Genome sequence and experimental infection of calves with bovine gammaherpesvirus 4 (BoHV-4).

Bovine gammaherpesvirus 4 (BoHV-4) is ubiquitous in cattle worldwide, and it has been detected in animals exhibiting broad clinical presentations. The virus has been detected in the United States since the 1970s; however, its clinical relevance remains unknown. Here, we determined the complete genome sequences of two contemporary BoHV-4 isolates obtained from respiratory (SD16-38) or reproductive (SD16-49) tract specimens and assessed clinical, virological, and pathological outcomes upon intranasal (IN) inoculation of calves with the respiratory BoHV-4 isolate SD16-38. A slight and transient increase in body temperature was observed in BoHV-4-inoculated calves. Additionally, transient viremia and virus shedding in nasal secretions were observed in all inoculated calves. BoHV-4 DNA was detected by nested PCR in the tonsil and regional lymph nodes (LNs) of calves euthanized on day 5 post-inoculation (pi) and in the lungs of calves euthanized on day 10 pi. Calves euthanized on day 35 pi harbored BoHV-4 DNA in the respiratory tract (turbinates, trachea, lungs), regional lymphoid tissues, and trigeminal ganglia. Interestingly, in situ hybridization revealed the presence of BoHV-4 DNA in nerve bundles surrounding the trigeminal ganglia and retropharyngeal lymph nodes (day 35 pi). No histological changes were observed in the respiratory tract (turbinate, trachea, and lung), lymphoid tissues (tonsil, LNs, thymus, and spleen), or central nervous tissues (olfactory bulb and trigeminal ganglia) sampled throughout the animal studies (days 5, 10, and 35 pi). This study contributes to the understanding of the infection dynamics and tissue distribution of BoHV-4 following IN infection in calves. These results suggest that BoHV-4 SD16-38 used in our study has low pathogenicity in calves upon intranasal inoculation.

Bovine Viral Diarrhea Virus in Cattle From Mexico: Current Status.

Bovine viral diarrhea (BVD) is an infectious disease, globally-distributed, caused by bovine Pestiviruses, endemic of cattle and other ruminant populations. BVD leads to significant economic losses to the cattle industry due to the wide range of clinical manifestations, including respiratory and gastrointestinal diseases and reproductive disorders. Within the Pestivirus genus of the family Flaviviridae three viral species are associated with BVD; Pestivirus A (Bovine viral diarrhea virus 1, BVDV-1), Pestivirus B (Bovine viral diarrhea virus 2, BVDV-2), and Pestivirus H (HoBi-like pestivirus, atypical ruminant pestivirus). These species are subdivided into subgenotypes based on phylogenetic analysis. The extensive genetic diversity of BVDV has been reported for several countries, where the incidence and genetic variation are more developed in Europe than in the Americas. The first report of BVDV in Mexico was in 1975; this study revealed seropositivity of 75% in cows with a clinical history of infertility, abortions, and respiratory disease. Other studies have demonstrated the presence of antibodies against BVDV with a seroprevalence ranging from 7.4 to 100%. Recently, endemic BVDV strains affecting cattle populations started to be analyzed, providing evidence of the BVDV diversity in several states of the country, revealing that at least four subgenotypes (BVDV-1a, 1b, 1c, and 2a) are circulating in animal populations in Mexico. Little information regarding BVD epidemiological current status in Mexico is available. This review summarizes available information regarding the prevalence and genetic diversity viruses associated with BVD in cattle from Mexico.

Effects of Multivalent BRD Vaccine Treatment and Temperament on Performance and Feeding Behavior Responses to a BVDV1b Challenge in Beef Steers.

