Electron Microscopy of Intestinal Epithelial Cells of Piglets Infected with a Transmissible Gastroenteritis Virus

An electron microscopic study of intestinal epithelial cells of neonatal piglets infected with transmissible gastroenteritis (TGE) virus revealed a unique parasite-host cell interaction. Entry of the TGE virus into intestinal epithelial cells of newborn piglets is mediated through a network of cytoplasmic tubules of plasmalemma origin. the tubules, called microcanaliculi, are morphologically distinct from endoplasmic reticulum and Golgi. In uninfected animals similar tubules appear to be responsible for the indiscriminate uptake of large quantities of macromolecules from colostrum during the first few days of life.

Thin-section profiles of plasmalemma invaginations resembled tubules or canals and frequently contained viral particles. TGE viral particles developed and accumulated within cytoplasmic vacuoles. Initially the vacuoles were continuous with the microcanaliculi formed by deep plasmalemma invagination. Mature viral particles were 60 to 85 mu in diameter with an electron dense doughnut-shaped nucleoid surrounded by a trilaminar membrane which resembled the vacuolar wall. Abundant evidence of viral effects was observed in absorbtive epithelial cells of the jejunum and ileum but not of the duodenum.

The ability of absorbtive intestinal epithelial cells to form deep cytoplasmic tubular invaginations is temporally related to the pathogenesis of TGE and may explain in part why pigs usually are fatally affected by TGE only during the neonatal period.

     

Effects of bovine lactoferrin on in vitro replication of feline herpesvirus

Objective To investigate the effects of bovine lactoferrin on in vitro replication of feline herpes virus (FHV‐1) and to determine at what points during viral replication these effects occur. Sample population Cultured Crandell‐Reese feline kidney (CRFK) cells and FHV‐1 strain 727. Procedure Five concentrations of bovine lactoferrin (0.5, 1, 2, 5, and 10 mg/mL) were added at one or more of three time points during conventional plaque reduction assays: (a) uninfected CRFK cells were incubated in lactoferrin‐containing medium for 30 min prior to viral adsorption; (b) virus was suspended in lactoferrin‐containing medium prior to and during adsorption, or (c) CRFK cells were incubated with lactoferrin‐containing medium for 48 h following viral adsorption. Plaques were counted and antiviral effect expressed as percent inhibition relative to control medium that contained no lactoferrin. Results Exposure of CRFK cells to lactoferrin prior to or during viral adsorption inhibited FHV‐1 replication by 87–96% (mean: 91%). Application of lactoferrin following viral adsorption had no appreciable effect on FHV‐1 replication. No additive or synergistic effects were noted when lactoferrin was added at multiple steps. These effects were similar at all concentrations of lactoferrin tested. Cytotoxic effects of lactoferrin on CRFK cells were not observed at any concentration tested. Conclusions and clinical relevance Bovine lactoferrin has a notable inhibitory effect on the in vitro replication of FHV‐1 prior to and during, but not following viral adsorption. These findings strongly suggest that lactoferrin inhibits FHV‐1 adsorption to the cell surface and/or penetration of the virus into the cell. Clinical effects of topical lactoferrin in acute or recrudescent herpetic episodes in cats warrant investigation.     

Caprine herpesvirus-1 (CapHV-1) induces apoptosis in goat peripheral blood mononuclear cells

Programmed cell death (PCD), or apoptosis, is initiated in response to various stimuli, including virus infection. A number of studies have shown that deregulation of apoptosis is an important feature of virus-induced immunosuppression for various viral diseases. In the present study, CapHV-1 was found to cause apoptosis in mitogen-stimulated as well as nonstimulated caprine peripheral blood mononuclear cells (PBMC). Apoptotic index, as quantified by fluorescent dyes, revealed a significant increase in the percentage of apoptotic cells at 24 and 48 h postinfection as compared to their respective noninfected controls. Apoptosis specific internucleosomal laddering in DNA from CapHV-1 infected PBMC was seen in agarose gel electrophoresis. No DNA fragmentation was observed in control noninfected PBMC. Virus-induced apoptosis was reduced by Z-VAD-FMK, an aspecific caspase inhibitor, by AC-DEVD-CHO (caspase-3-specific) and AC-VEID-CHO (caspase-6-specific) treatment. PCD in CapHV-1 infected peripheral blood mononuclear cells occurs at the G0/G1 phase of the cell cycle. However, penetration of virus particles and infection was not required for PCD, as UV-inactivated CapHV-1 induced apoptosis of mitogen-stimulated bovine peripheral blood mononuclear cells in vitro.     

