The role of innate immune responses against two strains of PEDV (S INDEL and non-S INDEL) in newborn and weaned piglets inoculated by combined orogastric and intranasal routes
Porcine epidemic diarrhea (PED) is a severe gastrointestinal disease in swine caused by PED virus (PEDV), leading to significant economic losses worldwide. Newborn piglets are especially vulnerable, with nearly 100% mortality, unlike older pigs. Disease severity also varies depending on the PEDV strain, with non-S INDEL strains being more virulent than S INDEL ones. This study examined early pathogenesis and innate immunity in 1-week-old suckling and 5- week-old weaned piglets (n=8 per age group, 4 per strain) inoculated with S INDEL or non-S INDEL PEDV strains via combined orogastric and intranasal route. Age-matched negative controls (n=3 per age group) were included. Body weight, temperature, and clinical signs were monitored for 48 hours post-inoculation (hpi). PEDV RNA levels were assessed in rectal swabs (RS) at 0 and 48 hpi, while pathological analyses and viral RNA loads were measured in jejunal content and intestinal mucosa. Gene expression of 75 selected antiviral and inflammatory genes were measured in laser capture microdissection (LCM)-derived jejunal samples using microfluidic qPCR at 48 hpi. Suckling piglets showed severe clinical signs, while weaned piglets were mostly asymptomatic at 48 hpi. In general, clinical signs and lesions in suckling piglets were similar, regardless of the PEDV strain. Both viral strains produced comparable viral RNA loads in the small intestine and feces, as well as consistent villous atrophy and fusion across age groups. In LCM-derived jejunal samples, weaned piglets had higher expression of antiviral genes (type I/III interferons, ISGs) and Th1/Th17 pro-inflammatory genes, particularly with the non-S INDEL strain. Conversely, the anti-inflammatory cytokine IL-10 was overexpressed in suckling compared to weaned piglets for both strains. Overall, PEDV-induced intestinal damage, viral replication, and excretion were similar regardless of viral strain or piglet age. The reduced clinical severity in weaned piglets may result from their stronger intestinal antiviral and pro-inflammatory response. AUTHOR SUMMARYPorcine epidemic diarrhea virus (PEDV) is the causative agent of a major gastrointestinal disease in piglets worldwide, characterized by severe watery diarrhea. The disease is particularly devastating in newborn piglets, especially when caused by non-S INDEL PEDV strains, while weaned piglets demonstrate resistance regardless of the strain. In this study, during the acute infection phase (48 hpi), both highly virulent non-S INDEL and less virulent S INDEL strains caused comparable intestinal atrophy, viral replication in the intestine, and viral loads in feces in both weaned and suckling piglets. However, weaned piglets mounted a robust antiviral response involving type I and III interferons (IFNs) and the induction of Th1- and Th17-related pro-inflammatory responses in the intestinal mucosa. Additionally, interferon-stimulated genes (ISGs) were broadly upregulated across the intestinal mucosa of weaned piglets in response to both PEDV strains. In contrast, suckling piglets exhibited a weaker innate immune response, coinciding with more severe clinical signs. The observed inverse relationship between disease severity and intestinal innate immune activation highlights the potential role of IFNs, ISGs, and pro-inflammatory cytokines in mitigating PEDV severity and underscores their relevance in developing novel pharmacological prevention strategies.