Deltavirus: a young researcher supported by ANRS MIE is helping to ‘expand the horizons of what is possible’

Expanding our understanding of little-known pathogens

On 6 March 2026, a team of researchers led by the Montpellier Institute of Molecular Genetics (IGMM), a research institute of the CNRS and the University of Montpellier, published a groundbreaking study in the journal Cell. Unprecedented in its subject matter: deltaviruses, microscopic viruses whose mode of operation is particularly poorly understood.

This family of viruses, which includes the hepatitis D virus (which uses the hepatitis B virus as a ‘helper’), borrows surface proteins from other viruses to infect cells. This new study shows that these deltaviruses do much more than that. “When I joined Dr Karim Majzoub’s laboratory at the IGMM, deltaviruses bearing a strong resemblance to the hepatitis D virus had just been discovered in certain snakes and rodents,” recalls Dr Joe McKellar, the study’s lead author. The young researcher and his colleagues wanted to investigate the type of proteins they use and whether these are specific to particular viral families or not. A doctor of virology specialising in microscopy, Joe McKellar focused his work on the microscopic observation of viral particles following the co-infection of cells replicating deltaviruses with ‘helper’ viral particles (from vesicular stomatitis virus, a pathogen affecting livestock, or herpes simplex virus type 1) in vitro in a level 3 biosafety laboratory.

Together with his colleagues, he had to develop virus separation techniques to examine the identity of the different types of particles, which required some time to optimise. “With the help of Aurélien Fouillen from the Institute of Functional Genomics (University of Montpellier, CNRS, Inserm), we were able to image the different types of particles using electron microscopy. ” The result: not only can a single deltavirus utilise several different viruses, including those affecting humans, but it does not merely ‘borrow’ their surface proteins; it can also insert itself into these viruses in the form of hybrids. A discovery which, for Joe McKellar, “opens up a world of possibilities”. Next step: understanding how these deltaviruses manage to infiltrate so many different viruses.

Start Programme: promoting the profile of young scientists

As the study’s lead author, Dr Joe McKellar contributed to it as part of a postdoctoral fellowship at the IGMM funded by the ANRS Emerging Infectious Diseases (ANRS MIE) through its Start Programme for young researchers. “Having my own funding allowed me to enjoy a certain degree of independence from the rest of the team and to showcase my personal expertise,” says the young researcher. “I didn’t just participate in the collective effort; I had the opportunity to take more initiative and thus make my own contribution. ”

This autonomy prompted him to reorient his career. “It was whilst leading these projects that I realised just how much the impact of a scientific discovery depends on how it is visualised,” explains the young researcher. Upon completing his post–doctoral research in November 2025, Joe McKellar launched the start–up Viroscope, an agency producing stylised visuals derived from microscopic imagery for scientific communication. “Doing science is essential, but making it visible is just as crucial.”