Demonstration of equine infectious anemia virus in primary leukocyte cultures by electron microscopy.

Electron microscopy was used to demonstrate the presence of viral particles in primary cultures of leukocytes taken from a horse after SC inoculation with the Wyoming strain of equine infectious anemia virus. Unlike previous studies, the exposure virus was not passaged through cell culture prior to horse inoculation. Cultures were begun approximately 1 week before and 1 week after the 1st pyrexic period after inoculation. In both samples, viral particles and cytoplasmic alterations were observed resembling those previously reported in equine infectious anemia virus and other retravirus-infected cells.     

Ultrastructure and protein A-gold immunolabelling of HRT-18 cells infected with turkey enteric coronavirus

The Minnesota strain of turkey enteric coronavirus (TCV) was propagated in HRT-18 cells, a cell line derived from human rectum adenocarcinoma. A productive non-cytopathic infection was established, without a previous adaptation, in these cells as shown by the specific hemagglutinating activity in cell culture supernatants. A post-embedding immunochemical technique, using specific antiserum directed against the original egg-adapted virus and colloidal-gold-labelled protein A as the electron-dense marker, was used for the identification of the virus and related antigens in the cells by electron microscopy. Budding of typical coronavirus particles, through intracytoplasmic membranes and accumulation of complete virus within cytoplasmic vesicles or the lumen of rough endoplasmic reticulum, were the main features of the viral morphogenesis. Late in infection, numerous progeny viral particles were shown at the outer surface of infected cells, but budding could not be demonstrated at this level. Two different types of surface projections were observed on the extracellular particles of this avian coronavirus. These morphological characteristics have been thus far described only for mammalian hemagglutinating coronaviruses.     

Importance of the medullary macrophage in the replication of lymphoid leukosis virus in the bursa of Fabricius of chickens

Electron microscopy and immunocytochemistry were used to study the development of lymphoid leukosis virus infection in the bursa of Fabricius of experimentally infected chicken embryos and chickens. In embryos infected at 7 days of incubation and killed 10 days later, virus particles and group-specific viral antigen were confined mainly to the connective tissue of the lamina propria of the bursal mucosal folds; a few developing follicles had discrete virions and group-specific antigen between cells. In chickens infected at 1 day of age, infection (as determined by use of electron microscopy and immunocytochemistry) was maximal in 1- to 4-month-old birds, and the greatest concentration of virus and group-specific viral antigen was in the medulla of the follicles. Although lymphoid leukosis virus was released from lymphocytes, epithelial cells, and macrophages, virus replication in the medullary macrophages was more active than that in the other cells. Normal medullary macrophages had cell membrane vesicles (50 to 80 nm in diameter) that covered part of all of the cell membrane surface. In infected chickens, virus particles frequently developed within these vesicles. Comparable vesicles were not found on cortical macrophages. Results of the present study indicated that the medullary macrophage was the principal host cell for replication of lymphoid leukosis virus in the bursa of Fabricius of the chicken.     

Evaluation of ultrastructural changes associated with encephalomyocarditis virus in the myocardium of experimentally infected piglets

OBJECTIVE: To evaluate the ultrastructural changes and localization of encephalomyocarditis virus (EMCV) and viral pathogenesis in the myocardium of experimentally infected piglets. ANIMALS: Eight 20-day-old piglets. PROCEDURE: Six piglets were inoculated oronasally with 5 ml (10(6) median tissue culture infective dose/ml) of EMCV suspension, and 2 were used as uninfected controls. Piglets were euthanatized or died between postinoculation days 1 and 3. Samples of heart tissue from all piglets were evaluated histologically, by virus isolation, and by use of immunohistochemistry and electron microscopy. RESULTS: All infected piglets had gross or microscopic lesions of interstitial myocarditis. immunohistochemically, EMCV antigen was detected in the cytoplasm of cardiac muscle cells, Purkinje fibers, and endothelial cells and in the nucleus of cardiac muscle cells and Purkinje fibers. Ultrastructural lesions were characterized by degeneration and necrosis of cardiac muscle cells and Purkinje fibers. Virus was present intracytoplasmically in cardiac muscle cells, Purkinje fibers, and endothelial cells of capillaries and intranuclearly in cardiac muscle cells. The cell membranes of the Purkinje fibers and endothelial cells had distinct protrusions that contained virus particles. In control piglets, no lesions were found, and no EMCV antigen was detected. CONCLUSIONS: Localization of EMCV intracytoplasmically or intranuclearly in various myocardial cells may well reflect the sites of viral proliferation. The presence of virus particles in cell membrane protrusions and in vacuoles within the lumen of capillaries indicates that virus is released not only by disintegration of the host cell but also via exocytosis.     

