SCHISTOSOMA

Schistosomiasis, also known as bilharzia, is  a disease caused by parasitic worms. Although the worms that cause schistosomiasis are not found in the United  States, more than 200 million people are infected worldwide. In terms of impact this disease is second only to malaria as the most devastating parasitic disease. Schistosomiasis  is considered one of the Neglected Tropical Diseases (NTDs).

The parasites that  cause schistosomiasis live in certain types of freshwater snails. The  infectious form of the parasite, known as  cercariae, emerge from the snail, hence  contaminating water. You can become infected when your skin comes in contact  with contaminated freshwater. Most human  infections are caused by Schistosoma mansoni, S. haematobium, or S. japonicum.

FAQS

What is schistosomiasis?

Schistosomiasis,  also known as bilharzia, is a disease caused by parasitic worms. Infection with Schistosoma mansoni, S. haematobium, and S. japonicum causes illness in humans; less commonly, S. mekongi and S. intercalatum can cause disease. Although the worms that cause schistosomiasis are not found in the United  States, more than 200 million people are infected worldwide.

How can  I get schistosomiasis?

Infection  occurs when your skin comes in contact with contaminated freshwater in which  certain types of snails that carry schistosomes are living.

Freshwater becomes  contaminated by Schistosoma eggs when infected people urinate or defecate in the water. The eggs hatch, and  if certain types of freshwater snails are present in the water, the parasites develop  and multiply  inside the snails. The  parasite leaves the snail and enters the water where it can survive for about  48 hours. Schistosoma parasites can penetrate the skin of persons who are wading, swimming, bathing,  or washing in contaminated water. Within several weeks, parasite mature into  adult worms, residing in the blood  vessels of the body where the females produce eggs. Some of the eggs travel to  the bladder or intestine and are passed into the urine or stool.

What are the signs and symptoms of schistosomiasis?

Within  days after becoming infected, you may develop a rash or itchy skin. Fever,  chills, cough, and muscle aches can begin within 1-2 months of infection. Most  people have no symptoms at this early phase of infection.

Eggs  travel to the intestine, liver or bladder, causing inflammation or scarring. Children who are repeatedly infected can develop anemia, malnutrition, and  learning difficulties. After years of infection, the parasite can also damage  the liver, intestine, lungs, and bladder. Rarely, eggs are found in the brain  or spinal cord and can cause seizures, paralysis, or spinal cord inflammation.

Symptoms  of schistosomiasis are caused by the body's reaction to the eggs produced by  worms, not by the worms themselves.

What should I do if I think I have schistosomiasis?

See your health care provider. If you have traveled to countries where schistosomiasis is found and had contact with freshwater, describe in detail where and for how long you traveled. Explain that you may have been exposed to contaminated water.

How is schistosomiasis diagnosed?

Your health care provider may ask you to provide stool or urine samples to see if you have the parasite. A blood sample can also be tested for evidence of infection. For accurate results, you must wait 6-8 weeks after your last exposure to contaminated water before the blood sample is taken.

What is the  treatment for schistosomiasis?

Safe and  effective drugs are available for the treatment of schistosomiasis. You will be given pills to take for 1-2 days.

Am I at  risk?

If you live in or travel to areas where schistosomiasis occurs and your skin comes in contact with freshwater from canals, rivers, streams, ponds, or lakes, you are at risk of getting schistosomiasis.

In  what areas of the world does schistosomiasis occur?

• Africa: all freshwater in southern and sub-Saharan Africa–including the great lakes and rivers as well as smaller bodies of water–are at risk for schistosomiasis transmission. Transmission also occurs in the Mahgreb region of North Africa and the Nile River valley in Egypt and Sudan.
• South America: Brazil, Suriname, Venezuela
• Caribbean: Antigua, Dominican Republic, Guadeloupe, Martinique, Montserrat, Saint Lucia (risk is low)
• The Middle East: Iran, Iraq, Saudi Arabia, Yemen
• Southern China
• Parts of Southeast Asia and the Philippines, Laos

How  can I prevent schistosomiasis?

