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Rosen Reveals Parasite Research

During the past several years, 19 Berea College students have had first hand experience in biology research under the direction of Dr. Ron Rosen, BC biology professor. Grants obtained through research proposals have allowed this work to continue over four different summers, beginning in 1998.

Dr. Rosen and Students Collaborate on Research

Rosen presented research findings of their work in studying digenetic trematodes, a type of flatworm parasite, in the first Friday Faculty Colloquium of the semester Sept. 15.

Digenetic trematodes are flatworm parasites responsible for several serious diseases in humans. Rosen and his students studied a digenean species found in regional snails and freshwater fish called proterometra macrostoma.

Using a PowerPoint presentation, Rosen began his lecture by citing parasitic research done at the college in the 1920s regarding parasitic infestations in members of the student body. The professor explained that even today digenetic trematodes, especially in Asia and Africa, can cause serious damage to the vital organs of their human hosts, sometimes even resulting in death. In 1998, for example, UNICEF reported that globally about 1.5 billion people had roundworms, over 1.3 billion had hookworms, 1 billion were infected with whipworms and 265 million people are infected with schistosomes. Snail fever is a common name for schistosomias, a disease caused by schistosomes. It is a widespread problem in countries like China, where the parasites are found in freshwater and strike the liver, gastrointestinal tract and the bladder of a human host.

In order to understand the habits and life cycles of these parasites, Rosen and his students collected affected snails and fish from North Elkhorn Creek in Scott County. According to the professor, the fish become infected by eating the large cercarial larval stage of the flatworms, which are active in the water after emerging from the snails. The snails, in turn ingest the parasite’s eggs, passed into the water with the fish feces.

Studying the larvae inside the snails proved difficult due to the thick shell of the animal and its soft tissue, which is hard to preserve. So Rosen and the students used Cal-Ex II, a fixative and de-calcification mixture, which made the shell dissolve and thickened the tissue.

Very thin sections of snail tissue under a microscope revealed that the eggs or rediae collected in a cavity of the snail, which is unusual, according to Rosen, who stated that usually parasites entwine in organs. The students found that the rediae shed very slowly, only one or two going through the life cycle process per day.

In the lab they did experiments to document how the parasite’s cercarial larval stage reacted to light and their patterns of swimming. The researchers found that they are most active in the dark, usually from midnight to noon. Electrodes were used on the worms to record increased activity.

Researchers watched fish feed on the larva in the lab. Three types of fish were compared. A warmouth bass was found to be infected with more parasites than bluegill or sunfish; sunfish were least infected. It was noted that bass are night feeders, meaning they are more likely to eat the active, dark-loving larva than sunfish, which are day feeders.
Regarding physical damage to the fish, Rosen showed photos of the parasites feeding on the host body tissue, but noted that “they seem to tolerate these worms very well.”

In the future, Rosen would like to do DNA analysis of the different strains of the parasites. This will be “the ultimate goal to confirm or reject whether or not there are true genetic differences.” The studies did yield five peer review publications Rosen co-authored with students that were made available to the scientific community.

BC junior Emilie Throop was in the last group of students to do summer research with Rosen. She says the field work aspect was especially interesting to her and she found it very beneficial. “The lab work we did really helped me to understand the way in which research is conducted, how to ask the right questions when doing research and simply how to work in a lab session.

Sectioning the snail tissue and then staining it to reveal the body cavity containing the parasites was Throop’s favorite part of the project. “That felt like one of the biggest accomplishments … the fact that we came away from the research with such a solid and interesting contribution …. This has been such a good opportunity for students on campus to learn outside of the classroom and I really appreciate the work (Dr. Rosen) has put into it.”

According to Rosen, research at the undergraduate level helps in “providing a window for students regarding the nature of sustained, basic research.” Several biology majors have gone on to pursue advanced degrees and over the long run the professor feels they could have an impact in the field of biomedical research. He has put together a research proposal in order to continue his work and, if funding comes through, several students will be selected to continue the project next summer.

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