Derivation of a DNA clone corresponding to the viral agent of sheep-associated malignant catarrhal fever

Malignant catarrhal fever is a fatal lymphoproliferative and degenerative disease of ruminants. One causative agent is the gammaherpesvirus alcelaphine herpesvirus 1 (AHV-1), which produces no disease in its natural host, the wildebeest (Connochaetes species). Epidemiological evidence implicates sheep as the carrier of a similar virus. However, attempts to culture this virus from sheep or from animals affected with sheep-associated malignant catarrhal fever (SA-MCF) have failed. Lymphoblastoid cells have been propagated from cattle, deer and rabbits with SA-MCF. Although these cells show no evidence of viral particles or antigens, hybridisation experiments now show that they contain DNA sequences homologous to those of AHV-1. A genomic library was constructed from one of these lymphoblastoid cell lines and a clone identified which hybridised to cloned AHV-1 DNA. The authors believe that this clone contains part of the SA-MCF viral genome, and that the SA-MCF virus and AHV-1 are closely related gammaherpesviruses.     

A potential live vector, foamy virus, directed intra-cellular expression of ovine interferon-tau exhibited the resistance to HIV infection

Interferon-tau (IFN-tau), produced by the embryonic trophectoderm, is a member of type I IFNs required for the establishment of pregnancy in the ruminant ungulates. Although this IFN possesses antiviral activity similar to other type I IFNs, the effectiveness of IFN-tau as an antiviral agent has not been well characterized. To investigate possible antiviral effects of ovine IFN-tau (oIFN-tau), oIFN-tau-GST fusion protein was expressed in E. coli BL21, from which the purified protein isolated possessed anti-viral activity. An apathogenic human foamy virus (hFV) was then used to establish a potential recombinant live vector consisting of oIFN-tau cDNA sense (+) or antisense (-) sequence, oIFN-tau(+)/hFV or oIFN-tau(-)/hFV, respectively. Human hematopoietic and other mammalian cell lines that had been transduced with hFV vector consisting of no oIFN-tau, oIFN-tau(+)/hFV or oIFN-tau(-)/hFV construct were cultured initially for 12 days, and three of cell lines were then maintained for up to 90 days. These cells with oIFN-tau expression directed by hFV exhibited the in vitro cytopathic effect minimally. Transduced cell lines that had been cultured for 90 days were subjected to studies on human immunodeficiency virus type-1 (HIV-1) infection, which was measured with infectivity of viral particles resulted from the GFP inserted T-cell tropic HIV SF2 or macrophage tropic HIV SF162: the number of HIV-1 positive cells was reduced by the hFV driven-intra-cellular oIFN-tau expression. Since oIFN-tau/hFV transduced cells exhibited the resistance to HIV-1 infection and/or replication, oIFN-tau could be considered as one of effective antiviral agents against HIV-1. These results suggest that the hFV genome could be an effective recombinant live vector for the expression of a targeted gene in various cell types.     

Effects of cidofovir on cell death and replication of feline herpesvirus-1 in cultured feline corneal epithelial cells

