Clinical response and immunomodulation following experimental challenge of calves with type 2 noncytopathogenic bovine viral diarrhea virus

Integrative Transcriptomics and Proteomics Analysis Reveals Immune Response Process in Bovine Viral Diarrhea Virus-1-Infected Peripheral Blood Mononuclear Cells

Bovine viral diarrhea virus (BVDV) causes bovine viral diarrhea-mucosal disease, inflicting substantial economic losses upon the global cattle industry. Peripheral blood mononuclear cells (PBMCs) are the central hub for immune responses during host-virus infection and have been recognized as crucial targets for BVDV infection. In order to elucidate the dynamics of host-BVDV-1 interaction, this study harnessed RNA-seq and iTRAQ methods to acquire an extensive dataset of transcriptomics and proteomics data from samples of BVDV-1-infected PBMCs at the 12-h post-infection mark. When compared to mock-infected PBMCs, we identified 344 differentially expressed genes (DEGs: a total of 234 genes with downregulated expression and 110 genes with upregulated expression) and 446 differentially expressed proteins (DEPs: a total of 224 proteins with downregulated expression and 222 proteins with upregulated expression). Selected DEGs and DEPs were validated through quantitative reverse transcriptase-polymerase chain reaction and parallel reaction monitoring. Gene ontology annotation and KEGG enrichment analysis underscored the significant enrichment of DEGs and DEPs in various immunity-related signaling pathways, including antigen processing and presentation, complement and coagulation cascades, cytokine-cytokine receptor interaction, and the NOD-like receptor signaling pathway, among others. Further analysis unveiled that those DEGs and DEPs with downregulated expression were predominantly associated with pathways such as complement and coagulation cascades, the interleukin-17 signaling pathway, cytokine-cytokine receptor interaction, the PI3K-Akt signaling pathway, the tumor necrosis factor signaling pathway, and the NOD-like receptor signaling pathway. Conversely, upregulated DEGs and DEPs were chiefly linked to metabolic pathways, oxidative phosphorylation, complement and coagulation cascades, and the RIG-I-like receptor signaling pathway. These altered genes and proteins shed light on the intense host-virus conflict within the immune realm. Our transcriptomics and proteomics data constitute a significant foundation for delving further into the interaction mechanism between BVDV and its host.

Transcriptome sequencing analysis for the identification of stable lncRNAs associated with bovine Staphylococcus aureus mastitis

Background

Staphylococcus aureus (S. aureus) mastitis is one of the most difficult diseases to treat in lactating dairy cows worldwide. S. aureus with different lineages leads to different host immune responses. Long non-coding RNAs (lncRNAs) are reported to be widely involved in the progress of inflammation. However, no research has identified stable lncRNAs among different S. aureus strain infections. In addition, folic acid (FA) can effectively reduce inflammation, and whether the inflammatory response caused by S. aureus can be reduced by FA remains to be explored.

Methods

lncRNA transcripts were identified from Holstein mammary gland tissues infected with different concentrations of S. aureus (in vivo) and mammary alveolar cells (Mac-T cells, in vitro) challenged with different S. aureus strains. Differentially expressed (DE) lncRNAs were evaluated, and stable DE lncRNAs were identified in vivo and in vitro. On the basis of the gene sequence conservation and function conservation across species, key lncRNAs with the function of potentially immune regulation were retained for further analysis. The function of FA on inflammation induced by S. aureus challenge was also investigated. Then, the association analysis between these keys lncRNA transcripts and hematological parameters (HPs) was carried out. Lastly, the knockdown and overexpression of the important lncRNA were performed to validate the gene function on the regulation of cell immune response.

Results

Linear regression analysis showed a significant correlation between the expression levels of lncRNA shared by mammary tissue and Mac-T cells (P < 0.001, R² = 0.3517). lncRNAs PRANCR and TNK2–AS1 could be regarded as stable markers associated with bovine S. aureus mastitis. Several HPs could be influenced by SNPs around lncRNAs PRANCR and TNK2–AS1. The results of gene function validation showed PRANCR regulates the mRNA expression of SELPLG and ITGB2 within the S. aureus infection pathway and the Mac-T cells apoptosis. In addition, FA regulated the expression change of DE lncRNA involved in toxin metabolism and inflammation to fight against S. aureus infection.

Conclusions

The remarkable association between SNPs around these two lncRNAs and partial HP indicates the potentially important role of PRANCR and TNK2–AS1 in immune regulation. Stable DE lncRNAs PRANCR and TNK2–AS1 can be regarded as potential targets for the prevention of bovine S. aureus mastitis. FA supplementation can reduce the negative effect of S. aureus challenge by regulating the expression of lncRNAs.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40104-021-00639-2.

The Effect of Bovine Viral Diarrhea Virus (BVDV) Strains and the Corresponding Infected-Macrophages' Supernatant on Macrophage Inflammatory Function and Lymphocyte Apoptosis

Bovine viral diarrhea virus (BVDV) is an important viral disease of cattle that causes immune dysfunction. Macrophages are the key cells for the initiation of the innate immunity and play an important role in viral pathogenesis. In this in vitro study, we studied the effect of the supernatant of BVDV-infected macrophage on immune dysfunction. We infected bovine monocyte-derived macrophages (MDM) with high or low virulence strains of BVDV. The supernatant recovered from BVDV-infected MDM was used to examine the functional activity and surface marker expression of normal macrophages as well as lymphocyte apoptosis. Supernatants from the highly virulent 1373-infected MDM reduced phagocytosis, bactericidal activity and downregulated MHC II and CD14 expression of macrophages. Supernatants from 1373-infected MDM induced apoptosis in MDBK cells, lymphocytes or BL-3 cells. By protein electrophoresis, several protein bands were unique for high-virulence, 1373-infected MDM supernatant. There was no significant difference in the apoptosis-related cytokine mRNA (IL-1beta, IL-6 and TNF-a) of infected MDM. These data suggest that BVDV has an indirect negative effect on macrophage functions that is strain-specific. Further studies are required to determine the identity and mechanism of action of these virulence factors present in the supernatant of the infected macrophages.