This study examined the effects of multivalent respiratory vaccine treatment (VT) and animal temperament classification on feeding behavior traits, feed intake and animal performance in response to a bovine viral diarrhea virus (BVDV) challenge. Nellore-Angus crossbred steers (n = 360; initial body weight (BW) 330 ± 48 kg) were assigned to one of three vaccine treatments: non-vaccinated (NON), modified live (MLV) and killed (KV) regarding respiratory viral pathogens, and inoculated intranasally with the same BVDV1b strain. Cattle temperament categories were based on exit velocity. Overt clinical signs of respiratory disease were not observed, yet the frequency and duration of bunk visit events as well as traditional performance traits decreased (p < 0.01) following BVDV challenge and then rebounded in compensatory fashion. The reduction in dry matter intake (DMI) was less (p < 0.05) for MLV-vaccinated steers, and MLV-vaccinated steers had longer (p < 0.01) durations of bunk visit and meal events and slower (p < 0.01) eating rates compared with KV- and non-vaccinated steers following BVDV challenge. Greater differences in most feeding behavior traits due to VT existed within calm vs. excitable steers. Respiratory vaccination can reduce the sub-clinical feeding behavior and performance effects of BVDV in cattle, and the same impacts may not occur across all temperament categories.

Epidemiology of Pestivirus H in Brazil and Its Control Implications.

Along with viruses in the Pestivirus A (Bovine Viral Diarrhea Virus 1, BVDV1) and B species (Bovine Viral Diarrhea Virus 2, BVDV2), members of the Pestivirus H are mainly cattle pathogens. Viruses belonging to the Pestivirus H group are known as HoBi-like pestiviruses (HoBiPev). Genetic and antigenic characterization suggest that HoBiPev are the most divergent pestiviruses identified in cattle to date. The phylogenetic analysis of HoBiPev results in at least five subgroups (a-e). Under natural or experimental conditions, calves infected with HoBiPev strains typically display mild upper respiratory signs, including nasal discharge and cough. Although BVDV1 and BVDV2 are widely distributed and reported in many South American countries, reports of HoBiPev in South America are mostly restricted to Brazil. Despite the endemicity and high prevalence of HoBiPev in Brazil, only HoBiPev-a was identified to date in Brazil. Unquestionably, HoBiPev strains in BVDV vaccine formulations are required to help curb HoBiPev spread in endemic regions. The current situation in Brazil, where at this point only HoBiPev-a seems present, provides a more significant opportunity to control these viruses with the use of a vaccine with a single HoBiPev subtype. Despite the lack of differentiation among bovine pestiviruses by current BVDV tests, the reduced genetic variability of HoBiPev in Brazil may allow reliable identification of cases within the region. On the other hand, introducing foreign ruminants, biologicals, and genetic material to South America, especially if it originated from other HoBiPev-endemic countries, should consider the risk of introducing divergent HoBiPev subtypes.

Evaluation of Antigenic Comparisons Among BVDV Isolates as it Relates to Humoral and Cell Mediated Responses.

Antigenic differences between bovine viral diarrhea virus (BVDV) vaccine strains and field isolates can lead to reduced vaccine efficacy. Historically, antigenic differences among BVDV strains were evaluated using techniques based on polyclonal and monoclonal antibody activity. The most common method for antigenic comparison among BVDV isolates is determination of virus neutralization titer (VNT). BVDV antigenic comparisons using VNT only account for the humoral component of the adaptive immune response, and not cell mediated immunity (CMI) giving an incomplete picture of protective responses. Currently, little data is available regarding potential antigenic differences between BVDV vaccine strains and field isolates as measured by CMI responses. The goal of the current paper is to evaluate two groups of cattle that differed in the frequency they were vaccinated, to determine if similar trends in CMI responses exist within each respective group when stimulated with antigenically different BVDV strains. Data from the current study demonstrated variability in the CMI response is associated with the viral strain used for stimulation. Variability in IFN-γ mRNA expression was most pronounced in the CD4+ population, this was observed between the viruses within each respective BVDV subgenotype in the Group 1 calves. The increase in frequency of CD25+ cells and IFN-γ mRNA expression in the CD8+ and CD335+ populations were not as variable between BVDV strains used for stimulation in the Group 1 calves. Additionally, an inverse relationship between VNT and IFN-γ mRNA expression was observed, as the lowest VNT and highest IFN-γ mRNA expression was observed and vice versa, the highest VNT and lowest IFN-γ mRNA expression was observed. A similar trend regardless of vaccination status was observed between the two groups of calves, as the BVDV-1b strain had lower IFN-γ mRNA expression. Collectively, data from the current study and previous data support, conferring protection against BVDV as a method for control of BVDV in cattle populations is still a complex issue and requires a multifactorial approach to understand factors associated with vaccine efficacy or conversely vaccine failure. Although, there does appear to be an antigenic component associated with CMI responses as well as with humoral responses as determined by VNT.

