Severe acute bovine viral diarrhea in Ontario, 1993-1995

Distribution of Viral Antigen and Tissue Lesions in Persistent and Acute Infection with the Homologous Strain of Noncytopathic Bovine Viral Diarrhea Virus

Viral distribution and lesions were compared between calves born with persistent infection (PI) and calves acutely infected with the same bovine viral diarrhea virus (BVDV) isolate. Two PI calves from 1 dairy herd were necropsied. The PI viruses from these calves were isolated, characterized by sequencing, and found to be identical. This virus strain, designated BVDV2-RS886, was characterized as a noncytopathic (ncp) type 2 BVDV. To establish acute infections, BVDV2-RS886 was used to inoculate clinically healthy, seronegative calves which were 3 weeks to 3 months old. Nine calves received 106–107 tissue culture infective dose of BVDV2-RS886 intranasally. Four additional age-matched animals served as noninfected controls. Infected calves were necropsied at 3, 6, 9, or 13 days postinoculation (dpi). Viral antigen was detected by immunohistochemistry in frozen sections, and lesions were evaluated in hematoxylin eosin–stained paraplast sections. In the PI calves, a wide distribution of viral antigen was found in all tissues and was not associated with lesions. In the acutely infected calves, viral antigen was widespread in lymphoid tissues at 6 dpi but had been mostly eliminated at 9 and 13 dpi. Depletion of lymphoid tissues was seen at 6, 9, and 13 dpi and repopulation at 9 and 13 dpi. In 1 of the calves at 13 dpi, severe arteritis was present in lymph nodes and myocardium. This comparison shows that an ncp BVDV strain that causes no lesions in PI animals is able to induce marked depletion of lymphoid tissues in calves with acute infection. Therefore, the failure to eliminate PI cattle from a herd causes problems not only in pregnant cattle but may also affect other age groups.

Origination and consequences of bovine viral diarrhea virus diversity

The potential consequences of BVDV genetic and antigenic diversity are far ranging. The complexity of clinical presentations associated with BVDV likely arises from factors encoded by the virus genome. More importantly,prevention and control of BVDV may be complicated by diagnostic and immunization failure resulting from virus diversity. Evolutionary pressures will continue to drive further diversity, making control of BVDV challenging. Current and the potential for future BVDV strain diversity should be considered when designing BVDV control programs both at the individual farm and national herd level.

Laboratory diagnosis of bovine viral diarrhea virus infections

The past 20 years have witnessed dramatic improvements in laboratory methods for diagnosing bovine viral diarrhea virus(BVDV) infections. However, improvements in diagnostic technology have not necessarily led to improved diagnosis of BVDV at the individual animal or herd level. This article reviews BVDV laboratory diagnostic methods in the context of their rational application for improved detection of BVDV in the field.

Comparative analysis on the 5'-untranslated region of bovine viral diarrhea virus isolated in Korea

Samples of 249 bovine abortuses, one intestine, and four diarrheal stools from 254 cows were collected, and bovine viral diarrhea virus (BVDV) was detected by reverse transcription-polymerase chain reaction (RT-PCR). Subsequently, virus isolation was preformed with PCR-positive samples, and then PCR product of 5^′-untranslated region (UTR) of BVDV isolate was sequenced and analyzed. Among the samples collected, 20 (from 17 bovine abortuses, one intestine, and two diarrheal stools) were positive for BVDV RT-PCR; four BVDVs (from two bovine abortuses, one intestine, and one diarrheal stool) were isolated. When the four isolates were biotyped in cell culture, one BVDV isolate from a bovine abortus was cytopathic and the others were non-cytopathic. In addition, three isolates were genotyped as BVDV-1 and one isolate from a diarrheal stool as BVDV-2. In phylogenetic analysis, it suggested that the BVDV-2 isolate in Korea is closer to the North American strains than Asian strains. This is the first report on the identification and isolation of BVDV-2 in Korea.

Effect of bovine viral diarrhea virus infection on fertility of dairy heifers

A prospective field study in heifers from birth to first breeding was undertaken on two commercial dairies to assess the effect of bovine viral diarrhea virus (BVDV) congenital and post-natal infection (PNI) on fertility. A high BVDV Type 2 antibody titer (1:4096) at 10 months of age was associated with 32 more days to conceive, compared with a low titer (1:128). Conversely, infection with BVDV by 5-6 months of age and high BVDV Type 2 titers 1 month before conception or breeding was associated with improved fertility. Heifers with evidence of congenital BVDV infection had lower fertility than non-infected heifers (15-42 days longer time-to-first AI), which depended on BVDV Type 2 titers at 10 months of age. Neospora caninum infection was associated with additional services per conception (SPC) and Leptospira interrogans infection was associated with a delay in the time-to-first breeding. It appears that under field conditions, the effect of subclinical BVDV infection on subsequent heifer fertility may be due to a complex of interrelationships among multiple BVDV infections that depend on the type and timing of infection relative to reproductive development and events.

Effect of bovine viral diarrhea virus in the feedlot

It could be argued that bovine viral diarrhea virus (BVDV) is one of the most economically significant infectious pathogens of feedlot cattle. Although the direct economic losses caused by this virus have not been well quantified, the role it plays as an immunosuppressive agent and as a potentiator for other diseases, most notably bovine respiratory disease, have been well documented. It is also a difficult disease for the feedlot veterinarian to control effectively. Individual cattle persistently infected with BVDV often serve as the source of infectious virus within a group of feedlot cattle, and the ultimate responsibility for preventing persistent infections in cattle rests with the cow-calf producer and not with the feedlot owner. The enormous impact of the virus on the livestock industry has led the Academy of Veterinary Consultants to draft a position statement that resolves that the beef and dairy industries adopt measures to control and target eventual eradication of BVDV from North America.