Evaluation of protection against bovine viral diarrhea virus type 2 after vaccination of the calves with bovine viral diarrhea virus type 1 combo inactivated vaccine

ABSTRACT This study was designed to evaluate the extent of the protection for bovine viral diarrhea virus type 2 (BVDV-2) infection, afforded by vaccination with a combo inactivated vaccine, which contains bovine viral diarrhea virus type 1 (BVDV-1) and infectious bovine rhinotracheitis virus (IBRV). Five 3-4-month-old calves were intramuscularly vaccinated with a single dose of the combo vaccine and boosted with same dose three weeks after the first vaccination, with five mock immunized calves serving as a control group. Twenty-one days after the second vaccination, all calves were challenged with BVDV-2 SX08 strain by spray into nostril. The unvaccinated animals developed typical clinical signs of high rectal temperature, diarrhoea with erosions and a dramatic drop in leukocyte counts. These signs occured markedly less in all vaccinated animals, the rectal temperature, leukopenia and virarmia of which, were significantly less than the mock immunized calves. It can be concluded that vaccination with the combo inactivated vaccine affords cross-protection against clinical effects of a challenge-infection with BVDV-2 SX08 strain, although it was part protection.

Comparative humoral immune response against cytopathic or non-cytopathic bovine viral diarrhea virus infection

Bovine viral diarrhea virus (BVDV) infection causes immune dysfunction. The current study investigated the effect of cytopathic (cp) or noncytopathic (ncp) strains of BVDV on immunomodulation by the levels of total serum immunoglobulin G (IgG), the IgG1, IgG2, BVDV neutralizing antibodies and total white blood cell (WBC) count. Twenty (20) BVDV seronegative dairy calves (5-6 months old) were divided in two groups of ten. The animals were infected with either a cp or ncp virus isolated from the same animal (ncp BVDV1b-TGAN or cp BVDV1b-TGAC). One group of 10 was infected with ncp TGAN while the other group of 10 was infected with cp TGAC. Calves infected with cp BVDV had a significant decrease in total IgG as well as IgG1 concentration at 7 days post infection (DPI) that recovered by 21 DPI (total IgG) and 35 DPI (IgG1), respectively. There was no effect of ncp BVDV infection on total IgG concentration in the first 7 days of infection (DOI); however, IgG1 concentration was significantly reduced and IgG2 concentration was significantly increased at 7 DOI. At 35 DPI, ncp TGAN-infected calves had significantly higher total IgG, IgG1 as well as IgG2 compared to cp TGAC-infected calves. Ncp BVDV induced higher BVDV homologous and heterologous neutralizing antibodies compared to the cp BVDV strain. Calves infected with ncp BVDV had significantly reduced WBC counts at 7 DPI that recovered by 14 DPI. Overall, these findings indicate that humoral immunosuppression occurs early following BVDV infection with the largest effect on IgG1 levels.

BVDV permissiveness and lack of expression of co-stimulatory molecules on PBMCs from calves pre-infected with BVDV

Bovine viral diarrhea virus (BVDV) has been detected in peripheral blood mononuclear cells (PBMCs) of immunocompetent animals, not being clear whether the development of a specific humoral immune response can prevent BVDV infection. The aim of this study was to evaluate the ability of non-cytopathic BVDV to replicate and produce infectious virus in PBMCs from calves pre-infected with BVDV and to elucidate the immunomodulatory effect of BVDV on these cells in an in vitro model. Quantification of virus was by quantitative PCR, while its replicative capacity and shedding into the extracellular environment was evaluated by viral titration. Apoptosis was assessed by flow cytometry analysis of annexin V and propidium iodide, and by expression of caspase-3/7. Flow cytometry was used to analyze the expression of CD14/CD11b/CD80, CD4/CD8/CD25, MHC-I/MHC-II and B-B2 markers. Our results showed that PBMCs from cattle naturally infected with BVDV were more susceptible to in vitro BVDV infection and showed a more severe apoptosis response than those from naïve animals. Non-cytopathic BVDV in vitro infection also resulted in a lack of effect in the expression of antigen presentation surface markers. All these findings could be related to the immunosuppressive capacity of BVDV and the susceptibility of cattle to this infection.

Mechanisms linking bovine viral diarrhea virus (BVDV) infection with infertility in cattle

Bovine viral diarrhea virus (BVDV) is an important infectious disease agent that causes significant reproductive and economic losses in the cattle industry worldwide. Although BVDV infection is known to cause poor fertility in cattle, a greater part of the underlying mechanisms particularly associated with early reproductive losses are not clearly understood. Previous studies reported viral compromise of reproductive function in infected bulls. In females, BVDV infection is thought to be capable of killing the oocyte, embryo or fetus directly, or to induce lesions that result in fetal abortion or malformation. BVDV infections may also induce immune dysfunction, and predispose cattle to other diseases that cause poor health and fertility. Other reports also suggested BVDV-induced disruption of the reproductive endocrine system, and a disruption of leukocyte and cytokine functions in the reproductive organs. More recent studies have provided evidence of viral-induced suppression of endometrial innate immunity that may predispose to uterine disease. Furthermore, there is new evidence that BVDV may potentially disrupt the maternal recognition of pregnancy or the immune protection of the conceptus. This review brings together the previous reports with the more recent findings, and attempts to explain some of the mechanisms linking this important virus to infertility in cattle.

Experimental infection of mice with noncytopathic bovine viral diarrhea virus 2 increases the number of megakaryocytes in bone marrow

Background

Bovine viral diarrhea virus (BVDV) causes significant economic losses worldwide in the cattle industry through decrease in productive performance and immunosuppression of animals in herds. Recent studies conducted by our group showed that mice can be infected with BVDV-1 by the oral route. The purpose of this study was to assess the clinical signs, hematological changes, histopathological lesions in lymphoid tissues, and the distribution of the viral antigen after oral inoculation with a Korean noncytopathic (ncp) BVDV-2 field isolate in mice.

