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Schistosomiasis

Overview

Schistosomiasis, also referred to as bilharzia, is a parasitic infection caused by trematode worms (flukes) of the Schistosoma species. The parasite lives in freshwater bodies in tropical and subtropical regions. There are 5 species, of which 3 can cause human disease: S.haematobium, S.japonicum and S.mansoni. S.haematobium is the causative factor for urogenital schistosomiasis whilst S.japonicum and S.mansoni cause intestinal schistosomiasis. Certain snails carry the parasite and infect individuals who enter contaminated bodies of water. Symptoms begin as flu-like with a rash and pruritus but the disease later progresses to damage the liver, spleen, intestine, lungs and bladder. Without treatment, schistosomiasis can persist for years leading to chronic infection and increased risk if bladder cancer.

 

Schistosomiasis is reported mainly in Africa but can also occur in areas of South America, the Caribbean, the Middle East and throughout Asia. It is prevalent in poor communities with little/no access to safe drinking water or adequate sanitation. The World Health Organisation reported at least 261 million individuals required preventive treatment for schistosomiasis and more than 40 million individuals were treated for schistosomiasis in 2013. At least 90% of individuals requiring treatment live in Africa. The number of deaths is difficult to estimate due to hidden pathologies such as hepatic/renal failure and bladder cancer. Estimates vary widely between 20,000 to 200,000 deaths per year.

 

Signs and symptoms

Initial signs and symptoms include a rash and pruritus. Within 1-2 months further

symptoms develop:

  • Fever

  • Chills

  • Cough

  • Myalgia

  • Malaise

 

Chronic schistosomiasis can lead to intestinal schistosomiasis with symptoms of:

  • Abdominal pain

  • Diarrhoea

  • Blood in stools

  • Liver enlargement

  • Spleen enlargement

  • Anaemia

 

Chronic schistosomiasis can also lead to urogenital schistosomiasis with symptoms of:

  • Cystitis

  • Dysuria

  • Frequent urination

  • Haematuria

  • Fibrosis of the bladder and ureter

  • Kidney damage

  • Genital lesions

  • Vaginal bleeding

  • Pain during sexual intercourse

  • Infertility

 

In rare cases, eggs have been found in the brain and spinal cord which cause symptoms of seizures, headaches, paralysis and spinal cord inflammation.

 

Causes

Bodies of freshwater become contaminated by

Schistosoma eggs when infected individuals urinate

or defecate in the water. The eggs hatch and release

miracidia which infect specific species of snails.

Once the parasites develop and multiply, they leave

the snail intermediate host and can survive for up to

48 hours in water. Schistosoma parasites penetrate

the skin of any individual who come into contact with

contaminated freshwater, usually when wading,

swimming, bathing, or washing. Over several weeks,

parasites migrate through host tissue and develop

into adult worms inside blood vessels. Once they

have matured, the worms mate and females

produce eggs. Depending on the species of worm,

the eggs travel to the bladder or to the intestine.

Each species can move between sites but tend to

accumulate most often in one location. Eggs are

released with faeces or urine depending on site of

accumulation.

 

Risk factors / at risk groups

  • School aged children – more likely to swim and play in water

  • Adults with occupations working near/in water - fishermen, farmers, irrigation workers, and women whose domestic tasks bring them in contact with infested water

  • Living in endemic areas

 

Diagnosis / microbiology testing

  • Detection of parasite eggs in stool or urine specimens

  • Antibodies and/or antigens detected in blood or urine samples

  • Haematuria detected by chemical reagent strips

  • Eggs of intestinal schistosomiasis can be detected in faecal specimens through                                                                 Kato-Katz technique

  • Serological and immunological tests in non-endemic areas

 

Treatment

Infections with all Schistosoma species can be treated with praziquantel. Praziquantel is most effective against mature, adult worms and requires a mature antibody response to be present. Treatment should therefore be initiated at least 6-8 weeks after last exposure to contaminated freshwater. A single course is usually curative but the host immune response can vary. Therefore, a follow up examination should be carried out 1-2 months after treatment completion. There is a lack of safety trial data for pregnant women and children aged under 4 years old.

 

 

 

 

 

Vaccination / preventative measures

There is currently no vaccine available.

Preventative measures include:

  • Avoid swimming or wading in freshwater in endemic areas. Swimming in the ocean and in chlorinated swimming pools is safe.

  • Drink boiled / bottled water - although schistosomiasis is not transmitted by ingetsing contaminated water, if the mouth or lips come into contact with contaminated water, there is a risk of infection.

  • Using boiled water for bathing. Water held in a storage tank for 1-2 days should be safe for bathing.

  • Vigorous towel drying after an accidental and brief exposure to contaminated water may prevent Schistosoma penetration (should not be relied upon).

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