6326 – Schistosomiasis

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Definition

Schistosomiasis, also known as bilharzia or snail fever, is a disease caused by parasitic flatworms called schistosomes or blood flukes. It's a significant health issue in tropical and subtropical regions, particularly in areas with poor sanitation and freshwater contact. The disease is characterized by an infection from parasitic flatworms that enter the body through the skin during contact with contaminated freshwater. 

Etiology

Schistosomiasis (Bilharziasis) is caused by some species of blood trematodes (flukes) in the genus Schistosoma. The three main species infecting humans are Schistosoma haematobium, S. japonicum, and S. mansoni. 

Signs & Symptoms

Schistosomiasis, also known as bilharzia or snail fever, is a disease caused by parasitic worms (blood flukes) that infect humans through contact with contaminated freshwater. 

The symptoms can vary depending on the species of worm and the stage of the infection. 

Early signs (within days of exposure)

• Rash or itchy skin (swimmer's itch): This is often the first sign, appearing where the parasites penetrated the skin. 

Acute symptoms (1–2 months after infection)

These flu-like symptoms are caused by the body reacting to the adult worms and eggs. 

• Fever
• Chills
• Cough
• Muscle aches
• Fatigue
• Headache
• Abdominal pain (around the liver or spleen) 

Chronic symptoms (months or years after infection)

If left untreated, schistosomiasis can become chronic and cause serious complications as the parasite eggs become trapped in organs, leading to inflammation and damage. 

Intestinal schistosomiasis

• Abdominal pain
• Diarrhea (which may be bloody)
• Loss of appetite
• Enlarged liver and spleen 

Urogenital schistosomiasis

• Blood in the urine (hematuria)
• Painful or frequent urination
• Kidney and bladder damage
• Bladder cancer (in severe cases)
• Genital lesions and infertility (in women)
• Painful intercourse and abnormal vaginal discharge (in women)
• Genital lesions, painful ejaculation, and hematospermia (in men) 

Other potential complications

• Anemia
• Malnutrition and stunted growth (especially in children)
• Learning difficulties (in children)
• Pulmonary hypertension and heart failure
• Neurological complications (seizures, paralysis, spinal cord inflammation) (rare)

Tests

Schistosomiasis is a parasitic disease caused by blood flukes, and its diagnosis depends on the suspected species and the stage of infection. 

Here's an overview of the key diagnostic methods:

1. Detection of parasite eggs (microscopy)

• Purpose: Primary method for diagnosing active schistosomiasis by identifying eggs in stool or urine.
• Types of samples:
  • Stool: Used for diagnosing intestinal schistosomiasis (Schistosoma mansoni, S. japonicum, S. mekongi, S. intercalatum, S. guineensis).
  • Urine: Used for diagnosing urogenital schistosomiasis (S. haematobium).
• Techniques:
  • Kato-Katz method: Used for stool examination, involves preparing a thick smear for microscopic examination and quantifying eggs per gram (EPG) of feces.
  • Urine filtration: Standard technique for detecting S. haematobium eggs in urine, often using nylon, paper, or polycarbonate filters.
• Limitations:
  • Low sensitivity: Especially in light or early infections, eggs may be scarce or shed intermittently.
  • Requires expertise and equipment: Microscopy requires skilled personnel and a microscope. 

2. Serologic tests (antibody detection)

• Purpose: Detects antibodies produced by the body in response to the parasite.
• Used for:
  • Screening individuals from non-endemic areas with potential exposure.
  • Retrospective diagnosis of past infections.
  • Identifying asymptomatic individuals at risk.
• Techniques:
  • ELISA (Enzyme-Linked Immunosorbent Assay): Detects IgG antibodies to Schistosoma species, with variants available for different species (e.g., S. mansoni).
  • Indirect Haemagglutination Assay (IHA): Detects antibodies against Schistosoma antigens.
  • Immunochromatographic rapid diagnostic tests (ICT): Detects both IgM and IgG antibodies.
• Limitations:
  • Cannot differentiate active vs. past infection: Antibodies can persist even after successful treatment.
  • Potential for cross-reactivity: May show false positives due to reactions with other helminth infections.
  • Window period: Antibodies may not be detectable in very early infections. 

