New disease-causing virus in humans

Not harmless: For the first time, doctors have discovered a representative of the circoviruses that can also make us humans ill. The new species, dubbed HCirV-1, can damage liver cells and cause hepatitis, as shown in an immunocompromised patient. These circoviruses could also be behind other cases of liver inflammation of unknown cause, as the researchers explain. So far, this group of viruses was considered harmless to us humans, it was only known to trigger some animal diseases in birds and pigs.

Circoviruses were only discovered in 1974 and have hardly been studied to date. The viruses, which are very small with a diameter of up to 30 nanometers, have a simple structure and do not have a shell. Their genome consists of single-stranded DNA that is formed into a ring – from which the name “Circo-” is derived. So far, these viruses have been considered pure animal pathogens, among other things they are known to be the causative agent of a deadly disease in parrots and two diseases in pigs. For humans, however, the circoviruses have so far been considered completely harmless.

A patient with mysterious liver inflammation

This has changed now. Because a newly discovered variant of the circoviruses can not only infect us humans, it can also make us ill. This was discovered by Philippe Pérot from the Institut Pasteur in Paris and his colleagues when they were investigating a patient with a mysterious liver infection. The elderly woman had received a heart and lung transplant 17 years earlier and was therefore taking immunosuppressive drugs. In early 2022, she was hospitalized for chronic hepatitis.

When the doctors looked for the cause of her liver inflammation, they could not find anything at first: neither one of the common hepatitis pathogens nor any other infection with known bacteria or viruses could be detected. In addition, the woman had not consumed alcohol, illegal drugs, paracetamol or herbal preparations of unclear composition. Still, her liver showed clear signs of inflammation. But why?

First human pathogenic circovirus

Only a computer-assisted search for gene sequences of unknown origin brought clarity. They revealed the presence of a previously unknown circovirus in the patient’s blood and liver tissue. This is the first time researchers have discovered a circovirus that can make us humans ill. “That was completely unexpected,” says Pérot’s colleague Marc Eloit. Because the discovery of new human pathogenic viruses in Europe is extremely rare. The researchers have named this new virus “human circovirus-1”, or HCirV-1 for short.