Variation in time and magnitude of immune response and viremia in experimental challenges with Porcine circovirus 2b.

BACKGROUND: Porcine circovirus 2 is the primary agent responsible for inducing a group of associated diseases known as Porcine Circovirus Associated Diseases (PCVAD), which can have detrimental effects on production efficiency as well as causing significant mortality. The objective of this study was to evaluate variation in viral replication, immune response and growth across pigs (n = 974) from different crossbred lines. The approach used in this study was experimental infection with a PCV2b strain of pigs at an average of 43 days of age. RESULTS: The sequence of the PCV2b isolate used in the challenge was similar with a cluster of PCV2b isolates known to induce PCVAD and increased mortality rates. The swine leukocyte antigen class II (SLAII) profile of the population was diverse, with nine DQB1 haplotypes being present. Individual viremia and antibody profiles during challenge demonstrate variation in magnitude and time of viral surge and immune response. The correlations between PCV2 specific antibodies and average daily gain (ADG) were relatively low and varied between - 0.14 to 0.08 for IgM and -0.02 and 0.11 for IgG. In contrast, PCV2 viremia was an important driver of ADG decline following infection; a moderate negative correlation was observed between viral load and overall ADG (r = - 0.35, P < 0.001). The pigs with the lowest 10% level of viral load maintained a steady increase in weekly ADG (P < 0.0001) compared to the pigs that had the 10% greatest viral load (P < 0.55). In addition, the highly viremic group expressed higher IgM and IgG starting with d 14 and d 21 respectively, and higher tumor necrosis factor - alpha (TNF-α) at d 21 (P < 0.005), compared to low viremic group. CONCLUSIONS: Molecular sources of the observed differences in viremia and immune response could provide a better understanding of the host factors that influence the development of PCVAD and lead to improved knowledge of swine immunity.

Herpesvirus infections in rock hyraxes (Procavia capensis).

Seven juveniles and 3 adults from a closed group of 19 rock hyraxes (Procavia capensis) housed in a zoo's indoor rock exhibit died or were euthanized after developing blepharoconjunctivitis and orofacial ulcers over a 2-week period. Histopathologic examination of dermal ulcers and ulcerated tongues revealed amphophilic to basophilic intranuclear inclusion bodies in epithelial cells bordering ulcers. Epithelial cells with inclusion bodies were often characterized by cytomegaly and karyomegaly, and many cells had formed syncytia. Examination of inclusion bodies in tongue epithelium by transmission electron microscopy revealed icosahedral nucleocapsids, approximately 80-95 nm in diameter, with morphologic features consistent with herpesvirus. Cytopathic effect (CPE) typical of alphaherpesvirus infection was seen in bovine turbinate, equine dermal, and Vero cell monolayers after inoculation with homogenates of the skin lesions, but CPE was not seen after inoculation onto Madin-Darby canine kidney or swine testicle cell monolayers. Polymerase chain reaction analysis using degenerate primers that targeted a portion of the herpesvirus polymerase gene generated a product of approximately 227 base pairs. The product was cloned, sequenced, and then analyzed using BLAST. At the nucleotide level, there was 86%, 77%, and 76% shared identity with Eidolon herpesvirus 1, Human herpesviruses 1 and 2, and Cercopithecine herpesvirus 2, respectively. Herpesvirus infections in rock hyraxes have not been characterized. The data presented in the current study suggest that a novel alphaherpesvirus caused the lesions seen in these rock hyraxes. The molecular characteristics of this virus would tentatively support its inclusion in the genus Simplexvirus.

Duration of infection and proportion of pigs persistently infected with porcine reproductive and respiratory syndrome virus.

Understanding the dynamics of porcine reproductive and respiratory syndrome virus (PRRSV) persistence in individual pigs is essential to the development of successful control programs. The objectives of this study were to investigate the proportion of inoculated pigs that become persistently infected with PRRSV and the duration of their infection. Additionally, different diagnostic techniques that detect persistent infections were compared. Twenty-eight 35-day-old pigs were inoculated with PRRSV. Serum and tonsil biopsy samples were collected on days 0, 7, 14, and 28 and then approximately monthly thereafter until day 251 postinoculation (p.i.). Tonsil, lymph node, and lung samples were collected following euthanasia on day 251 p.i. Virus was isolated from serum and tonsil biopsy samples that had been collected through days 28 and 56 p.i., respectively. Viral RNA was detected by reverse transcription (RT)-PCR in serum and tonsil biopsy samples that had been collected through day 251 p.i., although no serum samples collected from days 84 to 196 p.i. were positive and the presence of infectious PRRSV was not detected by swine bioassay of tissue samples collected at necropsy. The results confirmed that RT-PCR is more sensitive than virus isolation in identifying PRRSV-infected pigs. Six pigs that were persistently infected through days 225 or 251 p.i. remained seropositive throughout the study, although one pig had an enzyme-linked immunosorbent assay sample-to-positive ratio that was only slightly above the cutoff value of 0.40. Twenty of 28 tonsil biopsy samples collected on day 84 p.i. were positive by RT-PCR compared to only 1 positive biopsy sample out of 28 collected on day 119 p.i. The study's results indicate that most pigs clear PRRSV within 3 to 4 months, but that some may remain persistently infected for several months.