Detection and genotyping of bovine viral diarrhea virus found contaminating commercial veterinary vaccines, cell lines, and fetal bovine serum lots originating in Mexico.

In this communication, we report the presence of RNA of bovine viral diarrhea virus (BVDV) as a contaminant of different biological products used in Mexico for veterinary vaccine production. For this purpose, six batches of monovalent vaccines, eight cell line batches used for vaccine production, and 10 fetal bovine serum lots (FBS) commercially available in Mexico from different suppliers were tested by reverse transcription polymerase chain reaction (RT-PCR). Viral RNA was detected in 62.5% of the samples analyzed. Phylogenetic analysis revealed the presence of the subgenotypes BVDV-1a, 1b, and BVDV-2a in the tested samples. Collectively, these findings indicate that contamination by BVDV RNA occurs in commercial vaccines and reagents used in research and production of biological products. The ramifications of this contamination are discussed.

Persistent infection of American bison (Bison bison) with bovine viral diarrhea virus and bosavirus.

Bovine viral diarrhea viruses (BVDV) are significant pathogens of cattle, leading to losses associated with reproductive failure, respiratory disease and immune dysregulation. While cattle are the reservoir for BVDV, a wide range of domestic and wild ruminants are susceptible to infection and disease caused by BVDV. Samples from four American bison (Bison bison) from a captive herd were submitted for diagnostic testing due to their general unthriftiness. Metagenomic sequencing on pooled nasal swabs and serum identified co-infection with a BVDV and a bovine bosavirus. The BVDV genome was more similar to the vaccine strain Oregon C24 V than to other BVDV sequences in GenBank, with 92.7 % nucleotide identity in the open reading frame. The conserved 5'-untranslated region was 96.3 % identical to Oregon C24 V. Bosavirus has been previously identified in pooled fetal bovine serum but its clinical significance is unknown. Sequencing results were confirmed by virus isolation and PCR detection of both viruses in serum and nasal swab samples from two of the four bison. One animal was co-infected with both BVDV and bosavirus while separate individuals were positive solely for BVDV or bosavirus. Serum and nasal swabs from these same animals collected 51 days later remained positive for BVDV and bosavirus. These results suggest that both viruses can persistently infect bison. While the etiological significance of bosavirus infection is unknown, the ability of BVDV to persistently infect bison has implications for BVDV control and eradication programs. Possible synergy between BVDV and bosavirus persistent infection warrants further study.

Changes in circulating lymphocytes and lymphoid tissue associated with vaccination of colostrum deprived calves.

The objective of this study was to compare immunological responses and lymphoid depletion in young, colostrum deprived calves following administration of vaccines containing modified-live bovine viral diarrhea virus (BVDV). A group of calves exposed to a typical virulence non-cytopathic (ncp) BVDV-2 field strain (ncp exposed) was included to compare responses of calves receiving vaccine to responses generated against a field strain (mimicking a natural infection). A negative control group administered a placebo was used in all comparisons. All vaccines used in the study were administered per manufacturer recommendations while ncp BVDV exposed calves received 5 ml intranasally (2.5 ml/nare; 4.2 × 106 TCID50/ml) of the BVDV-2 field strain. Samples collected at each time point included nasal swabs for virus detection, blood samples for complete blood counts and detection of viremia, PBMCs for flow cytometric analysis, serum for virus neutralization titers, and thymus tissue at necropsy for evaluation of lymphoid depletion. A measurable neutralizing BVDV titer was observed for all treatment groups excluding the control animals, which remained negative during the study period. Virus shedding was only detected from the ncp vaccinated and ncp exposed calves. A decline from baseline was observed for peripheral lymphocyte and CD4+ cells for the groups receiving the adjuvanted cytopathic (cp) vaccine, the double deleted genetically modified (ddGM) vaccine, the ncp vaccine and ncp exposed calves, but not for the control group or groups receiving cp vaccines. Thymus depletion was observed for the ncp vaccine and ncp exposed calves and to a lesser extent for the ddGM vaccine calves. Collectively, these data suggest that the virus biotype, method of attenuation, presentation, and use of adjuvant will influence vaccine impacts on lymphoid tissues and the immune response. As such, multiple variables should be considered when determining costs and benefits of vaccination.

