Schistosomiasis

Schistosomiasis, also known as bilharzia, is a disease caused by parasitic worms. More than 200 million people are infected worldwide and over 650 million live in areas where the parasite is regularly found. Schistosomiasis causes severe disease and long-term sequelae, and it continues to have a significant economic impact on world economies.

Contents 1 Other Names 2 Symptoms 2.1 Dermatitis 2.2 Katayama fever 2.3 Chronic schistosomiasis 3 Causes 4 Diagnosis 5 Treatment 6 Prevention 7 Chances of Developing 7.1 Areas where schistosomiasis occurs 8 How Schistosomiasis is Spread 9 References 10 External Links

Other Names

• Bilharzia
• Katayama fever
• Swimmer's itch
• Blood fluke
• Schistosome dermatitis

Symptoms

Most people who are infected with Schistosoma species have few worms in their body and, hence, may have few if any symptoms. When the parasitic burden increases, symptoms can occur and usually take the form of three clinical syndromes. These syndromes correlate with the stage of the life cycle of the parasite in the human body.

Dermatitis

People become infected with schistosomiasis when a form of the parasite called a cercaria, penetrates the skin. If this is the first time that a person has been exposed to the organism, a skin reaction can occur called swimmer's itch or schistosome dermatitis. Symptoms typically occur within 24 hours of skin penetration and include the following:

• Itching
• Redness
• Development of skin rash or bumps on the skin at the site of penetration

The rash and itching can come and go, but typically resolves in a few days.

Katayama fever

Once the Schistosoma worms have matured in the human body, they begin to produce eggs into the blood stream. In some people, this can lead to an acute syndrome called Katayama fever. Symptoms usually begin four to eight weeks after infection and can include the following:

• Sudden onset of fever and chills
• Sweating
• Headache
• Cough
• Muscle aches
• Enlargement of the liver, spleen, and lymph nodes

The symptoms seen in this stage represent an immune response by the body to the eggs that are being produced by the worms. Signs and symptoms usually resolve in a few weeks, but in some cases where there are a large number of worms, death can result.

Chronic schistosomiasis

Mature worms in the body can produce a large number of eggs each day. The continued immune response to this egg burden can lead to chronic inflammation and eventual formation of scar tissue in areas of the body where the worms are located. If the worms are mainly around the liver, symptoms can include the following:

• Tiredness
• Crampy abdominal pain
• Intermittent diarrhea
• Occasional blood in the stool
• Anemia
• Enlargement of the liver and spleen
• Ascites, a buildup of fluid in the abdomen
• Vomiting of blood (hematemesis)

In rare cases, the disease can progress to liver failure and death.

If the worms are mainly located around the urinary bladder, symptoms can include the following:

• Blood in the urine
• Difficulty urinating
• Pain or burning with urination

If the disease progresses, kidney failure can ensue. There have also been reports of bladder cancer associated with schistosomiasis.^[1]

There have been rare cases of schistosomiasis causing appendicitis^[2] and infection of the brain.^[3]

Causes

There are three major species of the parasite that cause disease: Schistosoma mansoni, S. haematobium, and S. japonicum. Two minor species have also caused human disease, S. intercalatum and S. mekongi. Humans are infected when they are in freshwater, such as lakes or streams, that contain the infective form of the parasite called a cercaria. The cercaria penetrates into the skin and is eventually transported to the lungs and the liver by the bloodstream. These forms mature to adults in about six weeks and then move to veins in and around the liver (in the case of S. mansoni, S. japonicum, S. intercalatum, and S. mekongi) or the veins around the urinary bladder (in the case of S. haematobium). The adults then produce eggs which are shed from the body in stool or in urine. In fresh water, the eggs hatch into a form called a miracidia. This form infects a particular species of snail which, in this parasitic life-cycle, represent an intermediate host. In the snail, the miracidiae multiply asexually and in four to six weeks, hundreds of forked-tail cercariae emerge into the water to start the cycle again.

