Using DNA and RNA data collected in sewage treatment plants, the team discovered a surprising diversity of existing (DNA) and also active (RNA) parasites in the influent of the plants. They also found a large proportion of so-called ‘complex unicellular organisms’: protists such as Giardia, which causes giardiasis, an infection of the small intestine, or Entamoeba, which causes amoebic dysentery. They also found Blastocystis, an intestinal parasite that is common around the world. ‘We were able to confirm that the parasites are reduced during wastewater treatment, and attribute this to predator–prey interactions in the bioreactors,’ said doctoral researcher Jule Freudenthal, the lead author of the study.
The research further shows impressive activity by Rosculus, a small amoeba known mainly for multiplying explosively in cow dung. ‘We showed that this is also applies to the influent of wastewater treatment plants,’ said study leader Dr Kenneth Dumack. So-called network analyses, which show how microorganisms occur in relation to each other, also showed that ciliates and rotifers are important ‘cleaners’ that rid sewage water of parasites and thus enable the safe use of treated water.
Full monitoring and research into the mechanisms that reduce parasites in wastewater treatment plants will help to optimize the treatment process. Future research incorporating both DNA and RNA data can thus help reduce the public health risks associated with inadequately treated wastewater.