A Retrospective Analysis of Porcine Circovirus Type 3 in Samples Collected from 2008 to 2021 in Mexico

Abstract

Porcine circovirus type 3 (PCV3) is a nonenveloped virus of the Circoviridae family. This virus has been identified in pigs of different ages and pigs with several clinical manifestations of the disease or even in apparently healthy pigs. While PCV3 was first reported in 2015, several retrospective studies have reported the virus before that year. The earliest report indicates that PCV3 has been circulated in swine farms since 1996. In this study, we evaluated the presence of PCV3 in samples collected in Mexico in 2008, 2015, 2020, and 2021. This study assessed PCV3 DNA by qPCR and antibodies against CAP protein by indirect ELISA. The results showed that PCV3 (DNA and anti-CAP antibodies) was detected in the samples collected from 2008 to 2021. The highest prevalence was in 2008 (100%), and the lowest was in 2015 (negative). Genetic analysis of ORF2 showed that the virus identified belonged to genotype a, as most of the viruses identified thus far. PCV3 was detected in samples from piglets with respiratory signs and growth retardation, sows with reproductive failure, or asymptomatic piglets and sows. Pigs with respiratory signs, growth retardation, or reproductive failure had a higher prevalence of antibodies and qPCR-positive samples. In conclusion, this study showed that PCV3 has been circulating in Mexico since 2008 and that PCV3 DNA and antibodies were more prevalent in samples from pigs with clinical manifestations of diseases.

Keywords: ELISA; growth retardation; porcine circovirus 3 (PCV3); real-time PCR; reproductive failure.

Figure 1

The phylogenetic tree using ORF2. The tree was obtained using multiple sequence alignment, and sequence comparisons were made in DNAstar Lasergene software version 17.3 and by the Randomized Accelerated Maximum Likelihood (RAxML) 1000 repetitions. Interactive Tree of Life (iTOL) was used for tree visualization. The scale bar indicates nucleotide substitutions per site. The sequences obtained in this study are highlighted in bold.

Figure 2

Standardization of an indirect ELISA to detect IgG antibodies against PCV3. PCV3-positive samples were used as a positive control. Negative samples consisted of serum from colostrum-deprived (CD) piglets. The ROC curve (a) was constructed and used to set the cutoff at 0.4170 (b).

Figure 3

Prevalence of PCV3 antibodies. PCV3 IgG antibodies were evaluated in all the samples ((a), n = 443 samples) or in the same samples, but according to the year of sampling ((b), 2008 n = 125; 2015 n = 58; 2020 n = 27; 2022 n = 233). Significant differences between PCV3 IgG antibodies between years were analyzed by the Kruskal—Wallis test and multiple comparisons with Dunn’s test.

Figure 4

Distribution of PCV3 IgG antibody levels according to health status. Samples were grouped according to the clinical history of the animals (growth retardation or reproductive failure, or asymptomatic) and divided into samples from sows (a) or piglets (b). Significant differences between PCV3 IgG antibodies between years were analyzed with the Mann—Whitney test.