Serologic titers to Leptospira in vaccinated pigs and interpretation for surveillance.

Diagnosis and surveillance of pathogenic Leptospira is difficult as organisms may be intermittently shed and in small numbers. Therefore, serologic testing by the microscopic agglutination test (MAT) is the primary screening method for leptospirosis. While a MAT titer ≥1:100 is considered to be a positive result, interpretation is complicated by the use of commercial vaccines in pigs. Most guidelines for interpretation of MAT titers in pigs were published in the 1970's and 1980's, prior to the development of the current multivalent vaccines. We evaluated MAT titers in routinely vaccinated healthy research pigs compared to their unvaccinated cohorts. Our study confirmed previous reports that the Pomona serovar elicits minimal antibody response even after a second booster 6 months after initial vaccination. However, MAT titers of ≥1:3,200 were detected as early as 4 weeks post initial vaccination for serovars Bratislava and Icterohaemorrhagiae and remained as high as ≥1:1,600 prior to booster at 24 weeks post vaccination. Our study determined that high levels of MAT titers can occur from vaccination alone and high titers are not necessarily indicative of infection. Therefore, the interpretation of MAT titers as indicators of Leptospira infection should be readdressed.

Genetic engineering alveolar macrophages for host resistance to PRRSV.

Standard strategies for control of porcine reproductive and respiratory syndrome virus (PRRSV) have not been effective, as vaccines have not reduced the prevalence of disease and many producers depopulate after an outbreak. Another method of control would be to prevent the virus from infecting the pig. The virus was thought to infect alveolar macrophages by interaction with a variety of cell surface molecules. One popular model had PRRSV first interacting with heparin sulfate followed by binding to sialoadhesin and then being internalized into an endosome. Within the endosome, PRRSV was thought to interact with CD163 to uncoat the virus so the viral genome could be released into the cytosol and infect the cell. Other candidate receptors have included vimentin, CD151 and CD209. By using genetic engineering, it is possible to test the importance of individual entry mediators by knocking them out. Pigs engineered by knockout of sialoadhesin were still susceptible to infection, while CD163 knockout resulted in pigs that were resistant to infection. Genetic engineering is not only a valuable tool to determine the role of specific proteins in infection by PRRSV (in this case), but also provides a means to create animals resistant to disease. Genetic engineering of alveolar macrophages can also illuminate the role of other proteins in response to infection. We suggest that strategies to prevent infection be pursued to reduce the reservoir of virus.

Hepatitis and enteritis caused by a novel herpesvirus in two monitor lizards (Varanus spp.).

Reported cases of herpesvirus-induced disease are uncommon in most species of reptiles, with the majority of reports in chelonians. Two monitor lizards (Varanus spp.) presented for postmortem examination at the Veterinary Medical Diagnostic Laboratory at the University of Missouri. Tan, 1-2-mm foci were grossly visible on the mucosal surface of the intestine and in the liver. Microscopically, there was multifocal necrosis in the lamina propria of the small intestine and in the liver. Many of the degenerate cells contained large, eosinophilic intranuclear inclusions. Enveloped icosahedral virions consistent with herpesvirus were detected by electron microscopy. A 180-bp DNA fragment was amplified by polymerase chain reaction from samples of small intestine and liver using primers that targeted a portion of the herpesvirus DNA polymerase gene. The sequence of the fragment was determined to be most closely related to Varanid herpesvirus 2 (80% nucleotide identity, 82% amino acid identity). Based on histological and molecular findings, a novel pathogenic herpesvirus of lizards in the family Varanidae is proposed.

Detection of Leptospira interrogans DNA and antigen in fixed equine eyes affected with end-stage equine recurrent uveitis.

Equine recurrent uveitis (ERU) is the most frequent cause of blindness in horses worldwide. Leptospira has been implicated as an etiologic agent in some cases of ERU and has been detected in fresh ocular tissues of affected horses. The objective of this study was to determine the presence of Leptospira antigen and DNA in fixed equine ocular tissues affected with end-stage ERU. Sections of eyes from 30 horses were obtained. Controls included 1) 10 normal equine eyes and 2) 10 equine eyes with a nonrecurrent form of uveitis. The experimental group consisted of 10 eyes diagnosed with ERU based on clinical signs and histologic lesions. Sections were subjected to immunohistochemical staining with an array of rabbit anti-Leptospira polyclonal antibodies. DNA extractions were performed by using a commercial kit designed for fixed tissue. Real-time PCR analysis was completed on extracted DNA. The target sequence for PCR was designed from alignments of available Leptospira 16S rDNA partial sequences obtained from GenBank. Two of 10 test samples were positive for Leptospira antigen by immunohistochemical assay. Zero of 20 controls were positive for Leptospira antigen. All test samples and controls were negative for Leptospira DNA by real-time PCR analysis. Leptospira was detected at a lower frequency than that previously reported for fresh ERU-affected aqueous humor and vitreous samples. Leptospira is not frequently detectable in fixed ocular tissues of horses affected with ERU when using traditional immunohistochemical and real-time PCR techniques.

Simultaneous detection of North American and European porcine reproductive and respiratory syndrome virus using real-time quantitative reverse transcriptase-PCR.

