INTESTINAL TREMATODES
INTESTINAL TREMATODES
INTRODUCTION
Manifestations that include:
Cystitis and ureteritis (S. haematobium) with hematuria, which can
progress to bladder cancer.
Schistosomiasis – is caused by digenetic blood trematodes.
Pulmonary hypertension (S. mansoni, S. japonicum, more rarely S.
haematobium); glomerulonephritis, and CNS lesions.
3 Main Species affecting Humans:
DIAGNOSTIC FINDINGS:
Schistosoma haematobium (Primary concern)
Microscopy
Schistosoma japonicum
Antibody Detection (Antigen Testing) useful in both clinical
management and epidemiologic surveys.
Schistosoma mansoni
Note: Schistosomes that parasitize birds and mammals (also snails)
can cause CERCARIAL DERMATITIS in humans.
TREATMENT: Praziquantel; Oxamniquine has been effective in
treating infections caused by S. mansoni in some areas in which
Praziquantel is less effective.
GEOGRAPHIC DISTRIBUTION:
Schistosoma mansoni – South America and the Caribbean, Africa
and the Middle East
Schistosoma haematobium – Africa and the Middle East
Schistosoma japonicum – Far East (Asian Countries)
LIFE CYCLE:
FASCIOLA HEPATICA (Sheep Liver Fluke)
Disease: Fascioliasis, “Liver Rot”
Site in Host: Bile Ducts
Portal of Entry: Mouth
IS – Four-tailed Cercaria
Definitive Host: Sheep, Cattle and other mammals, including
Humans.
DS – Fluke worm ova in stool or urine
Intermediate Host: Snail (Lymnaea)
Dwellings in the body
Source of Infection: Eating Watercress, Lettuce, or Radishes or
drinking water infested with metacercariae.
S. japonicum – more frequently found in the superior mesenteric
veins draining the small intestine
S. mansoni – occurs more often in the superior mesenteric veins
draining in the large intestine
S. haematobium – often occurs in the venous plexus of bladder, but
it can also be found in the rectal venules
PATHOLOGY
S. mansoni and S. japonicum schistosomiasis includes: Katayama
fever, hepatic perisinusoidal egg granulomas, Symmers’ pipe stem
periportal fibrosis, portal hypertension, and occasional embolic egg
granulomas in brain or spinal cord.
S. haematobium schistosomiasis includes: hematuria, scarring,
calcification, squamous cell carcinoma (transitional cell carcinoma or
bladder cancer), and occasional embolic egg granulomas in brain or
spinal cord.
NOTE: Reservoir for parasites in water: S. japonicum and S. mekongi
in dogs.
CLINICAL FEATURES:
Many infections are ASYMPTOMATIC; Acute Schistosomiasis
(Katayama’s fever) may occur weeks after the initial infection
especially by S. mansoni and S. japonicum. Manifestations include
fever, cough, abdominal pain, diarrhea, hepatosplenomegaly and
eosinophilia.
Occasional central nervous system lesions occur: Cerebral
granulomatous disease may be caused by ectopic S. japonicum eggs
in the brain, and granulomatous lesions around ectopic eggs in the
spinal cord from S. mansoni and S. haematobium infections may
result in a transverse myelitis with flaccid paraplegia.
Continuing infections may cause granulomatous reactions and
fibrosis in the affected organs which may result in manifestations
that include:
Colonic polyposis with bloody diarrhea (Schistosoma mansoni
mostly)
Portal hypertension with hematemesis and splenomegaly (S.
mansoni, S. japonicum, S. mansoni)
Infective Stage: Metacercariae
Lab Dx: Eggs in Stool
Fasciola Hepatica Eggs: Ellipsoidal with small, barely distinct
operculum. The operculum can be opened. Thin shelled and slightly
thicker at the abopercular end. THEY ARE PASSED
UNEMBRYONATED. “Hen’s Egg”
Causal Agents: Aside from F. hepatica, there is also Fasciola
gigantica, parasites of herbivores that can infect humans
accidentally.
Geographic Distribution: Worldwide; Found in areas where sheep
and cattle are raised and where humans consume raw watercress,
including Europe, the Middle East, and Asia.
F. Gigantica – Asia, Africa and Hawaii.
IS: Metacercariae on water plant, ingested by human, sheep or
cattle.
DS: Unembryonated eggs passed in feces.