Methods

Mice were orally administered a low or high dose of BVDV-2; blood and tissue samples were collected on days 2, 5, and 9 postinfection (pi). We monitored clinical signs, hematological changes, histopathological lesions, and tissue distribution of a viral antigen by reverse transcription-polymerase chain reaction (RT-PCR) and immunohistochemistry (IHC) and then compared these parameters with those in ncp BVDV-1 infections.

Results

None of the infected mice developed any clinical signs of the illness. Significant thrombocytopenia was found in both low- and high-dose-inoculated mice on day 2 pi. Leukopenia was apparent only in low-dose-inoculated mice on day 2 pi, whereas lymphopenia was not observed in any ncp BVDV-2-infected animal. Viral RNA was found in the spleen in of low- and high-dose-inoculated mice by RT-PCR. According to the results of IHC, the viral antigen was consistently detected in lymphocytes of bone marrow and spleen and less frequently in bronchus-associated lymphoid tissue (BALT), mesenteric lymph nodes, and Peyer’s patches. Despite the antigen detection in BALT and mesenteric lymph nodes, histopathological lesions were not observed in these tissues. Lympholysis, infiltration by inflammatory cells, and increased numbers of megakaryocytes were seen in Peyer’s patches, spleens, and bone marrow, respectively. In contrast to ncp BVDV-1 infection, lympholysis was found in the spleen of ncp BVDV-2-infected mice. These histopathological lesions were more severe in high-dose-inoculated mice than in low-dose-inoculated mice.

Conclusions

Our results provide insight into the pathogenesis of ncp BVDV-2 infection in mice. Collectively, these results highlight significant differences in pathogenesis between ncp BVDV-1 and ncp BVDV-2 infections in a murine model.

Establishment of a Bovine Viral Diarrhea Virus Type 2 Intranasal Challenge Model for Assessing Vaccine Efficacy

The objective of this study was to develop a bovine viral diarrhea virus type 2 (BVDV-2) challenge model suitable for evaluation of efficacy of BVDV vaccines; a model that mimics natural infection and induces clear leukopenia and viremia. Clinical, hematological and virological parameters were evaluated after infection of two age groups of calves (3 and 9 months) with two BVDV-2 strains (1362727 and 502643). Calves became pyrexic between 8 and 9 days post inoculation and exhibited symptoms, such as nasal discharge, mild depression, cough, and inappetence. Leukopenia with associated lymphopenia and neutropenia was evident in all groups with lowest leukocyte and lymphocyte counts reached 8 dpi and granulocyte counts between 11 and 16 dpi, dependent on the strain and age of the calves. A more severe thrombocytopenia was seen in those animals inoculated with strain 1362727. Leukocyte and nasal swab samples were positive by virus isolation, as early as 3 dpi and 2 dpi respectively, independent of the inocula used. All calves seroconverted with high levels of BVDV-2 neutralizing antibodies. BVDV RNA was evident as late as 90 dpi and provides the first evidence of the presence of replicating virus long after recovery from BVDV-2 experimental infection. In summary, moderate disease can be induced after experimental infection of calves with a low titer of virulent BVDV-2, with leukopenia, thrombocytopenia, viremia, and virus shedding. These strains represent an attractive model to assess the protective efficacy of existing and new vaccines against BVDV-2.

Effect of timing of challenge following short-term natural exposure to bovine viral diarrhea virus type 1b on animal performance and immune response in beef steers

Bovine respiratory disease (BRD) is the most common and economically detrimental disease of beef cattle during the postweaning period, causing the majority of morbidity and mortality in feedlots. The pathogenesis of this disease often includes an initial viral infection, which can predispose cattle to a secondary bacterial infection. The objective of this experiment was to determine the effects of timing of an intratracheal (MH) challenge relative to 72 h of natural exposure to bovine viral diarrhea virus (BVDV) type 1b persistently infected (PI) calves on performance, serum antibody production, total and differential white blood cell (WBC) count, rectal temperature, clinical severity score (CS), and haptoglobin (Hp). Steers ( = 24; 276 ± 31 kg initial BW) were randomly allocated to 1 of 3 treatments (8 steers/treatment) in a randomized complete block design. Treatments were steers not exposed to calves PI with BVDV 1b and not challenged with MH (CON), steers intratracheally challenged with MH 84 h after being exposed to calves PI with BVDV 1b for 72 h (LateCh), and steers intratracheally challenged with MH 12 h after being exposed to calves PI with BVDV 1b for 72 h (EarlyCh). Performance (ADG, DMI, and G:F) was decreased ( < 0.001) for both EarlyCh and LateCh from d 0 to 4. From d 5 to 17, LateCh appeared to compensate for this lost performance and demonstrated increased ADG ( = 0.01) and G:F ( = 0.01) compared with EarlyCh. Both EarlyCh and LateCh had decreased platelet counts ( < 0.001) compared with CON. Antibody concentrations of BVDV and MH were higher ( < 0.05) for both EarlyCh and LateCh compared with CON. Rectal temperature, CS, and Hp increased ( < 0.001) across time from h 4 to 48, h 4 to 36, and h 8 to 168, respectively. Within 24 h of MH challenge, WBC and neutrophil concentrations within the blood increased whereas lymphocyte concentrations decreased. The timing of BVDV exposure relative to a MH challenge appears to influence the CS and acute phase response associated with BRD. As typical beef cattle marketing channels allow for variation in the timing of respiratory pathogen exposure, understanding the physiological changes in morbid cattle will lead to improved management of BRD.

