Transplacental transmission and neonatal infection with swine influenza virus (Hsw1N1) in swine.

To study the question of chronicity or latency of swine influenza virus (Hsw1N1) infections in swine, newborn pigs were exposed to the virus in two experiments, and pregnant gilts were exposed in another experiment. Of five pigs exposed at 5 days of age, virus was isolated from throat swab samples of all (up to 10 postexposure days (PED) in one pig) and from a blood sample from one pig on PED 1 and 3. Virus was not isolated from urine, tissues, or explants of organs from pigs euthanatized PED 20 to 67, and disease was not evident. Of 11 pigs exposed within 2 hours of birth (before consuming colostrum), virus was shed for longer periods (for 10 and 11 days in four pigs) and severe respiratory tract pathologic changes developed. However, there was no evidence of chronic or latent infections. There was evidence of transplacental transmission of virus in one of ten pigs born to pregnant gilts that were exposed 10, 24, and 39 days before parturition, respectively.