Schistosomiasis: Symptoms, Treatments, Medications and Prevention

Schistosomiasis, also known as bilharzia, is a parasitic disease caused by infection with flatworms (flukes) of the genus Schistosoma. It is one of the most significant neglected tropical diseases, affecting millions of people, particularly in regions with poor access to clean water and sanitation. Schistosomiasis is considered a waterborne disease because the parasites are transmitted through contact with contaminated freshwater, where infected snails release the parasite’s larval form. The disease can cause both acute and chronic symptoms, and if left untreated, it can lead to severe organ damage and long-term health complications.

What is Schistosomiasis?

The Causative Agent: Schistosoma Species

Schistosomiasis is caused by parasitic trematode worms of the genus Schistosoma. The major species that infect humans include:

• Schistosoma mansoni: Found mainly in Africa, South America, and the Caribbean. It primarily causes intestinal schistosomiasis.
• Schistosoma haematobium: Found in Africa and the Middle East. It primarily causes urinary schistosomiasis.
• Schistosoma japonicum: Found in parts of East Asia, especially China and the Philippines. It causes intestinal schistosomiasis.
• Schistosoma mekongi: Found in Southeast Asia, especially in Cambodia and Laos.
• Schistosoma intercalatum: Found in certain parts of Central and West Africa.

These parasites have a complex life cycle that involves both humans and freshwater snails. Humans become infected when they come into contact with freshwater contaminated by cercariae, the larval stage of the Schistosoma parasites. These larvae penetrate the skin, migrate through the bloodstream, and develop into adult worms that reside in blood vessels near the intestines or bladder.

Life Cycle of Schistosoma

The life cycle of Schistosoma involves two main hosts: freshwater snails and humans. The cycle is as follows:

1. Larval form (cercariae): Infective cercariae are released from infected snails into freshwater environments.
2. Human infection: Cercariae penetrate human skin upon contact with contaminated water.
3. Migration: Once inside the human body, the larvae travel through the bloodstream to the liver, where they mature into adult worms.
4. Maturation: Adult worms pair up and migrate to blood vessels in the intestines (S. mansoni, S. japonicum) or bladder (S. haematobium).
5. Egg production: The worms lay eggs, which can either be excreted in urine (S. haematobium) or feces (S. mansoni, S. japonicum).
6. Contamination of water: The eggs hatch in water, releasing miracidia, which infect freshwater snails, thus continuing the life cycle.

Mode of Transmission

Humans become infected when they come into contact with freshwater bodies such as rivers, lakes, or ponds that are contaminated with Schistosoma larvae. Activities that involve skin contact with contaminated water, such as swimming, fishing, washing clothes, or bathing, increase the risk of infection. Schistosomiasis is not transmitted person-to-person but rather through environmental contamination by infected human excreta.

Who is at Risk of Schistosomiasis?

Geographic Risk Factors

Schistosomiasis is predominantly found in tropical and subtropical regions where freshwater snail species, which serve as intermediate hosts for Schistosoma parasites, are present. The disease is most prevalent in the following regions:

• Sub-Saharan Africa: Africa bears the highest burden of schistosomiasis, particularly in countries such as Nigeria, Tanzania, Uganda, Ghana, and Mozambique.
• Middle East: Countries such as Egypt, Sudan, and Yemen have significant rates of infection.
• Southeast Asia: Schistosomiasis is endemic in parts of Cambodia, Laos, and the Philippines.
• East Asia: Regions in China are also affected, particularly along the Yangtze River basin.
• South America and the Caribbean: Brazil and some Caribbean islands report cases of schistosomiasis, particularly S. mansoni.

Occupational and Behavioral Risk Factors

Several groups are more likely to be exposed to contaminated freshwater environments and, therefore, are at higher risk of contracting schistosomiasis:

1. Agricultural Workers

Farmers and workers involved in irrigation, rice cultivation, and fishing are at a high risk of exposure to Schistosoma-infested waters. In some regions, agricultural practices that involve frequent contact with freshwater make these populations highly vulnerable.

