A putative PCV3-associated disease in piglets from Southern Brazil

Abstract

Porcine circovirus type 3 (PCV3) is widely distributed worldwide, and its association with clinical disease in pigs has been studied in recent years. This study describes a novel PCV3-associated clinical disease in piglets from Brazil. Since September 2020, we received 48 piglets with large caudally rotated ears, weakness, and dyspnea. Most piglets were from gilts and died 1-5 days after birth. Two piglets that presented similar clinical signs and survived until 35-60 days had a marked decrease in growth rate. At post-mortem examination, the lungs did not collapse due to marked interlobular edema. Microscopically, the main feature was multisystemic vasculitis characterized by lymphocytes and plasma cells infiltrating and disrupting the wall of vessels, lymphohistiocytic interstitial pneumonia, myocarditis, and encephalitis. Viral replication was confirmed in these lesions through in situ hybridization (ISH-RNA). Seventeen cases were positive for PCV3 in PCR analysis, and all samples tested negative for porcine circovirus (PCV1, and PCV2); porcine parvovirus (PPV1, 2, 5, and 6); atypical porcine pestivirus (APPV); porcine reproductive and respiratory syndrome (PRRSV); and ovine herpesvirus-2 (OvHV-2). Phylogenetic analysis of the ORF2 sequence from five different pig farms showed that the PCV3a clade is circulating among Brazil's swineherds and causing neonatal piglet losses. This is the first report of PCV3a-associated disease in neonatal pigs from farms in Brazil.

Keywords: Diagnosis; Diseases of swine; Dyspnea; Infectious diseases; PCV3; Vasculitis.

Fig. 1

a One-day-old piglets presenting large caudally rotated ears and piglets with normal size and correctly inserted ears. b Thirty-five-day-old piglet presenting large caudally rotated ears, and had a marked decrease in growth rate

Fig. 2

a Non-collapsed lungs, with a shiny red appearance, due to interlobular edema. b The vessel walls of the mesenteric plexus are disrupted by marked infiltration of lymphocytes and plasma cells, besides fibrinoid degeneration, HE, Bar. 120 µm. c Lung with alveolar septa diffusely distended by lymphocytes and macrophages (interstitial pneumonia), HE, Bar. 200 µm. d Lungs with multifocal staining representing PCV3 mRNA, inflammatory cells mainly in perivascular areas. ISH, Bar. 200 µm. e Multifocal areas of mild lymphocytic myocarditis, HE, Bar. 120 µm. f Cardiomyocytes with multifocal staining representing PCV3 mRNA, inflammatory cells mainly in perivascular areas. ISH, Bar. 200 µm

Fig. 3

Phylogenetic tree analysis of PCV3 720 pb of Capsid gene (ORF2). The maximum likelihood tree was constructed with the Tamura–Nei model with Gamma plus I distribution (1000 replicates). Sequences obtained in the present study are marked (highlighted) and clustered into PCV3a clade. GenBank accession number: PCV3/BR/RS_02/21, MW820301; PCV3/BR/RS_854/20, MW820305; PCV3/BR/RS_17/21, MW820302; PCV3/BR/RS_623/20, MW820304; and PCV3/BR/RS_596/20, MW820303