Hepatic Lipidosis in the Bearded Dragon (Pogona vitticeps): Diagnostic and Therapeutic Investigations
Hepatic lipidosis is prevalent in pet bearded dragons (Pogona vitticeps). The objectives of this study were to develop a microscopic histological system to score the severity of hepatic lipidosis in this species, determine the prevalence and epidemiological risk factors associated with hepatic lipidosis, survey bearded dragon owners to learn more about their feeding practices and supplement use, to understand the metabolic derangement associated with hepatic lipidosis, to identify novel plasma biomarkers that could be used for non-invasive diagnosis and monitoring of hepatic lipidosis, to evaluate computed tomography (CT) as a diagnostic tool for hepatic lipidosis in bearded dragons, and to assess gemfibrozil’s efficacy at reducing hepatic fat content and improving plasma biomarkers. The final grading system developed included 2 semi-quantitative and 1 quantitative category: percent of cytoplasm occupied by lipid vacuoles in hepatocytes, fibrosis, and disruption of hepatic cords. Hepatic cord disruption was indirectly quantified by counting the number of nuclei per unit area. Cut-off values defined severity tiers into mild (final score 1-4), moderate (5-7), and severe (>/8). The study cohort showed a high prevalence (219/571 cases, 38.3%, 95%CI: 34.4-42.3%) of hepatic lipidosis. On multiple logistic models, the occurrence of infectious disease and neoplasia were associated with decreased hepatic lipidosis grade and severity, while the female sex and adult age were associated with increasing grade and severity. Nutritional survey analysis revealed that approximately half of the survey participants, especially the younger respondents, were feeding imbalanced diets with less than 50% plant material and more than 50% insects. Hounsfield units from CT were negatively associated with increased hepatic vacuolation while ultrasound and gross evaluation of the liver was not reliable. On biochemistry, low beta-hydroxybutyric acid (BHBA) was significantly associated with increased disease severity. Metabolomics and lipidomics data found BHBA and succinic acid to be the best biomarkers for diagnosis of moderate to severe disease. Succinic acid was significantly lower in the gemfibrozil group and there was a tendency for improvement of biomarkers and reduced fat in the liver of bearded dragons with moderate to severe disease in this group, though not statistically significant.