2. Children

Children living in endemic areas are at particular risk of infection because they often play or swim in contaminated lakes, rivers, and ponds. The risk is heightened by poor sanitation practices that contribute to the contamination of water sources.

3. People Living in Poverty

Communities without access to clean water and adequate sanitation are at greater risk for schistosomiasis. Open defecation and improper waste disposal can contaminate freshwater bodies, perpetuating the transmission cycle.

4. Tourists and Travelers

Tourists who swim, bathe, or engage in water sports in endemic regions may unknowingly expose themselves to the parasite. Travelers to Africa, Southeast Asia, or the Middle East should be cautious about contact with freshwater.

5. Women and Domestic Workers

Women who engage in daily activities such as washing clothes or fetching water from contaminated rivers or lakes are at increased risk of infection, especially in rural areas.

Symptoms of Schistosomiasis

Schistosomiasis can present with a range of symptoms, depending on the stage of infection, the species of parasite, and the overall health of the individual. Symptoms may appear weeks or even months after initial exposure.

Early (Acute) Schistosomiasis

Acute schistosomiasis, also known as Katayama fever, occurs shortly after the initial infection as the body mounts an immune response to the invading parasites. Symptoms usually appear 2 to 6 weeks after exposure and include:

1. Skin Rash

• “Swimmer’s itch”: The first symptom of schistosomiasis is often an itchy rash or small red bumps at the site where the cercariae penetrated the skin.
• Localized swelling: The rash is usually confined to areas of the body that were submerged in water.

2. Fever and Chills

• High fever: Fever is one of the earliest systemic symptoms of acute schistosomiasis.
• Chills and sweats: Alternating chills and sweating episodes are common during this phase.

3. Muscle Aches and Joint Pain

• Myalgia (muscle pain): Patients may experience widespread muscle aches and joint pain, similar to flu-like symptoms.
• Fatigue: Generalized weakness and tiredness often accompany these symptoms.

4. Gastrointestinal Symptoms

• Abdominal pain: Mild to moderate abdominal discomfort may occur due to inflammation in the intestines.
• Diarrhea: Some individuals experience intermittent diarrhea, which may be blood-tinged in more severe cases.

Chronic Schistosomiasis

If left untreated, schistosomiasis can progress to a chronic infection, particularly in individuals who are repeatedly exposed to contaminated water. The chronic phase is marked by ongoing inflammation and immune responses to the parasite’s eggs trapped in tissues, leading to long-term damage. Chronic schistosomiasis can be classified into two forms: intestinal and urinary.

1. Intestinal Schistosomiasis

This form of the disease is caused by S. mansoni, S. japonicum, and S. mekongi and primarily affects the gastrointestinal system.

• Chronic abdominal pain: Persistent discomfort or pain in the abdomen, particularly in the lower abdomen.
• Diarrhea: Recurrent episodes of diarrhea, sometimes with blood in the stool (hematochezia).
• Hepatosplenomegaly: Enlarged liver and spleen due to chronic inflammation and fibrosis caused by trapped parasite eggs.
• Intestinal fibrosis: Over time, the immune response to the parasite’s eggs can cause scarring (fibrosis) of the intestines, leading to bowel dysfunction.

2. Urinary Schistosomiasis

Caused primarily by S. haematobium, this form of schistosomiasis affects the urinary tract and can lead to serious complications if untreated.

• Hematuria: One of the hallmark symptoms is blood in the urine (hematuria), which may appear intermittently.
• Painful urination: Patients may experience pain or burning during urination, along with increased frequency of urination.
• Bladder fibrosis: Chronic inflammation caused by trapped eggs can lead to scarring and fibrosis of the bladder.
• Increased risk of bladder cancer: Long-term infection with S. haematobium is associated with an increased risk of developing squamous cell carcinoma of the bladder.

Severe Complications

In some cases, untreated or poorly managed schistosomiasis can lead to severe complications, including:

• Liver fibrosis and portal hypertension: Chronic schistosomiasis can cause liver fibrosis (scarring), which may progress to cirrhosis and portal hypertension (increased blood pressure in the liver’s blood vessels).
• Kidney damage: Chronic urinary schistosomiasis can lead to hydronephrosis (swelling of the kidneys) and impaired kidney function.
• Pulmonary hypertension: In some cases, the infection may lead to pulmonary arterial hypertension, a condition in which the blood pressure in the lungs’ arteries increases, leading to heart failure.