• Avoid swimming or wading in freshwater when you are in countries in which schistosomiasis occurs. Swimming in the ocean and in chlorinated swimming pools is  safe.
• Drink safe water. Although schistosomiasis is not transmitted by swallowing contaminated water, if your mouth or lips come in contact with water containing the parasites, you could become infected. Because water coming directly from canals, lakes, rivers, streams, or springs may be contaminated with a variety of infectious organisms, you should either boil water for 1 minute or filter water before drinking it. Boiling water for at least 1 minute will kill any harmful parasites, bacteria, or viruses present. Iodine treatment alone WILL NOT GUARANTEE that water is safe and free of all parasites.
• Bath water should be heated for 5 minutes at 150°F. Water held in a storage tank for at least 48 hours should be safe for showering.
• Vigorous towel drying after an accidental, very brief water exposure may help to prevent the Schistosoma parasite from penetrating the skin. You should NOT rely on vigorous towel drying to prevent schistosomiasis.

EPIDEMIOLOGY & RISK FACTORS

Schistosomiasis  is an important cause of disease in many parts of the world, most commonly in  places with poor sanitation. School-age children who live in these areas are  often most at risk because they tend to spend time swimming or bathing in water  containing infectious cercariae. If  you live in, or travel to, areas where schistosomiasis is found and are exposed  to contaminated freshwater, you are at risk. Areas  where human schistosomiasis is found include:

Schistosoma  mansoni            

• distributed throughout Africa: There is risk of infection in freshwater in southern and sub-Saharan Africa–including the great lakes and rivers as well as smaller bodies of water. Transmission also occurs in the Nile River valley in Sudan and Egypt
• South America: including Brazil, Suriname, Venezuela
• Caribbean (risk is low): Antigua, Dominican Republic, Guadeloupe, Martinique, Montserrat, and Saint Lucia.

S. haematobium           

• distributed throughout Africa: There is risk of infection in freshwater in southern and sub-Saharan Africa–including the great lakes and rivers as well as smaller bodies of water. Transmission also occurs in the Nile River valley in Egypt and the Mahgreb region of North Africa.
• found in areas of the Middle East

BIOLOGY

Causal Agent:

Schistosomiasis is caused by   digenetic blood trematodes. The three main species infecting humans are Schistosoma haematobium, S. japonicum, and S. mansoni. Two other species, more localized geographically, are S. mekongi and S. intercalatum. In addition, other species of schistosomes, which parasitize   birds and mammals, can cause cercarial dermatitis in humans.

Life Cycle:

Eggs are eliminated with feces or urine. Under optimal conditions the eggs hatch and release miracidia , which swim and penetrate specific snail intermediate hosts. The stages in the snail include 2 generations of sporocysts and the production of cercariae. Upon release from the snail, the infective cercariae swim, penetrate   the skin of the human host, and shed their forked tail, becoming schistosomulae. The schistosomulae migrate through several tissues and stages to   their residence in the veins. Adult worms in humans reside in the mesenteric venules in various   locations, which at times seem to be specific for each species. For instance, S. japonicum is more frequently found   in the superior mesenteric veins draining the small intestine, and S. mansoni occurs more often in the superior   mesenteric veins draining the large intestine. However, both species can occupy either location, and they   are capable of moving between sites, so it is not possible to state   unequivocally that one species only occurs in one location. S. haematobium most often occurs in the venous plexus of bladder, but it can also be found in the rectal venules. The females   (size 7 to 20 mm; males slightly smaller) deposit eggs in the small venules of   the  portal and perivesical systems. The eggs are moved progressively toward   the lumen of the intestine (S. mansoni and S. japonicum) and of   the bladder and ureters (S. haematobium), and are eliminated with feces   or urine, respectively.  Pathology of S. mansoni and S. japonicum schistosomiasis includes: Katayama fever, hepatic perisinusoidal egg granulomas,   Symmers’ pipe stem periportal fibrosis, portal hypertension, and occasional   embolic egg granulomas in brain or spinal cord. Pathology of S. haematobium schistosomiasis includes: hematuria, scarring, calcification,   squamous cell carcinoma, and occasional embolic egg granulomas in brain or   spinal cord.

