What Is Schistosomiasis (Bilharzia)? What Causes Schistosomiasis (Bilharzia)?
Schistosomiasis, or bilharzias, bilharziosis, or snail fever is a parasitic disease caused by various species of fluke of the genus Schostosoma. Schistosomiasis has a low mortality rate; however, as it is commonly a chronic illness it can cause serious damage to internal organs, and may even undermine growth and cognitive development in children.
When the urinary system is infected there is a significantly higher risk in adults of developing bladder cancer. Schistosomiasis may infect the gastrointestinal tract and the liver.
The WHO (World Health Organization) believes that approximately 200 million people globally are infected. London's (England) Hospital for Tropical Diseases sees about 200 cases per year, all of them UK citizens coming home from abroad.
Schistosomiasis may be found in the following geographical areas (Source: National Health Service, UK):
- Africa - mainly in sub-Saharan Africa. However, the NHS (National Health Service), UK, says that cases of infection among travelers returning from Lake Malawi are not uncommon. In the Nile River Valley, Egypt, there are also cases.
- South America - Venezuela, Suriname and Brazil.
- Caribbean - Antigua, Dominican Republic, Guadeloupe, Martinique, Saint Lucia
- The Middle East - Saudi Arabia, Yemen, Iraq and Iran
- Southern China
- Southeast Asia - Philippines, Laos, Cambodia, Central Indonesia, and the Mekong Delta
According to Medilexicon's medical dictionary
- Schistosomiasis is " Infection with a species of Schistosoma; manifestations of this often chronic and debilitating disease vary with the infecting species but depend in large measure on tissue reaction (granulation and fibrosis) to the eggs deposited in venules and in the hepatic portals, the latter resulting in portal hypertension and esophageal varices, as well as liver damage leading to cirrhosis."
What are the signs and symptoms of schistosomiasis?A symptom is something the patient feels and reports, while a sign is something other people, such as the doctor detect. For example, pain may be a symptom while a rash may be a sign.
The types of signs and symptoms with Schistosomiasis depend on the species of fluke (worm) and the stage of infection. In the majority of cases signs and symptoms are the result of the body's reaction to the worms' eggs, and not the worms themselves.
Early symptoms may be:
Swimmer's itch, which includes..
- Itchy skin
- A skin rash
Signs and symptoms weeks after infection may include:
- Elevated body temperature (fever)
- Muscle aches
- Weight loss
- Liver enlargement
- Spleen enlargement
- Blood in urine - this is later, when the eggs pass into the urinary system
How do people get schistosomiasis?People may become infected if they have direct contact with contaminated fresh water which is inhabited by a certain types of water snail - the snails carry the worm. Contact includes swimming, washing or paddling in the water, as well as drinking it or eating food that has been washed in untreated water.
The following types of Schistosomiasis can infect humans:
- Schistosoma mansoni (ICD-10 B65.1) and Schistosoma intercalatum (B65.8) cause intestinal Schistosomiasis
- Schistosoma haematobium (B65.0) causes urinary Schistosomiasis
- Schistosoma japonicum (B65.2) and Schistosoma mekongi (B65.8) cause Asian intestinal Schistosomiasis
The cercariae can penetrate human skin and enter our bloodstream. In the bloodstream 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 and/or intestine and eventually leave the body through urine or feces; and thus the cycle starts again.
It is not possible to catch Schistosomiasis from a person who is infected. Human infection is only possible from contaminated water in which the snails reside.
How is Schistosomiasis diagnosed?Anybody who has been in areas of the world where schistosomiasis is endemic or known to exist, has been in contact with fresh water and has some of the signs and symptoms mentioned above, they should tell their doctor or contact a health clinic. In Europe, the USA, Canada and Japan the GP (general practitioner, primary care physician) will interview and examine the patient and refer him/her to an infectious disease or tropical medicine specialist.
The National Health Service (NHS), UK, advises anybody who has been to an area where Schistosomiasis is known to occur, and was in contact with contaminated fresh water, to have a check-up three months after the last possible exposure - even if they have no signs or symptoms.
The patient will be asked by the doctor where they have travelled, how long they were there, and whether there was any contact with contaminated water. If there are any symptoms, the doctor will ask about them, such as when they first appeared and whether the individual has an itchy rash or blood in his/her urine.
A stool or urine sample will probably be taken to determine whether any eggs are present. The stool exam is more common. Eggs can be detected in the urine in infections with S. japonicum and with S. intercalatum.
A blood sample will generally also be required. The worm takes about 40 days to mature; so it may take three months after exposure to contaminated water before the blood sample can provide any reliable results.
If the patient has intestinal symptoms a biopsy of the rectum may be ordered. The doctor may also order a biopsy if he/she suspects infection, but urine and blood samples are negative. A biopsy of the bladder for S. haematobium may be taken.
What are the treatment options for Schistosomiasis?Praziquantel - a medication which is given as a short course generally clears up the infection. Even patients in advanced stages will be effectively treated. However, the medication does nothing to prevent re-infection.
MASTA (Medical Advisory Services for Travelers Abroad) warns about fake or poor quality medications which may be on sale in various parts of the world.
A course of Praziquantel is usually very effective as long as significant damage or complications have not yet occurred.
In areas where schistosomiasis is endemic, a single oral dose of Praziquantel annually can help keep infection rates and complications down.
Research is currently underway into developing a schistosomiasis vaccine which will halt the parasite's lifecycle in humans.
If the patient does not receive treatment and the eggs stay in the body, the patient may eventually experience long term effects, which include:
- Bleeding of the bladder
- Ulceration of the bladder
- Liver damage
- Eventual kidney failure
Recurrent infections, especially over a period of years, can result in serious damage to vital organs.
PreventionNot swimming or coming into contact with potentially contaminated fresh water in areas where schistosomiasis is known to occur helps.
The elimination of the water-dwelling snails that are a natural reservoir of the disease may be effective - they may be eradicated with acrolein, copper sulfate, and niclosamide.
Some studies have shown that the introduction of crayfish populations to areas where the snails exist may help control the snail population. As with any ecological intervention, this must be carried out with caution.
It is possible to design irrigation schemes that make it difficult for the snails to colonize the water; thus reducing potential human exposure.