Neutralizing Antibody Decay and Lack of Contact Transmission after Inoculation of 3- and 4-Day-Old Piglets with Porcine Respiratory Coronavirus

Abstract

Ten female neonatal piglets were infected with porcine respiratory coronavirus (PRCV) to measure the decay of a specific neutralizing antibody. By 42 weeks after exposure, 1 of the gilts was serologically negative (<5) for PRCV, and by 48 weeks 2 more gilts were serologically negative. These data demonstrate that young mature gilts can be serologically negative, yet they could have been exposed to PRCV Sentinel pigs were commingled with the PRCV-infected pigs at 8 weeks after exposure, and no virus transmission occurred.

Increased litter survival rates, reduced clinical illness and better lactogenic immunity against TGEV in gilts that were primed as neonates with porcine respiratory coronavirus (PRCV)

“…Piglets (principals) were born at the National Animal Disease Center (NADC) from serologically negative sows. Prior to infection the principals were serologically negative for TGEV/PRCV serum neutralizing (SN) antibodies and, at 3 and 4 days of age, they were infected intranasally with 6×10 6 plaque forming units (PFU) of the avirulent Ind/89 PRCV strain (Wesley, 2002). The PRCV-primed female piglets were maintained in an isolation room for 8 weeks and then commingled in a single outside pen with age-matched control females from another litter.…”

“…The PRCV-primed female piglets were maintained in an isolation room for 8 weeks and then commingled in a single outside pen with age-matched control females from another litter. The serological status of the pigs was followed while they matured and after they were bred to TGEV/PRCV serologically negative boars (Wesley, 2002). The experimental design using these principals was to stimulate lactogenic immunity by exposure to a low oral dose of TGEV before farrowing and then to determine whether the litters of the PRCV-primed gilts were better able to resist and to survive a challenge exposure to TGEV.…”

“…In a previous experiment it was determined that low oral doses of TGEV were adequate to stimulate lactogenic immunity in control gilts but provided limited protection for their litters (Wesley, 2000). At the time that the pre-farrowing dose was given, all of the control animals were negative for TGEV/PRCV neutralizing antibody, 3 of the primed gilts were seronegative and the other 6 primed gilts had low SN titers of 12 or less (Wesley, 2002).…”

“…Since young piglets are most susceptible to TGEV, this heightened immunity, therefore, would be beneficial for the litters of primed female pigs. Thus, the purpose of this study was to measure increases in protective passive immunity against TGEV in gilts that were primed with PRCV when they were 3-and 4-day-old neonates (Wesley, 2002). These PRCV-primed gilts were boosted with a low oral dose of TGEV (doses that were insufficient to provide complete protection, Wesley, 2000) at 13-18 days prior to farrowing and their secondary antibody response and milk titers were measured.…”

Lessons for COVID-19 Immunity from Other Coronavirus Infections

“…Because this virus provides protection against TGEV infection, including in newborn piglets, it represents a natural TGEV vaccine ( Brim et al., 1995 ; Wesley and Woods, 1996 ). Interesting and perhaps relevant for COVID-19 immunity, IgA-mediated mucosal immunity following PRCV infection wanes over time, requiring reinfection or reimmunization prior to farrowing to produce protective lactogenic immunity ( Callebaut et al., 1990 ; Wesley, 2002 ).…”