Zooplankton protect viruses from sunlight disinfection

Sunlight disinfection is an important inactivation process for enteric viruses in water. Understanding how dark biotic processes, such as zooplankton filter feeding, impact sunlight disinfection for viruses has important implications for public health. This research quantifies the uptake of MS2, a model for enteric viruses, by the filter feeder <i>Branchionus plicatilis</i> (rotifer) and the effects of such uptake on subsequent sunlight inactivation of MS2. Experiments co-incubating MS2 with rotifers showed 2.6 log viral removal over 120 hours. Viable virus was recovered from rotifer bodies after co-incubation, indicating incomplete viral inactivation via ingestion. When live rotifers were co-incubated with MS2 and the system was treated with sunlight, experimental treatments with rotifers showed that the virus was protected with 2-3 log viral inactivation compared to 4.5 log inactivation for sunlight controls without rotifers. Dead rotifers placed in the system did not show the same magnitude of protection effects, indicating that active filter feeding of rotifers is associated with protection from sunlight. Data from this study show that zooplankton may serve as a vector for viruses and reduce the efficiency of sunlight inactivation.IMPORTANCEEnteric viral contamination in water is a leading global cause of waterborne disease outbreaks. Sunlight inactivation is an important disinfection mechanism in natural waters, but accurately modeling inactivation is challenging due to the complex nature of aquatic systems. Zooplankton play a critical role in natural systems and are known to inactivate bacteria, but their interaction with viruses is not well understood. Our research examines the impact of a model zooplankton species on the sunlight disinfection of viruses. The results from this study address knowledge gaps in the importance of dark processes such as zooplankton filter feeding and their impact on viral fate.