Probe size and fixation time for detecting Porcine circovirus–2 (PCV–2) by in situ hybridization in formalin-fixed, paraffin-embedded lymph nodes from experimentally infected pigs were optimized. In situ hybridization using a 169–base pair (bp) probe detected significantly fewer PCV–2–positive cells than when using 8 other larger probes ( P < 0.05). The difference in hybridization intensity between smaller probes (169 and 225 bp) and larger probes (416, 473, 571, 631, 693, and 753 bp) was statistically significant ( P < 0.05). The PCV–2–positive cells were consistently detected in lymph nodes fixed up to 3 days; thereafter, the number of positive cells declined. The PCV–2–positive cells were detected in lymph nodes fixed for up to 730 days. The difference in hybridization intensity between samples fixed for a short term (1 or 3 days) and a longer term (4–730 days) was statistically significant ( P < 0.05). The data demonstrates that the optimal probe size and fixation time for detecting PCV–2 in formalin-fixed, paraffin-embedded lymph nodes is 473 bp and 1–3 days, respectively.
Comparative Study of In situ Hybridization and Immunohistochemistry for the Detection of Porcine Circovirus 2 in Formalin-Fixed, Paraffin-Embedded Tissues