Bilharzia, also known as "snail fever" is a disease caused by a parasite. The parasite is a fluke, or worm, and there are different species. It affects the intestines and the urinary system first, but because it lives in the blood, it can affect other systems.
The part of the of the body that is affected depends on the species of parasite. Some species can affect the lungs and the spinal cord, or the brain and the central nervous system (CNS).
Bilharzia is not often immediately fatal, but it is a chronic illness that can seriously damage the internal organs. It may even lead to reduced growth and cognitive development in children.
It is also known as schistosomiasis or bilharziosis.
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How do people get schistosomiasis?
People may become infected through direct contact with contaminated fresh water where certain types of water snail live, because the snails carry the worm.
Bilharzia is a parasite transmitted from freshwater snails to humans.
This can be through swimming, washing, or paddling in water, from drinking it or eating food that has been washed in untreated water.
Bilharzia enters the body when the larvae of the fluke, or parasite, pass through the skin. The larvae emerge from snails, enter the skin when people are in the water, and develop into adult worms that live in the blood.
If the urinary system is infected, it can increase the risk of developing bladder cancer among adults. It can infect the gastrointestinal tract and the liver.
There are various types of schistosomiasis that can infect humans:
- Schistosoma mansoni and schistosoma intercalatum cause intestinal schistosomiasis
- Schistosoma haematobium causes urinary schistosomiasis
- Schistosoma japonicum and schistosoma mekongi cause Asian intestinal schistosomiasis.
If a person develops a chronic infection from these species, it can affect the liver, spleen, lungs, spinal cord, or brain.
The infection cycle begins when fresh water becomes infected with the eggs of the parasite through the feces and urine of infected humans.
The eggs hatch in the water, and the worms reproduce inside the water snails. Tiny larvae are released into the water. The larvae can survive for up to 48 hours in the water.
The larvae can penetrate human skin and enter the bloodstream. There, they travel through the blood vessels of the lungs and liver, and then to the veins around the bowel and bladder.
Some weeks later, the worms are mature. They mate and start producing eggs. These eggs pass through the walls of the bladder, or intestine, or both. Eventually, they leave the body through urine or feces. The cycle starts again.
It is not possible to catch schistosomiasis from a person who is infected. Humans can only be infected through contaminated water that has the snails living in it.
Where is schistosomiasis found?
According to the Centers for Disease Control and Prevention (CDC), more than 200 million people are infected with schistosomiasis, globally. After malaria, it is seen as the second most devastating parasitic disease in the world. It is categorized as a Neglected Tropical Disease (NTD).
The World Health Organization (WHO) estimate that at least 258 million people needed preventive treatment for schistosomiasis in 2014, and over 61.6 million people were treated for schistosomiasis in 2014.
Different species of bilharzia, or schistosomiasis, are found around the world. The main areas, according to the CDC, are:
- Africa: southern, central, west, and sub-Saharan Africa, in the great lakes and rivers, and in smaller bodies of water; the Nile River valley in Sudan and Egypt and the Maghreb region of North Africa
- South America: including Brazil, Suriname and Venezuela
- Asia: Indonesia, parts of China and Southeast Asia, including Cambodia and Laos
- Middle East: Yemen.
There is a low risk in parts of the Caribbean, in the Dominican Republic, Guadeloupe, Martinique, and Saint Lucia.
Schistosomiasis can affect people of any age, but especially children who are living in developing countries.
People who swim in contaminated fresh water rivers, canals, lakes, and streams in areas where the disease is found have a higher chance of becoming infected.
Bilharzia does not generally in the United States, but people have developed swimmer's itch, or cercarial dermatitis, in some places, and outbreaks have been investigated in Stubblefield Lake in northern New Mexico, and one in Prospect Lake in the heart of Colorado Springs, Colorado.
In addition, Americans can become infected if they travel to areas where the disease exists.
What are the symptoms of schistosomiasis?
The symptoms of schistosomiasis depend on the type of worm and the stage of infection, but they are mostly the result of the body's reaction to the worms' eggs, and not caused by the worms themselves.
Early symptoms are swimmer's itch, which include itchy skin and a rash. They may appear within hours of being infected, and they can last for up to around 7 days.
Approximately 3 to 8 weeks after infection, the person may experience:
- Fever and chills
- Muscle aches
- Weight loss
- Enlargement of the liver and spleen
- Abdominal pain.
Later, when the eggs pass into the urinary system, there may be blood in the urine.
How is schistosomiasis diagnosed?
If a person returns home after traveling in areas where bilharzia is prevalent, and they have symptoms, they should see their physician.
People who live in or travel to certain parts of the world should see a doctor if they develop symptoms.
They may then need to see an infectious disease or tropical medicine specialist.
It may be a good idea to have a check-up 3 months after returning home, even if there are no symptoms, because the symptoms may not show up until later.
The doctor will ask the patient where they have traveled, how long they were there, and whether there was any contact with contaminated water.
The patient should tell the doctor about any symptoms, when these first appeared, and whether they have had an itchy rash or blood in the urine.
A stool or urine sample will indicate whether any eggs are present, and a blood test may be done.
The worm takes about 40 days to mature; so it may be 3 months after exposure to contaminated water before the blood sample can provide reliable results.
If the patient has intestinal symptoms, they may need a biopsy of the rectum, even if urine and blood tests are negative. The patient may also have a bladder biopsy.
What is the treatment for schistosomiasis?
Praziquantel is a medication that can be given as a short course to clears up the infection. It can help, even if a patient's disease has reached an advanced stage.
It is usually effective, as long as significant damage or complications have not yet occurred. However, it does not prevent re-infection.
People who live in areas where schistosomiasis is endemic can take a single oral dose of Praziquantel each year, to reduce the chance of infection and complications.
Researchers are working to develop a schistosomiasis vaccine which will stop the parasite's lifecycle from continuing in humans.
If the patient does not receive treatment, and the eggs stay in the body, there may be long-term effects. These include:
- Bleeding of the bladder
- Ulceration of the bladder
- Liver damage
- Eventual kidney failure
- Bladder cancer.
If the eggs get into the bloodstream they can get into various vital organs, resulting in lung, heart, intestinal and CNS (central nervous system) damage.
Recurrent infections, especially over a period of years, can result in serious damage to vital organs.
If possible, it is better not swimming or to come into contact with potentially contaminated fresh water in areas where schistosomiasis occurs.
In some places, there are projects to eliminate of the water-dwelling snails that carry the disease. This can be done with acrolein, copper sulfate, and niclosamide.
In other places, introducing crayfish to areas where the snails exist can help to control the snail population. As with any ecological intervention, this must be done with caution.
It is possible to design irrigation schemes that make it difficult for the snails to colonize the water. This can reduce the possibility of humans being exposed to the disease.