeworm
• Eggs of Taenia solium can be found in human stool
• Taenia solium


  • Infection acquired through ingestion of improperly cooked or raw pork meat containing infective larva called cysticercus cellulosae
  • Infection can also occur through ingestion of food or water contaminated with human feces containing parasite eggs
  • Has two infective stages: eggs and larvae
  • Pigs serve as intermediate host, humans serve as both intermediate and definitive hosts
• Taenia Saginata - Beef Tapeworm
• 69 bns yooloias
• Infection acquired through ingestion of undercooked or raw pork meat

  1. Larval form transforms into adult worm in infected individual's intestines

  2. Humans serve as definitive hosts
• Infection acquired through ingestion of worm eggs

  1. Eggs hatch in small intestines, burrow through intestinal wall into blood vessel, disseminate to various organs

  2. Humans serve as intermediate hosts
• Cysticerci develop into adult tapeworms in the small intestines of man
• Infection with the pork tapeworm is acquired through ingestion of improperly cooked or raw pork meat which contains the infective larvae called cysticercus cellulosae. 
• T. Solium has two infective stages 

  • Egss 
  • Larvae 

  Pigs as the Intermediate host while humans serve as both intermediate and definitive hosts.
• king

  Number of uterine branches on each side of uterus
• Number of uterine branches on each side of uterus

  • 15-30
  • 7-15
• T. solium infection is more prevalent in underdeveloped communities with poor sanitation and where people eat raw or undercooked pork
• Higher rates of illness have been seen in people in Latin America, Eastern Europe, sub-Saharan Africa, India, and Asia
• Adult worms produce little damage in the intestines
• Encysted larvae may produce damage in the tissues where they disseminate