Minimal residues of porcine reproductive and respiratory syndrome virus in pig carcases and boar semen.

Porcine reproductive and respiratory syndrome (PRRS) is a highly contagious disease that affects pigs of all ages worldwide. One of the key features of PRRS pathogenesis is the prolonged viremia in which the virus coexists with antibody. Prolonged viremia raises the concern that porcine products and boar semen may be contaminated by residues of the PRRS virus serving as vehicles for spreading of the virus. To answer this question, we sampled blood, muscles and viscera organs from market pigs slaughtered using an on-the-rail system and utilized a direct reverse transcription-polymerase chain reaction (RT-PCR) to detect residual viral RNA. We found that the overall seropositive rate of the market pigs was 85.4% (205/240), yet only 7.9% (11/140) of the blood samples contained detectable amounts of virus residues, and all tested carcase specimens (n = 472) were negative. The clinical sensitivity of this PCR varied with the tissues tested, with 5 TCID50 per 50 microliters of serum, as determined by means of a spiking experiment. Semen samples (n = 38) of clinically healthy seropositive and seronegative boars were collected from six herds which were routinely subjected to artificial insemination for production purposes. None of the seminal plasma or sperm-rich fractions contained PCR detectable virus residues. However, the possibility of PRRS virus present in semen cannot be totally excluded. We conclude that in naturally infected albeit clinically healthy pigs, the amounts of PRRS virus residues in carcases or semen are minimal. Thus, the risk of these products causing animal health hazards is low.