TREMATODES OF MEDICAL IMPORTANCE Flashcards
INTRODUCTION
Trematodes, or flukes, are parasitic flatworms with unique life cycles :
- sexual reproduction in mammalian and other vertebrate definitive hosts
- asexual reproduction in snail intermediate hosts
These organisms are divided into four groups on the basis of their final habitats in humans:
1) Blood flukes (bisexual Schistosoma), which live in the intestinal or vesical (urinary bladder) venules and infect humans by direct penetration through the skin.
2) Liver flukes (hermaphroditic which reside in the bile ducts (Fasciola) (Clonorchis and Opisthorchis)
3) Intestinal flukes (hermaphroditic Fasciolopsis),
4) Lung fluke (hermaphroditic (Paragonimus), which infects humans on ingestion of raw crabs or crayfish
FLUKES DO NOT MULTIPLY IN HUMAN
TREATMENT OF ALL FLUKE INFECTIONS HAS BEEN GREATLY IMPROVED BY INTRODUCTION OF PRAZIQUANTEL
BLOOD FLUKES (SCHISTOSOMA)
SCHISTOSOMIASIS (BILHARZIASIS)
The schsitosomes cause intestinal, urogenital, pulmonary, hepatosplenic, cerebral and other forms of schistosomiasis.
Schistosome is the only fluke with separate sexes and are threadlike in shape.
The female worm lies in the gynecophoral canal of the male. This condition is important for transportation.
MEDICALLY IMPORTANT SPECIES (HM, JIM)
1. Schistosoma Haematobium — Vesical(urinary) schistosomiasis
2. Schistosoma Mansoni — Intestinal schistosomiasis
3. Schistosoma Japonicum — intestinal too
4. Schistosoma Intercalatum — intestinal too
5. Schostosoma Mekongi — intestinal too
URINARY SCHISTOSOMIASIS (schistosoma haematobium)
The worm lives in the veins of the bladder of humans
Peak prevalence 10-14 yrs
The snail host that harbours it are the genera Bulinus(Bulinus Africanus and Bulinus Truncatus)
The females are larger than males
Males ranges from 1-1.5 and Females from 2-2.5
The males have 4-5 testes
The Females ovary are located in the posterior 3rd and lays 20-200 eggs daily
INTESTINAL SCHISTOSOMIASIS (Schistosoma Mansoni)
Lives in the veins of the intestine
Snail hosts are Genera Biomphalaria(B.glabrata) the possess oval shells
MORPHOLOGY
Females also larger than males, Males range from 1-1.4 and Females 1.5 - 2.0
The males have 6-9 testes
The female ovary present in the anterior third and it lays 100-300 eggs daily
OTHER INTESTINAL SCHISTOSOMES
SCHISTOSOMA JAPONICUM
The female adult worm lays about 500-3500 eggs daily.
The eggs are ovoid
It is found in Japan, China, and Philippines.
The snail hosts that harbor S. japonicum are of the genera Oncomelania.
SCHISTOSOMA INTERCALATUM This is the rarest and least pathogenic schistosome that matures in man. It is found in Western and Central Africa. The daily egg output is about 300. The eggs have a terminal spine.
LIFE CYCLE OF SCHISTOSOMES IN MAN
Human infection takes place during bathing or swimming when the cercariae penetrate the skin of man, are carried into the systemic circulation and pass through to the portal vessels.
Within the intrahepatic portion of the portal system, the worms feed and grow to maturity.
