Abstract
Porcine epidemic diarrhea virus (PEDV), is an economically important enteric coronavirus, with over a 90% mortality rate in neonatal piglets. The virus emerged in the US in 2013, resulting in severe production losses. Effective vaccine development against PEDV is a challenge. Inactivated vaccines are of questionable efficacy. Attenuated vaccines, while more effective, require a relatively long lead development time, are associated with safety concerns and are also unable to prevent new field outbreaks. To combine the safety and efficacy advantages of inactivated and attenuated PEDV vaccines, respectively, in this study, we tested the hypothesis that subjecting PEDV virions to heat treatment at 44°C for 10 min to reversibly unfold structural proteins, followed by exposure to RNAse to fragment the genome, would result in a vaccine preparation with intact viral structure/antigenicity but highly diminished replicative abilities. We expected the vaccine to be both safe and effective in a piglet challenge model. Following the heat and RNAse treatment, PEDV virions had an intact electron microscopic ultrastructure and were amplified only in the 3rd passage in Vero cells, indicating that diminished replication was achieved in vitro. Strong PEDV spike-protein specific and virus neutralizing antibody responses were elicited in vaccinated piglets. Upon challenge, all vaccinated pigs were protected against fecal viral shedding and intestinal pathology, while the unvaccinated controls were not. The vaccine virus was not detected in the fecal matter of vaccinated pigs prior to challenge; nor did they develop intestinal lesions. Thus, the described approach has significant promise in improving current approaches for PEDV immunization.
Highlights
Porcine epidemic diarrhea virus (PEDV) is an enteric coronavirus which causes diarrhea, vomiting, severe dehydration, and death in pigs
To achieve the targeted outcomes of maintaining structural integrity while achieving diminished viral replication, rather than complete inactivation, PEDV virus cultures were first exposed to temperatures ranging from 37 to 60◦C for 10 min and visualized by electron microscopy
Cultures treated at 37 and 45◦C remained viable as viral replication was visible by immunofluorescence (IFA) in infected Vero cells using a PEDV-specific antibody, without any amplification by serial passaging
Summary
Porcine epidemic diarrhea virus (PEDV) is an enteric coronavirus which causes diarrhea, vomiting, severe dehydration, and death in pigs. Neonatal pigs are susceptible, with mortality rates that can be as high as 90–100%. Classical strains of PEDV (G1 strains) were first detected in the UK in 1971, and spread to Asia and Europe. Rapid Vaccine Against PEDV (G2 strains) which emerged in China have spread to other countries, with the first case in the US being recorded in 2013 [1, 3, 4]. The availability of effective vaccines and the practice of stringent biosecurity measures are critical for the prevention of PEDV. The development of effective vaccines has been complicated by frequent viral evolution and the fact that PED is most severe in immunologically naïve neonates. Effective and safe vaccines development was challenging because active vaccine replication in the gut is required to induce good and lasting mucosal immunity
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