The Neglected Schistosome
Five different species of schistosome worms can infect humans, and together they cause roughly 200 million cases of a nasty disease known as schistosomiasis or snail fever. Minus the dyes used to see them under a microscope, they all look and act about the same. Pairs of adult male and female Schistosoma haematobium, Schistosoma mansoni and Schistosoma japonicum (pictured respectively above) take up residence in their human host, mate (also pictured above) and produce LOTS of eggs that can get trapped in various essential organs, causing varying degrees of mayhem.
You may be surprised then, even alarmed, to learn that when it comes to scientific research, not all schistosomes are treated equally. Dr. Paul Brindley of George Washington University and Dr. Peter Hotez of the Sabin Vaccine Institute recently compared the number of human cases caused by the three most common schistosomes to the number of corresponding research papers published in the last five years. They found that even though S. haemotobium causes the majority of schistosomiasis disease worldwide, it gets relatively little scientific attention when compared to its close cousins.
In general, neglected tropical diseases (NTDs) suffer from a dearth of scientific activity, a characteristic befitting their nomenclature. But what makes some parasites less popular than others to research groups?
S. haematobium infection results in a form of disease known as “urogenital schistosomiasis” due to inflammation caused by schistosome eggs that get trapped in urogenital organs of infected individuals. For some this causes painful swelling and bleeding. Women and girls infected with this particular parasite are at risk of “female genital schistosomiasis (FGS)”, sores from which are associated with pain during intercourse, diminished fertility, stigma and a 3-4 times increased risk of HIV infection. Urogenital schistosomiasis has also been shown to contribute to an increased risk of bladder cancer.
There is no lack in motivation to study S. haematobium. Brindley and Hotez propose other factors that may explain why research for this parasite is less active and fruitful. According to the authors, tools that help make parasite research possible were lacking.
Until recently… Here are a few examples of innovation described in the report that are helping make the future of S. haematobium research promising:
- A fully sequenced genome! In 2012, scientists released the sequence of ~13,000 S. haematobium genes.
- A method to study parasite infection in animals – so infection can be studied in the lab without subjecting human volunteers to the parasite and its many unsavory symptoms.
- An in vitro system (think parasites in Petri dishes), for genetic manipulation studies, aided now by the completed whole genome.
With a wormy world of research opportunities now possible, Brindley and Hotez believe that science will be able to go the “extra mile” to better understand the disease and to find new treatments, diagnostics and perhaps someday a vaccine. Collaboration will be essential, they say:
Breakthroughs in S. haematobium studies will require international cooperation and a new level of support. The community of S. haematobium researchers is not numerically large, but could easily embrace scientists working on other schistosomes as well as those involved in cancer and AIDS research.
And FYI, the Sabin Vaccine Institute Product Development Partnership is currently developing a vaccine against Schistosoma mansoni (the popular schistosome), which you can learn more about here.
Photos credits: Left- Wellcome Library, London. Wellcome Images, Center- CDC, right- David Brown, Florida Gulf Coast University