Schistosomiasis: what it is, symptoms, transmission, prevention

Have you ever heard of a water belly? It is a disease caused by a parasite and one of the symptoms causes the belly to become full of fluid, in addition to also causing the growth of some organs.


What is schistosomiasis?

Schistosomiasis, also called water belly , is a parasitosis, that is, caused by a parasite, which is a way of life that depends on another organism to survive.

This disease is caused by Schistosoma , which has the human as its definitive host and the snails as the intermediate host, often those of the species Biomphalaria glabrata .

It is a very common disease in Brazil, especially in the northeastern region and in the northern part of the southeastern region.

The continent that is most affected by the parasite is the African, where the worm can be found in the central region with ease.

Although there are 6 different parasites that cause schistosomiasis, in the Americas only Schistosoma mansoni can be found. It is the cause of schistosomiasis mansoni, also called intestinal because it affects the intestines.

The ICD-10 code for schistosomiasis is B65 . In the case of schistosomiasis mansoni, the one present in Brazil, is B65.1 , while urogenital has the code B65.0.

What is schistosomiasis mansoni?

Schistosomiasis mansoni is one that is present in Brazil. Caused by the parasite schistosoma mansoni, one of the six types of schistosoma, it causes intestinal schistosomiasis, since it is in the intestine that the worm reproduces.

It is especially common in the northeast, in addition to the interior of São Paulo and Minas Gerais, due to the abundance of regions without basic sanitation where people need to come into contact with water.

The parasite was brought to Brazil during the time of slavery and adapted well to the region and to the snails here.


There are 3 main types of schistosomiasis. Are they:


The intestinal form of schistosomiasis happens when the adult worm deposits in the intestine and starts to release its eggs.

This is the form present in Brazil, since Schistosoma mansoni is the only type in the country and it is one of the species that seeks to stay in the intestine. Contamination by this type of parasite is called schistosomiasis mansoni.


The urogenital form of the disease is not reported in the Americas.

It usually appears in African countries, caused by Schistosoma hematobium . Although not the only species capable of causing this type of schistosomiasis, it is the main species.

In this case, the parasite is deposited in the urinary canal. The mode of transmission is similar, but it uses urine instead of feces.

Spinal Schistosomiasis

Spinal cord schistosomiasis is rare, but it is also one of the most dangerous forms of the disease.

The worm seeks to position itself in the intestine or urinary canal, from where it can release its eggs and start the reproduction cycle again. However, in some cases, it can end up in the spinal cord by accident.

When this happens, the parasite is unable to reproduce, but it still causes damage. His presence in the spinal cord causes inflammation and, over time, can destroy the spinal cord, which can even lead to paralysis.

Causes of schistosomiasis disease

Schistosomiasis is caused by the schistosoma parasite. There are several species, but the most common in Brazil is schistosoma mansoni .

The definitive host of schistosoma is the human being.

A parasite needs another living thing to be able to develop and reproduce, releasing eggs for the cycle to repeat, and it is in the human body that the schistosoma does this.

The disease is usually contracted in rivers and lakes, where there is a snail that serves as an intermediate host of the worm. The intermediate host is the animal in which the larval phases of the parasite take place.

It is in the snail that the schistosoma larva develops before going into the water, in which it can survive for up to 48 hours looking for a human to infect.

The parasite can lodge in the intestine, urinary tract or liver, and when a couple of the animal is present, eggs are released into the feces and urine.

If the human that hosts the schistosoma defecates or urinates in a river, the eggs are released into the water and the larva can look for another snail.

Transmission: what is the cycle of schistosomiasis?

Schistosomiasis is contracted when a person comes into contact with contaminated water and the parasite penetrates the skin. However, this is the last step of the cycle, which passes through two hosts: intermediate, which is the snail, where the larva grows, and the final one, the human being, where the worm reproduces.

When a person has schistosomiasis, Schistosoma mansoni releases eggs into the patient’s feces and urine. The cycle only begins when that person makes his physiological needs – these contaminated with eggs – in the water.

The eggs hatch and release so-called miracidia . They are an embryonic stage of the parasite, which can stay alive in the water for a few days. If, in the course of those days, he does not find the intermediate host, the miracide dies.

However, when he encounters a snail of the species Biomphalaria glabrata , which is the intermediate host, the cycle continues.

Within the body of the snail, in the course of approximately 15 days, the miracide turns into a sporocyst. When sporocysts hatch, they release cercariae , which are a larva capable of swimming and living for 1 to 3 days.

Only then does the human being return to the cycle. When a person comes into contact with the water where the cercariae are present, they can penetrate the skin, moving on until they fall into the bloodstream.

From there, the cercariae go to the lungs and heart. Then they go to various parts of the body. The worm has a preference for the liver.

After maturing, Schistosoma mansoni goes to the intestine veins, where it finds another parasite of the opposite sex and, thus, release more eggs, restarting the whole process.

Risk factors

The main risk factor is contact with contaminated water.

