A neglected disease

Stije Leopold

 

Aswan, Lake Nasser, Egypt 

A 10-year-old girl complains about haematuria and dysuria for about two months. She also needs to go more frequently and urgently, thereby bringing relief of the pain in her lower abdomen. The haematuria is characterized by clots of bright red blood at the end of voiding and is worse in the morning and after walking. Physical examination reveals a mild splenomegaly and tenderness in her left flank. The girl doesn’t seem very ill, but signs of anaemia are present. A urine sample shows macroscopic parasite eggs of Schistosoma haematobium. The diagnosis: urinary schistosomiasis caused by S. haematobium affecting the urinary tract.
 

Introduction

Schistosomiasis, also known as Bilharzia or Snail fever, is a parasitic infection caused by blood flukes (schistosomes) after exposure to contaminated water.

The five species of schistosomes that infect humans belong to the class of trematodes (flatworms). Clinically the disease presents urinary or intestinal. The urinary form of schistosomiasis is caused by S. haematobium while the intestinal form of infection is caused by the species S. mansoni and S. japonicum. These are the most common species; other species that cause focal epidemics of intestinal schistosomiasis are S. intercalatum and S. mekongi.

Epidemiology

Schistosomiasis is associated with poor and remote rural areas, where communities are dependent on open water sources and have to deal with poor sanitation. Especially children are highly susceptible. However, it takes years before chronic complications manifest, leaving people with a reduced capacity to learn and work which eventually affects local economies. In Sub-Saharan Africa every year 280 000 people die due to complications. The WHO estimates that one in thirty individuals is infected globally. This resembles to more than 200 million people of whom 85% is living in Sub-Saharan Africa. Agricultural and water systems turn out to have unfavourable side effects by creating (new) sources for the disease fresh water snails. Another risk of spreading the disease is the migration of refugees.

Transmission  

Transmission of schistosomiasis occurs through penetration of the skin after contact with contaminated water. The water is contaminated by infected people urinating or defecating in the water, thus excreting the eggs of schistosomes. The fresh water snail functions as a host for the eggs where they transform into cercariae and are being excreted in a circadian rhythm. The cercariae enter the human skin and spread to the lungs, the heart and the liver, where they mature for one to four weeks. After their transformation to worms they migrate to the final destination to reside in a permanent state of copulation for seven to thirty years. In urinary schistosomiasis the final destination is the vesical venous plexus; in intestinal schistosomiasis this is the mesenteric venules of the intestines and the liver. The female worms produce hundreds to thousands eggs a day, which traverse to the lumen of the intestine or the urinary bladder where they will finally be excreted.

Pathophysiology and clinical presentation

Acute infection is often asymptomatic, but fatal in almost 25% of the cases. Occasionally a localized skin reaction occurs, caused by the penetration of the skin. In early stage of infection fever can occur (Katayama fever) in reaction to egg production. In chronic infection the two types of schistosomiasis give different clinical presentations related to the location of the adult worms. In urinary schistosomiasis, their eggs cross through the local tissue to the bladder lumen, releasing toxins and enzymes that cause inflammation. Eventually granuloma formation will occur around the invading eggs with subsequent fibrosis and scarring. Symptoms include haematuria and those related to obstructive uropathy, such as urinary tract infection. On the long term there is an increased risk of bladder cancer. In intestinal schistosomiasis abdominal pain, diarrhoea and anorexia contribute to malnutrition. An inflammatory colonic polyposis also results in a bloody stool, which can cause anaemia. Furthermore affected patients are more susceptible for co-infections. Additionally, the formation of inflammatory granulomas around eggs in the liver can cause portal hypertension leading to liver fibrosis (Symmer's pipestem fibrosis), hepatosplenomegaly, ascites, esophageal variceal bleeding and formation of portosystemic collaterals. Through these collaterals eggs can reach the pulmonary circulation resulting in lung fibrosis and eventually pulmonary hypertension and cor pulmonale. Co-infection with hepatitis B or hepatitis C can accelerate hepatic dysfunction and raise the risk for hepatocellular cancer. These late complications give a high mortality rate.

Diagnosis 

The diagnosis of schistosomiasis is based on clinical findings, laboratory tests and ultrasound imaging. Microscopic examination of urine samples will identify the type of parasite. When available, ultrasound can detect bladder lesions, kidney stones and hydronephrosis. In case of intestinal schistosomiasis, a Kato-Katz thick smear test from a stool sample or a rectal biopsy can help affirm the diagnosis. However in mild infections, when egg excretion is low, diagnosing can be difficult. An alternative is serology, although this is often too expensive. Also dipstick antibodies can be used, but these are not differentiating. In the future PCR assays could play an important role in quick confirmation of the diagnosis.

Treatment and prevention 

Praziquantel, an antihelminthic drug, is effective in all forms of schistosomiasis. It increases permeability of the parasites membranes to calcium ions. This paralyses the parasites and will discharge them in the bloodstream. Subsequently the immune system will eliminate them. Praziquantel is very well-tolerated and safe, also in pregnant women. 
Control and prevention of schistosomiasis requires a multifactorial approach. Measures taken are chemotherapy, snail control, improved sanitation and water supplies together with health education. There are several projects where all school-aged children in an endemic area are treated with a yearly administration of praziquantel tablets, the traditional deworming programme. The success depends on the continuation of the therapy over a longer period of time.

 

About the author

Stije Leopold is a third year medical student in Amsterdam with a special interest in infectious diseases.

Further reading

• Strickland, GT. Liver disease in Egypt: hepatitis C superseded schistosomiasis as a result of iatrogenic and biological factors. Hepatology. 2006

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Photo by USAID; Andrea Peterson, shared under Creative Common License