Evolution of bovine viral diarrhea virus vaccines

Control of bovine viral diarrhea virus (BVDV) infection is economically important to the cattle industry because the virus causes a variety of clinical diseases that adversely affect essentially all stages of the production cycle. Production losses primarily stem from reproductive failure and from immunosuppression during acute BVDV infection, which predisposes calves to respiratory or enteric diseases. Control is achieved by implementing herd health pro-grams focused on limiting exposure by avoiding persistently infected (PI) carrier cattle and by optimizing protective immunity through immunization. Vaccination cannot be relied upon solely to protect against fetal infection and losses due to BVD. This is because no single BVDV vaccine has been shown to give complete fetal protection. In addition to strategic use of vaccines, herd management practices should also be implemented to identify and eliminate PI carrier cattle and to avoid exposure to BVDV infection.

Biosecurity and biocontainment of bovine viral diarrhea virus

Infection of cattle with BVDV results in a variety of clinical illnesses costly to the cattle industry worldwide. The reservoir and primary source of transmission is cattle born PI with BVDV after transplacental infection in early gestation. It is a challenge to determine with certainty whether or not BVDV is circulating among a herd of cattle. If the virus is present in a herd,then biocontainment strategies are used to eliminate the virus by testing to removing PI cattle, preventing exposure of pregnant cattle to the virus, and increasing resistance to infection using vaccination. If it is clear that the virus is not present in a herd then, biosecurity actions must be taken to prevent introducing the virus into the herd.

Gene expression changes in MDBK cells infected with genotype 2 bovine viral diarrhoea virus

Bovine viral diarrhoea viruses (BVDVs) are ubiquitous viral pathogens of cattle. These viruses exist as one of two biotypes, cytopathic and noncytopathic, based on the ability to induce cytopathic effect in cell culture. The noncytopathic biotypes are able to establish inapparent, persistent infections in both cell culture and in bovine foetuses of less than 150 days gestation. Interactions with the host cell and the mechanism by which viral tolerance is established are unknown. To examine the changes in gene expression that occur following infection of host cells with BVDV, serial analysis of gene expression (SAGE), a global gene expression technology was used. SAGE allows quantitation of virtually every transcript in a cell type without prior sequence information. Transcript expression levels and identities are determined by sequencing libraries composed of concatamers of 14 base DNA fragments (tags) derived from the 3'-end of each cellular mRNA transcript. Comparison of data obtained from uninfected and BVDV genotype 2-infected cell libraries revealed changes in gene expression associated with distinct biochemical pathways or functions. Isotypes of both alpha- and beta-tubulins were down-regulated, indicating possible dysfunction in cell division and other functions where microtubules play a major role. Expression of genes encoding proteins involved in energy metabolism were expressed at essentially equivalent levels in both infected and uninfected cells. Genes encoding proteins involved in protein translation and post-translational modifications, functions necessary for viral replication, were generally up-regulated. These data indicate that following infection with BVDV, changes in gene expression occur that are beneficial for virus replication while having only minor changes in energy metabolism.

Assessment of the clinical and virological protection provided by a commercial inactivated bovine viral diarrhoea virus genotype 1 vaccine against a BVDV genotype 2 challenge

A new genotype of bovine viral diarrhoea virus (BVDV), designated BVDV-2, has emerged in the last decade and in recent years the prevalence of BVDV-2 strains has increased. A vaccination-challenge study was carried out to determine the cross-protective efficacy of a commercial inactivated vaccine containing a BVDV-1 strain. A group of five BVDV-free calves was vaccinated twice and a second group of five calves served as negative controls. Two months after the first vaccination, all the calves were challenged intranasally with BVDV-2 strain BVD890. The clinical signs of disease, the changes in haematological variables and the level of viraemia were significantly less in the vaccinated group.

Detection of inhibition of bovine viral diarrhea virus by aromatic cationic molecules

Bovine viral diarrhea virus (BVDV) is an economically significant pathogen of cattle and a problematic contaminant in the laboratory. BVDV is often used as an in vitro model for hepatitis C virus during drug discovery efforts. Aromatic dicationic molecules have exhibited inhibitory activity against several RNA viruses. Thus, the purpose of this research was to develop and apply a method for screening the aromatic cationic compounds for in vitro cytotoxicity and activity against a noncytopathic strain of BVDV. The screening method evaluated the concentration of BVDV in medium and cell lysates after 72 h of cell culture in the presence of either a 25 or 5 microM concentration of the test compound. Five of 93 screened compounds were selected for further determination of inhibitory (90 and 50%) and cytotoxic (50 and 10%) concentration endpoints. The screening method identified compounds that exhibited inhibition of BVDV at nanomolar concentrations while exhibiting no cytotoxicity at 25 microM concentrations. The leading compounds require further investigation to determine their mechanism of action, in vivo activity, and specific activity against hepatitis C virus.

A survey for BVDV antibodies in cattle farms in Slovakia and genetic typing of BVDV isolates from imported animals

A serological survey for bovine viral diarrhoea virus (BVDV) antibodies on a collection of 1295 serum samples obtained from 6-12 months old cattle originating from 45 farms in Slovakia was carried out. On 13 farms more than 90% of the examined animals were seropositive, on 14 farms 71-90% seroprevalence was observed, on 13 farms only 50-70% animals were found to be positive for BVDV antibodies, while the remaining 5 farms showed fewer than 50% seropositive animals. The average incidence of BVDV antibodies (around 70%) was similar as determined 30 years ago. Of 84 serum samples from seronegative animals originating from 14 farms in which 70-98% seropositivity was observed, six were positive in Ag-BVDV ELISA indicating persistently infected (PI) cattle. On a farm to which animals were imported from abroad, a BVD outbreak was observed. Of 110 animals tested, four were positive in Ag-ELISA indicating the presence of PI cattle on this farm. Genetic typing of two isolates from imported animals performed by RT-PCR (324/326 primers from 5'-UTR), sequencing of PCR products and computer-assisted phylogenetic analysis revealed that they belong to BVDV-1 h group.

