Evidence for biotype-specific effects of bovine viral diarrhoea virus on biological responses in acutely infected calves

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.

Cell-to-Cell Transmission Is the Main Mechanism Supporting Bovine Viral Diarrhea Virus Spread in Cell Culture

After initiation of an infective cycle, spread of virus infection can occur in two fundamentally different ways: (i) viral particles can be released into the external environment and diffuse through the extracellular space until they interact with a new host cell, and (ii) virions can remain associated with infected cells, promoting the direct passage between infected and uninfected cells that is referred to as direct cell-to-cell transmission. Although evidence of cell-associated transmission has accumulated for many different viruses, the ability of members of the genus Pestivirus to use this mode of transmission has not been reported. In the present study, we used a novel recombinant virus expressing the envelope glycoprotein E2 fused to mCherry fluorescent protein to monitor the spreading of bovine viral diarrhea virus (BVDV) (the type member of the pestiviruses) infection. To demonstrate direct cell-to-cell transmission of BVDV, we developed a cell coculture system that allowed us to prove direct transmission from infected to uninfected cells in the presence of neutralizing antibodies. This mode of transmission requires cell-cell contacts and clathrin-mediated receptor-dependent endocytosis. Notably, it overcomes antibody blocking of the BVDV receptor CD46, indicating that cell-to-cell transmission of the virus involves the engagement of coreceptors on the target cell.IMPORTANCE BVDV causes one of the most economically important viral infections for the cattle industry. The virus is able to cross the placenta and infect the fetus, leading to the birth of persistently infected animals, which are reservoirs for the spread of BVDV. The occurrence of persistent infection has hampered the efficacy of vaccination because it requires eliciting levels of protection close to sterilizing immunity to prevent fetal infections. While vaccination prevents disease, BVDV can be detected if animals with neutralizing antibodies are challenged with the virus. Virus cell-to-cell transmission allows the virus to overcome barriers to free virus dissemination, such as antibodies or epithelial barriers. Here we show that BVDV exploits cell-cell contacts to propagate infection in a process that is resistant to antibody neutralization. Our results provide new insights into the mechanisms underlying the pathogenesis of BVDV infection and can aid in the design of effective control strategies.

Microarray chip based identification of a mixed infection of bovine herpesvirus 1 and bovine viral diarrhea 2 from Indian cattle

Bovine herpesvirus 1 (BHV1) and bovine viral diarrhea virus 2 (BVD2) are endemic in India although no mixed infection with these viruses has been reported from India. We report first mixed infection of these viruses in cattle during routine screening with a microarray chip. 62 of the 69 probes of BHV1 and 42 of the 57 BVD2 probes in the chip gave positive signals for the virus. The virus infections were subsequently confirmed by RT-PCR. We also discuss the implications of these findings.

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.

Characterization of protection against systemic infection and disease from experimental bovine viral diarrhea virus type 2 infection by use of a modified-live noncytopathic type 1 vaccine in calves

Objective—To evaluate protection resulting from use of a modified-live noncytopathic bovine viral diarrhea virus (BVDV) type 1 vaccine against systemic infection and clinical disease in calves challenged with type 2 BVDV.

Animals—10 calves, 5 to 7 months of age.

Procedures—Calves were allocated (n = 5/group) to be nonvaccinated or vaccinated SC on day 0 with BVDV 1 (WRL strain). Calves in both groups were challenged intranasally with BVDV type 2 isolate 890 on day 21. Rectal temperatures and clinical signs of disease were recorded daily, and total and differential WBC and platelet counts were performed. Histologic examinations and immunohistochemical analyses to detect lesions and distribution of viral antigens, respectively, were performed.

Results—After challenge exposure to BVDV type 2, nonvaccinated calves developed high rectal temperatures, increased respiratory rates, viremia, leukopenia, lymphopenia, and infection of the thymus. Vaccinated calves did not develop high rectal temperatures or clinical signs of respiratory tract disease. Vaccinated calves appeared to be protected against systemic replication of virus in that they did not develop leukopenia, lymphopenia, viremia, or infection of target organs, and infectious virus was not detected in peripheral blood mononuclear cells or the thymus.