Experimental acute infection of alpacas with Bovine viral diarrhea virus 1 subgenotype b alters peripheral blood and GALT leukocyte subsets

Bovine viral diarrhea virus (BVDV) is a pathogen in cattle and alpacas ( Vicugna pacos), causing acute and persistent BVDV infections. We characterized the effect of acute BVDV infection on the immune system of alpacas by determining lymphocyte subpopulations in peripheral blood and gut-associated lymphoid tissues (GALT) as well as serum interferon levels. Alpacas were experimentally infected with BVDV-1b (strain CO-06). Peripheral blood leukocytes were isolated at 0, 3, 6, and 9 d postinfection (dpi), and leukocytes of GALT at 9 dpi, and evaluated using flow cytometry. Serum interferon levels were determined daily. Flow cytometric analyses of peripheral blood leukocytes showed a significant decrease in CD4+, CD8+, and αβ T-lymphocytes at 3 dpi. CD8+ lymphocytes were significantly increased, and activated lymphocytes were significantly decreased in the C3-stomach region in BVDV-infected alpacas. Serum interferon concentrations significantly increased in BVDV-infected alpacas at 3-6 dpi, peaking at 3 dpi. Our study confirms that BVDV can be a primary acute pathogen in alpacas and that it induces an interferon response and alters leukocyte subset populations. The changes in the proportion of T-lymphocytes during the early stages of BVDV infection may result in transient immunosuppression that may contribute to secondary bacterial and viral infections, similar to cattle.

Use of three-dimensional accelerometers to evaluate behavioral changes in cattle experimentally infected with bovine viral diarrhea virus

OBJECTIVE To assess the use of 3-D accelerometers to evaluate behavioral changes in cattle experimentally infected with a low-virulent strain of bovine viral diarrhea virus (BVDV). ANIMALS 20 beef steers (mean weight, 238 kg). PROCEDURES Calves were allocated to a BVDV (n = 10) or control (10) group. On day 0, calves in the BVDV group were inoculated with a low-virulent strain of BVDV (4 × 10(6) TCID50, intranasally), and calves in the control group were sham inoculated with BVDV-free medium (4 mL; intranasally). An accelerometer was affixed to the right hind limb of each calf on day -7 to record activity (lying, walking, and standing) continuously until 35 days after inoculation. Baseline was defined as days -7 to -1. Blood samples were collected at predetermined times for CBC, serum biochemical analysis, virus isolation, and determination of anti-BVDV antibody titers. RESULTS All calves in the BVDV group developed viremia and anti-BVDV antibodies but developed only subclinical or mild disease. Calves in the control group did not develop viremia or anti-BVDV antibodies. Mean time allocated to each activity did not differ significantly between the BVDV and control groups on any day except day 8, when calves in the BVDV group spent less time standing than the calves in the control group. Following inoculation, calves in both groups tended to spend more time lying and less time walking and standing than they did during baseline. CONCLUSIONS AND CLINICAL RELEVANCE Results indicated that behavioral data obtained by accelerometers could not distinguish calves subclinically infected with BVDV from healthy control calves. However, subtle changes in the behavior of the BVDV-infected calves were detected and warrant further investigation.

Noncytopathic bovine viral diarrhea virus 2 impairs virus control in a mouse model

Bovine viral diarrhea virus (BVDV) is an economically important pathogen that causes development of mild to severe clinical signs in wild and domesticated ruminants. We previously showed that mice could be infected by BVDV. In the present study, we infected mice intraperitoneally with non-cytopathic (ncp) BVDV1 or ncp BVDV2, harvested the blood and organs of the infected mice at days 4, 7, 10 and 14 postinfection (pi), and performed immunohistochemical analyses to confirm BVDV infection. Viral antigens were detected in the spleens of all infected mice from days 4 through 14 and were also found in the mesenteric lymph nodes, gut-associated lymphoid tissue (GALT), heart, kidney, intestine, and bronchus-associated lymphoid tissue (BALT) of some infected mice. In ncp BVDV2-infected mice, flow cytometric analysis revealed markedly fewer CD4(+) and CD8(+) T lymphocytes and lower expression of costimulatory molecules CD80 (B7-1) and CD86 (B7-2) and major histocompatibility complex (MHC) class II (I-A/I-E) than those in ncp BVDV1-infected mice. Production of the cytokines interleukin (IL)-6 and monocyte chemotactic protein (MCP)-1 was higher in the plasma of ncp BVDV2-infected mice than that in that of ncp BVDV1-infected mice. Our results demonstrate that ncp BVDV1 and ncp BVDV2 interact differently with the host innate immune response in vivo. These findings highlight an important distinction between ncp BVDV1 and ncp BVDV2 and suggest that ncp BVDV2 impairs the host's ability to control the infection and enhances virus dissemination.

Effects of Preinfection With Bovine Viral Diarrhea Virus on Immune Cells From the Lungs of Calves Inoculated With Bovine Herpesvirus 1.1

The aim of this work was to study the interstitial aggregates of immune cells observed in pulmonary parenchyma of calves preinfected with bovine viral diarrhea virus and challenged later with bovine herpesvirus 1. In addition, the intent of this research was to clarify the role of bovine viral diarrhea virus in local cell-mediated immunity and potentially in predisposing animals to bovine respiratory disease complex. Twelve Friesian calves, aged 8 to 9 months, were inoculated with noncytopathic bovine viral diarrhea virus genotype 1. Ten were subsequently challenged with bovine herpesvirus 1 and euthanized at 1, 2, 4, 7, or 14 days postinoculation. The other 2 calves were euthanized prior to the second inoculation. Another cohort of 10 calves was inoculated only with bovine herpesvirus 1 and then were euthanized at the same time points. Two calves were not inoculated with any agent and were used as negative controls. Pulmonary lesions were evaluated in all animals, while quantitative and biosynthetic changes in immune cells were concurrently examined immunohistochemically to compare coinfected calves and calves challenged only with bovine herpesvirus 1. Calves preinfected with bovine viral diarrhea virus demonstrated moderate respiratory clinical signs and histopathologic evidence of interstitial pneumonia with aggregates of mononuclear cells, which predominated at 4 days postinoculation. Furthermore, this group of animals was noted to have a suppression of interleukin-10 and associated alterations in the Th1-driven cytokine response in the lungs, as well as inhibition of the response of CD8+ and CD4+ T lymphocytes against bovine herpesvirus 1. These findings suggest that bovine viral diarrhea virus preinfection could affect the regulation of the immune response as modulated by regulatory T cells, as well as impair local cell-mediated immunity to secondary respiratory pathogens.