Porcine reproductive and respiratory syndrome (PRRS) is 1 of the most economically important diseases of swine. Detection of the etiologic agent, PRRS virus (PRRSV), represents a diagnostic challenge due to the heterogeneity of field isolates as well as the propensity for swine to develop persistent infection in which virus is difficult to detect. Recently European (EU) lineage PRRSV isolates, which are genetically divergent from North American (NA) isolates, have been introduced into NA swine further complicating efforts to diagnose this disease. In this study, real-time (TaqMan) reverse transcriptase (RT)-PCR assays were developed for multiplex detection, differentiation, and quantification of NA and EU PRRSV field isolates. Oligonucleotide primers and dual-labeled probes were selected from conserved regions of open-reading frame 7 and the 3'-untranslated region. The real-time RT-PCR assays described for the NA or EU genotype of PRRSV detected viral RNA from 83/83 strains (74 NA; 9 EU) previously isolated by cell culture between 1992 and 2003. The analytical sensitivity of both assays was consistently found to be less than a single TCID50, which corresponded to 5-10 RNA molecules, and was not significantly reduced when the reactions were performed in a multiplex format. When performing multiplex reactions, sensitive detection was possible even when 1 viral RNA concentration was up to 5,000-fold higher than the second. The diagnostic sensitivity and specificity of the multiplex reaction was found to be at a minimum equivalent to that of both nested RT-PCR and virus isolation.

Porcine reproductive and respiratory syndrome virus field isolates differ in in vitro interferon phenotypes.

Type I interferons (IFN-alpha and -beta) play an important role in the innate host defense against viral infection by inducing antiviral responses. In addition to direct antiviral activities, type I IFN serves as an important link between the innate and adaptive immune response through multiple mechanisms. Therefore, the outcome of a viral infection can be affected by IFN induction and the IFN sensitivity of a virus. North American porcine reproductive and respiratory syndrome virus (PRRSV) field isolates were studied with regard to IFN-alpha sensitivity and induction in order to understand the role of type I IFN in PRRSV pathogenesis. PRRSV isolates were differentially sensitive to porcine recombinant IFN-alpha (rIFN-alpha) and varied in their ability to induce IFN-alpha in porcine alveolar macrophages (PAM) cultures as measured by a porcine IFN-alpha specific ELISA on cell culture supernatants. Fifty-two plaques were purified from three PRRSV isolates (numbers 3, 7, and 12) and tested for IFN sensitivity and IFN induction. Plaque-derived populations were composed of heterogeneous populations in terms of IFN-inducing capacity and sensitivity to rIFN-alpha. When macrophages infected with isolates 3, 7, or 12 were treated with polycytidylic acid (polyI:C), IFN-alpha production was enhanced. Cells infected with isolate 3 and treated with polyI:C showed the most consistent and strongest enhancement of IFN-alpha production. It was demonstrated that the relatively low concentrations of IFN-alpha produced by isolate 3 contributed to the enhanced IFN-alpha synthesis in response to polyI:C. Isolates 7 and 12 significantly suppressed the enhanced IFN-alpha production by isolate 3 in polyI:C treated cells. To determine if suppression was at the level of IFN-alpha transcription, quantitative RT-PCR was performed for IFN-alpha mRNA and compared to GAPDH and cyclophilin mRNA quantification. However, the relative number of IFN-alpha transcript copies did not correlate with IFN-alpha protein levels, suggesting a post-transcriptional mechanism of suppression. In summary, these results demonstrate that PRRSV field isolates differ both in IFN-alpha sensitivity and induction. Furthermore, a PRRSV field isolate strongly enhance polyI:C-induced IFN-alpha production in PAM cultures and this priming effect was suppressed by other PRRSV isolates.

Association of two newly recognized herpesviruses with interstitial pneumonia in donkeys (Equus asinus).

Over a period of 6 years, antemortem and postmortem examinations were performed on a number of donkeys suffering from respiratory disease. For many cases, initial diagnostic efforts failed to identify an etiology consistent with the pathologic findings. However, retrospective examination of these cases using consensus primer polymerase chain reaction, designed to recognize herpesviruses from all 3 subfamilies of the Herpesviridae, amplified a fragment of the highly conserved herpesvirus DNA polymerase gene from a number of these animals. Two novel herpesviruses, herein designated asinine herpesvirus 4 (AHV4) and asinine herpesvirus 5 (AHV5), were consistently detected in lung tissue from donkeys in which the histopathology was characterized by interstitial pneumonia and marked syncytial cell formation but not in lung tissue from donkeys with evidence of bacterial or verminous pneumonia. Nucleotide sequence and phylogenetic analysis places these new viruses within the Gammaherpesvirinae subfamily and indicates that they are most closely related to the recently identified zebra herpesvirus and wildass herpesvirus as well as equine herpesviruses 2 and 5.

Detection and multigenic characterization of a herpesvirus associated with malignant catarrhal fever in white-tailed deer (Odocoileus virginianus) from Missouri.

Between 1998 and 2001, tissues from four captive white-tailed deer were observed to have histologic lesions of systemic lymphocytic vasculitis. These lesions suggested malignant catarrhal fever, although epizootic hemorrhagic disease and bluetongue were included in the differential diagnosis. Initial diagnostic efforts, including virus isolation and reverse transcription-PCR for epizootic hemorrhagic disease virus and bluetongue virus, failed to identify an etiologic agent. However, consensus primer PCR targeted to the herpesvirus DNA polymerase gene detected viral genomic DNA in each of these four cases. Nucleotide sequence analysis of the amplified product demonstrated that the detected virus was identical over the compared region to the recently described malignant catarrhal fever virus of white-tailed deer (H. Li, N. Dyer, J. Keller, and T. B. Crawford, J. Clin. Microbiol. 38:1313-1318, 2000). Additional nucleotide sequencing of both the DNA polymerase gene and DNA packaging gene followed by phylogenetic analysis solidified this newly recognized herpesvirus as a member of the Gammaherpesvirinae and suggests that this virus, along with ovine herpesvirus 2, alcelaphine herpesvirus 1, alcelaphine herpesvirus 2 and caprine herpesvirus 2, may be part of a separate clade within this subfamily.