Pathogenicity and transmissibility of North American triple reassortant swine influenza A viruses in ferrets.

North American triple reassortant swine (TRS) influenza A viruses have caused sporadic human infections since 2005, but human-to-human transmission has not been documented. These viruses have six gene segments (PB2, PB1, PA, HA, NP, and NS) closely related to those of the 2009 H1N1 pandemic viruses. Therefore, understanding of these viruses' pathogenicity and transmissibility may help to identify determinants of virulence of the 2009 H1N1 pandemic viruses and to elucidate potential human health threats posed by the TRS viruses. Here we evaluated in a ferret model the pathogenicity and transmissibility of three groups of North American TRS viruses containing swine-like and/or human-like HA and NA gene segments. The study was designed only to detect informative and significant patterns in the transmissibility and pathogenicity of these three groups of viruses. We observed that irrespective of their HA and NA lineages, the TRS viruses were moderately pathogenic in ferrets and grew efficiently in both the upper and lower respiratory tracts. All North American TRS viruses studied were transmitted between ferrets via direct contact. However, their transmissibility by respiratory droplets was related to their HA and NA lineages: TRS viruses with human-like HA and NA were transmitted most efficiently, those with swine-like HA and NA were transmitted minimally or not transmitted, and those with swine-like HA and human-like NA (N2) showed intermediate transmissibility. We conclude that the lineages of HA and NA may play a crucial role in the respiratory droplet transmissibility of these viruses. These findings have important implications for pandemic planning and warrant confirmation.

Pathogen exposure in feral swine populations geographically associated with high densities of transitional swine premises and commercial swine production.

Surveys for evidence of exposure to pseudorabies virus (PRV), Brucella suis, swine influenza virus (SIV; human-like H1N1, reassortant type H1N1, H1N2-like H1N1 and H3N2), porcine circovirus 2 (PCV 2), and porcine respiratory and reproductive syndrome virus (PRRSV) in feral swine (Sus scrofa) were conducted in areas where feral swine were geographically associated with high densities of transitional swine premises in South Carolina and high densities of commercial swine production in North Carolina. In South Carolina, 10/50 (20.0%), 7/50 (14.0%), and 29/49 (59.2%) feral swine tested antibody positive for PRV, B. suis, and PCV-2, respectively. Antibodies to PRRSV (0/49) and SIV (0/49) were not detected. In North Carolina, antibodies to PRV and B. suis were not detected in serum samples from 120 feral swine; however, antibodies to PRRSV (1/120 [0.8%]), PCV-2 (86/120 [71.7%]; these included 80 positives plus six suspects), and SIV (108/119 [90.7%]) were present. The presence of PRV and B. suis in South Carolina may have been due to the introduction of infected feral swine into the area or to a previous association of feral swine with infected transitional swine. Their absence in the North Carolina populations may have been due to the absence of these disease agents in the feral swine originally introduced into the area and the lack of a potential for contact with infected commercial swine. Feral swine associated with commercial swine in North Carolina may have been exposed to SIV subtypes circulating in commercial swine via airborne spread of SIV from commercial swine facilities. Feral swine seropositive for PCV-2 were prevalent in both states, which may indicate efficient transmission from commercial swine and transitional swine, or that PCV-2 is widespread in feral swine. The low prevalence of animals with antibodies against PRRSV may indicate a less-than-efficient means of transmission from commercial to feral swine. Additional epidemiologic studies are needed to understand the risks and mechanisms of transmission of disease agents among commercial, transitional, and feral swine, and the role of feral swine as reservoirs of these disease agents.

Interlaboratory comparison of Porcine circovirus-2 indirect immunofluorescent antibody test and enzyme-linked immunosorbent assay results on experimentally infected pigs.

A blinded interlaboratory assessment of the diagnostic agreement and accuracy of serologic tests for routine detection of antibodies against Porcine circovirus-2 (PCV-2), including indirect fluorescent antibody tests (IFATs) and enzyme-linked immunosorbent assays (ELISAs) was conducted in 7 North American laboratories. Serum samples were collected weekly, on trial days 0, 7, 14, 21, 28, 35, 42, and 49, from the following groups of animals: 1) negative controls (n  =  7), 2) PCV-2a (n  =  8), 3) PCV-2b (n  =  8), 4) PCV-1 (n  =  8), 5) PCV-2 vaccine A (n  =  8; Ingelvac® CircoFLEX™), 6) PCV-2 vaccine B (n  =  8; Circumvent® PCV2), and 7) PCV-2 vaccine C (n  =  8; Suvaxyn® PCV2 One Dose). Results from each laboratory were analyzed by kappa and receiver operating characteristic (ROC) analysis. Kappa analysis indicated that, by trial day 49, IFATs had almost perfect agreement, in-house ELISAs had fair to almost perfect agreement, and commercially available anti-PCV-2 immunoglobulin G ELISAs (I or S) had moderate to substantial agreement. From trial days 14-49, the area under the ROC curve for the 2 laboratories that offered IFATs, the 4 laboratories that offered in-house ELISAs, and the 3 laboratories that used commercially available ELISAs ranged from 0.94 to 1.00, 0.72 to 1.00, and 0.95 to 1.00, respectively. However, test sensitivities varied based on laboratory-specific cutoffs that were used to dichotomize test results.