Transmission of schistosomes

I am a PhD candidate in the Population Biology, Ecology, and Evolution program at Emory University. From a young age I knew I wanted to be a veterinarian, and so I pursued a DVM at Cornell University directly after my undergraduate degree. However, during vet school, I had my first experience with basic science research and I knew I wanted to combine these two arenas into one career, with a focus on infectious diseases. Therefore, after graduating and completing a competitive equine internship, I returned to academia to pursue my PhD.

For my dissertation I am studying the transmission of schistosomes, parasitic flatworms that infect humans and livestock. Schistosomes have a complex life cycle in which they must infect both a mammal and an aquatic snail before their life cycle is complete. Schistosomiasis is a Neglected Tropical Disease with over 200 million people infected worldwide, and while treatments exist, people can immediately become re-infected after treatment. Schistosomes can also infect livestock species, causing an even greater burden in regions where people with very low incomes depend on their livestock for their livelihoods.Public health efforts to control schistosomes have mostly focused on treating infected people and killing the snails that schistosomes need to complete their life cycle. However, killing snails requires the widespread use of pesticides resulting in the death of numerous other aquatic species. This is a problem not just because some of these species may be endangered or rare, but also because by indiscriminately killing aquatic species, pesticide use results in fewer sources of dietary protein for people living in these regions.

For my project, I want to take a different approach to fighting schistosomiasis. I want to investigate the importance of these other species that co-exist with snails because I think that they may actually play a role in regulating schistosome transmission from snails to people and livestock. This approach is rooted in the One Health principle that by preserving the health of the environment, we can protect the health of humans and animals.

I think that having a healthy ecological community with many species in it may decrease schistosome transmission because other species can both compete with the vector snails for resources and predate the vector snails as a more natural source of population control. Both of these interactions could decrease the overall abundance of vector snails, and therefore of the schistosome parasites. These ideas have been explored in other diseases of people, such as Lyme disease, and have been examined with snails and schistosomes in laboratory settings. However, a characterization of the relationship between biodiversity and schistosome transmission has never been done in a country in which schistosomiasis has a large burden.

In my current work at Emory University, I’m exploring these ideas in experimental “ponds” in which I include both vector snails and other snail species and track their population growth, their schistosome infection prevalence, and the impact on ecological variables such as algae production. While these experiments are crucial to investigate the drivers of schistosome risk, my goal is to couple them with similar investigations in regions with high schistosome prevalence in people and animals.

An example of the experimental lakes I use to conduct experiments at Emory University.
Sometimes we add aquatic plants, as pictured here, to reflect the vegetation of Lake Victoria.
Photo credit: Daniel Desautels

As a Soulsby Fellow, I plan to travel to Mwanza, Tanzania to work with Dr. Safari Kinug’hi at the National Institute for Medical Research. We will visit sites along Lake Victoria where schistosomes are present and quantify the abundance of vector snails, schistosome parasites, and other relevant species that interact with vector snails including other snails, insects, and birds. We hope that through careful and laborintense counting of all of these factors, we will be able to find a relationship between biodiversity and schistosome transmission. This information will help guide public health efforts in Tanzania and may also inspire researchers in other countries to conduct similar studies to help them control schistosomiasis.

Kelsey Shaw