Edward J. Dubovi

Viral cytopathogenicity correlated with integration of ubiquitin-coding sequences☆

Abstract The RNA genomes of cytopathogenic bovine viral diarrhea virus (BVDV) isolates contain insertions highly homologous to cellular sequences. For two of them the insert was identified as ubiquitin coding sequence. The genome of BVDV Osloss contains exactly one ubiquitin gene monomer. In the case of BVDV CP1 the cellular insertion comprises one complete ubiquitin gene and part of a second monomer. The host cell-derived element in the CP1 genome is embedded in a large duplication of about 2.4 kb of viral sequences. Cellular insertion and duplication were not found in the genome of NCP1, the noncytopathogenic counterpart of CP1. These results strongly suggest that recombination between viral and cellular RNA is responsible for development of the cytopathogenic viruses, which is linked to pathogenesis of a lethal disease in cattle.

Neutralizing monoclonal antibodies to bovine viral diarrhoea virus bind to the 56K to 58K glycoprotein.

A panel of murine monoclonal antibodies (MAbs) against the two major glycoproteins of bovine viral diarrhoea virus (BDV) was produced and assayed by serum neutralization, radioimmunoprecipitation (RIP) and immunoblotting. Based on their viral polypeptide specificity and on their ability to neutralize viral infectivity, the MAbs in the panel were divided into three classes: Class 1 MAbs reacted with the 56K to 58K glycoprotein and neutralized the virus, class 2 MAbs recognized the 56K to 58K glycoprotein but were not neutralizing, and class 3 MAbs reacted with the 48K glycoprotein and did not neutralize the virus. These results identify the 56K to 58K protein as one of the envelope glycoproteins of BDV. Evidence was obtained indicating that it is responsible for the induction of neutralizing antibodies. No large uncleaved precursors of the 56K to 58K protein could be identified unequivocally by RIP of infected cell extracts, suggesting that this polypeptide is proteolytically processed cotranslationally. A subset of MAbs that reacted with BDV isolates of the noncytopathic biotypes yielded similar results, indicating that these findings are applicable to both biotypes of BDV.

Serology-Enabled Discovery of Genetically Diverse Hepaciviruses in a New Host

ABSTRACT Genetic and biological characterization of new hepaciviruses infecting animals contributes to our understanding of the ultimate origins of hepatitis C virus (HCV) infection in humans and dramatically enhances our ability to study its pathogenesis using tractable animal models. Animal homologs of HCV include a recently discovered canine hepacivirus (CHV) and GB virus B (GBV-B), both viruses with largely undetermined natural host ranges. Here we used a versatile serology-based approach to determine the natural host of the only known nonprimate hepacivirus (NPHV), CHV, which is also the closest phylogenetic relative of HCV. Recombinant protein expressed from the helicase domain of CHV NS3 was used as antigen in the luciferase immunoprecipitation system (LIPS) assay to screen several nonprimate animal species. Thirty-six samples from 103 horses were immunoreactive, and viral genomic RNA was present in 8 of the 36 seropositive animals and none of the seronegative animals. Complete genome sequences of these 8 genetically diverse NPHVs showed 14% (range, 6.4% to 17.2%) nucleotide sequence divergence, with most changes occurring at synonymous sites. RNA secondary structure prediction of the 383-base 5′ untranslated region of NPHV was refined and extended through mapping of polymorphic sites to unpaired regions or (semi)covariant pairings. Similar approaches were adopted to delineate extensive RNA secondary structures in the coding region of the genome, predicted to form 27 regularly spaced, thermodynamically stable stem-loops. Together, these findings suggest a promising new nonprimate animal model and provide a database that will aid creation of functional NPHV cDNA clones and other novel tools for hepacivirus studies.

Coxiella burnetii in bulk tank milk samples, United States.

Dairy cattle are a primary reservoir of Coxiella burnetii, which causes Q fever. However, no recent nationwide studies have assessed the prevalence and risks of Q fever in dairy cattle. We report ≥94% prevalence in samples of bulk tank milk from U.S. dairy herds tested during the past 3 years.

Influenza A Virus (H3N8) in Dogs with Respiratory Disease, Florida

Genetic and antigenic characterization established the uniqueness of this virus circulating in dogs.

Climate extremes promote fatal co-infections during canine distemper epidemics in African lions.

Extreme climatic conditions may alter historic host-pathogen relationships and synchronize the temporal and spatial convergence of multiple infectious agents, triggering epidemics with far greater mortality than those due to single pathogens. Here we present the first data to clearly illustrate how climate extremes can promote a complex interplay between epidemic and endemic pathogens that are normally tolerated in isolation, but with co-infection, result in catastrophic mortality. A 1994 canine distemper virus (CDV) epidemic in Serengeti lions (Panthera leo) coincided with the death of a third of the population, and a second high-mortality CDV epidemic struck the nearby Ngorongoro Crater lion population in 2001. The extent of adult mortalities was unusual for CDV and prompted an investigation into contributing factors. Serological analyses indicated that at least five “silent” CDV epidemics swept through the same two lion populations between 1976 and 2006 without clinical signs or measurable mortality, indicating that CDV was not necessarily fatal. Clinical and pathology findings suggested that hemoparsitism was a major contributing factor during fatal epidemics. Using quantitative real-time PCR, we measured the magnitude of hemoparasite infections in these populations over 22 years and demonstrated significantly higher levels of Babesia during the 1994 and 2001 epidemics. Babesia levels correlated with mortalities and extent of CDV exposure within prides. The common event preceding the two high mortality CDV outbreaks was extreme drought conditions with wide-spread herbivore die-offs, most notably of Cape buffalo (Syncerus caffer). As a consequence of high tick numbers after the resumption of rains and heavy tick infestations of starving buffalo, the lions were infected by unusually high numbers of Babesia, infections that were magnified by the immunosuppressive effects of coincident CDV, leading to unprecedented mortality. Such mass mortality events may become increasingly common if climate extremes disrupt historic stable relationships between co-existing pathogens and their susceptible hosts.