OBJECTIVE: To assess the effect of cidofovir on viability of feline corneal epithelial (FCE) cells, replication of feline herpesvirus (FHV)-1, and virus-induced cytopathic changes. SAMPLE POPULATION: Healthy eyes from 14 recently euthanatized cats. PROCEDURE: Cidofovir at concentrations ranging from 0.05 to 0.000005 mg/mL was added to primary cultures of FCE cells, and cytopathic changes and effects on cell proliferation and cell viability were determined during the subsequent 48 hours. Efficacy of cidofovir (0.02 and 0.05 mg/mL) to prevent in vitro infection of FCE cells with FHV-1 was determined during 72 hours of culture by assessing viral cytopathic effects and viral titers. RESULTS: Cidofovir at concentrations of 0.05, 0.005, and 0.0005 mg/mL significantly reduced mean viable cell counts, and cidofovir at a concentration of 0.05 mg/mL significantly reduced the percentage viability of cultured FCE cells. Minimal cytopathic changes were observed at concentrations of 0.02 and 0.05 mg of cidofovir/mL. Cidofovir at concentrations of 0.05 and 0.02 mg/mL abrogated the cytopathic effects attributable to FHV-1 infection and reduced viral titers from > or =10(14) TCID(50)/mL to < or =10(3.5) TCID50/mL. CONCLUSIONS AND CLINICAL RELEVANCE: Cidofovir in vitro was highly efficacious against FHV-1 infection of a primary culture of FCE cells but had cytostatic effects on cultured cells.     

犬传染性肝炎病毒的形态发生学及抗原定位研究

应用免疫金电子显微镜技术研究了犬传染性肝炎病毒(ICHV)在犬肾传代细胞内的增殖过程及其病毒抗原在感染细胞内外的定位.结果显示:(1)吸附在细胞膜表面的病毒粒子,主要通过细胞吞饮作用侵入细胞,而吸附在微绒毛膜表面的病毒粒子则可直接“渗入”细胞;(2)在病毒感染不同时用的细胞核内观察到均质型、微粒型、颗粒型、副晶格型、病毒包涵体型及致密型等6种类型包涵体,其中前5种能被免疫金标记,它们是尚未形成病毒粒子的抗原蛋白、病毒装配后剩余的抗原蛋白或ICHV的病毒粒子结晶,致密型包涵体未被免疫金标记,可能是病毒DNA;(3)感染细胞内出现的某些特殊结构均不具有病毒抗原性,其中纤维样结构和管状结构在病毒增殖过程中起支持作用.     

In vitro cytopathogenicity and in vivo virulence of two strains of canine parainfluenza virus.

In vivo and in vitro properties of two strains of canine parainfluenza virus (CPIV) were investigated. One strain, designated CPIV(+), induced syncytial giant cell formation and cytolysis in vitro, whereas the second strain, CPIV(-), caused only a mild strand-forming cytopathic effect with few, small syncytial giant cells. Vero cells infected with CPIV(+) or CPIV(-) were 100% positive for CPIV antigen as determined by immunofluorescent staining; however, 100% of CPIV(+) and less than 10% of CPIV(-) infected cells were hemadsorption positive. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis analysis revealed no differences in electrophoretic mobility of viral polypeptides between both strains; however, in CPIV(-), reduced or absent synthesis of the putative HN and F1 proteins was observed. Isopycnic separation of CPIV(+) progeny virions showed a high proportion of viral particles with a buoyant density of 1.18 g/cm3. In contrast, CPIV(-) progeny virions had a heterogeneous density profile ranging from 1.08 to 1.18 g/cm3. Intracerebral infection of six ferrets with CPIV(+) resulted in moderate lymphocytic and histiocytic choroiditis, meningitis, and ependymitis, whereas CPIV(-) infection caused only mild to moderate inflammation. Immunohistologically, CPIV antigen was prominent in ependymal lining cells of the ventricles in CPIV(+)-infected ferrets and was reduced or lacking in CPIV(-)-infected ferrets (n = 6). Sham-injected ferrets (n = 6) did not have histologic lesions and no viral antigen was identified. The present findings suggest that certain changes in the activities of CPIV glycoproteins may lead to alterations of CPIV virulence in vivo.     

Induction of lymphopenia and inhibition of T cell function during acute infection of swine with foot and mouth disease virus (FMDV)

Foot and mouth disease virus (FMDV) is a picornavirus that causes an acute vesicular disease of cloven-hoofed animals. This virus continues to be a threat to livestock worldwide with outbreaks causing severe economic losses. The present study shows an analysis of immune system phenotype and function during the acute phase of FMDV infection in swine. In the first days of infection, a significant lymphopenia is observed that involves all T cell subsets, CD4(+), CD8(+), and CD4(+)/CD8(+). This marked lymphopenia is not a result of active infection of PBMC with the virus. Further, the response of residual peripheral blood T cells to the mitogen, Concanavalin A (ConA) is significantly reduced and occasionally eliminated. Animals usually resolve clinical signs of disease and develop antigen specific T cell responses to the virus and recover ConA reactivity. These characteristics of acute phase infection likely play an important role in viral pathogenesis, propagation and shedding of viral particles and may be targeted as a way of improving vaccine formulations.     

