MBP TREMA

• Trematodes


  Commonly known as flukes, belong to the class Trematoda or Digenea
• Trematodes


  • May be hermaphroditic or dioecious (reproduce via separate sexes)
  • Most flukes are hermaphroditic except Schistosoma spp. (blood flukes)
  • Morphologically, flukes are fleshy, leaf-shaped worms
  • Unlike tapeworms, flukes have a digestive tract
  • Have two (2) muscular suckers, an oral type and one (1) ventral sucker for attachment
• Eggs


  • Primary morphologic stage that usually recovered from humans
  • Some eggs may possess a lid-like operculum structure that can flip open to release its contents
• Unlike in cestodes infections, humans never serve as intermediate hosts for the flukes
• Flukes have two intermediate hosts except for the blood flukes where there is only one intermediate host
• First intermediate hosts are mollusks (snails and clams) where asexual reproduction takes place
• Sexual reproduction of flukes occurs in humans
• Humans acquire the infection through ingestion of undercooked or raw second intermediate host, except for blood flukes where skin penetration by the infective larvae is the major mode of transmission
• Blood-dwelling flukes


  Schistosoma spp.

  
• Schistosoma spp.


  • Dioecious, known as the "romantic parasites", the male and female worms are usually in a state of copulation (en copula)
  • Female worms are usually larger than the male worms
  • Obligate intravascular parasites
• Life cycle of Schistosoma spp.

  1. Eggs in fresh water develop into miracidium, that will then locate a snail as its host, where it transforms into cercariae

  2. Infection is acquired through skin penetration by the fork-tailed cercariae (larval form)

  3. The parasite migrates into the blood stream where they undergo maturation

  4. The adult worms lay thousands of eggs per day, which find their way into the colon (for S. japonicum and S. mansoni) or into urine (for S. haematobium) from which they are excreted

  
• Schistosoma species frequently associated with human disease

  • Schistosoma mansoni
  • Schistosoma japonicum
  • Schistosoma haematobium

  
• Schistosoma mansoni and Schistosoma haematobium are both distributed throughout Africa, while S. japonicum is endemic in Indonesia, some parts of China, and Southeast Asia including the Philippines
• Eggs of Schistosoma spp.

  Induce granuloma formation and damage the walls of the organs they are located in (liver, spleen, gut, urinary bladder)

  
• Schistosomiasis (Bilharziasis)


  Asymptomatic infection, early acute infection, Katayama fever, associated conditions like nephrotic syndrome, Salmonella infections, liver/bladder cancer

  
• Laboratory diagnosis of Schistosoma spp.

  Demonstration of characteristic eggs in feces, rectal biopsy, or urine

  
• Treatment for Schistosomiasis


  Praziquantel is the recommended drug, oxamniquine and anti-malarial drugs like artemether and artemisinins are alternatives
• Control of schistosomiasis transmission through snail control, health education, and provision of sanitary facilities and water supply
• Clonorchis sinensis (Asian Liver Fluke, Chinese Liver Fluke)

  • Three morphological stages - egg, larva, and adult
  • First intermediate host is freshwater snail, second intermediate host is freshwater fish
  • Humans acquire infection by ingesting raw or undercooked freshwater fish containing the infective metacercariae

  
• Clonorchis sinensis is found in Asia including Korea, China, Taiwan, Vietnam, Japan and Asian Russia
• Clonorchis sinensis infection

  Increases risk of developing cholangiocarcinoma (cancer of the bile ducts) and gallstones

  
• Clonorchiasis


  Most patients are asymptomatic, heavy worm burden can cause fever, abdominal pain, anorexia, hepatomegaly, diarrhea, eosinophilia, and liver dysfunction

  
• Laboratory diagnosis of Clonorchiasis


  Finding characteristic eggs in stool or duodenal aspirates, eosinophilia, anemia, imaging tests like ultrasonography, cholangiography, CT scan

  
• Treatment for Clonorchiasis


  Praziquantel is the drug of choice, albendazole is an alternative
• Infection with Clonorchis sinensis can be prevented by cooking fish prior to consumption, health education, proper waste disposal, and prompt treatment of infected persons

  
• Fasciola hepatica (Sheep Liver Fluke)


  • Eggs possess an operculum and shoulders
  • First intermediate host is snail, second intermediate hosts are edible aquatic plants
  • Humans acquire infection by ingesting raw edible aquatic plants or drinking water contaminated by metacercariae

  
• Life cycle of Fasciola hepatica


  Metacercariae excyst in the duodenum, penetrate the intestinal wall, migrate through the peritoneal cavity to the liver, mature into adult flukes in the bile ducts, and produce eggs that are excreted in feces

  
• Fasciola hepatica


  • Eggs possess an operculum and shoulders
  • First intermediate host is a snail
  • Second intermediate hosts are edible aquatic plants

  
• Infection in humans


  1. Ingesting raw edible aquatic plants

  2. Drinking water contaminated by metacercariae
• Parasite life cycle


  1. Metacercariae excyst in duodenum/jejunum

  2. Young flukes wander to liver capsule

  3. Flukes burrow through liver parenchyma

  4. Flukes enter bile ducts and mature

  5. Immature eggs carried by bile into intestines and excreted

  6. Eggs mature in water and infect first intermediate host

  7. Cercariae escape snail and encyst on aquatic plants

  
• Natural host for completion of life cycle is sheep
• Humans are accidental hosts
• Fasciola hepatica distribution

  • Found worldwide, especially in sheep and cattle-raising countries, and where humans consume raw watercress
• Acute/invasive phase


  Migration of parasite through liver parenchyma, leading to traumatic and necrotic lesions

  
• Chronic stage


  Localization of adult worms in bile ducts, can obstruct bile duct and stimulate inflammation

  
• During migration, parasite may wander to other sites and cause abscesses
• Fascioliasis (Sheep Liver Rot)


  • Tenderness and hepatomegaly
  • Right upper quadrant pain, fever, chills, eosinophilia
  • Hepatitis with biliary obstruction
  • Necrotic foci in liver
  • Temporary lodgment of adult worm in pharynx leading to suffocation

  
• Laboratory diagnosis


  Finding eggs in stool, differentiation from Fasciolopsis buski eggs, ELISA, Enterotest, liver ultrasonography

  
• Treatment


  Drug of choice is praziquantel, alternative is triclabendazole
• Prevention and control


  • Proper human waste disposal, hygiene improvement, snail population control, avoidance of raw aquatic plants and contaminated water, boiling water, avoidance of raw sheep liver