Blood Flukes Flashcards
What are the general characteristics of Schistosomes (blood flukes)?
- Sex: Schistosomes are dioecious, sexes are separate. Male worm possesses a sex canal (gynecophoric canal) on the ventral side in which the female worm reposes.
- Habitat: Venous plexus.
- Shape: Leaf-like unsegmented body (with fleshy thickness), 2 cup-like suckers with delicate spines. The body is covered by a thick (4 μm) tegument (except in S. japonicum which possesses a smooth tegument).
- Size: Males are shorter and broader than females.
- Eggs: They produce elongated, nonoperculated eggs with spine-like projections containing ciliated embryo, miracidium.
- Hosts: Definitive host (Man), Intermediate host (Freshwater snails). There is no second intermediate host.
- Infective form: Fork-tailed cercariae.
What is the habitat of Schistosoma haematobium?
Adult male worm holds the female worm in the gynecophoric canal and resides in the venous plexus of the urinary bladder and ureter.
What is the infective form of Schistosoma haematobium, and how does it infect humans?
The infective form is the cercaria. Man acquires infection by the penetration of the skin by the cercariae present in contaminated water. The free-swimming cercaria penetrates the intact epidermis with the help of oral and ventral suckers.
Describe the life cycle of Schistosoma haematobium.
- Definitive host: Man.
- Intermediate host: Freshwater snails of genus Bulinus.
- Mode of transmission: Man acquires infection by penetration of skin by the infective form (cercariae) present in contaminated water.
- The cercaria penetrates the skin, loses its tail, and becomes a schistosomula, which travels to the lungs and then to the liver.
- In the liver, the schistosomula develops into adult worms.
- Adult worms migrate to the vesical and ureteric venous plexus, where the female lays eggs.
- Eggs penetrate the urinary mucosa and are excreted in urine.
- Eggs hatch in water, releasing miracidia, which infect snails.
- In the snail, miracidia develop into cercariae, which are released into the water to infect humans.
What are the clinical features of acute schistosomiasis?
- During skin penetration of cercariae, intense irritation and skin rash may develop at the site of cercarial penetration (swimmer’s itch).
- Anaphylactic or toxic symptoms may develop during the incubation period due to the liberation of toxic metabolites by schistosomules.
- Migration of schistosomulae into the lungs may cause cough and mild fever.
What are the clinical features of chronic schistosomiasis caused by Schistosoma haematobium?
- Urogenital disease: Light infection may be asymptomatic. Symptoms develop usually after 3–6 months.
- Eggs passing into the urinary bladder cause mucosal damage, leading to dysuria and hematuria.
- Soluble antigens released from the eggs provoke a delayed-type hypersensitivity reaction, leading to the formation of egg granulomas.
- Granulomas may cause fibrosis, leading to sandy patches visible on cystoscopy.
- Fibrosis may cause obstruction of the lower end of the ureters, resulting in hydroureter and hydronephrosis.
- Metaplastic changes in the urinary mucosa may lead to carcinoma of the bladder.
How is Schistosoma haematobium diagnosed?
- Microscopic examination: Urine is collected and concentrated by centrifugation or membrane filtration and observed under a microscope for the presence of terminal-spined eggs.
- Biopsy: Histopathology of bladder mucosal biopsy detects terminal-spined eggs.
- Serodiagnosis: Antibody detection (serum) and antigen detection (serum and urine).
- Molecular diagnosis: PCR on clinical samples.
What is the treatment for Schistosoma haematobium infection?
Praziquantel is the drug of choice.
What are the prevention and control measures for Schistosoma haematobium infection?
- Proper disposal of human urine.
- Treatment of infected persons.
- Avoid swimming, bathing, and washing in snail-infested water.
- Control of snails by using molluscicides.
What is the morphology of the adult male and female Schistosoma haematobium?
• Male: It is 15 mm in length and 0.9 mm in breadth. It has 4–5 testes and is covered by a finely tuberculated cuticle. It has 2 muscular suckers: a small oral sucker and a large prominent ventral sucker. The gynecophoric canal is present immediately behind the ventral sucker.
• Female: It is 20 mm in length and 0.25 mm in breadth. It has oral and ventral suckers. The gravid female worm contains 20–30 eggs in its uterus at one time and may pass up to 300 eggs a day.
What is the habitat of adult Schistosoma mansoni worms?
Adult male and female worms reside in mesenteric veins draining the sigmoidorectal region.
What is the characteristic feature of Schistosoma mansoni eggs?
Eggs have a characteristic lateral spine (110–175 µm × 45–70 µm).
What is the intermediate host for Schistosoma mansoni?
Freshwater snails of Biomphalaria species are intermediate hosts.
What is the prepatent period for Schistosoma mansoni?
The prepatent period is around 5 weeks (35 days).
What are the clinical features of Katayama fever in Schistosoma mansoni infection?
Katayama fever is characterized by fever, generalized lymphadenopathy, and hepatosplenomegaly. There is a high peripheral blood eosinophilia.
What is the drug of choice for treating Schistosoma mansoni infection?
Praziquantel is the drug of choice.
What is the most pathogenic species among the schistosomes?
Schistosoma japonicum is the most pathogenic species among the schistosomes.
What is the habitat of adult Schistosoma japonicum worms?
Adult worms reside in the mesenteric veins draining the ileocecal region.
What is the egg output of Schistosoma japonicum?
The female worm lays more than 3,000 eggs/day (300 eggs on average, 50 in the uterus at one time).
What are the clinical features of Schistosoma japonicum infection?
Clinical features include cercarial dermatitis, Katayama fever, intestinal disease, hepatosplenic disease, carcinoma (colorectal and liver), and chronic secondary infection with Salmonella species and hepatitis B virus.
What is the intermediate host for Schistosoma japonicum?
Snails of Oncomelania species are the intermediate hosts.
What is the characteristic feature of Schistosoma japonicum eggs?
The eggs are smaller and more spherical than those of S. haematobium and S. mansoni. The egg has no spine, but shows a lateral small rudimentary knob.
What is the distribution of Schistosoma japonicum?
S. japonicum infection occurs most commonly in the Far East, including China, the Philippines, Japan, and Indonesia.
What is the treatment for Schistosoma intercalatum infection?
Praziquantel is the drug of choice.