Conclusions and Clinical Relevance—The modified-live BVDV type 1 vaccine protected against systemic infection and disease after experimental challenge exposure with BVDV type 2. The vaccine protected calves against infection and viremia and prevented infection of target lymphoid cells.

Noncytopathic bovine viral diarrhea virus can persist in testicular tissue after vaccination of peri-pubertal bulls but prevents subsequent infection

The objectives of this research were to evaluate the risk of prolonged testicular infection as a consequence of vaccination of peri-pubertal bulls with a modified-live, noncytopathic strain of BVDV and to assess vaccine efficacy in preventing prolonged testicular infections after a subsequent acute infection. Seronegative, peri-pubertal bulls were vaccinated subcutaneously with an approximate minimum immunizing dose or a 10x standard dose of modified-live, noncytopathic BVDV or were maintained as unvaccinated controls. Forty-nine days after vaccination, all bulls were intranasally inoculated with a noncytopathic field strain of BVDV. Semen and testicular biopsies collected after vaccination and challenge were assayed for BVDV using virus isolation, reverse transcription-nested PCR, or immunohistochemistry and the identity of viral strains was determined by nucleotide sequencing of PCR products. The vaccine strain of BVDV was detected in testicular tissue of vaccinated bulls as long as 134 days after immunization. Prolonged testicular infections with the challenge strain were detected only in unvaccinated bulls as long as 85 days after challenge. Whereas vaccination caused prolonged testicular infection in some bulls, it did prevent subsequent infection of testicular tissue with the challenge strain. This research demonstrates that subcutaneous vaccination of naïve, peri-pubertal bulls with a noncytopathic, modified-live strain of BVDV can result in prolonged viral replication within testicular tissue. The risk for these prolonged testicular infections to cause venereal transmission of BVDV or subfertility is likely to be low but requires further investigation.

Practical significance of heterogeneity among BVDV strains: Impact of biotype and genotype on U.S. control programs

In the early 1990s research groups in North America noted that a newly recognized severe acute form of bovine viral diarrhea virus infection, referred to as hemorrhagic syndrome or severe acute BVDV (SA BVDV), was associated with a genetically distinct subgroup of BVDV strains. This new subgroup was named BVDV genotype 2 or BVDV2. All BVDV strains previously characterized in the literature belonged to a separate genotype, BVDV1. However, not all strains identified as BVDV2 were associated with severe acute infections. If I did this deletion, I did not mean to do it. I think it was already here, though. I see there are some other big edits that I did not do; fine. Hollis subsequent surveys of BVDV strains isolated from clinical submissions to diagnostic laboratories and contaminated fetal calf serum suggested that the ratio of BVDV2 to BVDV1 strains in the U.S. approached 50%. Further, while antigenic cross reactivity is seen between BVDV1 and BVDV2 strains, a log or more difference is typically observed in titers against viruses from different genotypes. These observations prompted vaccine manufacturers in North America to produce vaccines against BVDV that contained antigens from both BVDV1 and BVDV2 strains. Under experimental conditions, these new vaccines offered improved protection against type 2 strains, however field data are still insufficient to assess their efficacy in practice. The BVDV genotypes may also be segregated into subgenotypes. Two subgenotypes of both BVDV1 (BVDV1a and BVDV1b) and BVDV2 (BVDV2a and BVDV2b) have been reported in North American. BVDV2a predominates with BVDV2b isolation a rare event. In contrast, BVDV1a and BVDV1b are both commonly isolated. Antigenic differences observed between strains from the BVDV1a and BVDV1b subgenotypes have led to the suggestion that protection may be improved by inclusion of strains from both BVDV1a and BVDV1b in vaccines in addition to BVDV2. The cost to benefit ratio of this proposal is currently a matter of debate.