Identification and molecular characterization of a novel flavivirus isolated from Pekin ducklings in China

A flavivirus-associated disease of egg-laying ducks was observed in eastern China in 2010, and a novel mosquito-borne flavivirus, Tembusu virus (TMUV), was isolated (Cao et al., 2011). Following up on the earlier study, a virus similar to TMUV was isolated recently from ducklings and characterized. We report that (1) the recently isolated virus, TMUV ZJ-6, replicated in vertebrate cells (DF-1, BHK-21) as well as in mosquito cells (C6/36) and caused cytopathic effect (CPE) in the cell lines tested; (2) extracellular viral particles examined by electron microscopy were approximately 45 nm in diameter and enveloped; (3) the full-length genome of the virus was determined, showing that the TMUV ZJ-6 is more closely related to the Ntaya group of viruses than other members of the Flaviviridae based on the data of phylogenetic analyses. Most importantly, the disease of ducklings was reproducible after administration of plaque-purified virus by intracerebral (i.c.), subcutaneous (s.c.) or intranasal (i.n.) inoculation. This is the first report that TMUV infects not only egg-laying ducks but also 3-21 days-old ducklings. The findings extend our understanding of how the virus spreads and causes disease.     

Inhibition of feline infectious peritonitis virus replication by recombinant human leukocyte (alpha) interferon and feline fibroblastic (beta) interferon

Replication of feline infectious peritonitis virus (FIPV) in feline cell cultures was inhibited after incubation of cells with either human recombinant leukocyte (alpha) interferon (IFN) or feline fibroblastic (beta) IFN for 18 to 24 hours before viral challenge exposure. Compared with virus control cultures, FIPV yields were reduced by ranges of 0.1 to 2.7 log10 or 2 to 5.2 log10 TCID50 in cultures treated with human alpha- or feline beta-IFN, respectively; yield reductions were IFN dose dependent. Sensitivity to the antiviral activities of IFN varied with cell type; feline embryo cells had greater FIPV yield reductions than did similarly treated feline kidney or feline lung cells. Comparison of the virus growth curves in IFN-treated and virus control cultures indicated marked reduction in intracellular and extracellular FIPV in IFN-treated cultures. Compared with virus control cultures, intracellular and extracellular infectivity in IFN-treated cultures was delayed in onset by 12 and 30 hours, respectively, and FIPV titers subsequently were reduced by 3 to 3.5 and 5 log10 TCID50, respectively. Frequently, immunofluorescent and electron microscopy of IFN-treated cells or cell culture fluids did not reveal virus; however, even in cultures without viral cytopathic changes, small amounts of virus occasionally persisted in cells.     

Characterization of classical swine fever virus associated with defective interfering particles containing a cytopathogenic subgenomic RNA isolated from wild boar

Classical swine fever virus (CSFV) strain WB82, isolated from a wild boar in 1982, induced a distinct cytopathic effect (CPE) in primary swine testicle cell culture and in most of the porcine cell lines. This strain of CSFV was found to be composed of two biotypes. cytopathogenic (cp) CSFV, as a minor population, and noncytopathogenic (noncp) CSFV, as a major population. The noncp CSFV (designated strain WB82/E+) was obtained by biological cloning, and it showed the exaltation of Newcastle disease virus phenomenon. In Northern blot analysis and RT-PCR assay, CSFV RNA with a subgenomic (sg) length was detected in addition to full-length viral RNA only in the cells in which a CPE had been revealed. These RNAs represent the genomes of typical defective interfering (DI) particles because of the strict dependence on a complementing helper virus and interference with replication of the helper virus. The sg RNA, which exhibits the genomes of the DI particles, lacked the nucleotides of the viral genomic region from Npro to NS2 (4764 bases). When extracted sg RNA was transfected to the cells infected with the WB82/E+ strain, a distinct CPE was observed. Interestingly, the CPE was observed in cells infected with other heterologous noncp CSFV ALD and GPE- strains by sg RNA transfection. The results suggested that these noncp CSFVs act as helper viruses for the replication of sg RNA (DI particles). It was also shown that the cytopathogenicity of strain WB82 is caused by apoptosis.     

