Biting spreads eel herpesvirus AngHV-1, challenging the water-only model of fish infection

A herpesvirus that harms European eels can pass between fish through bites during aggressive encounters, according to researchers at the University of Liège. Their work, published in the Journal of Virology, questions the long-held view that fish viruses spread mainly through water. It also offers an explanation for how disease persists in a critically endangered species whose wild populations are now sparse.

Why the eel matters

The European eel (Anguilla anguilla) migrates thousands of kilometres between its Atlantic breeding grounds and the inland waters of Europe, where it grows for several years. The number of young eels reaching European coasts is now only about 1% of the level estimated for the early 1980s. Migration barriers, pollution, overfishing and climate change all contribute to the decline.

Infectious disease adds further pressure. The herpesvirus AngHV-1 can cause haemorrhagic lesions on the skin and gills, and mortality of up to 30% has been reported in intensive aquaculture. What has been unclear is how the virus circulates among wild eels that live at low density and relatively far from one another.

Transmission by biting

The team, led by Professor Alain Vanderplasschen of the Laboratory of Virology and Vaccinology (Faculty of Veterinary Medicine and WEL Research Institute), focused on the fact that eels sometimes bite members of their own species, around the mouth or on the tail. The researchers reproduced several scenarios in which infected and uninfected eels interacted in this way. In all three scenarios tested, every exposed animal became infected, indicating that a single contact can be enough.

Laboratory results also point to why this route may matter. Under the conditions studied, the virus lost about 90% of its infectivity in water within 12 hours. The mucus covering eel skin also has properties that can neutralise the virus. Direct transfer through a bite would bypass both barriers.

Tracking infection with light

To follow the infection inside living animals, the researchers used in vivo bioluminescence imaging. They engineered the virus to carry a firefly enzyme, so that infected tissues emitted light detectable with specialised equipment, although not visible to the naked eye. This allowed the spread of infection to be followed over time in the same animal.

The imaging showed that susceptibility depends strongly on developmental stage. Glass eels, the translucent juveniles arriving on European coasts, resisted infection when exposed through water. Yellow eels, the growth stage in inland waters, were far more susceptible, with the gills and the mucous membranes of the mouth acting as the main entry points. Infected eels held in groups also developed more infection sites on the skin than those kept alone, which helped point to biting as a transmission route.

Limitations and next steps

The findings come from controlled experiments, and the source does not report how often biting-related transmission occurs in natural habitats. Whether the same route operates in other fish viruses remains to be tested, although the authors suggest the water-only model should be reassessed more widely.

For researchers, the work shows the value of combining molecular virology, epidemiology and behavioural ecology. In practice, the results could inform disease prevention in aquaculture, where crowding may raise the chance of aggressive contact, and the weighing of infection risk in conservation and restocking programmes for wild eels.

The study was led by first author Natacha Delrez with Mathieu Denoël, Michael Ovidio and Billy Nzau Matondo, and involved contributions from the University of Mons and the University of Glasgow.

Source: European eels transmit a herpesvirus through bites, revealing another route for fish infections (Phys.org, 11 November 2026).

Image: AI-generated illustration.