Economic impact of BVDV infection in dairies

The detrimental effects of bovine virus diarrhoea virus (BVDV) infections include reduced milk production, reduced reproductive performance, growth retardation, increased occurrence of other diseases, unthriftiness, early culling and increased mortality among young stock. These losses have been documented in several case descriptions and to some extent quantified in epidemiological studies. The detrimental effects together with information on population structure, incidence of infection and monetary value of production losses have been included in different models for estimating economic losses and benefits of different control strategies. This paper reviews different studies and methods for estimating economic losses and the economic effect of control strategies on both the local herd level and the national herd level. The estimated losses in individual herd outbreaks have varied from a few thousand up to $100000. There seems to be no universal truth for determining most optimal strategy at the herd level as it depends on herd-specific conditions. Most estimations of the losses at the national level range between 10 and 40 million $ per million calvings. In the few countries that have introduced eradication campaigns, the programmes have been shown to be cost effective. However, selection of a control strategy should always rely on thorough epidemiological investigations conducted under the same conditions in which the programme is going to be applied.

Gene expression changes in BVDV2-infected MDBK cells

Bovine viral diarrhoea virus (BVDV) is a ubiquitous viral pathogen of cattle. The virus exists as one of two biotypes, cytopathic and non-cytopathic, based on the ability to induce cytopathic effect in cell culture. The non-cytopathic biotypes are able to establish non-apparent, persistent infections in both cell culture and in bovine foetuses of fewer than 150 days gestation. The mechanism by which viral tolerance is established is unknown. To examine the changes in gene expression that occur following infection of host cells with BVDV, serial analysis of gene expression (SAGE), a global gene expression technology was used. SAGE, a sequence-based technology, allows quantification of virtually every transcript in a cell type without prior sequence information. Transcript expression levels and identities are determined by DNA sequencing of libraries composed of 14 base DNA fragments (tags) derived from the 3' end of each cellular mRNA transcript. Comparison of data obtained from non-infected and BVDV2-infected cell libraries revealed a number of changes in gene expression. Many of these transcriptional changes could be placed into distinct biochemical pathways or functions. Both alpha and beta tubulins were downregulated, indicating possible dysfunction in cell division and other functions where microtubules play a major role. Expression of several genes encoding proteins involved in energy metabolism were downregulated, indicating possible decreased ATP synthesis. Genes encoding proteins involved in protein translation and post-translational modifications were generally upregulated. These data indicate that following infection with BVDV, changes in gene expression occur that are beneficial for virus replication while placing the cell at a metabolic disadvantage.

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.

Prevention of persistent infection in calves by vaccination of dams with noncytopathic type-1 modified-live bovine viral diarrhea virus prior to breeding

OBJECTIVE

To determine the ability of a modified-live virus (MLV) bovine viral diarrhea virus (BVDV) type 1 (BVDV1) vaccine administered to heifers prior to breeding to stimulate protective immunity that would block transmission of virulent heterologous BVDV during gestation, thus preventing persistent infection of a fetus.

ANIMAL

40 crossbred Angus heifers that were 15 to 18 months old and seronegative for BVDV and 36 calves born to those heifers.

PROCEDURE

Heifers were randomly assigned to control (n = 13) or vaccinated (27) groups. The control group was administered a multivalent vaccine where-in the BVDV component had been omitted. The vaccinated heifers were administered a single dose of vaccine (IM or SC) containing MLV BVDV1 (WRL strain). All vaccinated and control heifers were maintained in pastures and exposed to BVDV-negative bulls 21 days later. Thirty-five heifers were confirmed pregnant and were challenge exposed at 55 to 100 days of gestation by IV administration of virulent BVDV1 (7443 strain).

RESULTS

All control heifers were viremic following challenge exposure, and calves born to control heifers were persistently infected with BVDV. Viremia was not detected in the vaccinated heifers, and 92% of calves born to vaccinated heifers were not persistently infected with BVDV.

CONCLUSIONS AND CLINICAL RELEVANCE

These results document that vaccination with BVDV1 strain WRL protects fetuses from infection with heterologous virulent BVDV1.

Genetic diversity of recent bovine viral diarrhoea viruses from the southeast of Austria (Styria)

To characterise the bovine virus diarrhoea virus (BVDV) isolates circulating in the southeastern region of Austria, namely in the province of Styria, 71 blood samples collected between 1998 and 2000 from persistently infected cattle in 62 herds were subjected to genetic typing. For this, 288bp fragments from the 5' untranslated region (5'-UTR) were amplified by polymerase chain reaction after reverse transcription (RT-PCR). The products were sequenced and used for phylogenetic analysis. Seventy virus isolates were typed as BVDV species 1 (BVDV-1). Only one isolate was typed as BVDV species 2 (BVDV-2), representing the first isolate of this pestivirus genotype found in Austria. In addition, phylogenetic analysis revealed that viruses belonging to five genetic groups within BVDV-1 are circulating in Styria. Most viruses (53) were found in group BVDV-1f, nine viruses in BVDV-1h, four viruses in BVDV-1b, three viruses in BVDV-1d and one virus in BVDV-1g. No virus was found in genetic group BVDV-1a, which is dominant in the UK and widely distributed in USA. Likewise, the BVDV isolates predominating in a neighbouring country, namely Germany, belonged to different genogroups than those circulating in Styria. We conclude that in a particular region and environment certain BVDV-1 genetic groups predominate. New groups, including BVDV-2, can be introduced, e.g. by trade of animals. The low incidence of BVDV-2 in Styria is in concert with the sporadic occurrence of these viruses in other regions of Europe.