The impact of BVDV infection on adaptive immunity

Bovine viral diarrhea virus (BVDV) causes immunosuppression of the adaptive immune response. The level of suppression of the adaptive immune response is strain dependent. The early events of antigen presentation require activation of toll-like receptors that results in the release of pro-inflammatory cytokines. Non-cytopathic (ncp) BVDV infection stimulates cytokines from macrophages in vitro but the effect of BVDV infection in vivo on macrophages or in vitro with monocytes is not clear. Antigen presentation is decreased and co-stimulatory molecules are down regulated. T-lymphocytes numbers are reduced following BVDV infection in a strain dependent manner. There is recruitment of lymphocytes to the bronchial alveolar space following cytopathic (cp) BVDV infection. Depletion of T-lymphocytes occurs in the lymphoid tissue and is strain dependent. BVDV cp T-lymphocyte responses appear to be primarily a T helper 1 response while the response following ncp BVDV induces a T helper 2 response. Cytotoxic T-lymphocytes (CTL), an important BVDV defense mechanism are compromised. The major neutralizing antigens are well characterized but cross-protection between strains is variable. PI animals have normal adaptive immune responses with the exception of the PI strain immunotolerance and mucosal disease may be a function of the level of gamma delta T cells.

Experimental infection of cattle, sheep and pigs with 'Hobi'-like pestivirus

To date, limited information is available on the ability of 'Hobi'-like pestiviruses (putative bovine viral diarrhoea 3) to infect and cause disease in animal species traditionally affected by pestiviruses. In order to obtain new insights into host range and pathogenic potential of this atypical pestivirus, BVDV-seronegative calves (n=5), lambs (n=5) and piglets (n=5) were experimentally infected with the European 'Hobi'-like strain Italy-1/10-1, whereas two animals per species served as uninfected controls. Appearance of clinical signs, leukopenia, viremia, viral shedding and seroconversion were monitored for 28 days post-infection. Calves and lambs were successfully infected, displaying respiratory signs (nasal discharge), moderate hyperthermia and leukopenia, viremia and viral shedding through the nasal and faecal routes. Antibody responses were observed in both animal species by ELISA and virus neutralisation assays. In contrast, inoculated piglets did not display any clinical signs nor leukopenia and viral RNA was not detected in any biological samples. Nevertheless, the presence of detectable antibodies by virus neutralisation accounted for a successful, albeit limited infection of these animals.

Response of proinflammatory and anti-inflammatory cytokines in calves with subclinical bovine viral diarrhea challenged with bovine herpesvirus-1

The aim of this work was to investigate the susceptibility of calves infected with bovine viral diarrhea virus (BVDV) against secondary infections. For this purpose, the profile of cytokines implicated in the immune response of calves experimentally infected with a non-cytopathic strain of BVDV type-1 and challenged with bovine herpesvirus 1.1 (BHV-1.1) was evaluated in comparison with healthy animals challenged only with BHV-1.1. The immune response was measured by serum concentrations of cytokines (IL-1β, TNFα, IFNγ, IL-12, IL-4 and IL-10), acute phase proteins (haptoglobin, serum amyloid A and fibrinogen) and BVDV and BHV-1.1 specific antibodies. BVDV-infected calves displayed a great secretion of TNFα and reduced production of IL-10 following BHV-1 infection, leading to an exacerbation of the inflammatory response and to the development of more intense clinical symptoms and lesions than those observed in healthy animals BHV-1-inoculated. A Th1 immune response, based on IFNγ production and on the absence of significant changes in IL-4 production, was observed in both groups of BHV-1-infected calves. However, whereas the animals inoculated only with BHV-1 presented an IFNγ response from the start of the study and high expression of IL-12, the BVDV-infected calves showed a delay in the IFNγ production and low levels of IL-12. This alteration in the kinetic and magnitude of these cytokines, involved in cytotoxic mechanisms responsible for limiting the spread of secondary pathogens, facilitated the dissemination of BHV-1.1 in BVDV-infected calves.

Long-term clinicopathological characteristics of alpacas naturally infected with bovine viral diarrhea virus type Ib

BACKGROUND

Substantial bovine viral diarrhea virus (BVDV)-related production losses in North American alpaca herds have been associated with BVDV type Ib infection.

OBJECTIVES

To classify and differentiate the long-term clinicopathological characteristics of BVDV type Ib infection of alpaca crias, after natural virus exposure. We hypothesized that persistently infected (PI) alpacas specifically demonstrate growth retardation, clinicopathological evidence of opportunistic infections, and early mortality.

ANIMALS

Thirty-five crias naturally exposed to BVDV (18 acute, 3 chronic, 14 PIs), and 19 healthy cohort controls of 5 northeastern alpaca farms were prospectively evaluated over 2 years (September 2005-September 2008).

METHODS

Observational cohort-control study.

RESULTS

Chronically (viremia >3 weeks) and PI crias demonstrated significantly lower birth weights, decreased growth rates, anemia, and monocytosis compared with control animals. Common clinical problems of PI alpacas included chronic wasting, diarrhea, and respiratory disease. Median survival of PI alpacas that died was 177 days (interquartile range, 555) with a case fatality rate of 50% within 6 months of life. Transplacental infection was confirmed in 82% (9/11) of pregnant females on 1 farm, resulting in the birth of 7 PI crias (7/10 deliveries; 1 animal was aborted). Mean gestation at the beginning and end of BVDV exposure was 64 and 114 days, respectively.

