Schistosomiasis is a disease caused by a parasite that affects millions worldwide. Also known as bilharzia, the disease spreads through contact with freshwater snails and is common in tropical and subtropical regions.
Over 240 million people are already infected, and 700 million live in areas where the disease is a constant threat.
According to the World Health Organization (WHO), it is a ‘disease of poverty’ in areas without access to clean water and adequate sanitation.
Let’s explore how the disease develops, its impact on health, and the efforts being made to control it.
Schistosomiasis is caused mainly by three species of blood flukes (trematodes) in the genus Schistosoma: S.haematobium, S. japonicum, and S. mansoni.
Each of these parasites has a distinct preference for blood vessels in different parts of the human body. S.haematobium settles in the veins of the urinary tract, while S.mansoni and S.japonicum are found in the intestines.
WHO estimates that schistosomiasis causes nearly 12,000 deaths annually, though this figure is likely an underestimate.
Schistosomiasis is particularly prevalent in the African subcontinent, which is home to about 90% of those requiring treatment.
However, the disease has been reported in 78 countries and is endemic in 51 countries, including Brazil, Venezuela, the Middle East, China, Indonesia, and Cambodia.
Schistosomiasis haematobium outbreaks include:
Schistosomiasis outbreak data is from GIDEON, a leading infectious disease database. Get GIDEON for more detailed information on schistosomiasis or other diseases.
While anyone can contract schistosomiasis in endemic areas, certain groups are at higher risk, including:
The life cycle of schistosomes begins when infected humans release schistosoma eggs in their urine or feces.
In freshwater, these eggs hatch into larvae called miracidia, which then infect specific species of freshwater snails. The parasites undergo several developmental stages in snails before emerging as cercariae (free-swimming larvae) into the water. Cercariae can penetrate human skin when people come into contact with infested water.
Once inside a human, the parasites migrate through the bloodstream, and develop in the liver. Adult worms then move to their final destination through the portal vein system towards blood vessels around the intestines or bladder. Here they mate and produce eggs which are then released again into the environment, continuing the cycle.
Some animals, such as cattle, dogs, cats, and rodents, can also act as reservoirs for the parasite. This can complicate efforts to control disease transmission.
Schistosomiasis can affect multiple organ systems, and symptoms are primarily caused by the body’s reaction to the worms and their eggs.
One of the earliest signs of the disease are skin reactions, particularly itchy skin lesions at the location where cercariae penetrated the body.
Common gastrointestinal issues include:
Urinary problems such as blood in urine (hematuria) and kidney damage can also occur.
Schistosomiasis can also lead to reproductive system complications, including genital lesions, painful intercourse, and infertility.
Systemic symptoms like fever, cough, anemia, and stunted growth may also be present.
In advanced cases, schistosomiasis can lead to severe complications such as liver and spleen enlargement, abdominal blood vessel hypertension, and even bladder cancer.
Schistosomiasis can remain undetected for years. Symptoms arise from the body’s reaction to the worms and eggs.
Diagnosing schistosomiasis often begins with a patient’s history, including travel to endemic areas and potential exposure to water containing infected snails.
Physical examinations can reveal signs like an enlarged liver or spleen. Diagnosis requires microscopic examination of stool or urine for parasite eggs, followed by serological tests to detect antibodies against the parasite. In some cases, tissue biopsies are also performed.
For urogenital schistosomiasis, a urine filtration technique is commonly used. For intestinal schistosomiasis, the Kato-Katz technique is often employed to examine stool samples.
Schistosomiasis is easily treatable. The drug of choice for all forms of schistosomiasis is praziquantel, an effective anthelmintic medication.
Prevention strategies for schistosomiasis focus on several key areas, which include:
Diseases like schistosomiasis demonstrate the lopsided nature of access to healthcare. Despite infecting a quarter of a million people worldwide, it remains on the list of neglected tropical diseases.
WHO is taking steps to control and eliminate human schistosomiasis, focusing on treatment, prevention, and managing the environment. Part of their approach is organizing preventive treatments for vulnerable groups in areas where the disease is common. The organization works with governments, NGOs, research centers, and international development agencies to make this happen.
Schistosomiasis remains a significant global health challenge, particularly in regions with limited access to clean water and adequate sanitation. However, with increased awareness and comprehensive control strategies, we can hope to diagnose and treat the disease quickly.
No, schistosomiasis is not transmitted in chlorinated swimming pools. The parasite needs specific freshwater snails to complete its life cycle.
Schistosomiasis is called “swimmer’s itch” because it causes an itchy rash when parasite larvae from infected freshwater penetrate the skin. These larvae, released by snails, trigger an allergic reaction, leading to the characteristic itch. While not all cases lead to full-blown schistosomiasis, the early rash gives it the name.
Schistosomiasis is called bilharzia after Theodor Bilharz, the German physician who first discovered the parasitic worms causing the disease in 1851. He identified the worms in patients in Egypt while studying tropical diseases. The name honors his contribution to understanding the parasite’s life cycle and its impact on human health.
Currently, there is no vaccine available for schistosomiasis. Prevention focuses on avoiding exposure and treating infected individuals.
Yes, when diagnosed and treated early, schistosomiasis can be effectively cured with praziquantel. However, reinfection is possible if exposed again.
People can harbor the parasite for years without severe symptoms, which is why it’s often called a “silent” disease.
No, schistosomiasis cannot be directly transmitted from one person to another. The parasite needs to go through its life cycle in water and snails before it can infect humans again.
GIDEON is one of the most well-known and comprehensive global databases for infectious diseases. Data is refreshed daily, and the GIDEON API allows medical professionals and researchers access to a continuous stream of data. Whether your research involves quantifying data, learning about specific microbes, or testing out differential diagnosis tools– GIDEON has you covered with a program that has met standards for accessibility excellence.
Learn more about more parasitic infections on the GIDEON platform.
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