Efficacy of bovine viral diarrhea vaccine used in Japan against bovine viral diarrhea virus type 2 strain 890

Bovine viral diarrhea virus (BVDV) has been segregated into two genotypes, type 1 and type 2. To determine the efficacy of the commercially available bovine viral diarrhea type 1 vaccine used in Japan against BVDV type 2, calves were infected with BVDV type 2 strain 890 4 weeks after administration of the vaccine. The vaccinated calves did not develop any clinical signs and hematological changes such as observed in unvaccinated calves after the challenge. Furthermore, the challenge virus was not recovered from the vaccinated calves throughout the duration of the experiment, whereas it was recovered from all unvaccinated calves. The bovine viral diarrhea vaccine used in Japan is efficacious against infection with BVDV type 2 strain 890.

Effect of passive immunity on the development of a protective immune response against bovine viral diarrhea virus in calves

OBJECTIVE

To determine whether passively acquired antibodies prevent development of a protective immune response to live virus in calves.

ANIMALS

18 calves.

PROCEDURES

Calves were caught immediately after birth and tested free of bovine viral diarrhea virus (BVDV) and serum antibodies against BVDV. Within 48 hours, 12 calves were fed colostrum that contained antibodies against BVDV and 6 calves received BVDV antibody free milk replacer. Three milk replacer fed and 6 colostrum fed calves were exposed to virulent BVDV2-1373 at 2 to 5 weeks of life when passively acquired serum antibody titers were high. After serum antibody titers against BVDV had decayed to undetectable concentrations (at 7 to 9 months of age), the 3 remaining milk replacer fed calves, 6 colostrum fed calves previously exposed to BVDV2-1373, and 6 colostrum fed calves that had not been exposed to the virus were inoculated with BVDV2-1373.

RESULTS

Passively acquired antibodies prevented clinical disease in inoculated colostrum fed calves at 2 to 5 weeks of life. Serum antibody titers did not increase in these calves following virus inoculation, and serum antibody titers decayed at the same rate as in noninoculated colostrum fed calves. Inoculated colostrum fed calves were still protected from clinical disease after serum antibody titers had decayed to nondetectable concentrations. Same age colostrum fed calves that had not been previously exposed to the virus were not protected.

CONCLUSIONS AND CLINICAL RELEVANCE

A protective immune response was mounted in calves with passive immunity, but was not reflected by serum antibodies titers. This finding has implications for evaluating vaccine efficacy and immune status.

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.

Clinical and epidemiologic observations of bovine viral diarrhea virus in the northwestern United States

Retrospective analyses of cases from which bovine viral diarrhea virus (BVDV) was isolated from 1980 to 2000 were conducted. These cases originated from the northwestern US and included both beef and dairy cattle. The results indicated that there was a shift in diseases associated with BVDV infection and in the animal age at onset of disease. Comparative results from the 1980 data indicated a low fetal infection rate (<5%), followed by steady increases of clinical cases and peaking at 6 months (30%). By 2000, the shift of BVDV cases was noticeable and indicated a biphasic occurrence of disease. The first phase was fetal infections, which increased to >25%, followed by a second phase at 6 months (>35%). Phylogenetic analysis was conducted on selected isolates from the time period 1998-2000 (n = 54). There were representative viral isolates from the two genotypes (BVDV1 and BVDV2), as well as subgenotypes, BVDV1a and BVDV1b. The types were further correlated with the clinical manifestation, which were reported as mucosal disease, persistently infected (PI)-poor doer, and abortion-open cows. The results indicated that BVDV were distributed throughout the clinical spectrum of disease, with BVDV2 representing the greatest frequency of isolation, and the greatest association with abortion-open cows. When the BVDV genotypes and subgenotypes were categorized into early (<100 days gestation) versus late (>100 days gestation) fetal infections, there was an inverse relationship noted. It was observed that BVDV1a was associated least with early infection (14%) and most with late infections (86%). BVDV1b was intermediate, followed by BVDV2, which was associated more with early infections (45%) and less with late infections (55%) when compared with BVDV1a and BVDV1b.

Comparative virulence of isolates of bovine viral diarrhea virus type II in experimentally inoculated six- to nine-month-old calves

OBJECTIVE

To determine the comparative virulence of 5 isolates of bovine viral diarrhea virus (BVDV) type II by inoculating 6- to 9-month-old beef calves with isolates originating from the tissues of cattle affected with naturally occurring, transient, acute, nonfatal infections or naturally occurring, peracute, fatal infections.

ANIMALS

22 calves that were 6 to 9 months old.

PROCEDURE

The study used BVDV isolates 17011, 713, and 5521 that originated from fetuses aborted from cows with transient, nonfatal, acute BVDV infections and isolates 23025 and 17583 that originated from the tissues of cattle with peracute, fatal BVDV infections. Calves were allotted to 6 groups (1, mock-infected control calves [n = 2]; 2, inoculated with BVDV 17011 [4]; 3, inoculated with BVDV 713 [4]; 4, inoculated with BVDV 5521 [4]; 5, inoculated with BVDV 23025 [4]; and 6, inoculated with BVDV 17583 [41]. Rectal temperatures and clinical signs of disease were recorded daily. Total and differential WBC and platelet counts were performed. Histologic examination and immunohistochemical analysis were conducted to detect lesions and distribution of viral antigens, respectively.

RESULTS

Calves inoculated with BVDV 23025 or 17583 developed more severe clinical signs of disease (fever and diarrhea), more severe lymphopenia, and more severe lesions (alimentary epithelial necrosis, lymphoid depletion, and BVDV antigen deposition in lymphatic tissues), compared with calves inoculated with BVDV 713, 5521, or 17011.

CONCLUSIONS AND CLINICAL RELEVANCE

Relative severity of experimentally induced infections corresponded to severity of clinical signs of naturally occurring infections with respective BVDV isolates.

