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A cross-sectional survey was designed to investigate the proportion of tetracycline residues in marketed pork in suburb and urban districts in Hanoi. A total of 290 raw muscle samples were randomly collected from open markets in these districts. The samples were qualitatively screened for tetracycline residues using the agar inhibition test, and Bacillus cereus (ATCC 11778) as the reference strain. The inconclusive samples were then analyzed using high-performance liquid chromatography (HPLC). The positive samples from either test were defined as positive results. Overall, 5.5% of all collected samples were positive for tetracycline residues. The proportion of positive samples from shops in suburb districts was significantly (P < 0.05) different from those collected from shops in urban districts. So, the factor of region was identified as a risk factor of tetracycline residue proportion in raw pork with an odds ratio (OR) of 4.03 (95% CI = 1.12, 14.45). For the other factors, such as season, type of shop, type of abattoir, origin of meat, etc., the difference in proportion of positive samples within each factor was substantial but not statistically significant. These factors were identified as nonrisk factors. Such a high proportion may pose a potential hazard to public health, particularly since they might induce drug resistance of pathogenic micro-organisms.

Abstract. This study evaluated the sensitivity of biotinyl-tyramide-based in situ hybridization (TISH) method by comparison with chromogenic in situ hybridization (CISH) and immunohistochemical staining (IHC) methods. This study also determined the effect of fixative and fixation time on the detection of Porcine reproductive and respiratory syndrome virus (PRRSV) in paraffin-embedded tissues. Lung samples were fixed in 4% paraformaldehyde (PFA) or 10% neutral buffered formalin (NBF) for various times before paraffin embedding. Of 30 paraffin-embedded lung samples, fixed for 1 day in 4% PFA or 10% NBF, 18 (60%) were positive for PRRSV by nested reverse transcription polymerase chain reaction (nRT-PCR). All 18 lung samples (100%) also were positive for PRRSV by TISH, but only 10 of these 18 specimens (56%) were positive for PRRSV by IHC and CISH. We demonstrated that TISH can detect PRRSV RNA in paraffin-embedded tissues after up to 90 days of fixation. PRRSV nucleic acids and antigens were better preserved in 4% PFA than in 10% NBF. Compared with CISH and IHC testing methods, TISH appeared to be more sensitive for the detection of PRRSV in paraffin-embedded tissues.