From Miracidia infecting the snail, will transform to SPOROCYSTS
then to REDIAE and then to CERCARIAE (Which will attach itself to
water plants)
Clinical Features:
During the acute phase (caused by the migration of the immature
fluke through the hepatic parenchyma), manifestations include:
Abdominal Pain, Hepatomegaly, Fever, Vomiting, Diarrhea, Urticaria,
and Eosinophilia, and CAN LAST FOR MONTHS.
During chronic phase (caused by the adult fluke within the bile
ducts), the symptoms are more discrete: Intermittent biliary
obstruction and inflammation. (Can cause Jaundice)
Occasionally, ectopic locations of infection (such as intestinal wall,
lungs, subcutaneous tissue and pharyngeal mucosa) can occur.
Diagnostic Findings: Microscopy and antibody detection.
Treatment: Praziquantel but F. hepatic infections may not respond.
So, the choice is Triclabendazole with bithionol as an alternative.
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FASCIOLOPSIS BUSKI (LARGEST INTESTINAL FLUKEWORM)
OPISTHORCHIS VIVERRINI
Geographic Distribution: Asia and the Indian subcontinent,
especially in areas where humans raise pigs and consume freshwater
plants.
Opisthorchis Viverrini is the Southeast Asian Liver Fluke
IS: Metacercariae on water plants ingested
Geographic Distribution: O. viverrine is found mainly in the
northeast of Thailand, Laos and Kampuchea. O. felineus is found
mainly in Europe and Asia including the former Soviet Union.
DS: Unembryonated eggs passed in feces.
Life Cycle: Same with F. hepatica.
Clinical Features: Most infections are light and asymptomatic. In
heavier infections, symptoms include diarrhea, abdominal pain,
fever, ascites, anasarca (severe genialized edema; protein not
produced because of lack of Albumin), and intestinal obstruction.
Diagnostic Findings: Microscopy
Treatment: Praziquantel
CLONORCHIS SINENSIS (Chinese or Oriental Liver Fluke)
Disease: Clonorchiasis
Site in Host: Bile Ducts
Portal of Entry: Mouth
Definitive Host: Humans, dogs and cat or other mammals.
1st Intermediate Host: Freshwater Snail (Bulinus, Parafossarulus)
Opisthorchis Felineus is the Cat Liver Fluke
IS: Metacercariae in flesh or skin of fresh water fish ingested by
human host.
DS: Embryonated eggs passed in feces.
Infection Cycle in Snail: Miracidia to Sporocysts to Rediae to
Cercariae.
Clinical Features:
Asymptomatic; In mild cases, manifestations are: Dyspepsia,
Abdominal Pain, Diarrhea, and Constipation.
With infections of longer duration: Symptoms are severe and
hepatomegaly and malnutrition may be present.
In rare case: Cholangitis, Cholecystitis and Cholangiocarcinoma
Infections due to O. felineus may present an acute phase resembling
Katayama fever (Schistosomiasis), with fever facial edema,
lymphadenopathy, arthralgias (joint pain), rash and eosinophilia
Infective Stage: Metacercariae
Chronic forms of O. felineus infections present the same
manifestations as O. viverrine with in addition involvement of the
pancreatic ducts.
Lab Dx: Eggs in stool
Diagnostic Findings: Microscopy
HERMAPHRODITIC
Treatment: Praziquantel
Has shoulders in adult worm
PARAGONIMUS WESTERMANI (Lung Fluke)
Eggs: Small Operculated Eggs; The Operculum at the smaller end of
the egg is convex and rests on a visible shoulder. At the opposite
side (larger, abopercular) end, a small knob or hooklike protrusion is
often visible. The miracidium is visible inside the egg.
Disease: Paragonimiasis, pulmonary distomiasis, lung fluke disease
Geographic Distribution: Endemic areas are Asia, including Korea,
China, Taiwan, and Vietnam. Clonorchiasis has been reported in nonendemic areas (including the US). In such cases, the infection is
found in Asian immigrants, or following ingestion of imported,
undercooked or pickled freshwater fish containing metacercariae.
Definitive Host: Humans and a variety of carnivores
2nd Intermediate Host: Freshwater Fish (Cyprinidae)
IS: Metacercariae in flesh or skin of fresh water fish, ingested by
human host.
DS: Embryonated eggs passed in feces.