Knowing this can be a challenge, but some indications may indicate this contamination, for example:

Lack of basic sanitation

The lack of basic sanitation in a region increases the chances that people’s faeces will come into contact with rivers and lakes, or that people will do their needs directly in the water.

This factor already increases the chances that the water is contaminated, since it is the way in which schistosoma eggs reach intermediate hosts (snails).

Presence of snails

The presence of snails in a water reservoir may indicate contamination.

The animals being present does not confirm that there are schistosomas in the water, but as they are the intermediate host, and are necessary for the development of cercariae, it is important to avoid the water where they are found.


The symptoms of schistosomiasis can be divided into two parts. The acute phase and the chronic phase .

The acute phase usually starts between 3 to 9 weeks after the penetration of cercariae and is usually more intense at the beginning of the deposition of the parasite’s eggs.

The Schistosoma mansoni can survive for years in the patient’s body if no treatment, in which case, you can install the phase chronic .

In this case, there are specific symptoms that are caused by the immune system attacking some of the parasite’s eggs.

The main causes of death from schistosomiasis are due to portal hypertension (increased pressure of the portal vein, which is in the liver) and severe hepatomegaly (enlarged liver).

The main symptoms are:

Acute phase

The main symptoms of the acute phase are:

  • Nausea;
  • Headache;
  • Weakness;
  • Diarrhea with blood;
  • Chills;
  • Cough (may be bloody);
  • Anemia (mainly in children);
  • Learning difficulties (also in children).
  • Slimming;
  • Lack of appetite;
  • Lack of air;
  • Joint pain;
  • Abdominal pain;
  • Liver enlargement (hepatomegaly);
  • Spleen enlargement (splenomegaly).

Chronic phase

In the chronic phase, symptoms usually affect the liver area. Are they:

  • Hepatomegaly (enlarged liver);
  • Ascites (accumulation of fluids in the membranes of the peritoneum);
  • Portal hypertension (in the portal vein, of the liver).

The ascites is the symptom that gives the popular name of the disease, the belly of water, due to the swelling of the abdomen.

Urogenital schistosomiasis

When it comes to urogenital schistosomiasis, symptoms can manifest in this system instead of in the intestine. The liver is still affected equally.

  • Difficulty urinating;
  • Hematuria (bloody urine);
  • Kidney diseases.

Spinal schistosomiasis

There are still symptoms related to spinal schistosomiasis, which occurs when the parasite is in the spinal cord, nearby or in the central nervous system.

It is the most dangerous form of the disease, but it is rare since it only happens due to an error in the position of the worm.

The main symptoms are:

  • Inflammation of the cord;
  • Low back pain radiating to the legs;
  • Loss of control of urine and feces;
  • Reduction of muscle strength;
  • Paralysis of the legs.

How is schistosomiasis diagnosed?

The diagnosis of schistosomiasis can be made by the gastroenterologist and the infectologist in several ways:

Stool examination

Stool examination is the simplest and most effective for diagnosing the disease in Brazil. In countries where the urogenital type is present, urine testing can be done instead.

This examination seeks to find the agent or its eggs in the patient’s feces.

Its sensitivity is high when the Schistosoma is laying eggs, but it can present false negatives when the infection is recent and the parasite has not yet had time to start to reproduce.

Up to three samples can be used for this exam to increase its accuracy.

Read more: Stool examination can be effective in preventing colorectal cancer

Blood test

The blood test, in cases of hypersensitivity to the parasite, may show antiparasitic cells of the immune system. In addition, other indications may raise the suspicion of the infection even if the patient does not have hypersensitivity.

Changes in liver function may show up on blood tests and blood counts, indicating the possibility of infection.

Rectal biopsy

The rectal biopsy has a sensitivity of up to 80% and consists of removing a sample from the patient’s rectum, which is then analyzed under a microscope. This test can find both the worm and its eggs, which confirms the infection.

To ensure reliability, the exam can be performed on more than one sample.


Ultrasound can be used to diagnose the infection as some structures may be altered by the infectious agent or by its presence. For example, hepatomegaly can be seen on this exam.


Magnetic resonance imaging is used to identify the parasite or inflammation in the spinal cord when spinal schistosomiasis is suspected. Often, the common version of the disease is also present in these cases.

My test was reagent, what does it mean?

When the serological test, which uses a blood sample, gives a reagent result, it confirms that there has already been contact between your immune system and the parasite.

The worm itself is not attacked by the immune system because it has mechanisms to defend itself, but schistosoma eggs do not have that same protection.

When the immune system identifies the eggs, it creates antibodies to attack them. If the test is reagent, it means that the antibodies have reacted to the test and are present.

However, this does not mean that the eggs or the parasite are in the person’s body, only that at some point in their life they have been.

They may still be. But to be sure, other tests are recommended.

Does Schistosomiasis have a cure?

-Yeah . Schistosomiasis can be cured with the use of antiparasitic drugs, which eliminate schistosoma from the host’s body.

