Giant virus discovered in wastewater treatment plant infects deadly parasite

The single-celled organism Naegleria fowleri is among the deadliest human parasites. In an international collaboration, researchers around Matthias Horn and Patrick Arthofer from the Center for Microbiology and Environmental System Sciences of the University of Vienna have discovered viruses that infect this harmful microbe.

These are called Naegleriavirus and belong to the giant viruses, a group known for their unusually large particles and complex genomes. The team describes their findings in Nature communication.

Naegleri species are single-celled amoebae, found in water bodies worldwide. One species, Naegleria fowleri, particularly thrives in warm water above 30°C and causes primary amoebic meningoencephalitis (PAM), a rare but almost always fatal brain infection. A research team led by Patrick Arthofer and Matthias Horn from the Center for Microbiology and Environmental Systems Sciences at the University of Vienna (CeMESS) has now isolated giant viruses that infect several Naegleria species.

Giant viruses, scientifically called Nucleocytoviricota, are a group of viruses identified only twenty years ago that mainly infect single-celled organisms. These viruses rival bacteria in size and possess unique structures and genetic properties previously thought to be exclusive to cellular life. Their discovery sparked discussions about the definition of viruses and the origin of life.

“The newly discovered Naegleriaviruses were isolated from a wastewater treatment plant in Klosterneuburg near Vienna and represent only the fourth isolate of a group called Klosneuviruses,” says Arthofer. This discovery and the characterization of Naegleriaviruses were made possible through international collaboration with researchers from the universities in Poitiers, the Canary Islands, and the US-based Joint Genome Institute.

Naegleria viruses are mistakenly taken as a food source but destroy their amoeba hosts within just a few hours. They exhibit a structure familiar to giant viruses and infect host cells through a so-called stargate structure that facilitates DNA entry. Within hours, a structure known as a virus factory forms inside the amoeba cell, replicating viral genetic material outside the nucleus and assembling hundreds of new virus particles.

To keep the host cell alive during this process, Naegleria viruses likely use special proteins that suppress the cell’s natural immune response and prevent premature cell death. Only after successful viral replication does cell destruction and virus release occur.

Viruses are used in phage therapy to combat bacterial pathogens.

“The newly identified Naegleria viruses may not be suitable to treat Naegleria infections, given the difficult accessibility of the brain, where infections occur. However, this discovery opens the door to the possibility of preventive treatment of high-risk water bodies, such as during swimming. treatment of swimming pool water, but this would require further research first. Regardless, the discovery of these viruses will advance our understanding of both Naegleria biology and the viruses they infect,” says Horn.