Schistosomiasis (Bilharziasis)

ICD-11

1F86.Z

(1F86.4 Swimmer’s itch)

Synonyms

Bilharziasis.

Epidemiology

The disease is most commonly affects children (playing in contaminated water) in tropical and developing countries of Africa, Asia and South America.

Definition

Systemic disease caused by parasitic trematode infection (schistosomes) of the gastrointestinal tract with deposition of the parasites into the perianal region, leading to skin irritation.

Aetiology & Pathogenesis

Disease-specific perianal dermatitis, common in freshwater, brackish, and marine habitats in shallow inshore water, along the coasts worldwide.

Contamination of freshwater with human feces or urine containing eggs from Schistosoma mansoni, S. haematobium, or S. japonicum. The first intermediate host is a water snail, in which it develops into sporocysts, and finally to cercaria, which penetrate human skin and mature. Adult worms migrate to the intestine (S. japonicum and S. mansoni) or the bladder (S. haematobium) and produce eggs, contaminating water through feces and urine respectively.

(Swimmer’s itch: genera responsible mostly are Trichobilharzia and Gigantobilharzia).

Signs & Symptoms

Cutaneous findings vary from a mild pruritus ani to a macular rash and to even severe perianal ulceration from uncontrolled scratching or superinfection. Humans infected develop a short-term immune reaction (cercarial dermatitis) within hours, lasting up to a week.

Pruritic papular dermatitis, preferentially on the legs (early), followed by allergic febrile reaction with accompanying urticaria, edema, arthritis, eosinophilia (intermediate stage). In chronic stage, internal organs (lungs, liver, bladder, CNS) may be involved. In the skin, often intensive inflammation with verrucous papules and nodules, preferentially at perineal and gluteal sites. These inflamed skin lesions may contain Schistosoma eggs, albeit in very low numbers.

Localisation

Perianal region, legs.

Classification

None.

Laboratory & other workups

Identification of parasite eggs in stool or urine. Blood cell count (eosinophilia). Detection of antibodies against Schictosomas.

Dermatopathology

Eggs are rarely found in chronic skin lesions. Leading histopathological changes are dense infiltrates mainly composed of neutrophils and eosinophils. In routine sections, cercariae can be found in exceptionally rare cases.

Course

Depending on visceral involvement. Effective treatment modalities available.

Complications

Systemic symptoms (fatigue, myalgia, diarrhea, hematuria, and abdominal pain ) due to immune reactions to the deposition of eggs in the host.

Bilharziasis cutanea tarda showing clusters of granulomas in the dermis may occur in patients with chronic, visceral involvement.

Superinfection.

Diagnosis

(Travel-) history. Clinical presentation. Investigation of stool or urine. Eosinophilia of the blood.

Differential diagnosis

Arthropod bites; urticaria; other worm infections.

Prevention & Therapy

Prevention: topical applications of water-resistant insect repellents.

Single dose of oral praziquantel.

Antihistamines orally.

Special