Diagnosis of Schistosomiasis

Diagnosing schistosomiasis involves clinical evaluation, laboratory testing, and sometimes imaging studies. Early diagnosis is crucial to prevent complications and manage the disease effectively.

1. Clinical Evaluation

Healthcare providers will evaluate the patient’s history, including exposure to freshwater in endemic areas. If the patient reports recent travel to or residence in a schistosomiasis-endemic region and presents with suggestive symptoms (such as skin rash, hematuria, or chronic diarrhea), further testing is warranted.

2. Laboratory Tests

1. Stool and Urine Examination

Microscopic examination of stool or urine samples is the most commonly used method for diagnosing schistosomiasis. Schistosome eggs are typically found in:

• Stool samples: Used to detect eggs of S. mansoni, S. japonicum, and S. mekongi.
• Urine samples: Used to detect eggs of S. haematobium.

Kato-Katz technique is a commonly used method for stool examination, allowing for the detection and quantification of schistosome eggs.

2. Serological Tests

Antibody detection tests can be used to identify the presence of antibodies to Schistosoma antigens in individuals who have been infected but may not yet be shedding eggs. These tests are useful for diagnosing early-stage infections, especially in travelers or individuals who may not be shedding detectable eggs.

3. Antigen Detection

Tests that detect circulating Schistosoma antigens in the blood or urine are also available. These tests can provide a more sensitive diagnosis, particularly in cases of light infection or after treatment.

3. Imaging Studies

In chronic cases, imaging studies may be necessary to assess the extent of organ damage caused by schistosomiasis. Imaging techniques include:

• Ultrasound: Used to evaluate liver and bladder damage, including fibrosis and organ enlargement.
• CT scan or MRI: In cases of suspected central nervous system involvement, imaging studies may be needed to assess the presence of schistosomal granulomas in the brain or spinal cord.

Treatments for Schistosomiasis

Antiparasitic Treatment

The cornerstone of treatment for schistosomiasis is antiparasitic medication, which aims to kill the adult worms and prevent further egg deposition.

1. Praziquantel

Praziquantel is the drug of choice for treating all forms of schistosomiasis. It works by causing the parasites to become paralyzed, allowing the host’s immune system to eliminate them. Praziquantel is highly effective, particularly when administered in the acute and early chronic phases of infection.

• Dosage: A typical regimen consists of 40-60 mg/kg of praziquantel administered as a single dose or in divided doses over one day. In some cases, a second course may be necessary, especially in individuals with heavy infections.
• Side effects: Common side effects include nausea, dizziness, headache, and abdominal pain, but these are usually mild and temporary.

2. Oxamniquine

Oxamniquine is an alternative medication that is effective against S. mansoni, but it is less commonly used compared to praziquantel. It is primarily available in South America and some parts of Africa.

Supportive Care

In addition to antiparasitic treatment, patients with severe or chronic schistosomiasis may require supportive care, including:

1. Treatment for Anemia

Patients with chronic blood loss due to intestinal or urinary schistosomiasis may develop iron-deficiency anemia. Iron supplementation or blood transfusions may be necessary in severe cases.

2. Management of Organ Damage

• Liver fibrosis: Patients with significant liver fibrosis may require treatment for portal hypertension, including medications or, in advanced cases, surgery.
• Bladder complications: In cases of urinary schistosomiasis with bladder fibrosis or obstruction, surgical intervention may be required.

3. Treatment of Pulmonary Hypertension

For patients who develop pulmonary arterial hypertension due to chronic schistosomiasis, medications such as vasodilators or anticoagulants may be needed to manage symptoms and improve lung function.

Most Common Medications for Schistosomiasis

The most common medications used to treat schistosomiasis include:

1. Praziquantel

Praziquantel is the first-line treatment for all forms of schistosomiasis, providing effective and rapid clearance of the adult worms from the body.

