Schistosomiasis, bilharziasis, Katayama fever, cutaneous cercariosis, blood fluke or snail fever is a parasitic, intestinal and urogenital infection, caused by a flatworm of the trematode class called schistosoma (‘Schistosoma’). It is prevalent in tropical and subtropical regions of Africa, Asia and South America without access to clean water or adequate sanitation. It is a very disabling disease.
Causes of schistosomiasis
Polluted waters
Infection usually occurs in contaminated fresh water where the parasite lives freely or where it is released in larval form (cercaria) by freshwater snails where they can infest the human host by penetrating the skin. When penetrating the skin, the cercariae lose their tail and become schistosomulae that travel to the liver through the blood. There they mature and transform into adult helminths, male and female, which reach the intestinal or rectal veins or the urogenital system where they lay their eggs. There are five species of schistosomas that infect humans: ‘Schistosoma haematobium’, ‘S. mansoni’, ‘S. japonicum’,’ S. mekongi’ and ‘S. intercalatum’ infect intestine and liver.
‘S. haematobium’ causes urinary tract infection. It is located throughout the African continent. There are also focuses in the Middle East, Türkiye and India.
‘S. mansoni’,’ S. japonicum’,’ S. mekongi’ and ‘S. intercalatum’ infect intestine and liver. S. mansoni is present in the Western Hemisphere in areas of South America and some Caribbean islands, in Africa and in foci in the Middle East; the ‘S. japonicum’ is found in Asia, especially in China, the Philippines, Thailand and Indonesia. The ‘S. mekongi’ is located in Southeast Asia. And the ‘S. intercalatum’ is located in Central and West Africa.
Humans are the main reservoir of the infection. Dogs, cats, rodents, pigs, horses and goats are reservoirs of ‘S. japonicum’ and dogs are reservoirs of ‘S. mekongi’.
Symptoms of schistosomiasis
They depend on the species of schistosome and its phase
When the worm first penetrates the skin, it can cause itching and a rash. Between two and four weeks later, some affected people experience the symptoms of so-called ‘Katayama fever’: fever, chills, cough, muscle aches, fatigue, general malaise, nausea and abdominal pain.
If the infection lasts a long time and the blood vessels of the intestine are chronically infected: abdominal discomfort, pain and blood in the stool are experienced, leading to anemia.
If the liver is affected, it may enlarge (hepatomegaly) and also the spleen (splenomegaly). It is also associated with fluid accumulation in the peritoneal cavity and hypertension in the abdominal blood vessels. There may be vomiting with a lot of blood.
If the bladder is chronically infected, there is frequent urination and pain when urinating. Urine contains blood.
If the urinary tract is chronically infected, the ureter, the tube that connects the kidney with the bladder, can become inflamed and scarred, which can cause urine to back up and damage the kidneys.
If the brain or spinal cord is chronically infected, there are seizures, muscle weakness, or paralysis.
If the genitals are infected, in both men and women, infertility may occur.
In children, schistosomiasis can affect growth and learning; In adults it can affect work capacity.
Diagnosis of schistosomiasis
Blood tests and examination of stool, urine, and tissue samples
The first suspicion for the doctor that there may be a case of schistosomiasis is that the traveler may comment that he or she has bathed in a river in areas where the parasite is present. He will request a blood test and, above all, a sample of feces, urine and intestinal or bladder tissue to look for parasite eggs through the microscope.
Ultrasound, computed tomography (CT), or magnetic resonance imaging (MRI) may also be performed to determine the extent of the infection.
Schistosomiasis treatment and medication
Antiparasitic
The reference treatment for schistosomiasis is praziquantel, an antiparasitic. A stool sample must be monitored since if parasite eggs are still excreted after three months, the treatment must be repeated. The same thing can happen after another three months. The rash can be relieved with cold compresses and corticosteroid creams.
If the symptoms of so-called ‘Katayama fever’ are severe, corticosteroids can be administered.
Prevention of schistosomiasis
Avoid unsafe waters
To prevent this infection, the main recommendation is to avoid bathing in waters that are not safe or that have the presence of freshwater snails. Those who have come into contact with the parasite should dry themselves thoroughly, vigorously, with a towel before the parasite can penetrate the skin.
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