Bizarre New Virus Behind a Century-Old Mystery Disease

Horses get hepatitis too. One of the most common forms is called Theiler’s disease, a condition that was first recognised in 1919 but has remained a mystery till now. It causes serious liver disease and kills anywhere from 50 to 90 percent of horses that show symptoms.  

What causes it? No one knew. How common is it? Again, a mystery. How does it spread? At least we knew the answer to that one: It seemed to afflict animals that had been given some sort of blood product, whether an anti-toxin or transfusion.

Now, a team of US scientists have uncovered what might be the cause of this enigmatic disease, solving a puzzle that has dogged vets for almost a century. Their prime suspect is a new virus, which they’ve called Theiler’s Disease-Associated Virus (TDAV).

It’s weird. It belongs to a family called flaviviruses, which includes the ones behind yellow fever, dengue fever, and hepatitis C. Within that family, it belongs to a more specific group called the Pegiviruses, most of which are also new discoveries. But even compared to its kin, TDAV is a black sheep. It shares just a third of its amino acid sequences with even its closest relative. It’s like living in a world of cats and discovering a dog for the first time.

You can read more about TDAV and its discovery in my piece for Nature News.