CONCLUSIONS AND CLINICAL IMPORTANCE

Natural BVDV type 1b infection during early pregnancy resulted in a high incidence of PI offspring. Although PI alpacas may have distinct clinical characteristics, verification of persistent viremia in the absence of endogenous, neutralizing antibodies is essential to differentiate persistent from chronic infection.

Variation in expression of membrane IgM, CD21 (CR2) and CD32 (Fcgamma RIIB) on bovine lymphocytes with age: a longitudinal study

Typically, neonatal calves have poor active antibody responses to vaccination, attributed to immaturity of the neonatal immune system and suppressive effects of maternal (colostral) antibodies. Responses of naïve B cells are regulated by ligation of opposing activating (CD21, membrane IgM [mIgM]) and inhibitory (CD32) receptors. Expression of these receptors on blood lymphocytes of 15 calves, from birth to 6 months of age, was investigated by three-colour flow cytometry. Although the absolute number of mIgM(+) B lymphocytes was low in calves under 6 weeks, the intensity of mIgM expression per cell was significantly higher than for adults and >90% expressed both CD21 and CD32. The intensity of CD21 expression in calves did not differ significantly from adults, whereas CD32 expression was lower. Paradoxically, these findings suggest that responses of neonates should bias toward activation at the B cell level, warranting further investigation to reveal strategies for development of vaccines that are efficacious at an early age.

Apoptosis in lymphoid tissues of calves inoculated with non-cytopathic bovine viral diarrhea virus genotype 1: activation of effector caspase-3 and role of macrophages

The mechanisms responsible for lymphocyte apoptosis in bovine viral diarrhoea have not yet been clarified. Previous work suggests that bovine viral diarrhea virus (BVDV) is only directly responsible for the destruction of a small number of lymphocytes. The aim of this study was to clarify, in vivo, the role of macrophages in lymphocyte destruction through indirect mechanisms linked to the biosynthetic activation of these immunocompetent cells on ileal Peyer's patches, as well as the distribution and quantification of apoptosis. Eight colostrum-deprived calves were inoculated intranasally with a non-cytopathic strain of BVDV genotype 1 and killed in batches of two at 3, 6, 9 and 14 days post-inoculation (p.i.). The progressive depletion of Peyer's patches was found to be due to massive lymphocyte apoptosis, with an increase in cleaved caspase-3 and TUNEL-positive cells. Lymphoid depletion was accompanied, from 3 days p.i., by a significant rise in macrophage numbers both in lymphoid follicles and in interfollicular areas. Some macrophages showed signs of viral infection, together with subcellular changes indicative of phagocyte activation and, in some cases, of secretory activity. However, the number of macrophages that showed positive immunostaining for tumour necrosis factor-α and interleukin-1α, cytokines with a proven ability to induce apoptosis, remained low throughout the experiment in lymphoid follicles, where most apoptotic cells were found. These results thus appear to rule out a major involvement of macrophages and macrophage-secreted chemical mediators in the apoptosis of follicular B lymphocytes during BVDV infection.

Impact of persistent bovine viral diarrhea viral infection on the duration and level of shedding of Escherichia coli O157 in calves

OBJECTIVES

The goal of this study was to determine whether calves persistently infected with bovine viral diarrhea virus (BVDV) and inoculated with Escherichia coli O157 will shed the organism at a higher concentration and for a longer duration than calves not infected with BVDV.

MATERIALS

Nine calves, 6-8 weeks old, persistently infected with noncytopathic BVDV and eight calves not infected with BVDV obtained from separate cow-calf operations were used in this study. BVDV status, positive or negative, of all calves was confirmed by repeated testing throughout the study. Both groups were orally inoculated with 10(9) colony-forming units (CFU) of five nalidixic acid-resistant strains of E. coli O157. All calves were examined daily, and fecal samples were collected three times a week for 55 days for detection and enumeration of the nalidixic acid-resistant E. coli O157. Calves were then necropsied, and samples from the gastrointestinal tract were taken for the detection of the nalidixic acid-resistant E. coli O157.

RESULTS

Data analysis indicated no statistical difference in the concentration of E. coli O157 shed or the duration of shedding between the persistently infected BVDV calves and the control calves throughout the length of the study.

CONCLUSIONS

Our data indicate that persistent infection with noncytopathic BVDV does not play a role in the level or duration of shedding of E. coli O157 in cattle.

Bovine viral diarrhea viruses modulate toll-like receptors, cytokines and co-stimulatory molecules genes expression in bovine peripheral blood monocytes

We have used noncytopathic (ncp) and cytopathic (cp) Bovine Viral Diarrhea Viruses (BVDV) to determine the expression levels of TLR genes, type I IFN, pro-inflammatory and Th1/Th2 cytokine gene expression in bovine monocytes. In general, both BVDV strains had similar effects. However, we found some significant differences that could be due to biological differences between cp and ncp BVDV strains. TLR3 was significantly up-regulated in 1h ncp, but not in cp BVDV- infected monocytes, whereas TLR7 expression dominated in 24h infection with both BVDV strains. Type I IFN and IL-12 gene expression was also significantly up-regulated in 1h ncp, but not cp BVDV infection that correlated with the enhanced TLR3 gene expression. Both BVDV biotypes suppressed pro-inflammatory cytokines TNF-alpha, IL-1beta, and IL-6, co-stimulatory molecules CD80 and CD86, but did not change Th1 type cytokine IL-12 and INF-gamma, gene expression after 24h infection. We hypothesize that BVDV may escape immune responses by altering the expression of TLR 3 and 7 and their signaling pathways.

