Duration of Infection and Proportion of Pigs Persistently Infected with Porcine Reproductive and Respiratory Syndrome Virus

Abstract

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.

Porcine Reproductive and Respiratory Syndrome Virus Subverts Repertoire Development by Proliferation of Germline-Encoded B Cells of All Isotypes Bearing Hydrophobic Heavy Chain CDR3

“…Thus, generalized polyclonal B cell activation characteristic of PRRS and LDV could generate autoantibodies to dsDNA, Golgi glycoproteins, and other autoantigens. The immune response to PRRSV is also characterized by a delay in responsiveness (45,46), a surprisingly weak inflammatory response in the lung (47,48), and the need for 150 days to clear the infection (4). This delay is believed to increase susceptibility to secondary infections that may also interfere with the effectiveness of vaccines (49 -51).…”

Lung inflammatory responses

“…Typically, infections are successfully resolved through the elimination of the causative organism. Examples of pathogens that induce chronic inflammation in the respiratory tract include Mycoplasma hyopneumoniae and porcine reproductive and respiratory syndrome virus (PRRSV) in pigs, respiratory syncytial virus (RSV) in cattle and the various mycobacterium species in most animals [46,107,142]. Allergic responses also tend to induce chronic inflammation in the respiratory tract and this will be discussed in a separate section below.…”

“…In contrast, infection with PRRSV, while systemic in nature and capable of inducing significant interstitial pneumonia, does not appear to produce significant levels of proinflammatory types of cytokines and inflammation [130]. The lack of significant inflammation associated with PRRSV may be one reason the virus persists in the host for long periods of time [131,142]. These examples demonstrate that in the swine, while a certain level of inflammation within the respiratory tract is necessary to clear the pathogen from the host, some pathogens can modulate the system to allow their survival in the host.…”

Antibody Repertoire Development in Fetal and Neonatal Piglets: XIX. Undiversified B Cells with Hydrophobic HCDR3s Preferentially Proliferate in the Porcine Reproductive and Respiratory Syndrome

“…By comparison swine influenza (SIV)-specific T cells are detected within 7 dpi (31). Although SIV induces a significant inflammatory response in the respiratory tract that appears related to viral clearance (32), no such inflammation is associated with PRRS (32,33). Despite a delay in virus-specific T cell responses, Ab responses to PRRSV of all major isotypes occur 6 -14 dpi in blood or BAL (34 -36).…”