Evaluation of the Efficacy of Lactogenic Immunity of Sow Induced by Porcine Epidemic Diarrhea Virus (PEDV) Vaccine By Intranasal Immunization

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Evaluation of the Efficacy of Lactogenic Immunity of Sow Induced by Porcine Epidemic Diarrhea Virus (PEDV) Vaccine By Intranasal Immunization

Background: Porcine epidemic diarrhea virus belongs to family of coronaviruses which are notorious for rapid spread of severe diarrhea among suckling piglets. The virus mainly replicates in the epithelial cells of duodenum, jejunum, ileum and colon and is a life threatening condition in pigs. A highly virulent strain “CHYJ130330” having high mortality rate was isolated from a field outbreak, identified as a new virulent genotype II/G2-b strain and adapted successfully to vero cells was used to prepare inactivated vaccine against PEDV. This newly prepared vaccine was given through intranasal route and is compared with the commercially available bi-combined (PEDV and TGEV) vaccine given by intramuscular injection. In this study milk or mucosal IgA and IgG antibody levels have been used to predict vaccine efficacy and the level of protective immunity against PED virus. Antibody titers in the milk of sows and intestines of suckling piglets were compared by enzyme-linked immunosorbent assay (ELISA). Results: It was shown that CHYJ vaccine induced significantly higher levels of PEDV IgA antibody in milk of sows and intestines of piglets as compared to commercial bi-combined vaccine. Both CHYJ and commercial vaccines were not able to induce detectable IgG levels in the intestines of piglets; the later however induced higher IgG levels when detected in the sow’s milk. Protective efficacy of vaccines was determined against a highly virulent PEDV strain. CHYJ intranasal vaccine gives a better protection 80% (4/5) rate as compared to commercial i.m. vaccine conferring 60% (3/5) immunity in suckling piglets. Conclusions: It is therefore concluded that PEDV inactivated CHYJ vaccine confer better lactogenic immunity and gives more protection to suckling piglets than available bi-combined TGEV and PEDV vaccine through passive immunization.

Efficacy of Needle-Less Intradermal Vaccination against Porcine Epidemic Diarrhea Virus

To prevent diarrhea in suckling piglets infected by porcine epidemic diarrhea virus (PEDV), porcine epidemic diarrhea (PED) vaccines are administered mainly through intramuscular (IM) or oral routes. We found that growing pigs vaccinated with an inactivated PEDV vaccine via the intradermal (ID) route had higher neutralizing antibody titers and cytokine (IFN-γ, IL-4, and IL-10) levels than non-vaccinated pigs. In addition, suckling piglets acquired lactogenic immunity from pregnant sows inoculated with an ID PED vaccine. We evaluated the efficacy of vaccination via this route, along with subsequent protection against virulent PEDV. At six days post-challenge, the survival rate of suckling piglets exposed to virulent PEDV was 70% for the ID group and 0% for the mock group (no vaccine). At necropsy, villi length in the duodenum and ileum of piglets with lactogenic immunity provided by ID-vaccinated sows proved to be significant (p < 0.05) when compared with those in piglets from mock group sows. Thus, vaccination using an inactivated PED vaccine via the ID route provides partial protection against infection by virulent PEDV.

Generation and Characterization of a Spike Glycoprotein Domain A-Specific Neutralizing Single-Chain Variable Fragment against Porcine Epidemic Diarrhea Virus

The emergence of the genotype (G) 2 and re-emergence of the G1 porcine epidemic diarrhea virus (PEDV) has caused severe economic impacts in the past decade. Developments of efficient vaccines against new variants of PEDV have been challenging, not least because of the difficulties in eliciting mucosal and lactogenic immunity. A single-chain fragment variable (scFv) capable of efficient antigen recognition is an alternative to vaccination and treatment of a viral infection. In the present study, the variable regions of the light chain and the heavy chain of a G2b PEDV spike domain A (S1A)-specific neutralizing monoclonal antibody (mAb) were sequenced, constructed with a (G4S) x3 linker, and produced by a mammalian protein expression system. Our results demonstrated that the PEDV S1A domain scFv was able to bind to S proteins of both G1 and G2b PEDVs. Nevertheless, the scFv was only capable of neutralizing the homologous G2b PEDV but not the G1 PEDV. The binding ability of the G2b-specific neutralizing scFv was not able to predict the neutralizing ability toward heterologous PEDV. The anti-PEDV S1A scFv presented herein serves as a potential therapeutic candidate against the virulent G2b PEDV.

Host Factors Affecting Generation of Immunity Against Porcine Epidemic Diarrhea Virus in Pregnant and Lactating Swine and Passive Protection of Neonates

Porcine epidemic diarrhea virus (PEDV) is a highly virulent re-emerging enteric coronavirus that causes acute diarrhea, dehydration, and up to 100% mortality in neonatal suckling piglets. Despite this, a safe and effective PEDV vaccine against highly virulent strains is unavailable, making PEDV prevention and control challenging. Lactogenic immunity induced via the gut-mammary gland-secretory IgA (sIgA) axis, remains the most promising and effective way to protect suckling piglets from PEDV. Therefore, a successful PEDV vaccine must induce protective maternal IgA antibodies that passively transfer into colostrum and milk. Identifying variables that influence lymphocyte migration and IgA secretion during gestation and lactation is imperative for designing maternal immunization strategies that generate the highest amount of lactogenic immune protection against PEDV in suckling piglets. Because pregnancy-associated immune alterations influence viral pathogenesis and adaptive immune responses in many different species, a better understanding of host immune responses to PEDV in pregnant swine may translate into improved maternal immunization strategies against enteric pathogens for multiple species. In this review, we discuss the role of host factors during pregnancy on antiviral immunity and their implications for generating protective lactogenic immunity in suckling neonates.

Oral vitamin A supplementation of porcine epidemic diarrhea virus infected gilts enhances IgA and lactogenic immune protection of nursing piglets

Vitamin A (VA) has pleiotropic effects on the immune system and is critical for mucosal immune function and intestinal lymphocyte trafficking. We hypothesized that oral VA supplementation of porcine epidemic diarrhea virus (PEDV)-infected pregnant gilts would enhance the gut-mammary gland-secretory IgA axis to boost lactogenic immunity and passive protection of nursing piglets against PEDV challenge. Gilts received daily oral retinyl acetate (30 000 IU) starting at gestation day 76 throughout lactation. At 3–4 weeks pre-partum, VA-supplemented (PEDV + VA) and non-supplemented (PEDV) gilts were PEDV or mock inoculated (mock + VA and mock, respectively). PEDV + VA gilts had decreased mean PEDV RNA shedding titers and diarrhea scores. To determine if lactogenic immunity correlated with protection, all piglets were PEDV-challenged at 3–5 days post-partum. The survival rate of PEDV + VA litters was 74.2% compared with 55.9% in PEDV litters. Mock and mock + VA litter survival rates were 5.7% and 8.3%, respectively. PEDV + VA gilts had increased PEDV IgA antibody secreting cells and PEDV IgA antibodies in serum pre-partum and IgA+β7+ (gut homing) cells in milk post piglet challenge compared with PEDV gilts. Our findings suggest that oral VA supplementation may act as an adjuvant during pregnancy, enhancing maternal IgA and lactogenic immune protection in nursing piglets.