Using diagnostic data from veterinary diagnostic laboratories to unravel macroepidemiological aspects of porcine circoviruses type 2 and 3 in the United States

Abstract

Porcine circoviruses (PCVs), including PCV2 and PCV3, have been associated with clinical disease syndromes in swine, resulting in significant economic losses for producers. To better understand the epidemiology and clinical relevance of PCV2 and PCV3, this study analyzed a vast dataset comprising diagnostic data from six Veterinary Diagnostic Laboratories (VDLs) in the United States. The data comprised PCR test results, sample type, and age group for PCV2 submissions from 2002 to 2023 and PCV3 submissions from 2017 to 2023. Confirmed tissue diagnostic data from 2019-2023 from ISU-VDL was used to correlate PCR Ct values with the probability of receiving a PCV2 or PCV3 diagnostic confirmation. The probability of PCV2 and PCV3 diagnoses based on Ct ranges was assessed based on the model's performance in terms of detecting true positive and negative cases. The analysis considered only cases tested for PCV2 and PCV3 by PCR with tissue evaluations by diagnosticians. Findings indicated a decrease in PCV2 positivity after the introduction of a commercial PCV2 vaccine in 2006 and a resurgence in positivity after 2018, particularly in breeding herds associated with an increased number of cases using processing fluid samples. PCV3 detection, first reported in the U.S. in 2016, had an upward trend, peaking in the spring of 2023. PCV3 detection was more frequent in adult/sow farms, while PCV2 was more frequently detected in the wean-to-market category. Optimal cycle threshold (Ct) value of 22.3 for PCV2 demonstrated a high probability of disease PCV2 diagnostic. However, due to limited clinical information on PCV3, establishing a reliable Ct value for PCV3 proved challenging, indicating the need for further research. The findings contribute to ongoing efforts to monitor and understand the clinical relevance of PCV2 and PCV3 PCR results, aiding producers and veterinarians in identifying potential disease challenges in swine farms.