Shedding Light on NTDs: Schistosomiasis

Aug 8, 2018 | Lauren Goodwin | Featured Series

 

As we continue to dive into the world of neglected tropical diseases, we find ourselves examining schistosomiasis, a parasitic disease whose impact reaches 200 million people globally and is second only to malaria as the most devastating parasite affecting humans (1). The parasitic Schistosoma worm is found in freshwater when infected individuals urinate or defecate into the water, releasing eggs into the water source (2). After the eggs hatch, the parasites find freshwater snails, in which they can develop (2). As it matures, the parasite leaves the snail and enters the water, where it can survive up for to 48 hours. During this time, the larvae penetrates the skin of people who are swimming, bathing or consuming the water (2). When in the body, the parasite reaches full maturity, where it lives in the blood vessels of the body and produces eggs, allowing the life cycle of the Schistosoma worm to continue (2).

 

There are six species of parasitic worms that cause human schistosomiasis globally: Schistosoma mansoni, found throughout Africa, South America and some areas of the Caribbean; S. haematobium, found throughout Africa and the Middle East; S. japonicum, found in Indonesia, China and Southeast Asia; S. mekongi, found in Cambodia and Laos; and, the related S. intercalatum and S. guineensis, which are both found in rain forest areas of Central and West Africa (3, 4). S. mansoni, S. japonicum, S. mekongi, S. intercalatum and S. guineensis cause intestinal schistosomiasis and S. haematobium causes urogenital schistosomiasis (4).

 

The first symptoms of infection are not caused by the worms themselves, rather, they are from the body’s reaction to the worm egg’s presence (5). The eggs are laid in the intestines and bladder, and if they do not pass through the digestive system, they can cause inflammation and scarring (5). Furthermore, they can cause malnutrition and permanent damage to the liver, intestines, spleen, lungs and bladder (5). Typical symptoms of disease include rash, fever, chills, cough and muscle aches, whereas chronic disease can lead to abdominal pain, enlarged organs and blood in the stool or urine (5). The most common symptom of infection is blood in the urine (5). Additionally, urogenital infection caused by S. haematobium worms is considered to be a risk factor for HIV, especially in women (4). Furthermore, infection can lead to an increased risk of bladder cancer. In rare cases, eggs can be found in the brain and spinal cord, where they can cause seizures, paralysis and death due to disease complications (5). Approximately 200,000-300,000 deaths a year are attributed to schistosomiasis infections (2, 4).

 

Treatment of schistosomiasis includes a short course of a medicine called praziquantel, that kills adult worms (6). However, this medicine is only effective in killing worms in the adult stage, so any eggs or worms that are still developing are unaffected and require repeated treatment (7). Furthermore, in some regions, praziquantel is not available or has very limited supply so if an outbreak occurs, the area has to rely on the World Health Organization (WHO) to be able to supply medication (4). Current strategies include research on the worms and the snails that host them to understand the lifecycle further, in order to be able to develop better treatments and potentially a vaccine to prevent disease.

 

With climate change, rising water temperatures and increased travel, especially through ecotourism, the fear now is that the worms can potentially make their way to water sources in Europe and North America (8). This would put more of the world’s population at risk as more freshwater sources become contaminated. Without having a way to ensure zero transmission will occur, it is imperative for individuals to minimize their risk of contraction through avoiding swimming in freshwater sources where schistosomiasis is endemic, boiling water before showers, drinking safe water and seek medical testing if potentially exposed (9).

 

Considering the global impact of schistosomiasis, as a society, we need to improve efforts to ensure those less fortunate have basic needs met. The burden of schistosomiasis could be drastically reduced simply by making sure that every person has safe and clean water for consuming and bathing. This is something that many take for granted every day, yet for 2.5 billion people worldwide, clean water and sanitation is not assessible. Without clean water, schistosomiasis is just one of many disparities faced by this population. However, preventing this parasitic disease could make a huge and invaluable global impact.

 

Sources:

[1] https://www.cdc.gov/parasites/schistosomiasis/index.html

[2] https://www.cdc.gov/parasites/schistosomiasis/gen_info/faqs.html

[3] https://www.cdc.gov/parasites/schistosomiasis/epi.html

[4] http://www.who.int/news-room/fact-sheets/detail/schistosomiasis

[5] https://www.cdc.gov/parasites/schistosomiasis/disease.html

[6] https://www.nhs.uk/conditions/schistosomiasis/

[7] https://www.news-medical.net/news/20180710/Stem-cell-study-brings-scientists-closer-to-understanding-schistosomiasis.aspx

[8] https://www.thesun.co.uk/news/6743224/parasitic-worm-schistosomiasis-lays-eggs-human-organs-europe/

[9] https://www.cdc.gov/parasites/schistosomiasis/prevent.html

 

 

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