Identification of a cell population that produces alpha/beta interferon in vitro and in vivo in response to noncytopathic bovine viral diarrhea virus

In vitro infection of bovine cells of many origins with the cytopathogenic bovine viral diarrhea virus (cpBVDV) results in the induction of alpha/beta interferon (IFN-alpha/beta), whereas noncytopathogenic BVDV (ncpBVDV) isolates have been shown not to induce IFN-alpha/beta in vitro. Similarly, cpBVDV induces IFN-alpha/beta in the early bovine fetus, but ncpBVDV does not. However, acute infection of naive cattle with ncpBVDV results in IFN-alpha/beta production. In this study, we identified and characterized a minor population of cells, present in lymph nodes that produce IFN-alpha in response to ncpBVDV. These cells expressed the myeloid markers CD14, CD11b, and CD172a but did not express CD4 and CD45RB. We also established that these cells produced IFN-alpha in the absence of detectable productive infection.

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.

Aspects of the innate and adaptive immune responses to acute infections with BVDV

The immune response can be divided into innate and adaptive components that synergise to effect the clearance of pathogens. Recently, it has been realised that these arms of the immune system do not act independently, the magnitude and quality of the adaptive response is dependent on signals derived from the innate response. Here, we review the innate immune responses to bovine viral diarrhoea virus infections of cattle and relate these changes to immunosuppression and the subsequent development of the adaptive immune response.

Patterns of cellular gene expression in cells infected with cytopathic or non-cytopathic bovine viral diarrhea virus

Bovine viral diarrhea virus (BVDV) infection in cattle is responsible for mucosal disease; an invariably fatal syndrome characterized by the recovery of two BVDV strains: cytopathic (cp) or noncytopathic (ncp). To understand the cellular responses to cp BVDV infection, we carried out differential display-polymerase chain reaction (DD-PCR) analysis of gene expression in infected cells. Altered expression of 14 genes involved in several functions was observed in cells infected with cp BVDV: (1) immune regulation, such as CD46, FKBP-12, and osteopontin (OPN); (2) apoptosis-related cysteine proteases like calpain; (3) signaling plasma membrane proteins such as integrin beta1, and prion protein; and (4) unknown function genes. Northern blot analysis of the expression of these genes in ncp BVDV infected cells revealed that while the expression of some genes was affected as in cp BVDV infected cells, others show a clearly contrary change. We postulate that a cause-effect relationship may exist between the differential gene expression alterations that characterize cp and ncp BVDV infections and the unique diseases associated with each BVDV biotype.

Rapid transplacental infection with bovine pestivirus following intranasal inoculation of ewes in early pregnancy

Despite the importance of congenital viral infections in both veterinary and human medicine, only limited experimental work has been carried out to elucidate the mechanisms involved in transplacental virus infections. To further an understanding of fetal infection with pestiviruses, the distribution of bovine pestivirus in the uterine and fetal tissues of ewes in early pregnancy, following a natural route of infection, was investigated. On the 18th day of pregnancy, nine ewes were inoculated by the intranasal route with 1 x 10(5) 50% tissue culture infective doses of an Australian isolate of noncytopathic bovine pestivirus (bovine viral diarrhea virus genotype 1). All ewes were ovariohysterectomized at approximately 100 hours postinfection. Samples from the reproductive tract and conceptus were examined histologically and tested for bovine pestivirus by nested reverse transcription-polymerase chain reaction (RT-PCR) and immunohistochemistry and for interferon-tau mRNA expression by nonnested RT-PCR. Although no histopathologic changes were observed in the maternal or fetal tissues, virus was detected in the reproductive tract of all nine ewes and in all of the conceptuses examined. At the time of surgery, only two of the nine ewes were demonstrably viremic. This study demonstrates that bovine pestivirus can spread from a natural site of infection to the ovine fetus within 4 days in the absence of maternal immunity and despite the presence of interferon expression in the reproductive tract.