Sequential exposure to bovine viral diarrhea virus and bovine coronavirus results in increased respiratory disease lesions: clinical, immunologic, pathologic, and immunohistochemical findings.

Bovine coronaviruses (BoCVs) have been found in respiratory tissues in cattle and frequently associated with bovine respiratory disease (BRD); however, pathogenesis studies in calves are limited. To characterize the pathogenesis and pathogenicity of BoCV isolates, we used 5 different BoCV strains to inoculate colostrum-deprived calves, ~ 2-5 wk of age. Later, to determine if dual viral infection would potentiate pathogenicity of BoCV, calves were inoculated with BoCV alone, bovine viral diarrhea virus (BVDV) alone, or a series of dual-infection (BVDV-BoCV) schemes. A negative control group was included in all studies. Clinical signs and body temperature were monitored during the study and samples collected for lymphocyte counts, virus isolation, and serology. During autopsy, gross lesions were recorded and fixed tissues collected for histopathology and immunohistochemistry; fresh tissues were collected for virus isolation. Results suggest increased pathogenicity for isolate BoCV OK 1776. Increased body temperature was found in all virus-inoculated groups. Lung lesions were present in calves in all dual-infection groups; however, lesions were most pronounced in calves inoculated with BVDV followed by BoCV inoculation 6 d later. Lung lesions were consistent with mild-to-moderate interstitial pneumonia, and immunohistochemistry confirmed the presence of BoCV antigen. Our studies demonstrated that BVDV-BoCV dual infection may play an important role in BRD pathogenesis, and timing between infections seems critical to the severity of lesions.

Measuring CMI responses using the PrimeFlow RNA assay: A new method of evaluating BVDV vaccination response in cattle.

Current methods for evaluating bovine viral diarrhea virus (BVDV) vaccination response typically rely on measurement of humoral responses as determined by virus neutralizing antibody titers (VNT) against BVDV. While VNT are correlated with increased protection, research has also shown that cell mediated immunity (CMI) is an important component of a protective response against BVDV. For example, improved protection against BVDV by modified-live viral (MLV) vaccines as compared to killed vaccines is thought to be due to better CMI induced by the MLV. The goal of this work was to evaluate the cell mediated response in vaccinated calves using a novel PrimeFlow RNA assay that incorporates cell surface marker staining with intracellular RNA expression of cytokines and viral RNA detection. Results from this study evaluating mRNA for IFN-γ and IL-2 at 24 h post-BVDV stimulation are similar to previous studies in which IFN-γ was detected in the CD4+ and CD8+ T cell population. However, a novel observation was the detection of IFN-γ mRNA in the NK cell population in vaccinated animals. The NK cell population contributed a significant portion of the IFN-γ produced. This study also demonstrated a decrease in the frequency and amount of BVDV in PBMCs, harvested from vaccinated calves and exposed to BVDV in vitro. Collectively data from this study highlights the association between an increase in IFN-γ and a decreased infection rate of isolated PBMC's, based on the frequency and amount of BVDV positive cells following in vitro exposure. This new method combines not only the ability to evaluate cellular responses, but also the ability to understand potential antiviral properties associated with cellular responses. This is the first assay to describe and simultaneously measure CMI responses and intracellular viral RNA quantity as a method to evaluate protective responses associated with vaccination.