3. Antigen detection tests

• Purpose: Detects schistosomal antigens in body fluids, indicating active infection.
• Potential advantages: May be useful for assessing treatment efficacy as antigen levels reflect parasite burden.
• Types of antigens: Circulating anodic antigen (CAA) and circulating cathodic antigen (CCA) are the most studied.
• Limitations: Currently not commercially available in the US and still undergoing evaluation, particularly for low-intensity infections. 

4. Molecular tests (nucleic acid amplification tests - NAATs)

• Purpose: Detects schistosome DNA in samples, offering high sensitivity and specificity.
• Types:
  • PCR (Polymerase Chain Reaction): Can detect and quantify schistosome DNA in various samples (stool, urine, blood, tissue).
  • Real-time PCR (qPCR): Offers higher sensitivity and the potential for multiplexed detection.
  • Loop-mediated isothermal amplification (LAMP): A simpler, field-friendly method that doesn't require expensive equipment.
• Limitations:
  • Cost and complexity: PCR assays can be expensive and require specialized laboratories and trained personnel.
  • Potential for false results: Possible due to contamination or poor sample quality. 

5. Other diagnostic methods

• Imaging studies: Ultrasound, CT scan, and MRI can help assess organ damage and complications, particularly in chronic infections.
• Biopsy: Tissue biopsies (e.g., rectal or bladder) can be used to detect eggs when other methods are negative.
• Haematuria testing: Urine reagent strips can detect blood in urine, a common sign of S. haematobium infection. However, this is not specific for schistosomiasis.

Treatment

Praziquantel is the standard and recommended treatment for all forms of schistosomiasis. It is effective against all major Schistosoma species. 

Dosing

• For Schistosoma mansoni, S. haematobium, and S. intercalatum: A single day of treatment with 40 mg/kg of praziquantel in two divided doses.
• For S. japonicum and S. mekongi: A single day of treatment with 60 mg/kg of praziquantel in three divided doses.

Residuals

Schistosomiasis, if left untreated, can have various long-term consequences and leave behind lasting effects, often referred to as residuals. These effects can range from organ damage to developmental issues in children, and may even lead to increased risk of other health problems. 

Here are some of the key residuals associated with schistosomiasis:

1. Organ damage and dysfunction

• Liver and spleen: Chronic schistosomiasis, especially intestinal forms, can lead to the development of liver fibrosis, a scarring of the liver tissue. This fibrosis can lead to portal hypertension (increased pressure in the veins leading to the liver) and enlargement of the liver and spleen (hepatosplenomegaly). In severe cases, it can cause gastrointestinal bleeding and even liver failure, although liver failure from schistosomiasis alone is uncommon.
• Urinary tract and bladder: Urogenital schistosomiasis, caused by Schistosoma haematobium, can lead to inflammation and scarring of the bladder and urinary tract, potentially resulting in conditions like cystitis, contracted bladder, and kidney damage. Chronic infection can also increase the risk of developing bladder cancer, typically squamous cell carcinoma.
• Lungs: Eggs migrating to the lungs can cause pulmonary hypertension, a condition where there is high blood pressure in the arteries of the lungs, potentially leading to cor pulmonale (right-sided heart failure).
• Brain and spinal cord: In rare cases, eggs can enter the central nervous system (CNS), potentially leading to seizures, paralysis, or inflammation of the spinal cord (transverse myelitis), according to the CDC. 

2. Impact on children and development

• Schistosomiasis can cause anemia, stunted growth, and a reduced ability to learn in children.
• These effects can have long-term consequences on a child's future prospects and ability to be productive members of society.

3. Reproductive health issues

• Female genital schistosomiasis (FGS): In women, urogenital schistosomiasis can manifest with genital lesions, vaginal bleeding, pain during sexual intercourse, and nodules in the vulva.
• FGS can also lead to infertility and increased susceptibility to sexually transmitted infections, including HIV.
• Male genital schistosomiasis (MGS): In men, urogenital schistosomiasis can affect the seminal vesicles, prostate, and other organs, potentially leading to infertility. 

4. Other complications

• Increased risk of other infections: Chronic schistosomiasis can weaken the immune system and increase susceptibility to other infections, such as Salmonella bacteremia and viral hepatitis (Hepatitis B and C).
• Malnutrition and anemia: Chronic inflammation and bleeding can lead to malnutrition and anemia, further impacting the health and productivity of infected individuals.