Passive immunity to transmissible gastroenteritis virus: intramammary viral inoculation of sows

Sows were injected intramammarily with live-attenuated TGE virus, an enteric coronavirus--one sow during pregnancy and three sows during lactation. All sows were TGE antibody seronegative prior to inoculation except for one naturally infected sow inoculated during lactation. The animal injected during pregnancy had primarily IgG TGE antibodies in milk from all glands. By contrast, sows injected during lactation had IgA and IgM initially, and later IgA and IgG TGE antibodies in milk from injected and noninjected glands. The seropositive sow had elevated IgA TGE antibody titers in milk after IMm injection. Both seronegative sows inoculated intramammarily during lactation shed TGE virus in milk from injected glands, and their nursing piglets developed mild diarrhea and shed virus in their feces at three to nine DPE of the sows. Milk from IMm injected glands generally had higher TGE antibody titers than milk from noninjected glands. These results suggest that TGE virus replicates in lactating mammary gland tissue, thereby stimulating IgA immunocytes, leading to secretion of IgA antibodies in milk. Whether the intramammary route presents a natural route of enteric virus exposure in lactating animals (by way of infected nursing piglets), leading to IgA-antibody secretion in milk, requires further investigation.