Site in Host: Lungs
Portal of Entry: Mouth
1st Intermediate Host: Freshwater Snail (Family Thieridae)
2nd Intermediate Host: Freshwater Crab (Eriocheir, Patamon,
Sesarma, Parathelphusa) or Crayfish (Cambarus, Astacus)
Source of Infection: Consumption of raw or undercooked infected
freshwater crustaceans
Infective Stage: Metacercariae
Infective Cycle in Snail: From Miracidia, to Sporocysts to Rediae then
to Cercariae.
Lab Dx: Eggs in Sputum and Stool
Clinical Features:
Common in Asia especially in Japan
Most pathologic manifestations result from inflammation and
intermittent obstruction of the biliary ducts. (Bile is for the
absorption of fats) Blockage can cause hepatitis, and jaundice
(excessive bilirubin)
Infective Stage: Cercariae invade the crustacean and encyst into
metacercariae
In the acute phase: Abdominal pain, nausea, diarrhea, and
eosinophilia can occur.
Diagnostic Stage: Unembryonated Eggs
Life Cycle into Snail: Miracidia to Sporocysts to Rediae to Cercariae
Exit: Cough or Stool
In long standing infections: Cholangitis, cholelithiasis, pancreatitis,
and cholangiocarcinoma (cancer of the biliary duct; aggressive
cancer) can develop which may be fatal.
Clinical Features: The acute phase (invasion and migration) may be
marked by diarrhea, abdominal pain, fever, cough, urticaria,
hepatosplenomegaly, pulmonary abnormalities and eosinophilia
Diagnostic Findings: Microscopy
During the chronic phase, pulmonary manifestations include cough,
expectoration of discolored sputum (rust colored or old blood),
hemoptysis, and chest radiographic abnormalities.
Treatment: Praziquantel or albendazole as an alternative.
Extrapulmonary locations of the adult worms result in more severe
manifestations, especially when the brain is involved.
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Diagnostic Findings: Microscopy and Antibody Detection is useful in
light infections and in the diagnosis of extrapulmonary
paragonimiasis
FASCIOLOPSIS BUSKI (Large or Giant Intestinal Fluke)
Treatment: Praziquantel; Bithionol is an alternative.
Site in Host: S.I.
METAGONIMUS YOKOGAWAI (Smallest Human Fluke)
Portal of Entry: Mouth
Geographic Distribution: Far East, Siberia, Manchuria, Balkan states,
Israel and Spain
Definitive Host: Pigs and Humans
Disease: Metagonimiasis
2nd Intermediate Host: Water Chestnuts and Lotus
Site in Host: Bile Ducts
Infective Stage: Metacercariae
Portal of Entry: Mouth
Lab Dx: Eggs in Stool
Definitive Host: Humans, dogs, cats, hogs, pelicans, and other fisheating birds.
Infective Stage: Metacercariae on water plant ingested by humans
or pigs causing infection
1st Intermediate Host: Snail (Semisulcospira, Thiara, and Hua)
Diagnostic Stage: Unembryonated Eggs passed in feces.
2nd Intermediate Host: Freshwater Fish (Salmonoids and
Cyprinoids)
Eggs always has attached fecal material
Infective Stage: Metacercariae
Disease: Fasciolopsiasis
1st Intermediate Host: Snail (Segmentina/Hippeutis)
SCHISTOSOMA MANSONI
Lab Dx: Eggs in Stool
Disease: Schistosomiasis, intestinal schistosomiasis, bilharziasis
“Snail Fever”
Infective Stage: Host becomes infected by ingesting undercooked
fish containing metacercariae
Site in Host: Veins of L.I.
Diagnostic Stage: Embryonated Eggs each with a fully-developed
miracidium are passed in feces.
Note: Metacercariae excysts in the small intestine; Found also in
brackish water.
Clinical Features:
Portal of Entry: Skin
Definitive Host: Humans, Baboons and Rodents
Intermediate Host: Snail (Biomphalaria sp and Tropicorbis sp)
Infective Stage: Cercariae
Lab Dx: Eggs in stool; Rectal or liver biopsy
Diarrhea and colicky abdominal pain; Migration of the eggs to
extraintestinal sites (heart, brain) can occur with resulting
symptoms.
