Schistosomiasis Quiz

Schistosomiasis Overview

• Schistosomiasis, also known as bilharzia or snail fever, is a parasitic disease caused by flukes (trematodes) of the genus Schistosoma.
• It's the third most devastating tropical disease globally, impacting morbidity and mortality in developing countries in Africa, South America, the Caribbean, the Middle East, and Asia.
• More than 140 million people are currently infected, with an estimated 700 million at risk in 76 countries.
• An estimated 200,000 deaths are attributed to schistosomiasis annually.

Epidemiology

• The World Health Organization (WHO) estimates 220.8 million people needed preventive treatment in 2017.
• 102.3 million received treatment in 2017.
• At least 236.6 million people required preventive treatment in 2019.
• Schistosomiasis disproportionately affects men due to exposure from activities including bathing, swimming, and agriculture.
• Children and adolescents are most heavily and frequently infected.
• In some endemic areas, prevalence in those aged 10-19 reaches nearly 100%.
• Affected individuals in travel show a different age distribution, with young adults at higher risk.

Etiological Agent and Species

• Schistosoma hematobium, Schistosoma mansoni, and Schistosoma japonicum are the prevalent species causing the most severe cases of the disease.
• Less prevalent species, such as S. mekongi and S. intercalatum, may also cause human disease.

Snail Hosts

• The different species of Schistosoma have different snail intermediate hosts.
• S. mansoni - Biomphalaria
• S. japonicum - Oncomelania
• S. mekongi - Tricula
• S. hematobium and S. intercalatum- Bulinus

Geographical Distribution

• S. mansoni - Africa, the Middle East, the Caribbean, Brazil, Venezuela, Suriname
• S. japonicum - China, Indonesia, the Philippines
• S. mekongi - Districts of Cambodia and the Lao People's Democratic Republic
• S. haematobium - Rain forests of Central Africa, the Middle East, Corsica
• S. guineensis and related S. intercalatum- rain forest areas of central Africa

Reservoir Hosts

• S. haematobium- Humans
• S. mansoni- Mainly humans but also reported in rodents
• S. japonicum- Humans and domestic animals (dogs, cats, and wild rodents)

Life Cycle

• The life cycle involves a complex interplay between humans, freshwater snails, and the schistosome parasite.
• The life cycle includes multiple steps: including miracidia, sporocysts, cercariae, schistosomulae and adult worms.

WHO Case Definition

• Urinary schistosomiasis:
  • Suspected: Visible hematuria or positive reagent strip for hematuria.
  • Confirmed: Eggs of S. haematobium in urine.
• Intestinal schistosomiasis:
  • Suspected: Non-specific abdominal symptoms, blood in stool, hepatosplenomegaly.
  • Confirmed: Presence of eggs in the stool.

Incubation Period

• Acute systemic manifestations (Katayama fever), including fever, urticaria, malaise, and diarrhea, may occur 2-6 weeks after exposure and during the initial egg deposition.
• This manifestation is less common with S. haematobium.
• Communicability lasts for over 10 years with S. haematobium and S. mansoni. Snail hosts can release cercariae for several weeks to 3 months.

Susceptibility

• Susceptibility to infection is universal.
• Immunity resulting from infection is variable and not fully researched.

Clinical Manifestations

• Intestinal schistosomiasis: Fatigue, abdominal pain, diarrhea, dysentery
• Urinary schistosomiasis: Dysuria, urinary frequency, terminal hematuria.
• Cardiopulmonary schistosomiasis: Larval pneumonitis with cough, mild wheezing, low-grade fever
• CNS schistosomiasis: Focal and generalized seizures, headache
• Female genital schistosomiasis: Postcoital bleeding, genital ulceration, irregular menstruation, pelvic pain.

Complications

• Gastrointestinal (GI) bleeding, GI obstruction
• Malnutrition
• Schistosomal nephropathy
• Renal failure, Pyelonephritis, hematuria, hemospermia
• Sepsis, Pulmonary hypertension
• Cor pulmonale
• Neuroschistosomiasis (transverse myelitis, paralysis, cerebral microinfarcts)
• Infertility, severe anemia
• Low birth-weight babies
• Spontaneous abortion
• Higher risk of ectopic pregnancies
• End-organ disease, portal hypertension, obstructive uropathy, pregnancy complications (vulvar or fallopian granuloma), carcinoma (liver, bladder, gallbladder)

Diagnosis

• Microscopic detection of eggs in stool or urine sample is common.
• S. haematobium eggs are oval with a spike.
• S. japonicum eggs are small and almost spherical with tiny spines.
• S. mansoni eggs have a spike on the side.
• Immunological tests (ELISA and IFA) are also used.

Treatment

• Antischistosomal drugs, particularly praziquantel, are the treatment of choice.
• Cure rates for single treatment with praziquantel often reach 65-90%.
• Steroids can reduce the inflammatory response caused by the drugs.
• Repeated treatments might be necessary for treatment of maturing worms.
• Drugs are ineffective after fibrosis development, necessitating management of resulting complications.
• Surgical interventions involve removal of tumor masses, ligation of esophageal varices, and porta-caval shunt surgeries.
• Alternative drugs (metrifonate, niridazole, oxamniquine) exist for specific schistosome species.

Methods of Control

• Preventive measures:
  • Treat patients in endemic areas with praziquantel for relief and prevention.
  • Treat high-risk groups (children, women of childbearing age, unique occupational groups).
  • Educate the population about the disease and precautionary measures.
  • Dispose of feces and urine properly to prevent the contamination of water sources.
  • Control of patient, contacts, and immediate environment:
  • Report to local health authorities.
  • Sanitize the places where feces and urine are deposited.
  • Examine and test people that come in contact with contaminated sources.
  • Administer necessary medication
• Epidemic Measures:
  • Examine and treat all infected individuals.
  • Provide clean water; avoid water contamination.
  • Treat areas with high snail populations with molluscides.
  • Provide advice for travelers visiting endemic areas.