Diversity among bovine pestiviruses

Bovine viral diarrhoea virus (BVDV) isolates are characterized by an important genetic, antigenic and pathogenic diversity. The emergence of new hypervirulent BVDV strains in North America has provided clear evidence of pathogenic differences between BVDV strains. The origin of BVDV diversity is related to high mutation rate occurring in RNA viruses but the consequences of mutations obviously depend on the genes which are involved. Mutations in genes encoding for structural proteins of immunological importance may have practical implications. Knowledge of BVDV diversity is important for understanding the wide variety of pathogenesis of diseases caused by the virus, for monitoring the epidemiology of the different types and for the design of optimum laboratory tests and vaccines. This review focuses on the origin and consequences of BVDV diversity with regard to pathogenesis, biotypes, and antigenic and genetic variations.

Differences in experimental virulence of bovine viral diarrhoea viral strains isolated from haemorrhagic syndromes

In the late 1980s, a new hypervirulent and epidemic form of bovine viral diarrhoea virus (BVDV) infection appeared in North America. A similar but sporadic syndrome was later reported in Europe. To compare the pathogenic characters of the North American and European hypervirulent strains, we inoculated BVDV naïve calves with BVDV strains isolated from haemorrhagic syndromes originating in Belgium, France and the USA. The experimental procedure comprised daily clinical examination and measurement of blood and virological parameters. The American BVD890/256 strain induced severe thrombocytopaenia, profuse diarrhoea and pneumonia in all calves, indicating that hypervirulent BVDV could be the primary infectious agent of pneumonia. Interestingly, a strong correlation was observed between the intense viraemia and a decreased platelet count. None of the European strains tested induced significant pathological signs, although isolated from cases presenting haemorrhagic syndrome.

Single amino acid differences are sufficient for CD4(+) T-cell recognition of a heterologous virus by cattle persistently infected with bovine viral diarrhea virus

Cattle that are persistently infected (PI) with one strain of bovine viral diarrhea virus (BVDV) can resolve infection with a second, antigenically heterologous strain but not the homologous strain. Since CD4(+) T cells are thought to be critical for the resolution of acute BVDV infection (Howard et al., 1992, Vet. Immunol. Immunopathol. 32, 303-314), we have examined the recognition of a heterologous virus (NADL) by CD4(+) T cells from Pe515-PI animals. The immune response of non-PI control cattle challenged with NADL or Pe515ncp was strain cross-reactive, whereas Pe515-PI animals responded to NADL only. The immune repertoire of both groups included NS3, which differs by approximately 1% (9/683) amino acids between these two viruses. Lymphoproliferative responses to proteins and synthetic peptides corresponding to three nonconservative differences in NS3 demonstrated that CD4(+) T cells from non-PI control animals responded well to proteins but poorly to the peptides from both viruses. In contrast, PI animals were responsive to heterologous proteins and peptides but nonresponsive to the homologous equivalents. A single amino acid difference between the two sequences was sufficient to allow responsiveness.

Distribution of bovine virus diarrhoea virus in tissues and white blood cells of cattle during acute infection

This study is performed to gain knowledge about the quantitative distribution of bovine virus diarrhoea virus (BVDV) in tissues and white blood cells (WBC) at different intervals after acute infection. Ten specific pathogen-free calves were intranasally inoculated with 10(5) 50% tissue culture infective dose of the non-cytopathic BVDV strain 4800. Twelve hours after inoculation tonsil biopsies were taken and WBC were collected daily for virus isolation and titration. Each day one calf was killed and virus isolations and titrations were performed from a range of tissues. The results indicate that BVDV first replicates in nasal mucosa and to high titers in the tonsil. The virus then appeared to spread to the regional lymph nodes and then disseminates throughout the body. The virus titers were highest in tonsil, thymus and ileum and were low in the WBC. Also after in vitro infection virus titers in WBC were very low, whereas, they were high in epithelial cells. Although the WBC might not be as important as other cells for replication of BVDV, they may play a role in the spread of the virus throughout the body.