Because the life-cycle of Schistosoma requires a particular snail as an intermediate host, many countries throughout the world that do not have this species of snail, including the United States, do not have indigenous cases of schistosomiasis. The disease can be seen in the United States and other countries due to cases brought in by travelers or migrant workers.^{[4] [5] [6]}

Diagnosis

Schistosomiasis is diagnosed by looking for the parasite's eggs in a sample of stool or urine. Blood tests can also be used to detect infection, but the results may take several weeks.^[7]

Treatment

Safe and effective drugs are available for the treatment of schistosomiasis. Praziquantel is the treatment of choice for schistosomiasis. Patients are given pills to take for 1-2 days. Resistance to Praziquantel has been reported.^[8]

Prevention

• Avoid swimming or wading in freshwater when living in or traveling to countries in which schistosomiasis occurs. Swimming in the ocean and in chlorinated swimming pools is generally thought to be safe.
• Drink safe water. Because there is no way to make sure that water coming directly from canals, lakes, rivers, streams or springs is safe, it is important to 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. Do NOT rely on vigorous towel drying to prevent schistosomiasis.

Chances of Developing

People who live in or travel to areas where schistosomiasis occurs are at risk of catching schistosomiasis if their skin comes in contact with fresh water. There is also some evidence that people of a certain genetic makeup are more susceptible to getting the disease.^[9]

Areas where schistosomiasis occurs

• Africa: all freshwater in southern and sub-Saharan Africa, including the great lakes and rivers as well as smaller bodies of water, is considered to be at risk for schistosomiasis transmission. Transmission also occurs in the Nile River valley in Egypt.
• South America: including 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
• Southeast Asia: Philippines, Laos, Cambodia, central Indonesia, Mekong delta

How Schistosomiasis is Spread

People who are infected with Schistosoma can shed eggs of the parasite in the feces or urine. If the feces or urine contaminate fresh water that contains a particular species of snail (the intermediate host), then an infectious form of the parasite, called a cercaria, can develop which can infect people who are exposed in the water.

References

1. ↑ Bedwani R, Renganathan E, El Kwhsky F, et al. Schistosomiasis and the risk of bladder cancer in Alexandria, Egypt. Br J Cancer. 1998 Apr;77(7):1186-9. Abstract
2. ↑ Nandipati K, Parithivel V, Niazi M. Schistosomiasis: a rare cause of acute appendicitis in the African American population in the United States. Am Surg. 2008 Mar;74(3):221-3. Abstract
3. ↑ Pittella JE. Neuroschistosomiasis. Brain Pathol. 1997 Jan;7(1):649-62. Abstract
4. ↑ Bottieau E, Clerinx J, de Vega MR, et al. Imported Katayama fever: clinical and biological features at presentation and during treatment. J Infect. 2006 May;52(5):339-45. Abstract
5. ↑ CDC. Schistosomiasis in U.S. Peace Corps Volunteers -- Malawi, 1992. MMWR. 1993 Jul 30;42(29):565-70. Full Text
6. ↑ Franco-Paredes C, Dismukes R, Nicolls D, et al. Persistent and untreated tropical infectious diseases among sudanese refugees in the United States. Am J Trop Med Hyg. 2007 Oct;77(4):633-5. Abstract
7. ↑ Tsang VC, Wilkins PP. Immunodiagnosis of schistosomiasis. Immunol Invest. 1997 Jan-Feb;26(1-2):175-88. Abstract
8. ↑ Doenhoff MJ, Pica-Mattoccia L. Praziquantel for the treatment of schistosomiasis: its use for control in areas with endemic disease and prospects for drug resistance. Expert Rev Anti Infect Ther. 2006 Apr;4(2):199-210. Abstract
9. ↑ Secor WE, del Corral H, dos Reis MG, et al. Association of hepatosplenic schistosomiasis with HLA-DQB1*0201. J Infect Dis. 1996 Nov;174(5):1131-5. Abstract

External Links

World Health Organization (WHO)

• Schistosomiasis
• Schistosomiasis Control Initiative

Centers for Disease Control and Prevention (CDC)

• Schistosomiasis
• Travelers' Health: Yellow Book - Schistosomiasis