Human contact with water   is thus necessary for infection by schistosomes. Various animals, such as dogs,   cats, rodents, pigs, hourse and goats, serve as reservoirs for S. japonicum, and dogs for S. mekongi.

Life cycle image and information courtesy of DPDx.

DISEASE

Infection occurs  when skin comes in contact with contaminated freshwater in which certain types  of snails that carry the parasite are living. Freshwater becomes contaminated  by Schistosoma eggs when infected people urinate or defecate in the water. The eggs hatch, and  if  the appropriate species of snails are  present in the water, the parasites infect, develop and multiply inside the  snails. The parasite leaves the snail and enters the water where it can survive  for about 48 hours. Schistosoma parasites can penetrate the skin of persons who come in contact with  contaminated freshwater, typically when wading, swimming, bathing, or washing. Over several weeks, the parasites migrate  through host tissue and develop into adult worms  inside the blood vessels of the body. Once  mature, the worms mate and females produce eggs. Some of these eggs travel to  the bladder or intestine and are passed into the urine or stool.

Symptoms of  schistosomiasis are caused not by the worms themselves but by the body’s  reaction to the eggs. Eggs shed by the adult worms that do not pass out of the  body can become lodged in the intestine or bladder, causing inflammation or  scarring. Children  who are repeatedly  infected can develop anemia, malnutrition, and learning difficulties. After  years of infection, the parasite can also damage the liver, intestine, spleen, lungs,  and bladder.

Common Symptoms

Most  people have no symptoms when they are first infected. However, within days after becoming infected, they may develop  a rash or itchy skin. Within 1-2 months of infection, symptoms may develop  including fever, chills, cough, and muscle aches.

Chronic  schistosomiasis

Without  treatment, schistosomiasis can persist for years. Symptoms of chronic  schistosomiasis include: abdominal pain, enlarged liver, blood in the stool or  blood in the urine, problems passing urine, and increased risk of bladder  cancer.

Rarely,  eggs are found in the brain or spinal cord and can cause seizures, paralysis,  or spinal cord inflammation.

DIAGNOSIS

Stool  samples can be examined microscopically for parasite eggs (S. mansoni or S. japonicum) or urine (S. haematobium). The eggs tend to be passed intermittently and in  small amounts and may not be detected, so it may be necessary to perform a  blood (serologic) test.

PREVENTION AND CONTROL

No vaccine is available. The best way to prevent schistosomiasis is to take the following steps if you are visiting or live in an area where schistosomiasis is transmitted:

• Avoid swimming or wading in freshwater when you are in countries in which schistosomiasis occurs. Swimming in the ocean and in chlorinated swimming pools is safe.
• Drink safe water. Although schistosomiasis is not transmitted by swallowing contaminated water, if your mouth or lips come in contact with water containing the parasites, you could become infected. Because  water coming directly from canals, lakes, rivers, streams, or springs may be contaminated with a variety of infectious organisms, you should either bring your water to a rolling boil for 1 minute or filter water before drinking it. Bring your water to a rolling boil for at least 1 minute will kill any harmful parasites, bacteria, or viruses present. Iodine treatment alone WILL NOT GUARANTEE that water is safe and free of all parasites.
• Water used for bathing should be brought to a rolling boil for 1 minute to kill any cercariae, and then cooled before bathing to avoid scalding. Water held in a storage tank for at least 1 - 2 days should be safe for bathing.
• Vigorous towel drying after an accidental, very brief water exposure may help to prevent the Schistosoma parasite from penetrating the skin. However, do not rely on vigorous towel drying alone to prevent schistosomiasis.

Those who have had contact with potentially contaminated water overseas should see their health care provider after returning from travel to discuss testing.

For more information view the source:Center for Disease Control

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