Revisiting Porcine Circovirus Disease Diagnostic Criteria in the Current Porcine Circovirus 2 Epidemiological Context

Abstract

Current knowledge on porcine circovirus diseases (PCVD) caused by Porcine circovirus 2 (PCV-2) includes the subclinical infection (PCV-2-SI), systemic (PCV-2-SD) and reproductive (PCV-2-RD) diseases, and porcine dermatitis and nephropathy syndrome (PDNS). Criteria to establish the diagnosis of these conditions have not changed over the years; thus, the triad composed by clinical signs, lesions and viral detection in lesions are still the hallmark for PCV-2-SD and PCV-2-RD. In contrast, PCV-2-SI diagnosis is not usually performed since this condition is perceived to be controlled by default through vaccination. PDNS is diagnosed by gross and histopathological findings, and PCV-2 detection is not recognized as a diagnostic criterion. Molecular biology methods as a proxy for PCVD diagnoses have been extensively used in the last decade, although these techniques should be mainly considered as monitoring tools rather than diagnostic ones. What has changed over the years is the epidemiological picture of PCV-2 through the massive use of vaccination, which allowed the decrease in infectious pressure paralleled with a decrease in overall herd immunity. Consequently, the need for establishing the diagnosis of PCVD has increased lately, especially in cases with a PCV-2-SD-like condition despite vaccination. Therefore, the objective of the present review is to update the current knowledge on diagnostic criteria for PCVDs and to contextualize the interest of using molecular biology methods in the overall picture of these diseases within variable epidemiological scenarios of PCV-2 infection.

Keywords: Porcine circovirus 2 (PCV-2); clinical signs; diagnosis; epidemiology; pathology; porcine circovirus disease; vaccination.

Figure 1

Effects of PCV-2 vaccination on the epidemiology of this viral infection. (A) Pre-vaccination scenario: farms infected with PCV-2 with corresponding triggering factors experienced PCV-2-SD in a proportion of pigs. (B) Initial vaccination scenario: PCV-2-SD is efficiently controlled by means of systematic vaccination of piglets. (C) Continuous vaccination scenario: Slow generation of subpopulations of naïve gilts/sows, promoting sows and offspring with relatively low immunity levels due to the lack of challenge with PCV-2. Altogether this would increase the risk of intrauterine and early piglet infections and eventual PCV-2-SD despite vaccination.