John A. Ellis

Effect of coinfection with genogroup 1 porcine torque teno virus on porcine circovirus type 2–associated postweaning multisystemic wasting syndrome in gnotobiotic pigs

OBJECTIVE To determine whether genogroup 1 porcine torque teno virus (g1-TTV) can potentiate clinical disease associated with porcine circovirus type 2 (PCV2). SAMPLE POPULATION 33 gnotobiotic baby pigs. PROCEDURES Pigs were allocated into 7 groups: group A, 5 uninoculated control pigs from 3 litters; group B, 4 pigs oronasally inoculated with PCV2 alone; group C, 4 pigs inoculated IP with first-passage g1-TTV alone; group D, 4 pigs inoculated IP with fourth-passage g1-TTV alone; group E, 6 pigs inoculated IP with first-passage g1-TTV and then oronasally inoculated with PCV2 7 days later; group F, 6 pigs inoculated IP with fourth-passage g1-TTV and then inoculated oronasally with PCV2 7 days later; and group G, 4 pigs inoculated oro-nasally with PCV2 and then inoculated IP with fourth-passage g1-TTV 7 days later. RESULTS 6 of 12 pigs inoculated with g1-TTV prior to PCV2 developed acute onset of postweaning multisystemic wasting syndrome (PMWS). None of the pigs inoculated with g1-TTV alone or PCV2 alone or that were challenge exposed to g1-TTV after establishment of infection with PCV2 developed clinical illness. Uninoculated control pigs remained healthy. CONCLUSIONS AND CLINICAL RELEVANCE These data implicated g1-TTV as another viral infection that facilitates PCV2-induced PMWS. This raises the possibility that torque teno viruses in swine may contribute to disease expression currently associated with only a single infectious agent.

Bovine respiratory syncytial virus.

Since the first report of BRSV in the 1970s, the understanding of this agent and its respective disease has increased dramatically. Current evidence supports a major role for this virus in bovine respiratory disease. Advances in diagnostics have increased the ability to demonstrate this virus in field outbreaks of respiratory disease. The clinical signs and pathologic features have been well described, and vaccines are available to aid in prevention and control. Still, many questions remain to be answered with respect to BRSV. It appears there may be antigenic subgroups of BRSV, but the epidemiologic significance and relevance to immunization of this remains unknown. The question of differences in virulence among isolates of this virus has yet to be addressed. From an epidemiologic standpoint, the means by which BRSV perpetuates in the cattle population has yet to be elucidated. Although progress has been made in understanding the pathogenesis and immune response to BRSV, the mechanism of disease production and immune protection is incomplete. Lastly, efficacy testing of existing vaccines need to continue, as well as the development of new vaccines and new approaches to vaccination.The current knowledge is reviewed in regards to the importance of bovine respiratory syncytial virus in the bovine respiratory disease complex. The epidemiology, clinical disease, pathologic findings, pathogenesis, diagnosis, treatment, and prevention of this viral disease are discussed.

Evaluation of induction of porcine dermatitis and nephropathy syndrome in gnotobiotic pigs with negative results for porcine circovirus type 2

OBJECTIVE To determine whether porcine dermatitis and nephropathy syndrome (PDNS) could be experimentally induced in gnotobiotic swine. SAMPLE POPULATION Plasma samples from 27 sows and 20 conventional weaned piglets were obtained, and 30 gnotobiotic pigs were used in experiments. PROCEDURES 3 experiments were conducted. Groups of 3-day-old gnotobiotic pigs were inoculated with pooled plasma samples obtained from healthy feeder pigs in a herd that was in the initial phases of an outbreak of respiratory disease; gross and histologic lesions of PDNS were detected in the inoculated pigs. In a second experiment, 2- and 3-day-old gnotobiotic pigs were inoculated with porcine reproductive respiratory syndrome virus (PRRSV) and with PRRSV-negative tissue homogenate containing genogroup 1 torque teno virus (g1-TTV). Lesions of PDNS were detected. RESULTS Pigs inoculated with pooled plasma or the combination of tissue-culture-origin PRRSV and g1-TTV tissue homogenate developed systemic hemostatic defects, bilaterally symmetric cutaneous hemorrhages, generalized edema, icterus, bilaterally symmetric renal cortical hemorrhage, dermal vasculitis with hemorrhage, and interstitial pneumonia consistent with a clinical and pathologic diagnosis of PDNS. The PRRSV RNAs and g1-TTV DNAs were detected in plasma; all pigs seroconverted to PRRSV, and all had negative results for porcine circovirus type 2 when tested by use of PCR assays. CONCLUSIONS AND CLINICAL RELEVANCE These data suggested that PDNS is a manifestation of disseminated intravascular coagulation in swine. For the experimental conditions reported here, combined infection with g1-TTV and PRRSV was implicated in the genesis of these lesions.