Comparison of slot blot nucleic acid hybridization, immunofluorescence, and virus isolation techniques to detect bluetongue virus in blood mononuclear cells from cattle with experimentally induced infection.

A slot blot hybridization technique was applied for detection of bluetongue virus (BTV) in blood mononuclear cells (BMNC) obtained from cattle with experimentally induced infection. This technique lacked sensitivity to detect the viral nucleic acid directly in clinical specimens. When aliquots of mononuclear cells from these cattle were cultivated in vitro for 10 days to amplify virus titer, only 33.3% of the samples collected during viremia gave a positive signal in the slot blot hybridization format. By contrast, results for 34.3% of noncultured and 63.3% of cultured mononuclear cell samples collected during viremia were positive by immunofluorescence. The average number of infected cells, as detected by immunofluorescence in the noncultured mononuclear cell samples, was 1 to 5/300,000, and was usually > 10/300,000 in the cultured cell samples. Virus was isolated from all postinoculation blood samples obtained from 4 heifers that were seronegative at the time of inoculation, but was not isolated from any of the preinoculation samples, or from any of the postinoculation samples obtained from 2 heifers that were seropositive at the time of inoculation. When virus isolation was attempted from separated mononuclear cells in 2 heifers, 43.7% of the noncultured and 87.5% of the cultured samples had positive results.     

Isolation of a herpesvirus from the cell culture of a malignant melanoma of a ground squirrel (Spermophilus tridecemlineatus).

A subcutaneous neoplastic mass in a 13-lined ground squirrel which metastasized to regional lymph nodes and lung was studied. Histopathologically, the tumor architecture and cellular morphology were compatible with that of a malignant amelanotic melanoma. Ultrastructurally, the neoplastic tissue was composed of oval cells, spindle-shaped cells, and spindle-shaped cells with electron-dense cytoplasmic granules. Virus particles were not seen in these cells. Cell cultures from neoplastic tissue grew in complete monolayers and on initial passages contained a few herpesvirus particles. Secondary monolayer cell culture, when exposed to 5-iodo-2'-deoxyuridine or made into several serial subculture passages, caused the appearance of cytopathic effect and the demonstration of many virus particles. The ground squirrel agent, because it contained DNA, was sensitive to chloroform treated and had herpesvirus characteristics on electron microscopy, was considered a herpesvirus. The buoyant density of the virus was 1.298 g/cm3 and the diameter of the enveloped virus particles was 146 nm. This ground squirrel herpesvirus was antigenically distinct from other known herpesviruses.     

Evaluation of cytotoxicity and antiviral activity of recombinant human interferon alfa-2a and recombinant human interferon alfa-B/D hybrid against bovine viral diarrhea virus, infectious bovine rhinotracheitis virus, and vesicular stomatitis virus in vitro

OBJECTIVE: To evaluate cytotoxicity and antiviral activity of recombinant human interferon alfa-2a and recombinant human interferon alfa-B/D hybrid against cytopathic and noncytopathic bovine viral diarrhea virus (BVDV), infectious bovine rhinotracheitis virus (IBRV), and vesicular stomatitis virus (VSV) in vitro. SAMPLE POPULATION: Primary bovine testicular cells and Mardin Darby bovine kidney cells. PROCEDURES: To evaluate cytotoxicity, cells were added to serial dilutions of each interferon. To evaluate antiviral activity of each interferon, interferons were serially diluted 1:10, and tissue culture cells were added; virus was then added at 3 time points. Prevention of viral infection by interferon was defined as failure to induce cytopathologic effect for VSV, IBRV, and cytopathic BVDV and failure to detect virus immunohistochemically for cytopathic and noncytopathic BVDV. RESULTS: No evidence of cytotoxicity in either cell line was detected after incubation with interferon alfa-2a or interferon alfa-B/D. However, reduced growth rates of tissue culture cells were detected for each interferon when undiluted interferon was tested. Comparable and profound antiviral activities against cytopathic and noncytopathic BVDV were evident for each interferon. Interferon alfa-2a and interferon a-B/D had comparable antiviral activities against VSV. Neither interferon had antiviral activity against IBRV. CONCLUSIONS AND CLINICAL RELEVANCE: The safety and marked in vitro antiviral activity against noncytopathic BVDV, cytopathic BVDV, and VSV suggest that interferons alfa-2a and alfa-B/D may be useful for treatment of natural disease after infection with these viruses.