Molecular Characterization of Pestiviruses in Fetal Bovine Sera Originating From Argentina: Evidence of Circulation of HoBi-Like Viruses.

Serological evidence suggests that HoBi-like viruses, an emerging species within the Pestivirus genus of the Flaviviridae family, are in circulation in Argentina. While HoBi-like viruses were first isolated from Brazilian fetal bovine serum (FBS), no survey of Argentine FBS has been conducted. Therefore, 124 local samples of non-irradiated FBS originating from Argentina were surveyed for the presence of pestiviruses using RT-PCR. Amplicons from pestivirus positive samples were genotyped. Four samples were positive for HoBi virus-specific RT-PCR, while the BVDV-positive samples (n = 45) were classified as BVDV-1b (82.2%), BVDV-1a (13.3%), and BVDV-2 (4.5%). Virus isolation and serological profile assessment were performed for the four HoBi-positive FBS lots. These results confirm the circulation of HoBi-like virus in some regions of the Argentinean territory, highlighting the need to review the diagnostic techniques currently used in the clinical cases suspected of BVDV and in contamination control protocols for adventitious agents in cells and biotechnological products.

Serosurvey for Influenza D Virus Exposure in Cattle, United States, 2014-2015.

Influenza D virus has been detected predominantly in cattle from several countries. In the United States, regional and state seropositive rates for influenza D have previously been reported, but little information exists to evaluate national seroprevalence. We performed a serosurveillance study with 1,992 bovine serum samples collected across the country in 2014 and 2015. We found a high overall seropositive rate of 77.5% nationally; regional rates varied from 47.7% to 84.6%. Samples from the Upper Midwest and Mountain West regions showed the highest seropositive rates. In addition, seropositive samples were found in 41 of the 42 states from which cattle originated, demonstrating that influenza D virus circulated widely in cattle during this period. The distribution of influenza D virus in cattle from the United States highlights the need for greater understanding about pathogenesis, epidemiology, and the implications for animal health.

Genomic and antigenic characterization of a cytopathic bovine viral diarrhea virus 1i isolated in the United States.

Bovine viral diarrhea viruses (BVDV) are a common global viral pathogen of ruminants. Considerable genetic variability is found amongst BVDV1 isolates, with at least 21 subgenotypes being described. In the United States, BVDV1a and 1b are the only subgenotypes described to date. Here, the genomic sequence of CA2005, a cytopathic BVDV1, was determined. This virus, isolated in California, did not segregate into either BVDV1a or 1b subgenotypes. BLAST analysis showed CA2005 was most closely related to BVDV1i isolates. CA2005 was also the first cytopathic BVDV1i and one of few non-1a, non-1b cytopathic viruses reported. The genomic sequence was 15,752 nucleotides in length. Cytopathogenicity was conferred by duplication of the NS3 protein with a small ubiquitin B insertion at the border of the NS2/NS3 proteins. Virus neutralization assays using antisera against BVDV1a vaccine viruses revealed variable neutralization, suggesting modified live vaccines may not be totally protective against CA2005 and similar viruses.

Analysis of tRNA halves (tsRNAs) in serum from cattle challenged with bovine viral diarrhea virus.

Acute infections of bovine viral diarrhea virus (BVDV) lead to a range of clinical presentations. Laboratory tests for detection depend on collection of samples during a short viremia. Acutely infected animals remain largely undiagnosed. Transfer RNA halves (tsRNAs) are hypothesized to function like microRNAs to regulate gene expression during an immune response. The objective of this study was to identify tsRNAs in cattle that had been challenged with a non-cytopathic field strain of BVDV. Colostrum-deprived neonatal Holstein calves were either challenged with BVDV (n=5) or mock challenged (n=4). Sera was collected prior to challenge and days 4, 9, and 16 post challenge. RNA was extracted and read counts of small non-coding RNAs were assessed using next-generation sequencing. A total of 87,838,207 reads identified 41 different tsRNAs. Two 5' tsRNAs, tsRNAProAGG and tsRNAValAAC, differed across time. Two 5' tsRNAs, tsRNAGlyCCC and tsRNAGlyGCC, differed between treatment groups across time. Four days post challenge, 5' tsRNAGlyCCC and tsRNAGlyGCC were significantly lower in the challenged group than the control group. Further studies are needed to identify the importance and function of 5' tsRNAGlyCCC and tsRNAGlyGCC in serum samples of cattle challenged with BVDV.

