Schistosomiasis is a parasitic disease caused by infection with Schistosoma worms found in freshwater environments, primarily in tropical and subtropical regions. It remains one of the most significant neglected tropical diseases, affecting millions worldwide.
History
Schistosomiasis has a long history dating back to ancient civilisations. Evidence of the disease has been found in ancient Egyptian mummies, where the parasites’ eggs were discovered in their tissues. The disease was later documented in Europe, Asia, and Africa, where it became a significant health concern due to its prevalence in many regions with poor sanitation.
The earliest scientific recognition of schistosomiasis occurred in the late 19th century. In 1851, Theodor Bilharz, a German physician, identified the Schistosoma species in the veins of an Egyptian patient, and thus the disease was originally called “Bilharziasis.” However, it was not until the 20th century that the connection between the Schistosoma parasite and human disease was fully understood. By this time, schistosomiasis was widespread in Africa, the Middle East, and parts of Asia and South America, where people came into contact with contaminated water sources.
The spread of the disease intensified due to population growth, urbanisation, and poor public health infrastructure, which made it difficult to control. Despite significant advances in understanding its transmission, schistosomiasis remains a public health challenge, especially in rural areas where sanitation and access to clean water remain limited.
Transmission and lifecycle
Schistosomiasis is caused by several species of Schistosoma worms, with Schistosoma mansoni, Schistosoma haematobium, and Schistosoma japonicum being the most common human pathogens. The life cycle of the parasite is complex, involving both human and snail hosts.
Humans typically become infected when they come into contact with water contaminated with the larvae (cercariae) of Schistosoma. These larvae are released by freshwater snails that serve as the intermediate host. Once in contact with human skin, the cercariae penetrate and enter the bloodstream, eventually migrating to the liver, where they mature into adult worms. The adult worms then move to different parts of the body, often residing in the blood vessels around the intestines or bladder.
In these sites, the worms lay eggs that can either pass out of the body through urine or faeces, or become trapped in tissues, causing inflammation, scarring, and damage to organs. The eggs that exit the body return to the water, where they hatch into larvae that infect snails, continuing the life cycle.
Prevention of Schistosomiasis
Preventing schistosomiasis largely depends on avoiding contact with contaminated water sources, particularly in regions where the disease is endemic. Several strategies have been proposed to reduce the transmission and impact of schistosomiasis:
Improved sanitation and clean water supply:
One of the most effective ways to prevent the disease is by ensuring access to safe, clean water and better sanitation systems. When people are less likely to come into contact with contaminated water, the risk of infection is significantly reduced.
Snail control:
Since snails are the intermediate host for the parasite, controlling their populations can reduce the incidence of the disease. This can be done through environmental management, such as eliminating standing water where snails breed, or through chemical treatments to kill the snails in infested water bodies.
Health education:
Informing populations about the risks of schistosomiasis and encouraging the use of safe water practices, such as avoiding swimming in contaminated water, is crucial in endemic areas. In some places, local initiatives also promote the use of safe toilets and proper disposal of human waste.
Mass Drug Administration (MDA):
In areas where schistosomiasis is widespread, health authorities often employ mass drug administration programmes, where entire populations at risk are given treatments to reduce the number of infections. These programmes are particularly beneficial in reducing the prevalence of the disease in areas with limited healthcare infrastructure.
Treatment
Schistosomiasis can be treated effectively with the use of antiparasitic medications, particularly praziquantel, which is the most widely used drug for the disease. Praziquantel works by disrupting the worm’s ability to regulate its environment, leading to paralysis and death of the parasite. The drug is generally safe and effective, especially when administered early in the course of the disease.
In addition to praziquantel, treatment may also include supportive care to manage complications arising from chronic infections, such as liver damage or bladder cancer. In some cases, surgery may be required to repair or remove severely damaged tissue.
Challenges in eradication
While the treatment of schistosomiasis is relatively straightforward, eradicating the disease remains a significant challenge due to the complexities of transmission and the lack of infrastructure in many endemic regions. The global burden of schistosomiasis, with millions of people infected and countless others at risk, calls for a multifaceted approach combining treatment, prevention, and education.
Ongoing research aims to develop new vaccines, better diagnostic tools, and alternative treatments to address the growing challenges of drug resistance and the environmental changes that affect snail populations.