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Comparison of Serum Pools and Oral Fluid Samples for Detection of Porcine Circovirus Type 2 by Quantitative Real-Time PCR in Finisher Pigs


Comparison of Serum Pools and Oral Fluid Samples for Detection of Porcine Circovirus Type 2 by Quantitative Real-Time PCR in Finisher Pigs

Gitte Blach Nielsen et al. Porcine Health Manag.


Background: Porcine circovirus type 2 (PCV2) diagnostics in live pigs often involves pooled serum and/or oral fluid samples for group-level determination of viral load by quantitative real-time polymerase chain reaction (qPCR). The purpose of the study was to compare the PCV2 viral load determined by qPCR of paired samples at the pen level of pools of sera (SP) from 4 to 5 pigs and the collective oral fluid (OF) from around 30 pigs corresponding to one rope put in the same pen. Pigs in pens of 2 finishing herds were sampled by cross-sectional (Herd 1) and cross-sectional with follow-up (Herd 2) study designs. In Herd 1, 50 sample pairs consisting of SP from 4 to 5 pigs and OF from around 23 pigs were collected. In Herd 2, 65 sample pairs consisting of 4 (SP) and around 30 (OF) pigs were collected 4 times at 3-week intervals.

Results: A higher proportion of PCV2-positive pens (86% vs. 80% and 100% vs. 91%) and higher viral loads (mean difference: 2.10 and 1.83 log(10) PCV2 copies per ml) were found in OF versus SP in both herds. The OF cut-off value corresponding to a positive SP (>3 log(10) PCV2 copies per ml) was estimated to 6.5 and 7.36 log(10) PCV2 copies per ml for Herds 1 and 2, respectively. Significant correlations between SP and OF results were found in Herd 1 (rho = 0.69) and the first sampling in Herd 2 (rho = 0.39), but not for the subsequent consecutive 3 samplings in Herd 2.

Conclusions: The proportion and viral loads of PCV2 positive pens were higher in collective OF (including up to 30 pigs) compared to SP (including 4-5 pigs) of the same pens. Also, OF seemed to detect the PCV2 infection earlier with OF values just below 6.5 (Herd 1) and 7.36 (Herd 2) log(10) being associated with a negative SP for the same pen. Nevertheless, a statistically significant correlation between SP and OF could not be found for all sampling time points, probably due to a high within-pen variation in individual pig viral load becoming very evident in SP of only four or five pigs. Consequently, the results imply that OF is well suited for detecting presence of PCV2 but less so for determining the specific viral load of pigs in a pen.

Keywords: Diagnostics; Finishers; Oral fluid; Pooling; Porcine circovirus type 2; Serum.

Conflict of interest statement

Permission to conduct the field trial in Herd 2 was received from the Danish Health and Medicines Authority (License no. 2014022507) and a written consent was obtained from the herd owner.Not applicable.At the time of submission of this article, John Haugegaard and the corresponding author are employed by MSD Animal Health, Denmark, the company partly sponsoring this work as mentioned above. However, the employment did not inflict any bias regarding the study and the work was conducted during the corresponding author’s enrolment as Industrial PhD student at the University of Copenhagen.Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.


Fig. 1
Fig. 1
ROC curves from Herd 1 (left) and first sampling in Herd 2 (right) to estimate the oral fluid cut-off for obtaining the best agreement with a PCV2-positive serum pool result for finishing pigs
Fig. 2
Fig. 2
Plots of serum pools and oral fluid sample pairs from finishing pigs for both herds and all samplings with serum pool viral loads on the x-axis and oral fluid viral loads on the y-axis
Fig. 3
Fig. 3
Evolution with time in Herd 2 of PCV2 viral loads in serum pools. Samplings were done at 3-week intervals and each line represents one pen
Fig. 4
Fig. 4
Evolution with time in Herd 2 of PCV2 viral loads in oral fluid. Samplings were done at 3-week intervals and each line represents one pen

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