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  • Author or Editor: Ignacio Lanza x
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Abstract

Passive protection provided by sows inoculated with the virulent Miller strain of transmissible gastroenteritis virus (tgev), or the isu-1 strain of porcine respiratory coronavirus (prcv), or both was evaluated in nursing pigs challenge exposed with virulent tgev. Four sows (group B) were inoculated with prcv oro- nasally twice at 4 and 2 weeks before parturition; 1 sow (group C) was inoculated similarly, but in 2 subsequent pregnancies; and 2 sows (group D) were oronasally primed with prcv at 4 weeks before parturition, and 2 weeks later were administered a booster inoculation of virulent tgev. Two additional sows (group E) remained uninoculated and served as seronegative controls, and 1 sow (group A) that had been naturally infected with tgev served as a seropositive control. The degree of passive immunity transferred by these sows to their litters was assessed by challenge exposing the pigs of sows in groups BE (only the second litter of group C) with virulent tgev at 3 to 5 days of age. After challenge exposure, clinical signs of infection and mortality were noted and fecal and nasal shedding of virus was assessed by EUSA. The IgA, IgG, and IgM antibody titers to tgev were quantified in colostrum and milk of the sows by use of an isotype-specific monoclonal antibody-capture ELISA, using biotinylated monoclonal antibodies against each porcine isotype as detecting reagents. A plaque-reduction assay was used to quantify neutralizing antibody titers in serum, colostrum, milk, and fractionated whey (IgG and IgA/ IgM). In the sow naturally infected with tgev (group A), there was a pronounced decrease in IgG antibody titers to tgev in the transition from colostrum to milk, and IgA tgev antibodies became predominant, with high titers maintained throughout lactation. The 4 group-B sows partially protected their pigs after tgev challenge exposure; mean mortality was 67%, compared with 100% in pigs suckling the 2 tgev seronegative control sows (group-E fitters). Although IgA tgev antibodies were detected in colostrum and milk of group-B sows, IgG tgev antibodies were the most abundant. The sow of group C had a marked increase in IgA tgev antibody titers in colostrum and milk after reinoculation with prcv during the second pregnancy, before tgev challenge exposure of the fitter. Its pigs were passively protected to a high degree after tgev challenge exposure (27% litter mortality). The sows in group D, primed with prcv and boosted with tgev, provided the best passive protection after tgev challenge exposure of their pigs. Not only fitter mortality (27%) but also morbidity was reduced, compared with those factors for the other challenge- exposed fitters, and the sows did not become ill. In these swine, the high degree of passive protection observed could not be associated with the presence of only IgA tgev antibodies in the milk, but high IgM tgev antibody titers also were detected in colostrum and milk. Results of this study suggest that prcv- inoculated sows are able to partially protect their pigs from tgev challenge exposure and, on the basis of preliminary data, the degree of protection may increase after multiple prcv exposures or after secondary exposure to tgev during pregnancy. Also, an IgA respiratory tract-mammary gland link may exist as evident by the low titer of IgA tgev antibodies in the milk of prcv-inoculated sows, but may not be as efficient in inducing lactogenic IgA immunity as is the gastrointestinal tract-mammary gland link.

Free access
in American Journal of Veterinary Research

Abstract

Objective

To determine the ability of porcine respiratory coronavirus (PRCV) infections to induce passive immunity in suckling pigs to transmissible gastroenteritis virus (TGEV) challenge exposure.

Design and Animals

4 TGEV seronegative sows and their litters (group A) served as controls, whereas 2 other groups (B and C) of sows (also TGEV seronegative) were oronasally inoculated with live PRCV during 1 or 2 subsequent pregnancies, respectively.

Procedure

Effectiveness of passive immunity provided to pigs via colostrum and milk was assessed after TGEV challenge exposure, and TGEV antibody responses in colostrum and milk were analyzed.

Results

Mortality in the 3 groups of young pigs correlated with severity of clinical signs of TGEV infection and was highest in control litters (86% in group-A pigs) and lowest in litters of sows inoculated with PRCV in 2 subsequent pregnancies (14% in group-C pigs). Virus-neutralization and IgA and IgG TGEV antibody titers of milk collected from sows at challenge exposure had significant positive correlation with litter survival. Significantly higher numbers of TGEV-specific IgA and IgG antibody-secreting cells were found in group-A pigs than in group-C pigs, suggesting that high titer of maternal antibodies (induced in group-C sows multiply exposed to PRCV) may interfere with active antibody responses.

Conclusions and Clinical Relevance

Results suggest that, in PRCV-infected pig herds, multiple exposures of pregnant sows are associated with higher IgA and IgG antibody titers to TGEV in milk, and these titers contribute to protection against TGEV infection. (Am J Vet Res 1996; 57:664–671)

Free access
in American Journal of Veterinary Research