The mature adults migrate to pelvic or mesenteric venous plexuses and females lay eggs in small venules
The ova pass through the tissue and viscera of the lumen and are voided while some gain general circulation and may land up anywhere
PATHOLOGY IN SCHISTOSOMIASIS
6 in number
- Penetration of Skin by Cercaria
—Skin penetration might not be apparent
— Causes Cercarial Dermatitis (Swimmer’s itch) - Migration and Maturation of immature worms
—There are general toxic and allergic symptoms known as KATAYAMA SYNDROME OR SNAIL FEVER, Consist of Urticaria, eosinophilia, fever, abdominal pain and tender Hepatosplenomegaly - Damage by egg in tissue
— An inflammatory granuloma forms(Hoeppli reaction), there is subsequent fibrosis and calcification
Such damage may be local or ectopic
4.URINARY SCHISTOSOMIASIS
Caused by S.haematobium
— Hypertrophy of bladder
— Cystitis and Calculi formation with calcification and squamous cell carcinoma
— Hydroureter or Hydronephrosis
— Ulceration, Frequency, Dysuria
- INTESTINAL SCHISTOSOMIASIS
Caused by S.mansoni
There are marked initial Toxic and Allergic effect
— The large intestine and rectum are involved in ulcers, abscesses, papules, papillomata and fistula
There can be ectopic lesions; the liver is frequently involved (receiving eggs via the portal vein with inflammatory reaction and fibrosis leading to periportal (pipestem) fibrosis with (portal hypertension, oesophageal varices, splenomegaly and ascites) - ORIENTAL SCHISTOSOMIASIS
Caused by S. japonicum.
Initial toxic and allergic symptoms are marked and can lead to myocarditis and death.
Intestinal lesions are similar to those of S. mansoni infection and the small intestine is often involved.
The liver is infected as in S. mansoni.
The brain may also become involved
SYMPTOMS AND COMPLICATION OF SCHISTOSOMIASIS
Urinary schistosomiasis:
—Within 24 hours of infection an intense irritation and skin rash, referred to as ‘swimmer’s itch’, may occur at the site of cercarial penetration.
—Haematuria (blood in urine) caused by eggs penetrating through the wall of the bladder, this usually presents as terminal haematuria.
—There is inflammation of the urinary bladder (cystitis) presenting with painful micturition, and frequency.
Following prolonged untreated infection and a marked cellular immune response:
- the ureters may become obstructed and the bladder wall thickened leading to abnormal bladder function,
- urinary tract infection, and
- eventually obstructive renal disease (hydroureter and hydronephrosis) with kidney damage.
There can be enlargement of spleen and liver.
Complications can arise from genital schistosomiasis.
S. haematobium infection can lead to squamous cell carcinoma of the bladder.
Intestinal Schistosomiasis
— Swimmer’s itch also, Dysentery (mucus and blood in stool with tenesmus)
— Host reaction to eggs lodged in intestinal mucosa leads to (thickening of bowel wall and formation of granulomata ulceration)
Large granulomata causes (colonic and rectal polyps)
Prolonged heavy infection can lead to a marked enlargement of the liver with fibrosis, portal hypertension, and ascites.
The spleen may also become enlarged.
Death from haematemesis can occur from ruptured oesophageal varices.
LABORATORY DIAGNOSIS OF SCHISTOSOMIASIS
S. haematobium in urine.
Examine the urine after allowing it to sediment in a conical urinalysis glass.
A drop from the sediment is taken and examined for eggs.
Egg has terminal spine.
Detecting eggs in a rectal biopsy or bladder mucosal biopsy.
Egg/ova may also be found in semen.
S. mansoni/S. japonicum
Microscopic examination of the stool for eggs after concentration by sedimentation method.
The egg has characteristic lateral spine in S. mansoni and a rudimentary spine in S. japonicum.
Rectal biopsy/snip to detect the egg
TREATMENT AND CONTROL OF SCHISTOSOMIASIS
Treatment:
Praziquantel is the drug of choice
Prevention/Control: 1. Health education: A. On use of clean latrines and safe water supply B. Avoid urination and defecation in canals, avoid contact with canal water
- Snail control:
A. Physical methods:
i. Periodic clearance of canals from vegetations.
ii. Manual removal of snails and their destruction.
B. Biological methods:
Use of natural enemies to the snails such as Marisa.