It is important that treatment is done as soon as possible to prevent the disease from causing damage.

Some of the damage caused by the worm, however, can be permanent. This is the case of some fibrosis (appearance of scar tissue in the organs) or paralysis in situations where the worm infects the spinal cord.

What is the treatment for schistosomiasis?

The treatment for schistosomiasis is by means of antiparasitic drugs. The main one is praziquantel , which acts by altering the parasite’s movement and muscle contraction capacity, which causes it to detach from the intestinal wall and be eliminated by the feces.

This medication usually has side effects such as diarrhea and abdominal pain.

Medicines for schistosomiasis

The main drugs used for schistosomiasis are the specific antiparasitic drugs for the disease. Are they:

  • Praziquantel (Cisticid);
  • Oxamniquina ( Mansil ).


NEVER self-medicate or stop using a medication without first consulting a doctor. Only he will be able to tell which medication, dosage and duration of treatment is the most suitable for his specific case. The information contained in this website is only intended to inform, not in any way intended to replace the guidance of a specialist or serve as a recommendation for any type of treatment. Always follow the instructions on the package insert and, if symptoms persist, seek medical or pharmaceutical advice.


The majority of patients undergoing treatment for schistosomiasis show gradual improvement and complete recovery.

Treatment is simple and effective. However, some patients may have recontamination as it is not always possible to avoid the situation that caused the disease in the first place.

When there is no treatment, the condition evolves and worsens, which can cause the patient’s death due to complications caused by the parasite, especially those related to the liver.

Complications of schistosomiasis

There are some possible complications for schistosomiasis. Are they:

Portal hypertension

The most common complication, which often happens when there is no treatment for the disease, is hypertension in the main liver vein, the portal vein. This complication almost always leads the patient to death when there is no treatment.

When portal hypertension is present, there may be a decrease in liver function, bleeding, edema and ascites, in addition to hepatomegaly (enlarged liver).

Ascites is the symptom that gives the name water belly for the disease, since it seems that the patient has a belly full of water. It is an indication that the patient is in a severe stage and treatment is essential.

Complications of the urinary system

Urinary complications are rare in the Americas, as the parasite species that cause urinary schistosomiasis do not exist here. However, when a person is infected, there may be kidney failure and even bladder cancer due to the presence of the worm.

Complications of the reproductive system

In the case of the urogenital version, sometimes the contamination can cause genital wounds in women, as well as pain during sex and vaginal bleeding. In the case of men, it can have effects on the seminal vesicle and prostate.

In some cases, in the long run, it can also cause permanent infertility in both men and women.


In cases where the parasite is deposited in the spinal cord, paralysis of the legs can be a complication, since the immune system can destroy the spinal cord trying to get rid of the infectious agent.

Prevention: what to do to prevent schistosomiasis?

The prevention of schistosomiasis occurs by cutting the cycle of the parasite. The ways to do this are:


Basic sanitation is not in the hands of the citizen, but of the city administration, and is the most effective way of preventing the disease.

If everyone has access to basic sanitation and treated water, the Schistosoma reproduction cycle is disrupted, as contaminated feces can be sent for treatment.

Instead of going to rivers and lakes, where the parasite can find the intermediate host, all potential eggs die in the sewer and in the treatment.

Snail control

Another way to eliminate the cycle is to control the population of the intermediate host. If the parasite cannot find the snail, it cannot develop and become a cercariae, which can contaminate humans.

Avoid contaminated water

One of the most effective ways is simply not to enter waters that may be contaminated, as this is how the cercaria manages to enter the human body.

However, due to the lack of water treatment, this is not always possible and, in certain regions, people may need to come into contact with this water, allowing transmission.

In some cases, it may be necessary to come into contact with potentially infected water. In such cases, you should wear gloves and rubber boots to minimize possible contact and prevent the worm from contaminating your body.

Common questions

Can schistosomiasis be transmitted by sex?

No, schistosomiasis cannot be transmitted through sexual intercourse. Although the worm may be present in the genital region, the most that can pass from one body to another during sex are eggs.

The parasite’s eggs are not able to survive in the human body for long. They need water and the snail, the intermediate host, to develop, and only then can they contaminate humans.

The adult parasite does not leave the human body unless it dies.

Is schistosomiasis serious?

Yes. Schistosomiasis, if left untreated, can cause serious complications and even lead to death. The patient can survive for a long time with the worm, but eventually the contamination causes serious problems.

What is the popular name of schistosomiasis?

Schistosomiasis is also called water belly (because of the swelling caused by ascites), snail fever (because of the intermediate host) or bilharzia .

The name bilharzíaze is due to Theodor Maximilian Bilharz, a doctor who first described the disease in the 19th century.

Schistosomiasis is a parasitic disease that can be contracted when coming into contact with contaminated water, being frequent in regions where there is no basic sanitation.

Despite being easy to treat, it is dangerous if left untreated. Share this text with your friends to let them know more about schistosomiasis!