Immune evasion and immunosuppression by Anaplasma phagocytophilum, the causative agent of tick-borne fever of ruminants and human granulocytic anaplasmosis

Anaplasma phagocytophilum, the causative agent of tick-borne fever (TBF) in sheep and cattle and human granulocytic anaplasmosis, has the unique ability to infect and multiply within neutrophils, eosinophils and monocytes, cells at the frontline of the immune system. Infection with A. phagocytophilum is also characterized by severe leukopenia due to lymphocytopenia, neutropenia and thrombocytopenia lasting for several days. By itself TBF does not cause high mortality rates but infected animals are more susceptible to other secondary infections, pregnant animals may abort and there is a severe reduction in milk yield in dairy cattle. The susceptibility to secondary infections can be attributed to the leukopenia that accompanies the disease and the organism's adverse effects on lymphocyte and neutrophil functions. One of its fascinating features is that it infects and actively grows in neutrophils by employing an array of mechanisms to subvert their bactericidal activity. These include its ability to inhibit phagosome-lysosome fusion, to suppress respiratory burst and to delay the apoptotic death of neutrophils. It is also able to survive within an apparently immune host by employing a complex mechanism of antigenic variation.

Factors affecting sensitivity and specificity of pooled-sample testing for diagnosis of low prevalence infections

Testing of pooled samples has been proposed as a low-cost alternative for diagnostic screening and surveillance for infectious agents in situations where the prevalence of infection is low and most samples can be expected to test negative. The present study extends our previous work in pooled-sample testing (PST) to evaluate effects of the following factors on the overall PST sensitivity (SE(k)) and specificity (SP(k)): dilution (pool size), cross-contamination, and cross-reaction. A probabilistic model, in conjunction with Monte Carlo simulations, was used to calculate SE(k) and SP(k), as applied to detection of bovine viral diarrhea virus (BVDV) persistently infected (PI) animals using RT-PCR. For an average prevalence of BVDV PI of 0.01 and viremia in each animal between 10(2) and 10(7)virusparticles/mL, the pool size associated with the lowest number of tests, and lowest cost, corresponded to eight samples/pool. However, the least-cost pool size (lowest number of tests) was associated with a SE(k) of 0.90 (0.75-1), which corresponded to a decrease of 0.04, relative to the assay sensitivity for a single sample. The SP(k) for the same pool size, considering the effect of detection of BVDV acutely infected animals and cross-contamination as source of false positive results, was 0.90 (0.85-0.95). The effect of a hypothetical cross-reacting agent was to markedly decrease SP(k), especially as the prevalence of the cross-reacting agent increased. For a pool size of eight samples and a prevalence of the cross-reacting agent of 0.3, SP(k) ranged from 0.67 to 0.86, depending on the probability that the assay would detect the cross-reacting agent. The methods presented offer a means of evaluating and understanding the various factors that can influence overall accuracy of PST procedures.

Comparison of Blood Non-Specific Immune Parameters in Bovine Virus Diarrhoea Virus (BVDV) Persistently Infected and in Immune Heifers

Several data from different authors show that Bovine virus diarrhoea virus (BVDV) could be a key component in multiple-etiology diseases, indeed a lower leukocytes number and their impaired functions decrease the resistance to infections. However, most of the information on the impairment of immune function during BVDV infections arise from circumstantial evidence and from experimental infection studies, and few from field data. To assess the effects of BVDV on blood cells parameters, cellular and humoral functions under field conditions, we designed a controlled study in commercial dairy herds, comparing persistent infected (PI) and healthy heifers. A total of 45 heifers were considered, the PI animals were nine, the control animals were 34, while two controls were considered as acute infected animals. The comparison of the mean values in PI calves showed a significant decrease for leukocytes and granulocytes, while platelets showed a significant increase, when compared with control animals. The total number of lymphocytes decreased not significantly in PI animals, while the proportion significantly increased. The number and proportion of monocytes was significantly reduced in PI animals, when compared with controls. The data collected on markers of cellular immunity during our study cannot be compared with the literature because there are no reference values. The presence of a persistent infection affected the cellular enzymes: NAGase, lysozyme and respiratory burst showed a large statistically significant decrease in PI animals when compared with controls. The presence of a persistent infection with BVD virus influenced blood cells number and impaired some blood cell functions. Such impairment confirms that PI animals represent a threat to the herd not only because they could spread BVDV, but also because they are more susceptible to other infectious diseases.

Changes in peripheral blood leucocyte counts and subpopulations after experimental infection with BVDV and/or Mannheimia haemolytica

Leucocyte counts and subpopulations were studied in peripheral blood from calves experimentally infected in the respiratory tract with either bovine virus diarrhoea virus (BVDV) or Mannheimia haemolytica (Mh), or with a combination of both agents (BVDV/Mh). A non-inoculated control group was included. Peripheral blood samples were obtained for total leucocyte counts, and for neutrophil, lymphocyte and monocyte counts. The numbers of blood lymphocytes expressing the surface antigens CD4, CD8, WC1, B and IL-2R were analysed using flow cytometry. The results showed that BVDV inoculation induced a significant decrease in total leucocyte counts and in neutrophil and lymphocyte numbers, while Mh inoculation induced significant increases in total leucocyte counts and neutrophils, while the lymphocyte count decreased. In the BVDV/Mh group, the total leucocyte count and the lymphocyte numbers decreased significantly. In this group, the lymphocyte numbers remained on a very low level throughout the rest of the study. The numbers of CD4+, CD8+ and WC1+ lymphocytes decreased significantly compared with before inoculations mainly in the BVDV and BVDV/Mh groups. The drops were most pronounced in the BVDV/Mh group. The numbers of B+ lymphocytes and IL-2R+ cells did not change significantly.

The immune response to bovine viral diarrhea virus: a constantlychanging picture

Bovine viral diarrhea virus (BVDV) is one of the major immuno-suppressive viruses of cattle. The effect on the innate and acquired immune system is unique and results in dramatic immune dysfunction. BVDV infection also has the ability to cause persistent infection (PI) in the developing fetus. This Pl syndrome creates a requirement for high levels of BVDV immunity from vaccines to prevent these infections. BVDV vaccines and their future development continue to be an enigma in the control of BVDV.

