Blood and Tissue Platyhelminthes

Echinococcus spp. - Epidemiology

• parasite: cestode

• worldwide distribution

• animal reservoirs: carnivores

• humans are accidental intermediate hosts

Life Cycle of Echinococcus

• infective stage: consumption of egg

• onocospheres are released in the intestines and hydatid cysts develop in organs (diagnostic stage)

Echinococcus spp. - Clinical Syndromes

• latency can be up to 15 years (asymptomatic)

• Cystic echinococcus (E. granulosus)

  • hydatid cysts (slow-growing, tumor-like lesion) form predominately in the liver (70%) and lungs (20%); cysts rupture can cause anaphylactic reactions, even death

• Alveolar echinococcus (E. multilocularis)

  • lesions form predominately in the liver; can cause liver failure and death

Echinococcus spp. - Diagnosis

• imagining techniques and ultrasound

• antibody detection

• molecular analysis

Echinococcus spp. Treatment and Prevention

• albendazole only (small cysts) or albendazole and surgical resection of the cyst (larger cysts)

• for alveolar (lung) lesions, surgery and albendazole for at least 2 years (recurrence is possible)

• PAIR (percutaneous aspiration, injection of chemicals and reaspiration)

• education and handwashing

Clonorchis sinensis - Epidemiology

• parasite: liver trematode

• distribution: mostly confined to Asia (85% China)

  • infecting an estimated 30 million people

• human and animal reservoirs: dogs and cats are most common

Life Cycle of Clonorchis

• infection occurs through ingestion of undercooked, salted, pickled, or smoked freshwater fish (second intermediate host) encysted with metacercariae (infective stage)

• metacercariae excyst in duodenum and ascend to the bilary tract

• develop into adults that release eggs in the stool (diagnostic stage)

• eggs in the environment get ingested by snail (first intermediate host)

• cercariae are released from the snail, invade the fish and encyst

Infective Stage of Clonorchis

freshwater fish encysted with metacercariae

Diagnostic Stage of Clonorchis

eggs

Intermediate hosts of Clonorchis

• snail - first intermediate host

• freshwater fish - second intermediate host

Clonorchis sinensis - Clinical Syndrome

• normally asymptomatic in light infections

• chronic infections have severe morbidity

  • abdominal pain with nausea and diarrhea due to the blockage of the biliary ducts

  • bile duct cancer

Clonorchis sinesis - Diagnosis

• recovery of eggs from the stool or from duodenal aspirates

• detection of parasite by imagining/ultrasound

Clonorchis sinensis - Treatment and Prevention

• praziquantel/albendazole

• do not eat raw or undercooked freshwater fish

  • freeze fish at -20 C or below for at least 7 days

Paragonimus - Epidemiology

• parasite: lung trematode

• distribution: most common in Far east Asia; also, in parts of Africa, North and South America

  • approx. 3 mil individuals infected (~1% of the Indochinese immigrants to the US are infected)

• human and animal reservoirs: variety of shore-feeding animals (pigs, wild boar)

Life Cycle of Paragonimus

• infection occurs through ingestion of undercooked, pickled, or salted crab/crayfish (second intermediate host) encysted with metacercariae (infective stage)

• metacercariae excyst in duodenum, pentrate the intestinal wall into the peritoneal cavity, then through the abdominal wall and diaphragm into the lungs

• develop into adults which release eggs in the sputum or are swallowed and passed in the stool (diagnostic stage)

• eggs in the environment release miracida which invade the snail (first intermediate host)

• cercariae are released from the snail and invade the crab where they encyst

Infective stage of Paragonimus

crab/crayfish encysted with metacercariae

Diagnostic stage of Paragonimus

eggs released in sputum or are swallowed and passed in the stool

Intermediate hosts of Paragonimus

• snail - first

• crab/crayfish - second

Paragonimus - Clinical Syndromes

• first three weeks after ingestion (during migration): diarrhea, abdominal pain, cough, and fever

• pulmonary form: often has no or mild symptoms

  • chronic cough and difficulty breathing

  • coughing fits with blood-tinged sputum (if large numbers); the sputum may be brown because of the Paragonimus eggs being coughed up

• extrapulmonary form: affects the liver, spleen, abdomen, skin and brain

Paragonimus - Diagnosis

• examination of sputum or stool for eggs

• antibody detection for extrapulmonary cases

Paragonimus - Treatment and Prevention

• praziquantel

• education and proper sanitation

  • properly cook crabs/crayfish

Schistosomes

• parasite: blood trematode

• schistosomiasis is a major parasitic infection of tropical areas (~240 million infections worldwide)

• trematode with both male and female adult worms (not hermaphroditic)

• major pathogens: Schistosoma mansoni, Schistosoma japonicum, Shistosoma haematobium

• collective cause schistosomiasis (bilarziasis or snail fever)

Life Cycle of Schistosoma

• infection occurs through penetration of the cercariae into the skin (infective stage)

• cercariae become schistosomulae that will migrate via venous circulation to the lungs, to the heart, and develop in the liver

• upon maturation adults migrate to the mesenteric venules of the bowel/rectum (or veins that drain the bladder) where they lay eggs

• eggs are passed in the stool or urine (species specific) (diagnostic stage)

• eggs in the environment release miracida which invade the snail (intermediate host)

• cercariae are released from the snail into the water

Infective Stage of Schistosoma

cercariae into the skin

Diagnostic stage of Schistosoma

eggs passed in the stool or urine

Intermediate host of Schistosoma

snail

Schistosoma mansoni

• Epidemiology:

  • Distribution: Africa, South America, Caribbean

  • Humans and animal reservoirs

• Clinical syndromes:

  • rash at penetration site followed by fever, chills, cough and muscle aches

  • chronic infection - hepatosplenomegaly

• Diagnosis:

  • microscopic analysis of the stool for eggs

  • antibody detection

Schistosoma japonicum

• Epidemiology:

  • Distribution: Far East Asia (China, Japan, Phiilippines)

  • mostly animal reservoirs

• Clinical syndromes:

  • rash at penetration site followed by fever, chills, cough and muscle aches

  • chronic infection - hepatosplenomegaly

• Diagnosis:

  • microscopic analysis of the stool for eggs

  • antibody detection

Schistosoma haematobium

• Epidemiology:

  • Distribution: Africa, Middle East

  • human and animal reservoirs

• Clinical syndromes:

  • rash at penetration site followed by fever, chills, cough and muscle aches

  • hematuria (blood in urine) and bladder cancer

• Diagnosis:

  • Microscopic analysis of the urine for eggs

  • antibody detection

Swimmer’s Itch

• nonhuman schistosomes have cercariae that penetrate human skin, producing severe dermatitis (cercarial dermatitis)

  • within mins to days, tingling, burining or ithcing of the skin

• dead-end human host

• natural hosts: birds and other shore-feeding animals from freshwater lakes throughout the world

Schistosome - Treatment and Prevention

• praziquantel

  • corticosteriod cream or antihistamines for swimmer’s itch

• Education and sanitation

  • avoid swimming in contaminated waters

• reduce snail burden, if possible