cestodes

• Presented by Alcantara, Christian Dave, Bantilan, Elisa Jane, Baraquiel Sophea
• MICROBIOLOGY AND PARASITOLOGY
• Learning Objectives


  • Describe the general characteristics of the cestodes
  • Understand cestode morphology and developmental stages
  • Characterize the different cestodes as their: a. general features, b. source of infection, c. mode of transmission, d. clinical manifestations, e. treatment, and f. prevention and control of infection
• Proglottid


  A segment of a tapeworm's body containing reproductive organs

  
• Hexacanth/Oncosphere


  Early larval form characterized of having six hooklets and an embryo sac

  
• Cysticercus


  Developmental stage of larva consisting of an inward premature scolex
• Bladder Worm


  Larva scolex is folded outward
• Neodermis/Tegument


  Surface of the parasite that is rich in microvilli allowing absorption of nutrients

  
• Taxonomy


  • Domain: Eukarya
  • Kingdom: Animalia
  • Phylum: Plathyhelminths
  • Class: Cestoda
  • Subclass: Eucestoda
• Often referred to as primitive worms, but commonly known as tapeworms
• Lacks nervous and digestive system. Absorbs and eliminate wastes through the tegument/neodermis
• Morphology


  • Head - contains the organ of attachment called the scolex. scolex of some species contain fleshy extension called rostellum
  • Neck - connects the head and the body. Region of growth
  • Body - divided into segments called proglottids. series of proglottids are called storbila/strobili. Each proglottid contain reproductive systems

  
• Life Cycle


  • Egg
  • Larva
  • Adult Worm

  
• Taenia saginata (Beef Tapeworm)


  • Intermediate host is cattle where the eggs enter the blood vessels within the cattle's intestines. The eggs are then transported to the skeletal muscles of the cattle where they develop into cysticerci (larvae). Infection with the beef tapeworm is acquired by ingestion of improperly cooked or raw beef containing the infective larva (called cysticercus). These larvae then mature into adult worms (pathogenic stage) in the small intestines within a period of approximately 3 months. These tapeworms are known to achieve a length of as much as 10 meters. Humans serve as the definitive hosts.

  
• 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).

  
• Laboratory Diagnosis


  Examination of fecal specimens from infected patients. Eggs or gravid proglottids may be recovered from the stool although eggs are less often found than the proglottids.

  
• Treatment


  The drug of choice against the adult worm is praziquantel.
• Prevention and Control


  Proper waste disposal, sanitation practices and adequate cooking of beef. Freezing of beef meat for approximately 10 days may kill the encysted larvae.
• Taenia solium (Pork Tapeworm)


  • Infection with the pork tapeworm is acquired through ingestion of improperly cooked or raw pork meat which contains the infective larva called cysticercus cellulosae. Unlike the beef tapeworm, T. solium infection can also occur following the ingestion of food or water contaminated with human feces that contain the eggs of the parasite. Therefore, unlike the beef tapeworm, T. solium has two infective stages-eggs and larvae. Autoinfection may also occur. Pigs serve as the intermediate host while humans serve as both intermediate and definitive hosts.

  
• Comparison of scolex and gravid segments of Taenia saginata and Taenia solium


  • Scolex: Number of suckers, Rostellum, Hooks

  Gravid Proglottid: Appearance, shape, Number of uterine branches on each side of uterus

  
• Taeniasis


  Most cases are asymptomatic.
• Cysticercosis


  The result of larval encystation in various tissues of the body. Neurocysticercosis can lead to increased intracranial pressure (seizures, headache, and vomiting). Ocular cysticercosis may lead to visual disturbances.
• Laboratory Diagnosis


  Microscopic examination of stool specimens. Biopsy or CT scan.
• Treatment


  Drug of choice: Praziquantel. Alternative drugs: Albendazole, Paromomycin, Quinacrine Hydrochloride. Anticonvulsants may be given in cases of neurocysticercosis.
• Prevention and Control


  Proper waste disposal and sanitary measures, thorough cooking of pork meat. Prompt treatment of infected persons to prevent the spread of the parasite.

