You are currently viewing What is bilharzia (schistosomiasis): Transmission, treatment, and symptoms

What is bilharzia (schistosomiasis): Transmission, treatment, and symptoms

Bilharzia, or the “snail fever,” is a parasitic worm disease. The parasite, or fluke, has different species in it. Preferentially it affects the intestines and the urinary system, but since it resides in the blood vessels it can also damage other structures inside the body.

The World Health Organization ( WHO ) describes bilharzia as both an acute and a chronic disease — now commonly known as schistosomiasis. Symptoms occur when the body responds to the presence of the parasite but long-term complications may remain.

The illness can affect various parts of the body, including the lungs, nervous system, and brain. The area of damage may depend on parasite species.

Bilharzia typically isn’t necessarily fatal, but it’s a chronic condition that can severely damage the internal organs. This may contribute to decreased growth in children, and cognitive development issues.

Some types of bilharzia, for example water buffalo, can affect birds and mammals.

Transmission: How do you get it?

Schistosomiasis or bilharzia is passed on by a parasite that is present in fresh water in some places.
Schistosomiasis or bilharzia is passed on by a parasite that is present in fresh water in some places.

The infection starts when a person enters direct contact with fresh water, where certain forms of water snail carry the worm, according to the WHO.

When a person swimmes, washes, or paddles in dirty water, the parasites invade the body. They may also become infected by drinking water or eating food that has been washed in untreated water by someone.

The contagious fluke type is known as cercariae. The cercariae emerges from the snails, passes through the skin of a person while in water, and grows into adult worms that live in the blood of the individual.

Depending on the type of worm, bilharzia can affect:

  • the intestines
  • the urinary system, increasing the risk of bladder cancer
  • the liver
  • the spleen
  • the lungs
  • the spinal cord
  • the brain

The parasite’s infection process starts when the worm’s eggs enter fresh water through the feces and urine of people who already have the infection.

The eggs hatch in the water, releasing tiny larvae, and the larvae grow inside the snails of the water.

Are released after they have infected water snails, the cercariae of the worm. The cercariae will live a maximum of 48 hours.

The cercariae can penetrate human skin and invade the stream of blood. There, they travel through the lungs and liver blood vessels, and then into the veins around the bowel and bladder.

The worms are mature, after a few weeks. They mate and begin egg development. These eggs go through bladder walls, intestines, or both. Ultimately, they leave the body through urine or feces. The process starts at this stage.

A person suffering from schistosomiasis can not pass it on to anyone else. It is only by polluted water that humans are tainted where snails stay.

Where it occurs

According to the Centers for Disease Control and Prevention (CDC) more than 200 million people worldwide have bilharzia, although the parasite is not present in the United States.

Places where the parasite occurs include:

  • Africa, including Egypt and the Nile Valley
  • South America and parts of the Caribbean
  • Southeast Asia
  • Yemen, in the Middle East

Bilharzia can affect people of any age in an affected area, but those who are most at risk include:

  • children
  • people who swim, work, or have other contacts with freshwater rivers, canals, lakes, and streams

Bilharzia does not occur in the U.S. but after exposure to a similar species of schistosomes, people acquired the rash known as swimmer’s itch, or cercarial dermatitis, the parasite that causes bilharzia.

Health officials investigated cercarial dermatitis outbreaks in Stubblefield Lake in northern New Mexico and one in Prospect Lake in the heart of Colorado Springs, Colorado.

If Americans move to areas where the disease occurs, they are at risk of infection. Someone who enters these regions will check out any measures they might need to take with a doctor.


The impact of an infection depends on the type of worm and the stage of infection.

Symptoms occur when the body reacts to the worm’s eggs.

Acute stage

Fever old man
A fever and a rash are symptoms of bilharzia.

According to the CDC, symptoms can take 14 to 84 days to develop.

The person may experience: About 3 to 8 weeks after infection.

  • a rash
  • fever
  • headache
  • body aches, or myalgia
  • breathing difficulties

Chronic stage

Most people may not have early signs but may experience symptoms as the disease progresses. Those later symptoms are again based on the parasite type.

When the liver or intestines are compromised by parasites, symptoms may include:

If the parasites affect the urinary system, there may also be:

  • blood in the urine
  • painful urination
  • higher risk of bladder cancer

Anemia can develop over time. The parasite can affect the central nervous system, in rare cases.

According to WHO, children may have stunted growesth and a decreased learning capacity.


When a person has symptoms, or feels they might have had contact with polluted water, a doctor should be seen. The doctor may refer them to a specialist in infectious disease or in tropical medicine.

They should be ready to tell the doctor:

  • where they have traveled
  • how long they were there
  • whether they were in contact with contaminated water
  • any symptoms and when these first appeared
  • whether they have had an itchy rash or blood in the urine

A review of the stool or urine will indicate whether any eggs are present. The health care professional can request a blood test.

It takes about 40 days for the worm to mature. A blood sample can not produce accurate results until after exposure, at least 6 to 8 weeks.

If intestinal symptoms are present, the person may need a rectum biopsy, even if the urine and blood tests are negative. We could even have a biopsy of the bladder.

This may be a good idea for a person to have a 3-month checkup after returning home, even though they have no symptoms, because the symptoms may not occur until later.


There is no vaccine available for schistosomiasis, but treatment can help lower the impact of the infection.

If the test result of a person is positive, a short course of a drug called praziquantel is typically successful as long as there is no serious harm or complications to the patient.

Also at an advanced stage, praziquantel can help but it does not prevent re-infection.

People living in a high-risk area can take a single oral dose of praziquantel to minimize infection chances and complications. Individuals will require this medication for many years annually.

Scientists are working on creating a vaccine which will stop the lifecycle of the parasite from continuing in humans.


African river water
Tourists in certain areas of Asia, Africa, and Central and South America should take care to get into touch with fresh water.

The CDC is recommending that people avoid contact with fresh water in places where pollution is possible.

People should take care when:

  • swimming unless in seawater or a chlorinated pool
  • drinking water
  • eating food washed in water
  • bathing

Use of iodine to treat water does not kill parasites. Anyone who lives or travels where the disease is present should drink bottled water only or boil the water at least 1 minute in advance.

But slight contact with polluted water may result in infection. Of this reason people should always boil before using it and then cool their bathing water. You can safely store the water for 1 to 2 days before using it for washing.

Ways in which authorities may reduce the probability of people being contaminated in areas at high risk include:

  • educing the levels of infection: Providing drug treatment to the population can help achieve this.
  • Snail control: This may involve the use of chemicals and redesigning or clearing irrigation schemes to make it harder for snails to proliferate. Another option is to introduce predators, such as crayfish.

Someone who travels to or spends time in an environment where bilharzia is prevalent should seek medical attention if symptoms occur or if they suspect they may have been exposed to fresh water or the parasite.

Chukwuebuka Martins

Chukwuebuka Martins is a writer, researcher, and health enthusiast who specializes in human physiology. He takes great pleasure in penning informative articles on many aspects of physical wellness, which he then thoroughly enjoys sharing to the general public.