Investigations into the Pathogenesis and Characteristics of Novel Swine Enteric Coronaviruses

Swine enteric coronaviruses are an important cause of enteritis in pigs, and are most devastating to naive suckling piglets, resulting in significant morbidity and mortality. Recently, virulent porcine epidemic diarrhea virus (PEDV) and a novel porcine deltacoronavirus (PDCoV) have emerged worldwide in important swine production regions, such as the United States. After initial detection, it was unclear if PDCoV was a disease causing agent, as Koch’s postulates had not been fulfilled. To prove the pathogenicity of PDCoV in the absence of cultivable virus, we generated a PDCoV inoculum from infectious clinical materials free of other pathogens and used it to infect sows and their nursing neonatal piglets. We demonstrated the virus causes clinically significant enteritis and neonatal piglet mortality and documented the virus kinetics and time course of infection. For PEDV, elimination of the virus from infected swine production sites has been the goal for disease control and methods for disposal of PEDV-infected carcasses were largely untested in their efficacy. Carcass composting has been used widely in the poultry industry and has shown efficacy in eliminating important pathogens. To determine if composting may be an effective and biosecure disposal method for PEDV-infected pig carcasses, we tested virus stability in growth media at temperatures and time treatments mimicking those reached during the composting cycle and also infected weaned piglets with PEDV and incorporated them into simulated compost windrows. We demonstrated that elevated temperature (35-55 °C) exposure over time combined with the complex microbial environment of carcass composting degrades the virus beyond detection and, therefore, may be a suitable method for on-farm disposal of infected carcasses providing an alternative biosecure disposal method. Finally, matrix assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS) is an emerging technology being used for microorganism identification. Our aim was to demonstrate the utility of this method for differentiation of uninfected cells from swine coronavirus-infected cells. We found that classification systems developed for use in bacteria can clearly discriminate between transmissible gastroenteritis virus (TGEV)-infected swine testicular (ST) cells and uninfected ST cells, but additional work is needed to distinguish PEDV-infected Vero cells from uninfected Vero cells