Phylogenetic analysis of Brazilian bovine viral diarrhea virus type 2 (BVDV-2) isolates: evidence for a subgenotype within BVDV-2

Phylogenetic analysis divides bovine viral diarrhea viruses (BVDV) into two different genotypes (BVDV1 and BVDV2). BVDV1 strains have been further subdivided into two to 11 subgenotypes. Phylogenetic analysis of BVDV2 isolates, however, has not been able to identify discrete subgenotypes. In this study, we identified six South American BVDV2 strains and one North American BVDV2 strain that cluster to a separate genetic group within BVDV2, thus representing a distinct subgenotype. The 5' untranslated region (UTR) sequence homology between these six strains and other BVDV2 from North America, Europe and Asia (81.7%) is lower than the homology used to segregate BVDV1 into BVDV1a and BVDV1b (83.6%). Most nucleotide differences observed between the two subgroups of BVDV2 were concentrated in two regions, which also harbor most of the differences seen between BVDV1a and BVDV1b. To determine if this segregation was real, an additional analysis was performed comparing NS2/3 sequences. Analysis of a conserved sequence located between nucleotides 6670 and 7186 of the NS2/3 coding region also segregated these isolates to a separate group. The sequence homology between the two subgroups (86.3%) was higher than the homology in the 5'UTR (81.7%), with mean sequence homologies of 91 and 87.2% within the proposed subgroups. In contrast to the 5'UTR, alignment of the NS2/3 sequences revealed nucleotide differences distributed across the region. These results demonstrate that BVDV2 isolates cluster to two genetically distinct subgroups within BVDV2. The differences in both the 5'UTR and NS2/3 are consistent and justify this segregation. We suggest that BVDV2 may thereafter be subgenotyped into BVDV2a and BVDV2b. The existence of subgroups within the BVDV2 genotype with genetic heterogeneity similar to that seen among BVDV1 subgroups argues against BVDV2 isolates arising from BVDV1 in a recent evolutionary event. Unless the evolutionary clocks for BVDV1 and BVDV2 isolates tick along at different rates, these results indicate that BVDV2 have existed as long as BVDV1.

Insemination of susceptible heifers with semen from a non-viraemic bull with persistent bovine virus diarrhoea virus infection localized in the testes

Bulls shedding bovine viral diarrhoea virus (BVDV) in semen and simultaneously having a high concentration of circulating antibodies may cause reproductive problems and spread the viral infection within cattle populations. To investigate this in detail, three heifers were inseminated with BVDV-infected semen from a non-viraemic, seropositive Holstein-Friesian bull, named 'Cumulus'. One control heifer was inseminated with semen from a healthy bull that was free of BVDV. All four heifers remained clinically healthy throughout the experiment. The conception succeeded in the control animal and in two of the three heifers inseminated with semen containing BVDV. The heifer with the failed conception was the only one that became systemically infected with BVDV. This animal was deemed non-pregnant by ultrasonic examination on day 34 after insemination and showed no signs of subsequent oestrus during the entire experimental period. At slaughter, 42 days after insemination, there were no histopathological changes in the ovaries and virus was not detected in ovarian tissue. The fact that seronegative dams served with semen from persistently infected bulls have occasionally produced persistently infected calves together with the present findings and the fact that non-viraemic, seropositive bulls can constantly shed BVDV, suggest that the use of semen from such bulls in BVDV-free herds could have far-reaching consequences, especially if it led to the birth of persistently infected (P1) calves.

Failure to spread bovine virus diarrhoea virus infection from primarily infected calves despite concurrent infection with bovine coronavirus

Previous reports on the spread of bovine virus diarrhoea virus (BVDV) from animals primarily infected with the agent are contradictory. In this study, the possibility of transmission of BVDV from calves simultaneously subjected to acute BVDV and bovine coronavirus (BCV) infection was investigated. Ten calves were inoculated intranasally with BVDV Type 1. Each of the 10 calves was then randomly allocated to one of two groups. In each group there were four additional calves, resulting in five infected and four susceptible calves per group. Virulent BCV was actively introduced in one of the groups by means of a transmitter calf. Two calves, susceptible to both BVDV and BCV, were kept in a separate group, as controls. All ten calves actively inoculated with BVDV became infected as shown by seroconversions, and six of them also shed the virus in nasal secretions. However, none of the other eight calves in the two groups (four in each) seroconverted to this agent. In contrast, it proved impossible to prevent the spread of BCV infection between the experimental groups and consequently all 20 study calves became infected with the virus. Following infection, BCV was detected in nasal secretions and in faeces of the calves and, after three weeks in the study, all had seroconverted to this virus. All calves, including the controls, showed at least one of the following clinical signs during days 3-15 after the trial started: fever (> or =40 degrees C), depressed general condition, diarrhoea, and cough. The study showed that BVDV primarily infected cattle, even when co-infected with an enteric and respiratory pathogen, are inefficient transmitters of BVDV. This finding supports the principle of the Scandinavian BVDV control programmes that elimination of BVDV infection from cattle populations can be achieved by identifying and removing persistently infected (PI) animals, i.e. that long-term circulation of the virus without the presence of PI animals is highly unlikely.

Proteção fetal frente a desafio com o vírus da Diarréia Viral Bovina (BVDV) em ovelhas imunizadas com duas amostras de vírus modificadas experimentalmente

