A novel approach to intrauterine viral inoculation of swine using PCV type 2 as a model.

Experimentally intrauterine (IU) viral inoculation has been commonly used to circumvent maternal interference with transplacental infection of fetuses and to assess the effect of viral infection on fetal development or reproductive parameters. However, IU inoculation requires surgical procedures such as laparatomy and surgical incision of the uterus. Post-surgical complications, that frequently result in abortion or fetal death, have been a major disadvantage. An animal trial was conducted to evaluate the non-surgical procedure of ultrasound needle-guided transabdominal injection for IU inoculation of porcine circovirus type 2 (PCV2) since this virus has been reported to cause reproductive failure in pigs. Two groups of seven pregnant sows at mid- and late-gestation, respectively, were inoculated with PCV2 using an ultrasound needle-guided technique that delivered PCV2 directly into one of the fluid-filled fetal compartments. The effect of transabdominal in utero virus challenge on fetuses and sows was assessed until term. While five of six sham-inoculated control sows had no or minimal adverse affects from in utero injection, 10 of 14 virus-inoculated sows had dead and/or stillborn piglets and PCV2 infection was evident by polymerase chain reaction and/or immunohistochemistry. These results supported previous field and experimental observations that PCV2 may cause reproductive failure. In conclusion, ultrasound needle-guided transabdominal injection was a safe and efficient method for IU inoculation of virus in pigs.

Evaluation of the reverse transcription-polymerase chain reaction/probe test of serum samples and immunohistochemistry of skin sections for detection of acute bovine viral diarrhea infections.

Bovine viral diarrhea viruses (BVDV) cause both acute and persistent infections. While diagnostic tests have been designed to detect animals persistently infected (PI) with BVDV, the reliability of these tests in detecting acute BVDV infections is not known. It is also possible that acute BVDV infections may be confused with persistent infections in surveys for PI animals. In this study, 2 tests presently in use in diagnostic laboratories to test for PI animals, polymerase chain reaction amplification followed by probe hybridization (RT-PCR/probe) of serum samples and immunohistochemical detection of viral antigen in skin biopsies (IHC), were evaluated for their ability to detect acute BVDV infections. Sixteen colostrum-deprived, BVDV-free, and BVDV-antibody-free calves were infected with 6 different BVDV strains. Clinical signs, seroconversion, and virus isolation indicated that inoculated animals did replicate virus. Virus could be detected in 19% (3/16) of acutely infected animals by the RT-PCR/probe technique. No acutely infected animals were positive by IHC.