Global knowledge gaps in the prevention and control of bovine viral diarrhoea (BVD) virus.

The significant economic impacts of bovine viral diarrhoea (BVD) virus have prompted many countries worldwide to embark on regional or national BVD eradication programmes. Unlike other infectious diseases, BVD control is highly feasible in cattle production systems because the pathogenesis is well understood and there are effective tools to break the disease transmission cycle at the farm and industry levels. Coordinated control approaches typically involve directly testing populations for virus or serological screening of cattle herds to identify those with recent exposure to BVD, testing individual animals within affected herds to identify and eliminate persistently infected (PI) cattle, and implementing biosecurity measures such as double-fencing shared farm boundaries, vaccinating susceptible breeding cattle, improving visitor and equipment hygiene practices, and maintaining closed herds to prevent further disease transmission. As highlighted by the recent DISCONTOOLS review conducted by a panel of internationally recognized experts, knowledge gaps in the control measures are primarily centred around the practical application of existing tools rather than the need for creation of new tools. Further research is required to: (a) determine the most cost effective and socially acceptable means of applying BVD control measures in different cattle production systems; (b) identify the most effective ways to build widespread support for implementing BVD control measures from the bottom-up through farmer engagement and from the top-down through national policy; and (c) to develop strategies to prevent the reintroduction of BVD into disease-free regions by managing the risks associated with the movements of animals, personnel and equipment. Stronger collaboration between epidemiologists, economists and social scientists will be essential for progressing efforts to eradicate BVD from more countries worldwide.

Frequency of bovine viral diarrhea virus detected in subpopulations of peripheral blood mononuclear cells in persistently infected animals and health outcome.

Bovine viral diarrhea viruses (BVDV) cause acute and persistent infections. Acute infection results in generalized immunosuppression characterized by a decrease in circulating lymphocytes as a result of depletion of CD4+ and CD8 + T cell populations. Persistent infection with BVDV is the result of immune tolerance and is generally not associated with lymphocytopenia. The health outcome of persistently infected (PI) calves varies widely; some die of mucosal disease, some succumb to ill thrift and others appear normal and survive to adulthood. Detection of BVDV at the single lymphoid cell level is important to the study of subpopulations of peripheral blood mononuclear cells (PBMC) during BVDV infections, however there are few methods available for the detection and quantification of BVDV at this level. To circumvent this difficulty, a novel flow cytometry-based PrimeFlow RNA assay using in-situ detection of BVDV was developed. This assay was used to evaluate differences in viral distribution within subpopulations of PBMC over time in PI calves carrying one of two different species of BVDV (type 1 and type 2). Calves were sampled at 3 different time points approximately one month apart. During the course of the study, a subset of the calves died from ill thrift. Mucosal disease was not indicated in any of the deaths. Using RNA probes specific for the BVDV Npro-Erns coding regions for each respective virus, BVDV RNA was detected in all PBMC of PI that appeared clinically healthy. Calves that succumbed to ill thrift were found to have no or little virus in T cells. The clearance of virus from T cells suggests a breakdown in immune tolerance in these calves. This is the first report of a pattern observed in the viral load in the T cell subpopulations and survival in PI calves.

Relative virulence in bison and cattle of bison-associated genotypes of Mycoplasma bovis.

