Schistosomiasis is a disease caused by parasitic flatworms, called flukes that burrow into the flesh. It can cause sterility or partial paralysis. The disease takes 3 to 4 months to incubate, but some symptoms may be immediately manifest, such as blood in the urine and diarrhoea.
The major types of worms that cause schistosomiasis in humans are Schistosoma mansoni, S. haematobium, and S. japonicum. Certain freshwater snails are the intermediate host for the worms. The infected snails release large numbers of very small, free-swimming larvae which are capable of penetrating the unbroken skin of a human host. They may pass through the heart, lungs, and liver before ending up as adult worms in the veins of the intestines. There they lay vast numbers of eggs that work their way into the intestinal tract and are eventually passed out in the faeces. The body's reaction to the eggs produced by these worms, and not the worms themselves, causes the symptoms of schistosomiasis.
The number of flukes acquired by an individual is related to the number of water contact episodes and to the degree of body exposure. People with the worm infections develop ballooning stomachs caused by water retention, along with large livers and spleens. The infection causes a variety of intestinal and liver complications which weaken the sufferer and eventually may cause severe disability and death. Although the direct mortality from infection is low, the importance of the disease lies in the sheer size of the epidemiological phenomenon. As the human population grows, the problem intensifies on two counts - increased excretal pollution of water, and the extended use of irrigation land for crop-growing - while the creation of man-made lakes has encouraged the spread of the disease. Disease conditions are maintained by poor agricultural practices and unsanitary habits. In many areas of the world, people defaecate in rivers and irrigation canals.
Praziquantel (PZQ) is used to treat schistosomiasis, but is not very effective and can produce potentially severe side-effects. Recently, products derived from myrrh from the tree Commophora molmol, and various other species of Commiphora, are becoming recognized as possessing significant antiseptic, anaesthetic, anti-parasitic and anti-tumour properties and appear to offer a natural (and ancient) remedy.
Schistosomiasis was known in ancient Egypt since remote times. A characteristic symptom of schistosomiasis, haematuria (blood in the urine) with urinary bladder disturbances, was mentioned in four Papyrus papers dated back to 1950-1900 BC, and schistosoma eggs were detected in a cirrhotic liver of a mummy from 1200 BC. At the height of the Roman Empire, Dhofar (Oman) was exporting immense quantities of frankincense, myrrh and other oils, by ship to Yemen and thence up the Red Sea, and by camel caravan overland to Petra and the Mediterranean. Myrrh is still harvested in Oman.
Schistosomiasis affects over 200 million people in 74 countries and territories worldwide (WHO, 1999) causing several chronic complications. It is estimated that over 600 million additional people are exposed to the risk of infection. Annually schistosomiasis causes an estimated 200,000 deaths and is expanding its range as human activities provide more suitable habitats in contaminated fresh water.
Following construction in 1968 of Egypt's Aswan High Dam and associated irrigation systems, prevalence of the Schistosoma mansoni organism in humans in the region increased from five percent to 77 percent.
Travellers are at risk when going to an area with reported incidence of the infection and when wading or swimming in lakes or rivers in rural areas where poor sanitation and the appropriate snails are present. 90% of the cases contracted by British tourists can be traced to Malawi.