  
• Diphyllobothrium latum (Broad Fish Tapeworm)


  • The infective stage of the fish tapeworm for humans is the larvae, known as plerocercoids, which are present in the muscle tissue of certain freshwater fish. When humans consume raw or undercooked fish containing these larvae, they become infected as the larvae develop into adult tapeworms in the intestines.

  
• Diphyllobothriasis


  1. Asymptomatic disease - the most common presentation among most individuals infected with the parasite

  2. Diphyllobothriasis - may manifest with symptoms of gastrointestinal involvement, which may include diarrhea and abdominal discomfort. When the adult worm attaches itself to the jejunum and ileum, the patient may develop deficiency of vitamin B12, leading to anemia similar to pernicious anemia and is characterized as megaloblastic anemia resulting from lack of maturation of red blood cells.

  
• Laboratory Diagnosis


  Diagnosis is based on finding of the characteristic eggs and/or the proglottids (less frequent) in a stool specimen.
• Treatment


  Ideal drug for diphyllobothriasis is praziquantel. Alternative drug is niclosamide.
• Prevention and Control


  Proper sanitary procedures, thorough cooking of fish prior to consumption, and the prompt treatment of infected individuals to prevent spread of the parasite. Freezing of the fish for 24-48 hours at -18 °C can kill all larvae.

  
• Hymenolepis nana (Dwarf Tapeworm)


  • Hymenolepis nana can complete its entire life cycle within a single host, which means humans can become both the definitive host (where the adult tapeworm lives) and the intermediate host (where the larvae develop).

  
• Hymenolepiasis


  Most patients are asymptomatic. In cases of high worm burden, patients may complain of nausea, weakness, loss of appetite, diarrhea, and abdominal pain. In young children with heavy infection, anal itchiness (pruritus ani) may occur leading to headaches due to difficulty sleeping. It can be confused with a pinworm infection. Autoinfection may lead to hyper-infection syndrome which can result in secondary bacterial infection and spread of the worms to other tissues of the body.

  
• Laboratory Diagnosis


  Diagnosis is established by finding the characteristic eggs in stool specimen.
• Treatment


  Praziquantel is the drug of choice. Niclosamide can be an alternative drug.
• Prevention and Control


  Important preventive measures include proper hygiene and waste disposal, control transport host population, and rodent control. Proper storage of grains and flour must be observed to prevent infestation with flour and grain beetles. Prompted flour must be instituted to prevent the spread of the parasite.
• Echinococcus granulosus (Dog Tapeworm or Hydatid Tapeworm)


  • A zoonotic type of infection. Dogs are the most important definitive hosts while sheep are usually the intermediate hosts. Dogs acquire the parasite by eating the visceral organs of the intermediate host. Infection is acquired after ingestion of eggs from food and water contaminated by dog feces or through contact with contaminated dog feces. The diagnostic stage of the parasite is its larval form, which is encased in a cyst wall and is called the hydatid cyst. Humans are considered as accidental and dead end hosts.

  
• Echinococcosis


  The two most important forms in humans are cystic echinococcosis (also known as hydatidosis) and alveolar echinococcosis.
• Laboratory Diagnosis


  Examination of biopsy specimens, Serologic tests (eg, ELISA or indirect hemagglutination test), Radiography to demonstrate the hydatid cysts (e.g., CT scan or ultrasound).
• Treatment


  Removal of the cyst has been considered as the treatment of choice. However, medical management alone may prove effective, especially if the cyst is located in inaccessible areas. Drugs that have been proven effective include mebendazole, albendazole, and praziquantel.
• Prevention and Control


  Personal hygiene practices, avoidance of feeding pet dogs with contaminated viscera, and the prompt treatment of infected canines and humans are some measures to prevent the spread of the parasite. Chemoprophylaxis should be given to dogs in endemic areas. Health education is essential.