Mycoplasma bovis, a frequent contributor to polymicrobial respiratory disease in cattle, has recently emerged as a major health problem in North American bison. Strong circumstantial evidence suggests it can be the sole pathogen causing disease manifestations in outbreaks of mortality in bison, but direct evidence is lacking. The goal of this study was to compare clinical signs and lesions in bison and cattle experimentally infected with field isolates of M. bovis recovered from bison. Bison (n = 7) and cattle (n = 6), seronegative for anti-M. bovis IgG, were exposed intranasally to M. bovis and necropsied 4-6 weeks later. Blood and nasal swabs were collected on day 0 (before exposure), day 11 and at necropsy. Samples of lung, lymph node, liver and spleen were also collected at necropsy. The only clinical sign observed was an elevation in the core body temperature of bison during the first few weeks post-exposure. Grossly visible lesions were apparent at necropsy in the lungs of five bison and the lymph node of one bison, while none were evident in cattle. Histologic evaluation revealed moderate to severe pulmonary lesions in four bison but none in cattle. M. bovis was recovered from tissues demonstrating gross lesions and from the lymph nodes of one additional bison and two cattle. All animals seroconverted by the time of necropsy. These data provide the first direct evidence that M. bovis can be a sole or primary cause of respiratory disease in healthy bison, although the isolates used were unable to cause disease in healthy cattle.

Evaluation of bovine viral diarrhea virus transmission potential to naïve calves by direct and indirect exposure routes.

Bovine viral diarrhea viruses (BVDV) can cause both acute and persistent infections in cattle. Exposure to BVDV persistently infected (PI) animals results in transmission of the virus to a naïve animal which causes a transient acute infection. While it is known that direct exposure to PI animals is a highly efficient means of transmission, less information is available regarding the potential for transmission from acutely infected either by direct or indirect exposure to naïve animals. Therefore, the objective of this study was to evaluate the potential for spread of the virus from calves acutely infected, with typical virulence field viruses know to have minimal shedding and viremia, to naïve contact animals either by direct or indirect exposure. To accomplish this objective, two BVDV isolates belonging to two species of BVDV, type 1 and type 2, were used to inoculate calves. Subsequently on day 2 post-infection, naïve calves were exposed to inoculated calves, either directly or indirectly, over a period of two weeks. All calves were evaluated for the presence of virus in blood samples and nasal swabs, pyrexia, lymphopenia and seroconversion. BVDV was isolated from inoculated calves but not from any of the direct and indirect contact animals or from control calves. Similarly, pyrexia and lymphopenia were observed in the inoculated calves, but not in contact and control calves. Only the inoculated calves seroconverted by day 38 of the study indicating that no transmission had occurred to the naïve contact calves. This data would suggest that there may be an infectious dose needed for transmission of virus for typical virulent isolates.

Feed Intake and Weight Changes in Bos indicus-Bos taurus Crossbred Steers Following Bovine Viral Diarrhea Virus Type 1b Challenge Under Production Conditions.

Bovine viral diarrhea virus (BVDV) has major impacts on beef cattle production worldwide, but the understanding of host animal genetic influence on illness is limited. This study evaluated rectal temperature, weight change and feed intake in Bos indicus crossbred steers (n = 366) that were challenged with BVDV Type 1b, and where family lines were stratified across three vaccine treatments of modified live (MLV), killed, (KV) or no vaccine (NON). Pyrexia classification based on 40.0 °C threshold following challenge and vaccine treatment were investigated for potential interactions with sire for weight change and feed intake following challenge. Pyrexia classification affected daily feed intake (ADFI, p = 0.05), and interacted with day (p < 0.001) for ADFI. Although low incidence of clinical signs was observed, there were marked reductions in average daily gain (ADG) and cumulative feed intake during the first 14 day post-challenge; ADG (CV of 104%) and feed efficiency were highly variable in the 14-day period immediately post-challenge as compared to the subsequent 14-day periods. A sire × vaccine strategy interaction affected ADFI (p < 0.001), and a sire by time period interaction affected ADG (p = 0.03) and total feed intake (p = 0.03). This study demonstrates that different coping responses may exist across genetic lines to the same pathogen, and that subclinical BVDV infection has a measurable impact on cattle production measures.