Infective Stage: Four-tailed Cercariae released by snail into water
and free-swimming
Diagnostic Findings: Microscopy
Diagnostic Stage: Fluke itself
Treatment: Praziquantel
Male has the vagina (Gynaecophoric canal; Worms are always in a
honeymoon period)
HETEROPHYES HETEROPHYES (Found in brackish water, “Minute
Intestinal Fluke”)
SCHISTOSOMA HAEMATOBIUM
Disease: Heterophyiasis
Disease: Urinary schistosomiasis, schistosomal hematuria, urinary
bilharziasis
Site in Host: Bile Ducts
Portal of Entry: Mouth
Definitive Host: Humans, dog, cat, or other fish-eating mammals
1st Intermediate Host: Brackish water snail (Pirenella, Cerithidea)
Site in Host: Veins of Urinary Bladder
Portal of Entry: Skin
Definitive Host: Humans, monkeys and baboons
Intermediate Host: Snail (Bulinus, Physopsis, and Biomphalaria sp)
2nd Intermediate Host: Brackish water fish (Mugil, Tilapia, and
Acanthogobus)
Infective Stage: Cercariae
Infective Stage: Metacercariae
Lab Dx: Eggs in Stool; Cystoscopy
Lab Dx: Eggs in Stool
Egg has spine, can severely damage intestine and urinary bladder.
Geographic Distribution: Egypt, Middle East and Far East
SCHISTOMA JAPONICUM
Infective Stage: Host becomes infected by ingesting undercooked
fish containing metacercariae
Disease: Schistosomiasis, Katayama Fever
Diagnostic Stage: Embryonated eggs each with a fully-developed
miracidium are passed in feces.
Portal of Entry: Skin
Similar to METAGONIMUS
Definitive Host: Humans, dogs, cats, horses, pigs, cattle, deer,
caribou and rodents
Clinical Features: Diarrhea and colicky abdominal pain; Migration of
the eggs to the heart, resulting in potentially fatal myocardial and
valvular damage has been reported from the Philippines; Migration
to other organs (e.g., Brain) has also been reported.
Laboratory Diagnosis: Microscopy
Site in Host: Veins of SI
Intermediate Host: Snail (Oncomelania)
Infective Stage: Cercariae
Lab Dx: Eggs in Stool; Liver biopsy
Snails: Kuhol in Visayas
Treatment: Praziquantel
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Japonicum egg has a rudimentary spine
TISSUE NEMATODES AND CESTODES
TRICHINELLA SPIRALIS
Disease: Trichinosis, trichiniasis, trichinelliasis
LYMPHATICS: Helps drain excess fluid in the body, connected to
Lymph Nodes important to immune system
Infective Stage: Mosquito takes a blood meal (L3 larvae enters the
skin)
Site in Host: Adult – S.I. Wall, Encysted larvae-striated muscle
Diagnostic Stage: Adults produce sheathed microfilariae that
migrate into lymph and blood channels
Portal of Entry: Mouth
ELEPHANTIASIS/FILARIASIS
Definitive Host: Human, pig, bear, and other
carnivorous/omnivorous animals
Common in Samar/Leyte or Southern Region
Sources of Infection: Encysted larvae in pork
Can also cause enlargement in genital area (testicles and labia
majora)
Lab Dx: Skin test, serology (Slide flocculation/ELISA), muscle biopsy
BRUGIA MALAYI
Infective and Diagnostic Stage: Ingestion of meat scraps or animals;
Ingestion of undercooked meat esp. pork; Encysted larva in striated
larvae; Encysted larva in striated muscle
Disease: Malayan filariasis
Clinical features: Severe muscle pain and myocitis
ECHINOCOCCUS GRANULOSUS (Cestode)
Disease: Echinococcosis, hydatid disease, hydatid cyst (mimics H
mole)
Site in Host: Lymphatics
Portal of Entry: Skin
Definitive Host: Human, Monkey and Cat
Intermediate Host: Mosquito (Mansonia, Aedes, Anopheles sp)
Sources of infection: Mosquitoes
Site in Host: Liver, Lungs, Brain, Bones
Lab Dx: Blood Smear
Portal of Entry: Mouth: Definitive Host: Dogs, wolves and other
Canidae
Periodic (Nocturnal) form: between 10am and 2am
Sources of Infection: Eggs from Dogs feces in soil
Subperiodic form: Between 9pm and 11pm
Lab Dx: Skin test, X-ray, CAT Scan, Serology
Microfilariae: Sheathed; nuclei extend to tip of tail with 2 separated
and swollen terminal nuclei
Infective Stage: Embryonated egg in feces
Infective Stage: L3 Larvae enter skin after mosquito takes blood
Diagnostic Stage: Hydatid cyst in liver, lungs etc.