Duas amostras do vírus da Diarréia Viral Bovina (BVDV) submetidas a múltiplas passagens em cultivo celular e exposição à radiação ultravioleta (UV) a cada passagem foram avaliadas como candidatos a vírus vacinais. As amostras foram testadas quanto à sua atenuação para bezerros e fetos ovinos, reatividade antigênica contra isolados de campo, e capacidade de induzir proteção fetal em ovelhas prenhes. Inoculação intramuscular (IM) dos vírus modificados em quatro bezerros produziu apenas uma elevação discreta e passageira da temperatura corporal, seguida de produção de altos títulos de anticorpos neutralizantes. O vírus não foi detectado em secreções nasais ou sangue nos dias seguintes à inoculação. Porém, a inoculação IM desses vírus em quatro ovelhas prenhes foi seguida de transmissão transplacentária e infecção em todos os fetos. Para os testes de proteção fetal, ovelhas prenhes previamente imunizadas com duas doses vacinais, foram inoculadas por via intranasal com amostras de BVDV-1 (SV-126.8, n=6) ou BVDV-2 (SV-260, n=5). No dia do desafio (134 dias após a segunda dose), todos os animais apresentavam altos títulos de anticorpos neutralizantes (256 a >4096) contra os vírus vacinais; além de títulos variados (8 a >4096) contra várias isolados brasileiros de BVDV-1 e BVDV-2. Quinze dias após o desafio, as ovelhas foram sacrificadas e os tecidos fetais foram examinados para a presença de vírus. Todos os fetos das ovelhas controle não-vacinadas apresentaram-se (n=4) positivos para os vírus utilizados no desafio. Em contraste, nenhum feto das ovelhas imunizadas (n=11) foi positivo para vírus, indicando que a resposta imunológica induzida pela vacinação com os vírus modificados foi capaz de prevenir a infecção fetal. Estes resultados indicam que é possível obter-se forte resposta imunológica e proteção fetal contra o BVDV com o uso de vacinas vivas modificadas.

The immunology of the bovine respiratory disease complex

The bovine respiratory disease complex continues to be an economically important syndrome in an era when immunologic control is likely to become increasingly important. Recent studies have yielded a better understanding of the interaction, at the molecular level, of various pathogens with the bovine immune system. Improved challenge models for important viral pathogens such as bovine viral diarrhea virus and bovine respiratory syncytial virus have provided evidence of the efficacy of immune responses stimulated by vaccination. This article highlights recent advances in understanding of the role of the immune response in the pathogenesis and prophylaxis of bovine respiratory disease complex.

Prevalence of genotypes 1 and 2 of bovine viral diarrhea virus in Lower Saxony, Germany

The aim of this study was to find whether an antigenic drift had occurred in Lower Saxony in the past 40 years. For this, the genetic diversity of bovine viral diarrhea virus (BVDV) isolates mainly from Lower Saxony was estimated by RT-PCR and sequencing of a 420 bp fragment of the E2 glycoprotein gene. Sixty-one field virus isolates collected during routine diagnostics between 1960 and 2000 in Lower Saxony, Northern Germany, were analyzed. Phylogenetic analysis allowed discrimination of genotypes BVDV 1 and 2. Excepting two isolates, which were of BVDV type 2, most of the isolates were classified as BVDV type 1. This group could be further subdivided into four subgroups and one disparate isolate. Independent of the year of isolation and geographical localization, 54 isolates clustered in two subtypes (BVDV subtypes 1b and 1d). Only one isolate was classified as BVDV type 1a, thus being similar to the North American NADL strain, and to the vaccine strain Oregon C24V, which was extensively used for vaccination in Germany. The remaining isolates belonged to new clusters tentatively designated as BVDV subtypes 1g and 1f. To compare the cluster designation with that of other studies, phylogenetic analysis of representatives of each of the subgroups based on the 5' untranslated region (5'UTR) was performed. It grouped the viruses similarly. The results indicate that the BVDV population seems to be relatively stable over 40 years in Lower Saxony.

Effect of maternal antibodies on induction and persistence of vaccine-induced immune responses against bovine viral diarrhea virus type II in young calves

OBJECTIVE

To determine the effect of maternally derived antibodies on induction of protective immune responses against bovine viral diarrhea virus (BVDV) type II in young calves vaccinated with a modified-live bovine viral diarrhea virus (BVDV) type I vaccine.

DESIGN

Blinded controlled challenge study.

ANIMALS

24 neonatal Holstein and Holstein-cross calves that were deprived of maternal colostrum and fed pooled colostrum that contained a high concentration of (n = 6) or no (18) antibodies to BVDV.

PROCEDURE

At 10 to 14 days of age, 6 seropositive and 6 seronegative calves were given a combination vaccine containing modified-live BVDV type I. All calves were kept in isolation for 4.5 months. Six calves of the remaining 12 untreated calves were vaccinated with the same combination vaccine at approximately 4 months of age. Three weeks later, all calves were challenged intranasally with a virulent BVDV type II.

RESULTS

Seronegative unvaccinated calves and seropositive calves that were vaccinated at 2 weeks of age developed severe disease, and 4 calves in each of these groups required euthanasia. Seronegative calves that were vaccinated at 2 weeks or 4 months of age developed only mild or no clinical signs of disease.

CONCLUSIONS AND CLINICAL RELEVANCE

Results indicate that a single dose of a modified-live BVDV type-I vaccine given at 10 to 14 days of age can protect susceptible young calves from virulent BVDV type II infection for at least 4 months, but high concentrations of BVDV-specific maternally derived antibodies can block the induction of the response.

The effect of infection with bovine viral diarrhea virus on the fertility of Swiss dairy cattle

