Finals

• Cestodes


  Classified under the sub-kingdom Metazoa, phylum Platyhelminthes, considered as primitive worms with no digestive system nor a nervous system, they absorb nutrients and eliminate waste products through their outer surface called the tegument, commonly known as tapeworms

  
• Tegument


  • The host-parasite interface, and metabolically active body covering performing all the vital activities such as protection, absorption and secretion

  
• Head


  • Contains an organ of attachment called the scolex, which may consist of either hooks, suckers, or sucking grooves, some species have a fleshy extension called a rostellum to which hooks may be attached
• Neck


  • Serves as the region of growth and connects the head to the body of the worm, the worm grows by adding new proglottids from the neck
• Body


  • Divided into multiple segments (proglottids), a series of proglottids is called strobila
• Reproductive Organs


  • All cestodes are hermaphroditic (self-fertilizing) with each proglottid containing both male and female reproductive organs, each proglottid is capable of laying eggs (gravid segment)
• Cestode life cycle


  1. Egg

  2. Larva

  3. Adult worm

  
• Infection in humans


  Usually acquired through ingestion of the undercooked or raw flesh of the intermediate host containing the infective larvae, the ingested larvae are transformed into adult worms in the intestines of the infected host, the adult worm then undergoes self-impregnation with the gravid segment rupturing to release the eggs in the intestines, the eggs are then passed out to the external environment during defecation

  
• Egg


  • Contains an embryo called the oncosphere, which represents the first larval or motile stage, equipped with small hooks (hooklets) that enable the parasite to pierce the wall of the intestines
• Intestinal Cestodes


  • Taenia saginata (Beef Tapeworm)
  • Taenia solium (Pork Tapeworm)
  • Diphyllobothrium latum (Broad Fish Tapeworm)
  • Echinococcus granulosus (Dog Tapeworm or Hydatid Tapeworm)

  
• Taenia saginata (Beef Tapeworm)


  The intermediate host is cattle where the eggs enter the blood vessels within the cattle's intestines

  
• Taenia solium (Pork Tapeworm)

  Infection is acquired through ingestion of improperly cooked or raw pork meat which contains the infective larvae called cysticercus cellulosae, can also occur following the ingestion of food or water contaminated with human feces that contain the eggs of the parasite, has two infective stages - eggs and larvae, pigs serve as the intermediate host while humans serve as both intermediate and definitive hosts

  
• Diphyllobothrium latum (Broad Fish Tapeworm)


  The longest of the tapeworms, can reach a length of about 13 meters, its eggs consist of ciliated larvae called coracidia, one end of the egg is occupied by a lid structure called an operculum, its scolex contains a pair of long sucking grooves, the gravid segments contain a uterine structure that is centrally located and assumes a rosette formation, human infection is through ingestion of improperly cooked or raw fish containing the plerocercoid (infective stage), the plerocercoid attaches to the intestinal mucosa and matures into the adult worm, the adult worm self-fertilizes and the eggs are passed out with the stool, if the eggs come to contact with fresh water, the coracidium hatches and is ingested by the first intermediate host, a tiny crustacean

  
• Diphyllobothrium latum


  Broad Fish Tapeworm

  
• Diphyllobothrium latum


  • The longest of the tapeworms, can reach a length of about 13 meters
  • Its eggs consist of ciliated larvae called coracidia
  • One end of the egg is occupied by a lid structure called an operculum
  • Its scolex contains a pair of long sucking grooves
  • The gravid segments contain a uterine structure that is centrally located and assumes a rosette formation

  
• Life cycle of Diphyllobothrium latum

  1. Human ingestion of improperly cooked or raw fish containing the plerocercoid (infective stage)

  2. Plerocercoid attaches to the intestinal mucosa and matures into the adult worm

  3. Adult worm self-fertilizes and the eggs are passed out with the stool

  4. Eggs hatch into coracidia which are ingested by a copepod (first intermediate host)

  5. Coracidium develops into procercoid in the copepod

  6. Copepod is eaten by a freshwater fish (second intermediate host) where the procercoid develops into the plerocercoid

  
• Definitive hosts for Diphyllobothrium latum are humans and other fish-eating mammals such as dogs, cats, bears and seals

