What is Schistosomiasis?
Schistosomiasis is a disease caused by parasitic larvae that live in fresh water in tropical and sub-tropical areas such as Africa, the Middle East, parts of South America and Asia. These larvae divide and multiply inside certain types of freshwater snails and then enter the water, in which they can survive for up to 48 hours. The disease affects about 240 million people around the world.
How is Schistosomiasis transmitted?
Schistosomiasis is transmitted when a person’s skin comes into contact with water infected by specific parasitic larvae. These larvae thrive inside of certain types of snails and are introduced to water bodies in the form of eggs when infected individuals defecate or urinate in them. Showering in water infected by these larvae, paddling through it or even touching it can cause these larvae to burrow into the skin and travel to the organs, tissues and blood vessels where they lay eggs and cause damage.
What are the symptoms of Schistosomiasis?
Schistosomiasis may have no symptoms or the symptoms may only become apparent many months or years after the infection sets in. The initial contact with the larvae can cause an itchy, papular rash.
The acute and symptomatic part of the disease is called Katayama syndrome and is due to an allergic reaction to larval eggs and larvae travelling through the body. It may occur 14-84 days after the primary infection and is often misdiagnosed. Symptoms of Katayama syndrome include:
- Raised, itchy skin rash
- Weight loss
- Blood in urine
- Joint and muscle pain
- Enlargement of the liver and spleen
In the long term, being infected with S. mansoni and S. japonicum larvae may lead to the following:
- Liver scarring (fibrosis)
- High pressure in the blood vessels of the liver (portal hypertension)
- Fluid in the abdomen (ascites)
- Dilated veins
Being infected with S. haematobium larvae may lead to the following:
- Bladder scarring
- Kidney obstruction
- Chronic urinary infection
- Bladder cancer
A condition called Neuroschistosomiasis can occur when larvae migrate to the brain or spinal cord. Eggs being deposited in the neural tissues may lead to complications such as raised intracranial pressure, myelopathy, and radiculopathy (dysfunction the spinal cord or nerve roots). Symptoms may include headache, visual impairment, limb pain and muscle weakness.
Is there a vaccine against Schistosomiasis?
There is no vaccine available for Schistosomiasis and no drug available which prevents infection.
What is the treatment for Schistosomiasis?
Schistosomiasis can usually be treated successfully with a short course of a medication called praziquantel. This medication eradicates the worms.
Praziquantel is most effective once the worms have grown a bit, so treatment may be delayed until a few weeks after you were infected, or repeated again a few weeks after your first dose.
Steroid medication can also be used to help relieve the symptoms of acute schistosomiasis, or symptoms caused by damage to the brain or nervous system.
Where is Schistosomiasis present?
Different species of the parasite or larvae that cause Schistosomiasis may occur in different countries. However, Schistosomiasis in general is a risk to all persons living in or planning to visit any of the following regions:
- Southern Africa
- Sub-Saharan Africa
- Mahgreb region of North Africa
- Nile River Valley in Egypt and Sudan
- Dominican Republic
- Saint Lucia
The Middle East
- Saudi Arabia
Recommendations for preventing Schistosomiasis
Since a vaccine that guarantees protection against this disease is not yet available, it is important that people visiting areas where the disease is endemic take steps to protect themselves.
Travellers should be advised of the risk of swimming and wading in rivers and lakes or other freshwater contact in endemic countries. This includes popular destinations such as Lake Malawi. Topical application of insect repellent before exposure to water, or towel drying after accidental exposure to schistosomiasis are not reliable in preventing infection.
Travellers should also drink safe water (either boiled, filtered or bottled) to prevent infection via contact with mouth or lips.