Spread of porcine circovirus associated disease (PCVAD) in Ontario (Canada) swine herds: Part II. Matched case-control study

Abstract

BackgroundThe emergence of porcine circovirus associated disease (PCVAD) was associated with high mortality in swine populations worldwide. Studies performed in different regions identified spatial, temporal, and spatio-temporal trends as factors contributing to patterns of the disease spread. Patterns consistent with spatial trend and spatio-temporal clustering were already identified in this dataset. On the basis of these results, we have further investigated the nature of local spread in this report. The primary objective of this study was to evaluate risk factors for incidence cases of reported PCVAD.ResultsA time-matched case-control study was used as a study design approach, and conditional logistic regression as the analytical method. The main exposure of interest was local spread, which was defined as an unidentified mechanism of PCVAD spread between premises located within 3 kilometers of the Euclidean distance. Various modifications of variables indicative of local spread were also evaluated. The dataset contained 278 swine herds from Ontario originally sampled either from diagnostic laboratory submissions or directly from the target population. A PCVAD case was defined on the basis of the producer's recall. Existence of apparent local spread over the entire study period was confirmed (OR = 2.26, 95% CI: 1.06, 4.83), and was further identified to be time-varying in nature - herds experiencing outbreaks in the later part of the epidemic were more likely than control herds to be exposed to neighboring herds experiencing recent PCVAD outbreaks. More importantly, the pattern of local spread was driven by concurrent occurrence of PCVAD on premises under the same ownership (OREXACTwithin ownership = 25.6, 95% CI: 3.4, +inf; OREXACToutside ownership = 1.3, 95% CI: 0.45, 3.3). Other significant factors included PRRSv status of a herd (OREXACT = 1.9, 95% CI: 1.0, 3.9), after adjusting for geographical location by including the binary effect of the easting coordinate (Easting > 600 km = 1; OREXACT = 1.8, 95% CI: 0.5, 5.6).ConclusionsThese results preclude any conclusion regarding the existence of a mechanism of local spread through airborne transmission or indirectly through contaminated fomites or vectors, as simultaneous emergence of PCVAD could also be a result of concurrent change in contributing factors due to other mechanisms within ownerships.

Spread of porcine circovirus associated disease (PCVAD) in Ontario (Canada) swine herds: Part I. Exploratory spatial analysis

“…Herd demographics are addressed in more detail in an accompanying article [ 19 ]. Briefly, 239 herds were positive for porcine reproductive and respiratory (PRRS) virus by polymerase chain reaction (PCR) testing, and 39 were assessed as PRRS-negative by the herd veterinarian.…”

“…Recommendations based on these findings were modified once other factors were taken into account. The results and methodological approaches taken are reported in an accompanying article [ 19 ].…”

“…This is consistent with the findings of Madec et al [ 16 ], who argued that contact between pigs is the main route of transmission for PCVAD. In agreement with direct contact as a major contributor to PCVAD spread, ownerships as proxy measurements for network memberships were investigated in the accompanying article [ 19 ]. However, regardless of whether spread through networks occurred or not, it should be stressed that detailed investigation of production-disease epidemics in intensive production systems that prevail today in industrialized countries is challenging if appropriate movement and contact information is not readily available.…”

Reduction of Postweaning Multisystemic Wasting Syndrome-Associated Clinical Symptoms by Virus-Like Particle Vaccine Against Porcine Parvovirus and Porcine Circovirus Type 2

“…PMWS is a wasting disease caused by PCV2 infection. Since it was first reported in Canada in 1991, the disease has been found to be prevalent worldwide and has caused huge economic losses to the swine industry (30,31). Many experiments have confirmed that PPV enhances PCV2 infiltration and aggravates the clinical symptoms of PMWS.…”

Immune efficacy of a porcine circovirus type 2 vaccine purified using Gram‐positive enhancer matrix surface display technology

“…Porcine circovirus type 2 (PCV2), the primary causative agent of porcine circovirus‐associated disease, is one of the most economically important pathogens in swine worldwide (Poljak et al ; Grau‐Roma et al ; Kwon et al ). Vaccination is currently one of the most effective strategies for preventing PCV2 infection (Beach and Meng ; Karuppannan and Opriessnig ).…”