National Geographic  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 spe