Detection of Porcine Deltacoronavirus RNA in the Upper and Lower Respiratory Tract and Biliary Fluid and the Effect of Infection on Serum Cholesterol Levels and Blood T Cell Population Frequencies in Gnotobiotic Piglets

ABSTRACT

Simple Summary Porcine deltacoronavirus is a newly emerged coronavirus infecting pigs. Deltacoronaviruses were previously reported mainly in birds. Porcine deltacoronavirus infects the small intestine of pigs and causes diarrhea, dehydration, and anorexia, leading to decreased body weight gain and deaths. Moreover, porcine deltacoronavirus can infect other avian or mammalian species, such as poultry and cattle, respectively. The virus has also been detected in febrile children. However, the pathogenesis in pigs or other animals is unclear. In this study, we infected germ-free piglets oronasally with porcine deltacoronavirus. We investigated the presence of the virus in various tissues, as well as differences in T cell populations (a type of immune cell), and cholesterol levels between infected and control animals. As expected, the infected piglets developed intestinal disease, but we also detected viral RNA in respiratory samples and in bile. Furthermore, the infected piglets showed trends toward lower frequencies of T cells in blood, and had higher levels of serum cholesterol compared with control animals. Our findings contribute to an understanding of porcine deltacoronavirus pathogenesis. Porcine deltacoronavirus (PDCoV) was first identified approximately a decade ago, but much is still obscure in terms of its pathogenesis. We aimed to further characterize PDCoV infection by investigating the presence of virus in respiratory and biliary tissues or fluids;T cell population frequencies in blood;and altered serum cholesterol levels. Twelve, 6-day-old, gnotobiotic piglets were inoculated oronasally with PDCoV OH-FD22 (2.6 × 107 FFU/pig). Six control piglets were not inoculated. Rectal swab (RS), nasal swab (NS), nasal wash (NW), bronchoalveolar lavage (BAL), and biliary fluid (BF) samples were collected at 2, 4, and 7 days post-inoculation (DPI) and tested for PDCoV RNA by RT-qPCR. Blood T cell populations and serum cholesterol levels were determined by flow cytometry and a colorimetric assay, respectively. Moderate to high, and low to moderate titers of PDCoV RNA were detected in RS and in NS, NW, BAL, and BF samples, respectively, of inoculated piglets. There were trends toward decreased CD4+CD8−, CD4−CD8+, and CD4+CD8+ blood T cell frequencies in inoculated piglets. Furthermore, serum cholesterol levels were increased in inoculated piglets. Overall, we found that PDCoV infection does not exclusively involve the intestine, since the respiratory and biliary systems and cholesterol metabolism also can be affected.