Evaluation of the effects of porcine genogroup 1 torque teno virus in gnotobiotic swine.

OBJECTIVE To determine whether porcine genogroup 1 torque teno virus (g1-TTV) can infect and cause disease in gnotobiotic swine. SAMPLE POPULATION 20 conventional baby pigs and 46 gnotobiotic baby pigs. PROCEDURES Porcine g1-TTV was transmitted from conventional swine to gnotobiotic pigs via pooled leukocyte-rich plasmas (n=18) that had positive results for g1-TTV DNA. Bone marrow-liver homogenates that had positive results for torque teno virus (TTV) were used in 4 serial passages in gnotobiotic pigs (2 pigs/passage). A pathogenesis experiment was conducted with in vivo passages of g1-TTV in various groups of gnotobiotic pigs. RESULTS All g1-TTV inoculated pigs had no clinical signs but developed interstitial pneumonia, transient thymic atrophy, membranous glomerulonephropathy, and modest lymphocytic to histiocytic infiltrates in the liver after inoculation with the TTV-containing tissue homogenate; these changes were not detected in uninoculated control pigs or pigs injected with tissue homogenate devoid of TTV DNAs. In situ hybridization was used to identify g1-TTV DNAs in bone marrow mononuclear cells. CONCLUSIONS AND CLINICAL RELEVANCE Analysis of these data revealed that porcine g1-TTV was readily transmitted to TTV-naïve swine and that infection was associated with characteristic pathologic changes in gnotobiotic pigs inoculated with g1-TTV. Thus, g1-TTV could be an unrecognized pathogenic viral infectious agent of swine. This indicated a directly associated induction of lesions attributable to TTV infection in swine for a virus of the genus Anellovirus.

Development and validation of a SYBR green real-time PCR for the quantification of porcine circovirus type 2 in serum, buffy coat, feces, and multiple tissues.

The emergence of multiple genotypes of PCV2, as demonstrated by phylogenetic analysis of whole genome or capsid sequences, makes it necessary to have quantitative diagnostic assays that perform equally well on all strains. The objectives of this study were to develop and validate a novel real-time polymerase chain reaction (PCR) assay targeting the highly conserved rep gene (ORF1) and investigate the effects of diagnostic specimen choice on its performance. The assay was tested in naturally infected conventional pigs, experimentally infected gnotobiotic pigs, and plasmid-spiked negative serum, lung tissue, and feces and found to have a linear detection range of 2.2x10(3) to 2.2x10(10) copies of PCV2 per mL. The assay successfully detected and quantified PCV2 DNA in serum, buffy coat, feces, and multiple lymphoid (bronchial, mesenteric, and superficial inguinal lymph nodes; thymus; tonsil; ileal Peyers patches; and spleen), and non-lymphoid (myocardium; lung; kidney; liver; and gluteal muscle) tissues from naturally infected pigs. Across all tissues and sera of naturally infected pigs, the mean PCV2 concentration was 3.0logs higher in wasting versus non-wasting pigs. PCV2 concentration measured by tissue culture and immunohistochemical staining in homogenized liver samples of experimentally infected gnotobiotic pigs were compared to the concentrations estimated by quantitative PCR. Similar trends were noted with increasing PCV2 concentration detected in subclinically infected to severely PMWS-affected pigs across all assays. Our diagnostic assay was developed with a conserved target sequence, and performed efficiently in quantification of PCV2 in a variety of tissues from naturally and experimentally infected pigs.

In utero transmission of porcine torque teno viruses

Sera and selected tissue homogenates collected from gnotobiotic swine never exposed to the environment or other swine tissues were tested for the presence of porcine torque teno virus (TTV) DNAs by nested and non-nested polymerase chain reactions (PCR) using primers specific for the untranslated region of porcine genogroups (g) 1 and 2. Twenty-three of 105 (21.9%) gnotobiotic piglets were g1- and/or g2-TTV DNA positive. Twenty-three of 27 (85.2%) sow sera, collected at the time of Caesarian derivation of the litters contained either or both TTV genogroup DNAs. These data demonstrate that porcine TTV may be transmitted to piglets by the in utero route and that the incidence of fetal infection is high.

