Schistosomiasis (Bilharziasis): Causes, Diagnosis and More

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Overview

Schistosomiasis is an acute and chronic parasitic disease caused by blood flukes (trematode worms) of the genus Schistosoma. Estimates show that at least 229 million people required preventive treatment in 2018. Preventive treatment, which should be repeated over a number of years, will reduce and prevent morbidity.

Schistosomiasis transmission has been reported from 78 countries. However, preventive chemotherapy for schistosomiasis, where people and communities are targeted for large-scale treatment, is only required in 52 endemic countries with moderate-to-high transmission.

Schistosomiasis Causes

Several species of parasitic blood flukes (trematodes), of which the most important are Schistosoma mansoni, S. japonicum, S. mekongi and S. haematobium.

Schistosomiasis Symptoms

Symptoms of schistosomiasis are caused by the body’s reaction to the worms’ eggs.

Intestinal schistosomiasis can result in abdominal pain, diarrhoea, and blood in the stool. Liver enlargement is common in advanced cases, and is frequently associated with an accumulation of fluid in the peritoneal cavity and hypertension of the abdominal blood vessels. In such cases there may also be enlargement of the spleen.

The classic sign of urogenital schistosomiasis is haematuria (blood in urine). Fibrosis of the bladder and ureter, and kidney damage are sometimes diagnosed in advanced cases. Bladder cancer is another possible complication in the later stages.

In women, urogenital schistosomiasis may present with genital lesions, vaginal bleeding, pain during sexual intercourse, and nodules in the vulva. In men, urogenital schistosomiasis can induce pathology of the seminal vesicles, prostate, and other organs. This disease may also have other long-term irreversible consequences, including infertility.

The economic and health effects of schistosomiasis are considerable and the disease disables more than it kills. In children, schistosomiasis can cause anaemia, stunting and a reduced ability to learn, although the effects are usually reversible with treatment. Chronic schistosomiasis may affect people’s ability to work and in some cases can result in death.

The number of deaths due to schistosomiasis is difficult to estimate because of hidden pathologies such as liver and kidney failure, bladder cancer and ectopic pregnancies due to female genital schistosomiasis.

Schistosomiasis Diagnosis

Schistosomiasis is diagnosed through the detection of parasite eggs in stool or urine specimens. Antibodies and/or antigens detected in blood or urine samples are also indications of infection.

For urogenital schistosomiasis, a filtration technique using nylon, paper or polycarbonate filters is the standard diagnostic technique. Children with S. haematobium almost always have microscopic blood in their urine which can be detected by chemical reagent strips.

The eggs of intestinal schistosomiasis can be detected in faecal specimens through a technique using methylene blue-stained cellophane soaked in glycerin or glass slides, known as the Kato-Katz technique. In S. mansoni transmission areas, CCA (Circulating Cathodic Antigen) test can also be used.

For people living in non-endemic or low-transmission areas, serological and immunological tests may be useful in showing exposure to infection and the need for thorough examination, treatment and follow-up.

Schistosomiasis Prevention and control

The control of schistosomiasis is based on large-scale treatment of at-risk population groups, access to safe water, improved sanitation, hygiene education, and snail control.

The WHO strategy for schistosomiasis control focuses on reducing disease through periodic, targeted treatment with praziquantel through the large-scale treatment (preventive chemotherapy) of affected populations. It involves regular treatment of all at-risk groups. In a few countries, where there is low transmission, the interruption of the transmission of the disease should be aimed for.

Groups targeted for treatment are:

  • School-aged children in endemic areas.
  • Adults considered to be at risk in endemic areas, and people with occupations involving contact with infested water, such as fishermen, farmers, irrigation workers, and women whose domestic tasks bring them in contact with infested water.
  • Entire communities living in highly endemic areas.

WHO also recommends treatment of preschool aged children. Unfortunately, there is  no suitable formulation of praziquantel to include them in current large-scale treatment programmes.

Geographical distribution

S. mansoni occurs in many countries of sub-Saharan Africa, in the Arabian peninsula, and in the Bolivarian Republic of Venezuela, Brazil and Suriname; transmission has also been reported from several Caribbean islands.

S. japonicum is found in China, in parts of Indonesia and in the Philippines. S. haematobium is present in sub-Saharan Africa and in eastern Mediterranean areas. S. mekongi is found along the Mekong River in northern Cambodia and in the south of the Lao People’s Democratic Republic.

Risk for travellers

In countries or areas at risk while swimming or wading in fresh water.

Precautions

Avoid direct contact (swimming or wading) with potentially contaminated fresh water in countries or areas at risk. In case of accidental exposure, dry the skin vigorously to reduce penetration by cercariae.

Avoid drinking, washing or washing clothing in water that may contain cercariae. Water can be treated to remove or inactivate cercariae by paper filtering or use of iodine or chlorine.

 

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