CategorySwine Health - General Disease
Date Full Report Received03/08/2019
Date Abstract Report Received03/08/2019
Enteric diseases are a major cause of mortality and morbidity in pigs and cause significant economic losses to producers. Intestinal diseases caused by viruses can be very severe, particularly in young animals, as was demonstrated by the recent outbreak of porcine epidemic diarrhea virus (PEDV) in North America that resulted in the death of 8 million pigs. Most of the economic losses incurred with PEDV are due to the extremely high mortality in suckling piglets.
Antibodies cannot cross the placenta of a sow. As a result, neonatal pigs are born without antibodies at birth and, although immunocompetent, they are unable to mount a rapid immune response to an infectious challenge. Their survival depends directly on the acquisition of passive lactogenic immunity via colostrum and milk. The importance of colostrum for passive transfer of IgG-type antibodies to piglets in the first 36 hours of life is well-documented; however, IgG does not prevent mortality due to PEDV. Protective passive protective immunity for PEDV from birth to weaning relies on continuous ingestion of IgA found in milk. The IgA in milk provides protective immunity in suckling piglets by bathing of intestinal mucosa with IgA which prevents the attachment and invasion of viruses such as PEDV on mucosal surfaces of the gut. Natural infections with PEDV stimulate a strong IgA response as a result of the intestinal replication of virus and resultant immune response. Stimulation of IgG in serum with PEDV infection occurs but this antibody isotype provides inadequate protection after 2 days of age as it is found predominantly in the colostrum.
There is little evidence that currently available inactivated commercial vaccines are effective in preventing neonatal mortality when used in PEDV-naïve sows subsequently challenged with PEDV at farrowing or in the first few days of life. There is a need to develop an effective vaccine to prevent PED in nursing piglets through the stimulation of lactogenic immunity in PEDV-naïve sows without the need for acclimatization. There is experimental evidence that intramammary vaccination with a similar disease agent, transmissible gastroenteritis virus (TGEV), will stimulate higher levels of protective IgA in milk.
The objective of this study was to develop and demonstration of efficacy of a novel intramammary vaccine delivery system for PEDV in PEDV-naïve gilts. A polymer-based vaccine platform with adjuvant and without inactivated PEDV was administered to Group 1 (negative control) and 2 (positive control) gilts. The polymer with inactivated PEDV and adjuvant was administered to Group 3 (vaccinated) gilts. Gilt serum and colostrum/milk and piglet serum and fecal samples were collected at various time points. Piglets in Group 2 and 3 were inoculated at 4 days of age with 1 mL of 1×103 TCID50/mL of PEDV.
Diarrhea and vomiting of variable magnitude were observed as soon as 1 day post-inoculation (DPI) in piglets in Group 2 and 3. At 7 days post farrowing (DPF)/3 DPI, PEDV was detected via qPCR in feces of all piglets from Group 2 and 3. By 14 DPF/10 DPI, two of the three animals that remained in Group 2 were still shedding virus, while 59% (13 of 22) of animals from Group 3 were negative by qPCR. At 18 DPF/DPI 14 a 100% survival rate was observed in Group 1, 0% in Group 2 and 37% in Group 3. ELISA results demonstrate detectable serum levels of IgA in piglets from Group 3 as soon as 2 DPF, in contrast to piglets in Group 2 where IgA was detected at 14 DPF. Log rank survival analysis for Group 2 and Group 3 was statistically significant at a level of α=0.05 (P = 3e-05).
The results from this study indicate that piglets from dams that seroconverted in Group 3 (vaccinated) had a higher survival rate than those in Group 2 (positive control). Based on these data, this intramammary vaccine delivery system seems to be a promising alternative to increase the survivability of piglets following a PEDV challenge. In the future, this platform could be customized to include other enteric pathogens diminishing the economic losses attributed to enteric diseases in nursing piglets and decreasing or eliminating the need for feedback.