Diagnostic Stage: Adults produce sheathed microfilariae that reach
the blood stream
HUMANS ARE ACCIDENTAL HOST – Incidental ingestion of
contaminated food.
LOA LOA
ECHINOCOCCUS MULTILOCULARIS
Disease: Loiasis, eye worm, fugitive swellings, calabar swellings
Disease: Alveolar Echinococcosis
Site in Host: Subcutaneous
Site in Host: Liver, Lungs, Brain, Bones
Portal of Entry: Skin
Port of Entry: Mouth
Definitive Host: Human and monkey
Definitive Host: Foxes, Cats, Dogs and other Carnivores
Intermediate Host: Fly (Chrysops)
Intermediate Host: Mouse, vole and lemming (HUMAN AGAIN IS AN
ACCIDENTAL HOST)
Sources of Infection: Fly
Sources of Infection: Eggs from dog/cat feces in soil
Lab Dx: Serologic test (ELISA and IHA)
MICROFILARIAE
WUCHERERIA BANCROFTI
Disease: Bancroftian filariasis, wuchereriasis
Site in Host: Lymphatics
Portal of Entry: Skin
Definitive Host: Human
Intermediate Host: Mosquito (Culex, Aedes, Anopheles sp)
Source of Infection: Mosquitoes
Lab Dx: Blood Smear
Periodic form: between 10am and 2am
Subperiodic form: between 2pm and 5pm
Microfilariae: Sheathed, nuclei do not extend to tip of tail
Lab Dx: Blood Smear
Diurnal periodicity between 11am and 1pm
Microfilariae: Sheathed, nuclei extend to tip of tail
Infective Stage: Fly (Genus Chrysops) takes a blood meal, L3 Larvae
Diagnostic Stage: Adults produce sheathed microfilariae that are
found in spinal fluid, urine, sputum, peripheral blood and in the
lungs
MANZONELLA OZZARDI and MANSONELLA PERSTANS
Disease: Ozzardi filariasis/Perstan filariasis
Site in Host: Body Cavities
Portal of Entry: Skin
Definitive Host: Human
Intermediate Host: Midge (A tick type) (Culicoides and Simulium)
Sources of Infection: Midge
Lab Dx: Blood Smear
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Microfilariae found in blood: No periodicity; Unsheathed; Nuclei do
not extend to tip of tail (M. ozzardi)/extend to tip of the tail
(M.perstan)
Infective Stage: Arthropod takes a blood meal (black fly – genus
Simulium and midge – genus Culicoides)
Diagnostic Stage: Adults produce unsheated microfilariae that reach
the blood stream
MANZONELLA STREPTOCERCA
Disease: Ozzardi filariasis/Perstan filariasis
Site in Host: Body cavities
Portal of Entry: Skin
Definitive Host: Human
Intermediate Host: Midge (Culicoides and Simulium)
Sources of Infection: Midge
Lab Dx: Blood smear
Microfilariae found in skin: No periodicity; Unsheathed, nuclei
extend to tip of tail
ONCHOCERCA VOLVULUS
Disease: Onchocerciasis, onchocercosis, river blindness “Sowda”
Site in Host: Subcutaneous
Portal of Entry: Skin
Definitive Host: Human
Intermediate Host: Fly (Simulium)
Sources of Infection: Fly
Lab Dx: Skin biopsy or snips, nodule aspirate
Microfilariae found in skin: No periodicity; Unsheathed; nuclei do
not extend to tip of tail
Infective Stage: Blackfly takes a blood meal
Diagnostic Stage: Adults produce unsheathed microfilariae that
typically are found in skin and in lymphatics of connective tissues,
but also occasionally in peripheral blood, urine and sputum
DRACUNCULUS MEDINENSIS (THE GUINEA WORM)
Disease: Dracontiasis, dracunculosis, guinea worm disease
Site in Host: Subcutaneous
Portal of Entry: Mouth
Definitive Host: Human and Domesticated and wild fur bearing
animals
Intermediate Host: Water Flea (Cyclops)
Sources of Infection: Fly
Lab Dx: Skin biopsy or snips, nodule aspirate
Microfilariae found in skin: No periodicity
Infective Stage: Larvae undergoes two molts in copepod and
becomes a L3 larvae
Diagnostic Stage: Female worm begins to emerge from skin one year
after infection, L1 larvae released into water from the emerging
female worm
Copepods – Water Crest
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