Bovine viral diarrhea virus is a major cattle pathogen with a worldwide distribution. Animals may be infected with BVD virus transiently or persistently. Transient infection leads to protective immunity. Persistent infection is unique because it is associated with an immunotolerance that is specific to the infecting strain of BVD virus. Persistent infection results from viral invasion of fetuses between the second and fourth month of development. Such animals are of prime importance in the epidemiology of BVD because they shed large amounts of virus, and thus serve as a constant source of infection for non-immune animals. Infection of pregnant animals during the first two months of gestation may result in an increased rate of return to estrus. Animals infected in the period of five months to birth may abort or give birth to calves with malformations. The effects of BVD virus on fertility and gestation are well documented from experimental infection. However, much less is known of the extent of losses under field conditions. The main reason for this may be the multitude of other causes of increased return rates and gestation failures. In addition, the incidence of infection with BVD virus may vary over time and depends on management practices. In this study, we investigated the impact of BVD virus on gestation failures under field conditions in a large cattle-breeding area of Switzerland, where no specific measures to control BVD are in effect. Our approach consisted of relating seroconversions to BVD virus with the rate of return to estrus, abortion, and birth of calves with apparent malformations. These parameters of fertility were compared to those of animals immune to BVDV infection due to previous exposure to the virus and animals without seroconversion. Our data show that infection with BVD virus during the first 45 days of gestation did not influence the rate of return to estrus. By contrast, we observed a statistically significant increase in the abortion rate in mid-term gestation (Days 46 to 210) while no such effect was observed in the later stages of gestation. No clinically manifest malformations were observed in the offspring of animals that had seroconverted to BVD virus. In our study population the prevalence of BVDV antibody positive cattle varied only slightly between 78% and 80% over the period of observation. Our data showed that 7% (CI: 2.4-14%) of fetal deaths may be attributable to infection with BVD virus.

Relationship between degree of viremia and disease manifestation in calves with experimentally induced bovine viral diarrhea virus infection

OBJECTIVE

To compare degree of viremia and disease manifestations in calves with type-I and -II bovine viral diarrhea virus (BVDV) infection.

ANIMALS

16 calves.

PROCEDURE

Colostrum-deprived calves obtained immediately after birth were assigned to 1 control and 3 treatment groups (4 calves/group). Calves in treatment groups were inoculated (day 0) by intranasal instillation of 10(7) median tissue culture infective dose BVDV 890 (type II), BVDV 7937 (type II), or BVDV TGAN (type I). Blood cell counts and virus isolation from serum and leukocytes were performed daily, whereas degree of viremia was determined immediately before and 4, 6, 8, and 12 days after inoculation. Calves were euthanatized on day 12, and pathologic, virologic, and immunohistochemical examinations were performed.

RESULTS

Type-II BVDV 890 induced the highest degree of viremia, and type-I BVDV TGAN induced the lowest. Virus was isolated more frequently and for a longer duration in calves inoculated with BVDV 890. A parallel relationship between degree of viremia and rectal temperature and an inverse relationship between degree of viremia and blood cell counts was observed. Pathologic and immunohistochemical examinations revealed more pronounced lesions and more extensive distribution of viral antigen in calves inoculated with type-II BVDV.

CONCLUSIONS AND CLINICAL RELEVANCE

Degree of viremia induced during BVDV infection is associated with severity of clinical disease. Isolates of BVDV that induce a high degree of viremia may be more capable of inducing clinical signs of disease. Strategies (eg, vaccination) that reduce viremia may control clinical signs of acute infection with BVDV.

An inactivated bovine virus diarrhoea virus (BVDV) type 1 vaccine affords clinical protection against BVDV type 2

This study was designed to answer to two distinct questions. Firstly, is it possible to reproduce clinical signs of acute bovine virus diarrhoea virus (BVDV) type 2 infection including signs of haemorrhagic disease under experimental conditions in cattle at 20 weeks of age? Secondly, what is the extent of the protection afforded by vaccination with an inactivated BVDV type 1 vaccine against BVDV type 2 infection? Calves were vaccinated at 12 and 16 weeks of age with a commercially available inactivated BVDV type 1 vaccine (Bovilis BVD). At 20 weeks they were challenge infected with BVDV type 2 virus together with unvaccinated control calves. The unvaccinated animals developed typical signs of respiratory disease, diarrhoea with erosions and haemorrhages along the whole length gastro-intestinal tract, and depletion of lymphocytes in lymphatic organs. These signs were either absent or markedly less severe in the vaccinated animals. The beneficial effects of vaccination were most striking in the haematological parameters thrombocytopenia and leukopenia. It can be concluded that vaccination with Bovilis BVD affords cross-protection against clinical effects of a challenge-infection with heterologous type 2 BVDV.

Experimental infection of pregnant ewes with bovine viral diarrhea virus type-2 (BVDV-2): effects on the pregnancy and fetus

The reproduction effects of bovine viral diarrhea virus type-2 (BVDV-2) infection were investigated in ewes inoculated with a non-cytopathic BVDV-2 isolate at three stages of gestation. Virus inoculation was followed by a transient viremia, accompanied by a transient and mild hyperthermia and nasal discharge in a few animals. Some ewes were sacrificed at different time-points after virus inoculation to study the kinetics of fetal infection. Infectivity and viral antigens were detected in placentomes from day 7 to 36 post-inoculation (pi) and in fetal fluids and tissues between days 10 and 28 pi. Cardiac petechial hemorrhages and hemoperitoneum accompanied by a severe fibrinous ulcerative placentitis were observed in fetuses examined at days 21, 28 and 36 pi. Inoculation of ewes at days 55-60 of gestation resulted in a prolonged virus replication in placentomes and fetal tissues; ewes that were allowed to proceed with pregnancy had 77% of abortions or fetal and perinatal deaths. Seven stillbirths, unviable and viable lambs born to these ewes were virus-positive at birth. Infectious virus was repeatedly isolated from leukocytes of two lambs up to 2 and 6 months of age, indicating they were persistently infected. Ewes inoculated at days 65-70 of gestation had 66.6% of fetal and perinatal losses. Three viable lambs born to these ewes were healthy, BVDV antibody-positive and virus-negative. A transient viral replication in placentomes and in a few fetal tissues, followed by the rise of fetal neutralizing antibodies and virus clearance was the result of inoculating ewes at days 120-125 of gestation. Lambs born to these ewes were healthy, antibody-positive and virus-negative. These results demonstrate that the biology of BVDV-2 infection in pregnant sheep is essentially similar to that of BVDV-1 in pregnant cattle and sheep. These features make this species an attractive animal model for studying the pathogenesis of congenital BVDV-2 infection.

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.