Lesions and tissue distribution of viral antigen in severe acute versus subclinical acute infection with BVDV2

Differences in the distribution and spread of viral antigen, development of lesions and correlation between presence of viral antigen and lesions were compared between a low and highly virulent strain of BVDV2. Two groups of two-week- to two-month-old colostrum-deprived calves were inoculated intranasally with the naturally occurring low virulent BVDV2 strain 28508-5 or the highly virulent strain 1373. To study the sequence of virus spread and lesion development, calves were necropsied at days three, six, eight-nine and 12 to 14 post inoculation (pi). Viral antigen was detected by the indirect immunoperoxidase method in cryostat sections and lesions were evaluated in H&E-stained paraffin sections. Clinical signs and changes in lymphocyte and thrombocyte numbers confirmed the difference in virulence between the two strains. Both strains showed comparable initial infection and spread at day three pi. At day six pi, they were found widespread in lymphoid tissues and multifocally in intestinal mucosa. Lesions were very mild despite the large amount of antigen in the lymphoid tissues. After day six pi, differences between the low and highly virulent strains became more prominent. The strain of low virulence was cleared from the tissues, but there was a transient phase of depletion. The highly virulent strain continued to spread to different organs and there was severe depletion of lymphoid tissues without recovery.

Distribution of viral antigen and development of lesions after experimental infection of calves with a BVDV 2 strain of low virulence

To examine the virus-host interaction in subclinical bovine viral diarrhea virus (BVDV) infections, the spread of a BVDV 2 strain of low virulence to different organs and the development of lesions were investigated. Eight colostrum-deprived, clinically healthy, 2-3-month-old calves were intranasally inoculated with 10(6) tissue culture infective dose of the naturally occurring BVDV 2 strain 28508-5 of low virulence, and 2 served as controls. Two calves each were euthanized at days 3, 6, 9, and 13 postinoculation (pi). Representative tissues were processed for histology and immunohistology. Signs of overt clinical disease were absent. However, a mild temperature elevation at days 7 or 8 pi and a moderate decrease of circulating lymphocytes occurred in all inoculated calves. The BVDV antigen was detected at day 3 pi in several lymphoid tissues. At day 6 pi, BVDV antigen was found widespread in lymphoid tissues and multifocally in intestinal epithelial cells but was associated with no or subtle lesions only. At day 9 pi, much less BVDV antigen was detectable, but there was severe depletion of lymphoid tissues. At day 13 pi, BVDV antigen had been cleared from most lymphoid tissues that were at variable phases of depletion and recovery. In conclusion, the BVDV strain of low virulence spread to lymphoid tissues and intestinal epithelial cells but was rapidly eliminated. Transient depletion of lymphoid tissues was followed by recovery.

Quantification, risk factors, and health impact of natural congenital infection with bovine viral diarrhea virus in dairy calves

OBJECTIVES

To estimate risk and identify risk factors for congenital infection with bovine viral diarrhea virus (BVDV) not resulting in persistent infection and examine effect of congenital infection on health of dairy calves.

ANIMALS

466 calves.

PROCEDURES

Calves from 2 intensively managed drylot dairies with different vaccination programs and endemic BVDV infection were sampled before ingesting colostrum and tested with their dams for BVDV and BVDV serum-neutralizing antibodies. Records of treatments and death up to 10 months of age were obtained from calf ranch or dairy personnel. Risk factors for congenital infection, including dam parity and BVDV titer, were examined by use of logistic regression analysis. Effect of congenital infection on morbidity and mortality rates was examined by use of survival analysis methods.

RESULTS

Fetal infection was identified in 10.1% of calves, of which 0.5% had persistent infection and 9.6% had congenital infection. Although dependent on herd, congenital infection was associated with high BVDV type 2 titers in dams at calving and with multiparous dams. Calves with congenital infection had 2-fold higher risk of a severe illness, compared with calves without congenital infection.

CONCLUSIONS AND CLINICAL RELEVANCE

The unexpectedly high proportion of apparently healthy calves found to be congenitally infected provided an estimate of the amount of fetal infection via exposure of dams and thus virus transmission in the herds. Findings indicate that congenital infection with BVDV may have a negative impact on calf health, with subsequent impact on herd health.

Distribution of viral antigen and development of lesions after experimental infection with highly virulent bovine viral diarrhea virus type 2 in calves

OBJECTIVE

To correlate tissue distribution with development of lesions after experimental infection with a virulent strain of noncytopathic bovine viral diarrhea virus (BVDV) type 2 in calves.

ANIMALS

Ten 14-day-old and two 2-month-old colostrum-deprived calves.

PROCEDURE

Calves were intranasally inoculated with BVDV type-2 strain 1373 from an outbreak of clinically severe bovine viral diarrhea (BVD). Two 14-day-old calves served as noninfected controls. Two calves each were euthanatized on postinoculation days 3, 6, and 12, and 1 each on days 8, 9, 13, and 14. Tissues were collected for immunohistologic and histologic examination.

RESULTS

Inoculated calves developed nonspecific clinical signs characterized by high fever and decreased numbers of leukocytes and thrombocytes. Viral antigen was detected focally in lymphoid tissues on day 3. On days 6, 8, 9, 12, and 14, viral antigen became increasingly widespread throughout organs and tissues. Viral antigen in lymphoid tissues was associated with severe depletion of all compartments. Lesions in other tissues were not well correlated with distribution of viral antigen. Depletion of lymphoid tissues was observed in a calf on day 13, but viral antigen had been cleared from most tissues and was detected in vascular walls only.

CONCLUSIONS AND CLINICAL RELEVANCE

Infection with a virulent BVDV strain resulted in wide dissemination of viral antigen in host tissues. Severe lymphoid depletion developed in lymphoid tissues, whereas viral antigen was generally not associated with lesions in other tissues. Findings suggest that development of lesions in acute BVD is not solely a function of viral replication and is also attributable to host reaction to infection.