  
• Diphyllobothriasis


  Disease caused by Diphyllobothrium latum infection
• Symptoms of diphyllobothriasis


  • Asymptomatic
  • Gastrointestinal symptoms (diarrhea, abdominal discomfort)
  • Vitamin B12 deficiency leading to megaloblastic anemia
• Diagnosis is based on finding the characteristic eggs and/or proglottids in stool specimen
• Praziquantel


  Drug of choice for treatment of diphyllobothriasis
• Niclosamide


  Alternative drug for treatment of diphyllobothriasis
• Preventive measures for diphyllobothriasis

  • Proper sanitary procedures
  • Thorough cooking of fish prior to consumption
  • Prompt treatment of infected individuals
  • Freezing of fish at -18°C for 24-48 hours
• Hymenolepis nana


  Dwarf Tapeworm

  
• Hymenolepis nana


  • Does not require an obligatory intermediate animal host
  • Eggs are directly infectious and humans get the infection after accidental ingestion
  • Eggs may be ingested through contaminated food/water, touching mouth with contaminated fingers, or ingestion of contaminated soil
  • Accidental ingestion of rice or flour beetles containing the infective larvae is another way of acquiring the infection
  • Rodents serve as additional source of infection

  
• Life cycle of Hymenolepis nana

  1. Ingestion of eggs (infective stage)

  2. Eggs transform into cysticercoid larvae which mature into adult worms

  3. Eggs are released after disintegration of gravid segments

  4. Some eggs may remain inside the human host and hatch into larvae, leading to autoinfection
• Hymenolepis nana is the most common tapeworm recovered in the United States

  
• Symptoms of hymenolepiasis


  • Asymptomatic
  • Nausea, weakness, loss of appetite, diarrhea, abdominal pain
  • Anal itchiness (pruritus ani) in children with heavy infection
  • Can be confused with pinworm infection
  • Autoinfection may lead to hyperinfection syndrome
• Diagnosis is established by finding the characteristic eggs in stool specimen
• Praziquantel


  Drug of choice for treatment of hymenolepiasis
• Niclosamide


  Alternative drug for treatment of hymenolepiasis
• Preventive measures for hymenolepiasis

  • Proper hygiene and waste disposal
  • Control of transport host population
  • Rodent control
  • Proper storage of grains and flour
• Echinococcus granulosus


  Dog Tapeworm or Hydatid Tapeworm

  
• Echinococcus granulosus


  • Primarily a zoonotic infection
  • Dogs are the most important definitive hosts, while sheep are usually the intermediate hosts
  • Humans are accidental and dead-end hosts
  • The diagnostic stage is the larval form called the hydatid cyst

  
• Life cycle of Echinococcus granulosus

  1. Ingestion of eggs (infective stage) from contaminated food/water or contact with dog feces

  2. Eggs transform into larvae in the intestines, penetrate the intestines, and migrate to different tissues

  3. Hydatid cyst (pathogenic stage) develops in the infected tissues

  4. Dogs acquire the parasite by eating the visceral organs of the intermediate host

  
• Echinococcus granulosus infection is common in Africa, Europe, Asia, the Middle East, Central and South America, and in rare cases, North America
• Hydatid cyst


  • Acts as a space-occupying lesion
  • Cyst fluid contains antigens that can sensitize the host
  • Rupture of the cysts may lead to anaphylaxis and widespread dissemination of the parasite
• Clinical manifestations of echinococcosis

  • Asymptomatic in early stages
  • Obstructive jaundice with liver involvement
  • Cough, chest pain, shortness of breath with lung involvement
  • Involvement of other organs like spleen, kidneys, heart, bone, CNS, brain, eyes
  • Cyst rupture may lead to anaphylactic shock
• Diagnostic methods for echinococcosis

  • Examination of biopsy specimen
  • Serologic tests (e.g. ELISA, indirect hemagglutination)
  • Radiography (CT scan, ultrasound) to demonstrate hydatid cysts
• Mebendazole, albendazole, praziquantel


  Drugs used for medical management of echinococcosis when cyst is in inaccessible areas