European eels spread the lethal herpesvirus AngHV-1 through aggressive biting during antagonistic interactions, researchers at the University of Liège reported in the Journal of Virology, upending the long-held aquatic virology consensus that fish viruses transmit exclusively via waterborne vectors.
The European eel, Anguilla, faces a severe population crisis. Young glass eel recruitment has plummeted to roughly 1 percent of 1980s levels due to migration barriers, pollution, overfishing, and climate change. Infectious diseases compound these environmental pressures, particularly AngHV-1, which triggers hemorrhagic skin and gill lesions with mortality rates hitting 30 percent in intensive aquaculture operations.
Eels Transmit AngHV-1 Through Biting and Contact
- Direct Transmission: The herpesvirus AngHV-1 does not just float through water; aggressive biting between eels transfers the virus efficiently on contact.
- Life-Stage Susceptibility: Transparent young glass eels arriving on coasts resist the infection, whereas growing yellow eels in inland waters are highly vulnerable.
- Environmental Breakdown: Viral infectivity drops by 90 percent in water within twelve hours, making direct physical contact a crucial survival mechanism for the pathogen.
Uncovering the Biting Transmission Route
Professor Alain Vanderplasschen and his team at the Laboratory of Virology and Vaccinology within the Faculty of Veterinary Medicine and WEL Research Institute investigated how the virus persists in low-density wild populations where individuals remain relatively isolated.
To prove this, the team designed experimental epidemiological scenarios mimicking natural biting behavior between infected and uninfected eels. In all three tested scenarios, every exposed animal developed an infection. This reveals that antagonistic social interactions drive viral spread in aquatic habitats just as effectively as fluid dynamics.
Tracking Infection via in Vivo Bioluminescence
The researchers tracked viral dissemination by genetically modifying the virus to express a firefly enzyme, producing light during tissue replication. This in vivo bioluminescence imaging exposed how the pathogen moves through the host anatomy, identifying gill mucous membranes and oral tissues as primary entry points.
Infected eels in communal groups developed more skin lesions than isolated specimens, confirming that social biting accelerates disease progression.
Conservation Implications for Endangered Aquatics
Because eel skin mucus possesses natural virus-neutralizing properties and water rapidly degrades viral particles, direct biting allows the pathogen to bypass environmental hurdles entirely. This biological workaround explains how the virus maintains circulation despite low population densities and fragile viral stability outside the host.
The research unites teams across the University of Liège, including first author Natacha Delrez, Mathieu Denoël, and Billy Nzau Matondo, alongside collaborators from the University of Mons and the University of Glasgow. These findings demand a complete reevaluation of fish pathology models, influencing both disease prevention protocols in commercial aquaculture and restoration strategies for endangered aquatic species.
References
- Delrez, N., et al. “Biting-mediated transmission of a herpesvirus in European eels.” Journal of Virology. University of Liège.
- Vanderplasschen, A., et al. In vivo bioluminescence imaging was used to study AngHV-1 replication and tissue tropism in Anguilla by researchers at the Faculty of Veterinary Medicine and WEL Research Institute.