Differences in virus-induced polypeptides in cells infected by cytopathic and noncytopathic biotypes of bovine virus diarrhea-mucosal disease virus

Two biotypes of bovine viral diarrhea-mucosal disease virus are present in nature: one that induces cytopathology in infected bovine cells and the other that infects cells without overt cytopathology. Infections with both types of virus yield similar amounts of infectious progeny virus. Field and laboratory isolates of both biotypes of bovine viral diarrhea (BVD) virus were analyzed by radioimmunoprecipitation and polyacrylamide gel electrophoresis of infected cell extracts. The noncytopathic biotype BVD (NCB-BVD) virus isolates can be differentiated from cytopathic biotype BVD (CB-BVD) isolates on the basis of peculiar polypeptide profiles they induce in the infected cell. The most abundant polypeptide in CB-BVD infected cells is the 80K polypeptide. NCB-BVD virus-infected cells lack the 80K polypeptide and induce a predominant 118K polypeptide. D-[2-3H]Mannose labeling of cells infected with NCB-BVD indicated that at least three polypeptides are N-glycosylated: 75K, 56K-58K, and 48K. In addition the sizes and ratios of the glycoproteins induced by all virus isolates showed a marked variation. We present evidence indicating that there is remarkable heterogeneity among the field viral isolates of BVD and this methodology is of potential value for molecular epidemiology studies.

Longitudinal Study of Viruses Associated with Canine Infectious Respiratory Disease

ABSTRACT In this investigation a population of dogs at a rehoming center was monitored over a period of 2 years. Despite regular vaccination of incoming dogs against distemper, canine adenovirus type 2 (CAV-2), and canine parainfluenza virus (CPIV), respiratory disease was endemic. Tissue samples from the respiratory tract as well as paired serum samples were collected for analysis. The development of PCR assays for the detection of CPIV, canine adenovirus types 1 and 2, and canine herpesvirus (CHV) is described. Surprisingly, canine adenovirus was not detected in samples from this population, whereas 19.4% of tracheal and 10.4% of lung samples were positive for CPIV and 12.8% of tracheal and 9.6% of lung samples were positive for CHV. As reported previously, a novel canine respiratory coronavirus (CRCoV) was detected in this population (K. Erles, C. Toomey, H. W. Brooks, and J. Brownlie, Virology 310:216-223, 2003). Infections with CRCoV occurred mostly during the first week of a dogs stay at the kennel, whereas CPIV and CHV were detected at later time points. Furthermore, the evaluation of an enzyme-linked immunosorbent assay for detection of antibodies to CPIV and an immunofluorescence assay for detection of antibodies to CHV is described. This study shows that CPIV is present at kennels despite vaccination. In addition, other agents such as CHV and CRCoV may play a role in the pathogenesis of canine respiratory disease, whereas CAV-2 and canine distemper virus were not present in this population, indicating that their prevalence in the United Kingdom is low due to widespread vaccination of dogs.

The Amino-Terminal Domain of Bovine Viral Diarrhea Virus Npro Protein Is Necessary for Alpha/Beta Interferon Antagonism

ABSTRACT The alpha/beta interferon (IFN-α/β) system is the first line of defense against viral infection and a critical link between the innate and adaptive immune responses. IFN-α/β secretion is the hallmark of cellular responses to acute RNA virus infections. As part of their survival strategy, many viruses have evolved mechanisms to counteract the host IFN-α/β response. Bovine viral diarrhea virus (BVDV) (genus Pestivirus) was reported to trigger interferon production in infected cultured cells under certain circumstances or to suppress it under others. Our studies with various cultured fibroblasts and epithelial bovine cells indicated that cytopathic (cp) BVDV induces IFN-α/β very inefficiently. Using a set of engineered cp BVDVs expressing mutant Npro and appropriate controls, we found that the IFN-α/β response to infection was dependent on Npro expression and independent of viral replication efficiency. In order to investigate whether the protease activity of Npro is required for IFN-α/β antagonism, we engineered Npro mutants lacking protease activity by replacement of amino acid E22, H49, or C69. We found that E22 and H49 substitutions abolished the ability of Npro to suppress IFN, whereas C69 had no effect, suggesting that the structural integrity of the N terminus of Npro was more important than its catalytic activity for IFN-α/β suppression. A catalytically active mutant with a change at a conserved Npro region near the N terminus (L8P) in both BVDV biotypes did not antagonize IFN-α/β production, confirming its involvement in this process. Taken together, these results not only provide direct evidence for the role of Npro in blocking IFN-α/β induction, but also implicate the amino-terminal domain of the protein in this function.

Genetic diversity and BVD virus

The various measures of genetic variation of BVD virus was reviewed with emphasis on the implications for future control of virus-induced disease and diagnosis. While experimental data does not support unique serotypes for BVDV, there is substantial antigenic variation among the isolates examined. This variation may permit fetal infections even in animals assumed to be well vaccinated. The genetic differences between cytopathic and noncytopathic strains of BVDV are expressed in infected cells by the production of a p80 protein by cytopathic strains. In addition, cellular gene inserts have been detected in cytopathic strains. Monoclonal antibodies have demonstrated a high degree of diversity with the pestivirus population. Grouping of BVDV isolates by monoclonal antibody analysis is suggestive at best. The use of nucleic acid probes as diagnostic reagents has been compromised by the nucleic acid sequence variation found in the BVDV isolates tested.