C. Chemical methods:
Molluscides are applied in the canals to kill the snails. e.g. Endod
HERMAPHRODITIC FLUKES
LIVER, INTESTINAL FLUKES AND LUNG FLUKES
Liver flukes includes
—Clonorchis sinensis; chinese liver fluke, lives in bile ducts
—Fasciola hepatica; Sheep liver fluke
— Fasciola gigantica; lives in the liver of cattle
Intestinal flukes includes
—Fasciolopsis buski; giant intestinal flukes
— Heterophyids; minutes flukes, ingestion of raw fresh water fish
Lung flukes includes
All belong to the genus Paragonimus
Best known specie is the Paragonimus westermani causing Paragonimiasis (lung disease)
STRUCTURE AND LIFE CUCLE OF HERMAPHRODITIC FLUKES
Hermaphroditic multicellular flatworms, leaf like shapes
Oral and ventral suckers
Digestive system consists of mouth and oesophagus
They reproduce Sexually in a definitive vertebrate host and Asexually in Snail, an Intermediate host
Life cycle
The adult hermaphroditic flukes inhabit the definitive host and lay eggs which are released through the Faeces and through the Sputum(in P.westermani).
The eggs enter the water bodies, free swimming CILIATED MIRACIDIA hatch from the eggs and infect SNAILS(1st intermediate host) in which they give rise to SPOROCYST AND REDIAE
The snails emits CERCARIAE which enters the 2nd intermediate host and encysts as METACERCARIAE which finally infects the Vertebrate host
CLINICAL FEATURES OF HERMAPHRODITIC FLUKES
Signs and symptoms of hermaphroditic flukes are largely related to the site of infection of their adult worms
The bile ducts— fasciola hepatica, clonorchis sinensis, opisthorchis viverrini
The intestines— Fasciolopsis buski
The lungs— Paragonimus Westermani
LIVER FLUKES
1) Fascioliasis (2 distinct phases)
First occurs in initial 6-9 weeks of infection when the larvae migrates through the liver
And the second phase occurs when they enter the bile ducts
Acute clinical symptoms include:
-prolonged fever
-right hypochondrium pain and hepatomegaly
-Asthenia, urticaria and marked eosinophila
Once the flukes enters the bile dicts, symptoms disappear completely
2) Clonorchiasis and Opisthorchiasis
Do not present with acute syndrome ad flukes enter directly into the bile ducts
Most individuals show no significant signs or symptoms
But those with severe chronic infection present with Cholangitis, Cholangiohepatitis and Cholangiocarcinoma
INTESTINAL FLUKES
Fasciolopsiasis— few or no disease manifestations
Cases of severe clinical illness
- diarrhea
- abdominal pain
- facial edema
- passage of undigested food in feces
LUNG FLUKES
Paragonimiasis usually comes to the attention of the physician when the patient complains about Cough and Intermittent hemoptysis
Chest pain of pleuritic type
Cerebral Paragonimus is manifested by
Jacksonian epilepsy
Tumors
Embolism
DIAGNOSIS HERMAPHRODITIC FLUKES
Demonstrating the eggs of the parasite in feces provides definitive diagnosis in most and In Sputum and Aspirate for paragonimiasis
—Egg of F.hepatica (yellow-brown large and oval with indistinct operculum)
—Egg of C.sinensis (yellow-brown and small, shaped like an electric light bulb) resembles O.viverrinini but smaller
—Eggs of F.buski (resembles F.hepatica) with smaller operculum
—Egg of P.westermani, yellow-brown too and asymmetrical with flat operculum
TREATMENT AND CONTROL
Treatment of all fluke infections other than Fascioliasis is accomplished by a one day course of the oral drug Praziquantel.
For Fasciola hepatica, the current drug of choice is BITHIONAL give orally for 15 days.
—A key control measure for all fluke infections is preventing egg-containing excreta from contaminating water sources
—Another approach is to control snail populations largely by use of molluscicides, manual removal of snails and destruction
—for hermaphroditic flukes, infection can be avoided by careful preparation and cooking of fresh water fish, crustacea and vegetables.
