Schistosomiasis is a parasitic infection caused by a worm that is commonly found in fresh water bodies in tropical as well as subtropical regions. The main causative agent is a parasite/ fluke (trematodes) belonging to the genus Schistosoma. It ranks third in the list of most destructive tropical disease in the world particularly in countries such as Africa, South America, Caribbean, Middle East and Asia.
What is Schistosomiasis?
Schistosomiasis is a contagious parasitic disease that was first discovered by a German surgeon named Theodore Bilharz. It was first discovered by him in 1851, when he identified the causative etiological agent Schistoma hemtobium while he was working in Cairo. It is also known by other names such as bilharziasis, bilharzias, or snail fever.
Symptoms of Schistosomiasis
In a large number of cases, the parasites may infect the host, but may not show any signs or symptoms. They remain in the body for a long period of time and gradually cause damage to organs such as the bladder, kidneys and the liver.
There may be tiny red bumps on the site infestation, i.e. where the worms enter the body. However, this fades off in a while. In some cases, the infected person may not show any symptoms of Schistosomiasis infection. They may not experience any symptoms for several years; even though the eggs are multiplying in the body. While in some cases, the Schistosomiasis symptoms begin to surface within a few weeks. These symptoms of Schistosomiasis include:
- Rash with itchiness, redness, and blotchiness
- High temperature (usually above 38 degree Celsius)
- Diarrhea with abdominal discomfort
- Muscle and joint pain
- General weakness and feeling of being unwell.
These are generally the symptoms of a condition called as acute schistosomiasis and they often improve within a few weeks. However, it is important to get it treated at the earliest, as these parasites can remain in the body and lead to complications in the future.
Prevalence Rate of Schistosomiasis
It has been estimated that 85% of the population living in Africa are infected with schistosomiasis at some point in their life. In terms of global estimation, around 200,000 deaths take place due to schistosomiasis every year. A total of 700 million people are at increased risk of developing schistosomiasis in about 76 countries where this disease is considered to be endemic. After intestinal helminthiasis and malaria, schistosomiasis is the third most cause of morbidity and mortality in the world.
Causes and Risk Factors of Schistosomiasis
Schistosomiasis is a parasitic disease and it is mainly caused by S. haematobium, S. mansoni and S. japonicum. There are few other species capable of causing schistosomiasis in humans, such as S. mekongi and S. intercalatum which are less prevalent than previously mentioned species. In rare occasions, some schistosomes with mammalian and avian primary hosts may lead to extreme dermatitis in human and lead to other conditions such as swimmer’s itch post Trichobilharzia ocellata.
Schistosomiasis is generally caused due to exposure to schistosomiasis causing worms that live in fresh water bodies such as ponds, rivers, lakes, reservoirs, canals etc. These worms are not found in sea water, adequately treated water supplies or chlorinated swimming pools. Water supplies that take unfiltered water from open water bodies such as rivers and ponds have higher chances of spreading the disease. Direct contact with contaminated water while swimming, bathing or washing helps the worms to enter into the body.
Once the worms enter the body they lay eggs inside. While some leave the body with urine and stool, the rest remain inside the body tissues and multiply further. If left untreated, there will be further multiplication of the causative agents. The eggs when passed out from the body into the water, they hatch into tiny larvae and grow inside freshwater snails. Thus, Schistosomiasis infection does not transmit by direct contact from the infected individual.
Pathophysiology of Schistosomiasis
Schistosomiasis is caused due to immunological reaction of the body to Schistosoma eggs trapped within the body tissues. These eggs release antigens which trigger a granulomatous reaction involving the T cells, eosinophils, and macrophages which lead to clinical symptoms. The signs and symptoms of the condition vary based on the number of eggs and the location of the eggs trapped in the tissues. In the initial stages, the inflammatory reaction that takes place is easily reversible. As the stages proceed, there is deposition and accumulation of collagen along with fibrosis which results in organ damage that might only be partially reversible.
Once the worm enters body, it travels through the blood stream and reaches vital organs such as liver and bowel. The eggs can get trapped in the tissues of skin, muscles, brain, adrenal glands and even eyes. When the eggs penetrate through the urinary system they reach the female genital area and they form granulomas within the fallopian tube, ovaries and the uterus. The embolization of eggs to the brain and spinal cord via paravertebral venous plexus might also lead to central nervous system involvement.
Diagnosis and Treatment of Schistosomiasis
Diagnosis of schistosomiasis is done by an experienced physician. A thorough medical history is taken to determine history of exposure to the causative pathogen and for analysing the existing signs and symptoms. A blood test is done to check for presence of pathogens in blood sample. A stool test and urine test is often helpful in reaching to a conclusion as eggs may be seen in urine/stool sample.
Treatment protocol for Schistosomiasis includes short course of medication called as praziquantel. Praziquantel is usually prescribed after 8 weeks of being infected as this drug is most effective when the worms have grown a bit. Steroids are prescribed for management of other associated symptoms of Schistosomiasis.
Prognosis of Schistosomiasis
If diagnosed early and treated early, the prognosis for Schistosomiasis is good, and the condition improves completely with appropriate treatment. Patients who may develop hepatic disorders, urinary issues and even fibrosis have shown improvement with treatment and therapy. Renal, intestinal and brain lesions have also shown improvement but this largely depends of the location and size of the lesion. Hepato-splenic schistosomiasis also improves with treatment as the hepatic function is preserved till the end of the disease. However, in case of variceal bleeding, there may be complications.
Patients in the end stage of portal hypertension and severe pulmonary hypertension are less likely to benefit from treatment. Cor pulmonale does not show significant improvement with treatment.
Complications of Schistosomiasis
Schistosomiasis patients, irrespective of whether they had symptoms or not over a period of time can develop serious complications, as the eggs may travel to different parts of the body. This condition is known as chronic schistosomiasis. It can lead to severe complication based on the site of infection. These may include:
- Infection in the digestive system may lead to severe anaemia, pain in the abdomen, swelling, diarrhoea and blood in stool.
- Infection in the urinary system can lead to cystitis or irritation in the bladder, painful micturition, increased urgency to urinate and also blood in urine.
- Infection in the respiratory system or the lungs and the heart can lead to wheezing, chronic cough, breathing difficulties, shortness of breath and coughing up of blood.
- Infection in the nervous system can lead to fits or seizures, extreme headache, weakness, numbness in legs and dizziness.
- If Schistosomiasis is left untreated it can lead to permanent damage to the affected organ and can even lead to death.
Schistosomiasis being a parasitic disease can lead to serious health complications. Hence, as soon as the symptoms of Schistosomiasis are observed, one must seek immediate medical help and get the condition treated promptly.
- Centers for Disease Control and Prevention (CDC) – Schistosomiasis: https://www.cdc.gov/parasites/schistosomiasis/index.html
- World Health Organization (WHO) – Schistosomiasis: https://www.who.int/news-room/fact-sheets/detail/schistosomiasis
- Mayo Clinic – Schistosomiasis: https://www.mayoclinic.org/diseases-conditions/schistosomiasis/symptoms-causes/syc-20377938
- Pan American Health Organization (PAHO) – Schistosomiasis: https://www.paho.org/en/topics/schistosomiasis