Update on viral pathogenesis in BRD.

Abstract Many viruses, including bovine herpesvirus-1 (BHV-1), bovine respiratory syncytial virus (BRSV), parainfluenzavirus-3 (PI3), bovine coronavirus, bovine viral diarrhea virus and bovine reovirus, have been etiologically associated with respiratory disease in cattle. This review focuses on the pathogenesis of BHV-1 and BRSV, two very different agents that primarily cause disease in the upper and lower respiratory tract, respectively.

Temporal Distribution of Porcine Circovirus 2 Genogroups Recovered from Postweaning Multisystemic Wasting Syndrome-Affected and -Nonaffected Farms in Ireland and Northern Ireland

Porcine circovirus type 2 (PCV2) is now recognized as the essential infectious component of porcine postweaning multisystemic wasting syndrome (PMWS). PMWS was first recognized in high-status, specific pathogen-free pigs in Canada in 1991 and is now an economically important disease that affects the swine industry around the world. Recently, reports of genomic studies on PCV2 viruses indicated that 2 distinctive genogroups of PCV2 exist. 4,10 This report involves the results of a study on the distribution of predominant PCV2 genogroups recovered from samples taken from PMWS-affected and PMWS-nonaffected farms on the island of Ireland over a 9-year period and the results of a study on PCV2 genogroup recovery from fecal samples taken from a farm in Northern Ireland from 2003 to 2005 that was first diagnosed as PMWS positive in August 2005. The results indicate that, although at least 2 distinct genogroups of PCV2 have been circulating on pig farms on the island of Ireland, there does not appear to be a direct relationship between infection with these different genogroups of PCV2 and the development of PMWS.

Dual heterologous porcine circovirus genogroup 2a/2b infection induces severe disease in germ-free pigs.

Our primary objectives were to determine: the relative virulence of porcine circovirus (PCV) 2a and PCV2b, if heterologous infection induces severe illness, and the relative concentration of PCV2a and PCV2b in tissues of heterologously infected pigs. In experiment 1, 18 germ-free piglets served as controls or were infected with PCV2a or PCV2b. Half were immune stimulated with keyhole limpet hemocyanin (KLH) emulsified in incomplete Freunds adjuvant (2aKLH, 2bKLH). No piglets demonstrated severe illness. Lesion severity did not differ, but PCV2 capsid staining was more intense in 2a- than 2b-infected pigs (P<.05). In experiment 2, 20 germ-free piglets were dual inoculated 7 days apart with PCV2a and PCV2b (2a2b, 2b2a), PCV2b twice (2b2b), or PCV2a (2a2a) twice. Five of 9 heterologous-infected pigs developed severe illness. All heterologously infected pigs demonstrated ascites or edema, and 8/9 developed thymic atrophy. By contrast, 1 of 5 2b2b-infected pigs developed bronchopneumonia and pleural effusion. No 2a2a-infected pig developed illness. Gross lesions were more severe in heterologously infected pigs than in 2b2b pigs (P<.05), and were more severe in 2b2b than 2a2a pigs (P<.05). PCV2 capsid staining intensity did not differ by group. In heterologously infected pigs, higher levels of PCV2 DNA reflective of the first inoculum compared to the second were found in mesenteric lymph node (P=.04), spleen (P=.004) and liver (P=.04). These results indicate that dual heterologous PCV2a/2b inoculation 7 days apart may induce severe clinical illness, but PCV2a and PCV2b when administered singularly or in combination with KLH appear to be of equivalent virulence.

Bovine parainfluenza-3 virus.

Bovine parainfluenza-3 virus (bPI(3)V) is a long-recognized, currently underappreciated, endemic infection in cattle populations. Clinical disease is most common in calves with poor passive transfer or decayed maternal antibodies. It is usually mild, consisting of fever, nasal discharge, and dry cough. Caused at least partly by local immunosuppressive effects, bPI(3)V infection is often complicated by coinfection with other respiratory viruses and bacteria, and is therefore an important component of enzootic pneumonia in calves and bovine respiratory disease complex in feedlot cattle. Active infection can be diagnosed by virus isolation from nasal swabs, or IF testing on smears made from nasal swabs. Timing of sampling is critical in obtaining definitive diagnostic test results. Parenteral and intranasal modified live vaccine combination vaccines are available. Priming early in calfhood with intranasal vaccine, followed by boosting with parenteral vaccine, may be the best immunoprophylactic approach.