In line with the Latin expression “sed parva forti” meaning “small but mighty,” the family Parvoviridae contains many of the smallest known viruses, some of which result in fatal or debilitating infections. In recent years, advances in metagenomic viral discovery techniques have dramatically increased the identification of novel parvoviruses in both diseased and healthy individuals. While some of these discoveries have solved etiologic mysteries of well-described diseases in animals, many of the newly discovered parvoviruses appear to cause mild or no disease, or disease associations remain to be established. Equine parvovirus-hepatitis (EqPV-H) was first reported in 2018 as the result of deep sequencing of tissue samples from a horse that had died of acute, fulminant hepatic necrosis. This disease, known as Theiler’s disease, was first reported in 1918 by Sir Arnold Theiler in South Africa. The overall goal of this dissertation was to study the pathology and pathogenesis of this novel virus and to shed light on this 100-year-old mystery. First, I present an overview on parvovirus discovery and characterization in the era of next generation sequencing and the contemporary criteria for fulfilling Koch’s postulates. This includes the current state of knowledge about EqPV-H, a general overview of parvovirus biology, and a review of the role the DNA damage response plays in viral genome replication. Next, I present three retrospective studies characterizing the pathology and prevalence of EqPV-H in horses. These studies are critical to understanding the pathogenesis of this virus and establishing its clinical significance. Moreover, I describe the development of a virus-like particle (VLP) using a baculovirus expression system of the putative VP2 capsid protein of EqPV-H. An analysis of VP2 demonstrates highly conserved core components and variable regions on the capsid surface loops. I then explore the potential host cell division status of infected hepatocytes to determine whether cellular division is necessary for EqPV-H genome replication. I then demonstrate that the EqPV-H nonstructural protein NS1 induces a DNA damage response through activation of key mediators. Lastly, I describe the development and characterization of three novel primary equine hepatocyte culture systems and their potential uses. While many questions remain about the molecular characteristics of EqPV-H, these studies contribute significantly to our knowledge on the pathology and pathogenesis of this novel virus and provide useful tools for future studies.