Schistosomiasis

• Schistosomiasis or Bilharzia describes a vector borne parasitic disease caused by trematode flatworms of the genus Schistosomes.
• it is second only to malaria in importance among the parasitic diseases
• affects more than 230 million people worldwide with close 800 million people at risk of infection
• prevalent in
  • tropical and subtropical areas
  • poor communities without access to safe drinking water and adequate sanitation.
• Exposure to contaminated water results in Schistosomiasis.
• infection is usually acquired through activities such as
  • swimming, bathing, fishing, farming, and washing clothes
  • Children are especially vulnerable since they tend to spend time swimming or bathing in water containing infectious cercariae.
• once the parasites penetrate the skin, the adult male and female worms live and reproduce sexually within the veins of their human host
  • intense itching follows the initial exposure (swimmer’s itch) when the parasites initially enter the skin
  • once entered these cercariae shed their forked tail, becoming schistosomulae.
  • the schistosomulae migrate through several tissues and stages to their residence in the veins
    • in perivesicular venules – S haematobium
    • in mesenteric venules – S mansoni, S japonicum, and others
  • adult worms may live for several years in the human host. During this time, the female lays eggs continuously. The eggs are excreted in either the faeces or urine.
  •  eggs, whether excreted or retained in the body, die within 1–2 weeks after being released by the female worm
  • freshwater becomes contaminated by Schistosoma eggs when infected people urinate or defecate in the water.
• There are main species of schistosomes:
  • S mansoni are seen in
    • Africa
    • Middle East
    • Caribbean
    • Brazil
      Venezuela
    • Suriname
  • S japonicum
    • China
    • Indonesia
    • Philippines
  • S mekongi
    • Mekong River basin in Cambodia
    • Lao People’s Democratic Republic
  • S guineensis and related S. intercalatum
    • Rain forest areas of central Africa
  • Schistosoma haematobium
    • Africa, the Middle East
    • Corsica (France)

There are two main forms of schitomiasis:

• urinary schistosomiasis
  • caused by Schistosoma haematobium
  • mainly affects the bladder, ureters and kidneys
  • develops due to the granulomatous inflammatory response to deposited eggs in tissues
    • adult worms are present in the peri-vesical venous plexus (migrated to this site via the porto-systemic anastomosis at the level of the third lumbar vertebra)
    •  females travel to the bladder and lay eggs. Eggs that fail in getting their freedom remain trapped in the bladder wall leading to granuloma formation
  • Symptoms
  • terminal haematuria
    • appears 10-12 weeks after infection
    • is the first sign of established disease
    • in severe cases, the whole urine sample can be dark coloured.
    • maybe confused with menses in girls
  • dysuria
  • increased frequency of micturition
  • late manifestations
    • proteinuria (often nephrotic syndrome)
    • bladder calcification
    • ureteric obstruction
    • secondary bacterial infection in the urinary tract
    • renal colic
    • hydronephrosis
    • renal failure
• intestinal schistosomiasis 
  • caused by S. mansoni and S. japonicum
  • the schistosomulae migrate through several tissues and stages to their residence in the veins. Maturing larvae (schistosomula) need about 5–7 weeks before becoming adults and producing eggs 
  • male and female schistosomes mature within the hepatic portal veins and then leave in pairs to lodge in the mesenteric (S. mansoni, S. japonicum) or pelvic (S. haematobium) venules where they mate
  • mainly affects the liver and spleen and causes intestinal damage and hypertension of the abdominal blood vessels 
  • Adult worms migrate from their initial site in the liver sinusoids to their final site in the mesenteric venules whereupon the female lays eggs continuously. Egg deposition in the gut wall sub mucosa leads to inflammation, hyperplasia, ulceration, micro-abscess formation, and polyposis. These may lead to following symptoms in an individual:
    • colicky hypogastric pain or pain in the left iliac fossa
    • diarrhoea (particularly in children) that may alternate with constipation, haematochezia (blood in the faeces)

Four acute presentations have been recognized:

swimmer’s itch

• occurs when the parasites initially enter the skin
• this is a local inflammatory, hardly visible wheal at the site of penetration
• duration and reaction of this reaction may vary with the duration of schistosomular stay in the dermis

cercarial dermatitis

• a temporary itchy maculopapular skin eruption, comprising discrete, 1 cm to 3 cm erythematous raised macules
• may develop at the site of entry of the parasite
• pathogenetically similar to the ‘‘swimmers itch’’
  • is not a sequela of acute schistosomiasis, but develops in sensitized people when they are re-infected by schistosomal species that do not colonize in humans

bronchopneumonia

• bronchial hyper-reactivity with radiologically demonstrable pulmonary infiltrates may occur during the migration of schistosomulae through the pulmonary capillaries
• may also occur with superinfection in previously infected people

Katayama fever/ Katayama syndrome –

• occurs 3 to 8 weeks after infection / after contact with contaminated water
• is a systemic hypersensitivity reaction to schistosome antigens and circulating immune complexes.
• is characterised by
  • fever
  • arthralgia
  • vasculitic skin eruption
• generally self-limiting and patients recover spontaneously after 2–10 weeks.
• some may develop persistent and more serious disease with 
  • weight loss
  • dyspnoea
  • diarrhoea  
  • diffuse abdominal pain
  • toxaemia
  • hepatosplenomegaly and widespread rash
• Katayama fever is more noticeable in S. japonicum infection than other forms
• serological testing and stool and urine testing will be negative in this phase of the illness. 
• Worms take six to ten weeks to start egg production and so screening tests for schistosomiasis should be delayed until about 12 weeks after last exposure.

Treatment

• praziquantel (adult and child) 20 mg/kg orally, for two doses, given 4 hours apart.    as per eTG
• Further treatment courses may be required in patients who have inadequate response to initial treatment.
• Acute schistosomiasis syndrome (Katayama fever)
  • Treatment includes prednis(ol)one followed by praziquantel. Seek expert advice.
• Symptomatic Measures:
  • Soothing applications:
    • Calamine lotion
    • Colloidal oatmeal soak
    • Baking soda paste
    • Cool compress
  • Topical steroids
• Systemic treatments:
  • Oral antihistamines
  • Short course of oral corticosteroid for severe reactions
  • Antibiotics for secondary infections

Preventative Measures:

• Avoid bird-feeding in areas where people swim
• Feed birds a drug that treats the parasite
• Reduce vegetation in high-risk areas to make the environment less favorable for water snails
• Use chemical molluscicides (copper sulphate or copper carbonate) in small lakes to kill potentially infested snails
• Towel off immediately after exiting the water to reduce skin penetration of parasites
• Avoid swimming in shallow, warm waters