2. Oxamniquine

Oxamniquine is an alternative treatment for S. mansoni infections, primarily used in regions where praziquantel may not be readily available.

3. Corticosteroids

In cases of acute schistosomiasis (Katayama syndrome) or when there is significant inflammation of the central nervous system, corticosteroids may be prescribed to reduce inflammation and prevent complications.

Where is Schistosomiasis Most Prevalent?

Schistosomiasis is prevalent in tropical and subtropical regions where freshwater sources are contaminated by infected snails. The disease is endemic in 74 countries worldwide, affecting an estimated 240 million people. The highest prevalence rates are found in the following regions:

1. Sub-Saharan Africa

Africa bears the greatest burden of schistosomiasis, accounting for more than 90% of global cases. Countries such as Nigeria, Tanzania, Uganda, Kenya, and Mozambique are heavily affected. Both S. mansoni (intestinal schistosomiasis) and S. haematobium (urinary schistosomiasis) are endemic in these regions.

2. Middle East

Countries such as Egypt, Sudan, and Yemen have long struggled with schistosomiasis, particularly urinary schistosomiasis caused by S. haematobium. The construction of large water projects, such as dams and irrigation systems, has contributed to the spread of the disease.

3. Southeast Asia

Schistosomiasis is endemic in parts of Cambodia, Laos, and the Philippines, particularly in rural communities where contact with contaminated freshwater is common.

4. East Asia

In China, schistosomiasis, particularly S. japonicum, is prevalent in regions along the Yangtze River. The Chinese government has implemented extensive control programs that have significantly reduced the disease’s prevalence, but cases still occur.

5. South America and the Caribbean

Brazil is the most affected country in South America, with S. mansoni infections occurring primarily in areas with poor sanitation. Some Caribbean islands, including Puerto Rico, also report cases of schistosomiasis.

Prevention of Schistosomiasis

Preventing schistosomiasis requires a combination of public health interventions, individual protective measures, and environmental control efforts.

1. Improved Sanitation and Safe Water Access

One of the most effective strategies for preventing schistosomiasis is improving access to clean water and sanitation facilities. This includes:

• Building latrines to prevent the contamination of freshwater with human feces and urine.
• Providing access to clean, treated water for drinking, bathing, and washing clothes, reducing the need for contact with contaminated freshwater sources.

2. Avoiding Contact with Contaminated Water

In endemic areas, individuals should avoid direct contact with freshwater sources that may be contaminated with Schistosoma parasites. This includes avoiding activities such as swimming, wading, or bathing in rivers, lakes, or ponds.

• Use of protective footwear: Wearing waterproof boots or waders when working in water can reduce the risk of skin contact with infective cercariae.

3. Snail Control Programs

Reducing the population of freshwater snails, which serve as intermediate hosts for Schistosoma parasites, is another key preventive measure. This can be achieved through:

• Molluscicides: Chemicals that kill snails can be applied to contaminated water bodies.
• Environmental management: Modifying water habitats, such as by reducing vegetation or drainage, can limit snail populations and interrupt the transmission cycle.

4. Health Education

Public health education is essential for raising awareness about schistosomiasis and promoting behavior changes that can reduce transmission. Education campaigns should focus on:

• Avoiding open defecation: Encouraging communities to use latrines and practice proper hygiene to prevent water contamination.
• Safe water practices: Teaching individuals how to treat water before use, such as by filtering or boiling, to avoid contact with contaminated sources.

5. Mass Drug Administration (MDA)

In regions with high prevalence rates, mass drug administration (MDA) programs are implemented to treat at-risk populations. These programs involve administering praziquantel to large groups of people, such as schoolchildren or entire communities, to reduce the parasite burden and prevent transmission.

• School-based deworming: In areas where children are at high risk, regular treatment with praziquantel can help control the disease and prevent long-term complications.

6. Travel Precautions

Travelers to endemic regions should be cautious about freshwater exposure. They should avoid swimming or wading in untreated water sources and opt for bottled or treated water for drinking and bathing.