Replication and persistence of different strains of bovine viral diarrhea virus in an in vitro embryo production system

Recent studies have shown that exposed, in vitro-derived embryos remain contaminated with bovine viral diarrhea virus (BVDV) after washing. However, introduction of a Genotype II versus Genotype I strain of BVDV into an IVF system was reported to provide greater potential for transmission of disease. The primary objective of this study was to compare the potentials for different strains of noncytopathic BVDV to replicate in an IVF system, associate with IVF embryos and infect co-cultured cells via association with washed embryos. The secondary objective was to compare the effect of different strains of BVDV on embryonic development. Two Genotype I (SD-1 and NY-1) and 2 Genotype II (CD-87 and PA-131) strains of BVDV were evaluated. After IVM and IVF of oocytes, presumptive zygotes were washed and transferred into in vitro cultures containing uterine tubal cells (UTC) and medium that was free of BVDV-neutralizing activity. Immediately before addition of zygotes, the cultures were inoculated with 10(5) cell culture infective doses (50%, CCID50) of a strain of BVDV or maintained as a negative control. Cultures of zygotes were then incubated for 7 d. Embryonic development was observed on Days 3 and 7, and attempts were made to isolate BVDV from UTC and medium on Day 7. Also on Day 7, groups of intact, washed blastocysts were either transferred into virus-free secondary cultures containing UTC or sonicated with sonicate fluid assayed by both virus isolation and single-closed-tube reverse transcription nested polymerase chain reaction (RT-nPCR). After 3 d in secondary culture, hatched embryos were enumerated, and medium from the cultures, washed UTC and embryos were tested for BVDV by virus isolation. In addition, washed UTC and embryos were tested for BVDV using RT-nPCR. All strains of BVDV persisted and replicated in the embryo culture environment, but cleavage beyond the 4-cell stage, blastocyst development and hatching varied among cultures contaminated with different strains of virus. Further, the quantity of BVDV associated with washed embryos from both initial and secondary cultures varied among strains, but the variation was unrelated to difference in genotype (SD-1 and PA-131 greater than NY-1 and CD-87). Although all strains of BVDV replicated in UTC in the initial in vitro cultures and remained associated with washed blastocysts, susceptible UTC in the secondary in vitro cultures were seldom infected by any strain of virus.

Bovine viral diarrhea virus types 1 and 2 antibody response in calves receiving modified live virus or inactivated vaccines

Serums from calves receiving eight different commercial vaccines containing modified live virus (MLV) or inactivated bovine viral diarrhea virus (BVDV) immunogens were assayed for antibodies to types 1 and 2 BVDV strains. The immune response to the types 1 and 2 BVDV strains were evaluated in 48 calves receiving one of the eight vaccines for each group. For 7/8 vaccines, the BVDV vaccine immunogen was only type 1 whereas the remaining vaccine contained both types 1 and 2 immunogens. Calves administered MLV vaccine received only one dose at day 0, whereas those calves receiving the inactivated vaccines were administered two doses initially at days 0 and 28. Selected calves were revaccinated with only one dose at day 140. Animals vaccinated with type 1 vaccines developed titers to a broad range of type 1 BVDV, both cytopathic (CP) and noncytopathic (NCP) biotypes, with lower titers evident to type 2 BVDV strains. For some animals, the BVDV serum antibodies did not persist. Revaccination at day 140 induced a significant four-fold increase in animals with intermediate to low antibody titers. There did not appear to be any clear differences in antibody responses between type 1 MLV or inactivated vaccines. The calves receiving the inactivated vaccine containing types 1 and 2 had similar antibody levels to both types.

Diagnosis of persistent bovine viral diarrhea virus infection by immunohistochemical staining of formalin-fixed skin biopsy specimens

The objective of this study was to evaluate the efficacy of immunohistochemical (IHC) staining for diagnosis of persistent bovine viral diarrhea virus (BVDV) infection using formalin-fixed, paraffin-embedded skin biopsy specimens. Skin from 41 of 42 calves shown to be persistently infected (PI) with BVDV by repeated virus isolation more than 3 weeks apart were immunohistochemically positive for BVDV antigen. Positive IHC staining was most pronounced in the keratinocytes and in hair follicle epithelium, hair matrix cells of the hair bulb, and the dermal papilla. All of the skin sections from 10 calves experimentally infected postnatally with BVDV (10(5) median tissue culture infective doses [TCID50]) and biopsied on days 0, 5, 7, and 9 postinfection were negative for viral antigen. Ten calves from a second group experimentally infected with a higher dose of BVDV (10(8) TCID50) were biopsied when viremic between 10 and 14 days postinfection and 4 calves exhibited positive IHC staining for BVDV; however, staining in these skin biopsies was confined to small foci in the nonfollicular epidermis and follicular ostia. This staining was distinct from that observed in skin obtained from PI cattle. Skin biopsy represents an effective method for identifying animals PI with BVDV.

Mechanism of action of a pestivirus antiviral compound

We report here the discovery of a small molecule inhibitor of pestivirus replication. The compound, designated VP32947, inhibits the replication of bovine viral diarrhea virus (BVDV) in cell culture at a 50% inhibitory concentration of approximately 20 nM. VP32947 inhibits both cytopathic and noncytopathic pestiviruses, including isolates of BVDV-1, BVDV-2, border disease virus, and classical swine fever virus. However, the compound shows no activity against viruses from unrelated virus groups. Time of drug addition studies indicated that VP32947 acts after virus adsorption and penetration and before virus assembly and release. Analysis of viral macromolecular synthesis showed VP32947 had no effect on viral protein synthesis or polyprotein processing but did inhibit viral RNA synthesis. To identify the molecular target of VP32947, we isolated drug-resistant (DR) variants of BVDV-1 in cell culture. Sequence analysis of the complete genomic RNA of two DR variants revealed a single common amino acid change located within the coding region of the NS5B protein, the viral RNA-dependent RNA polymerase. When this single amino acid change was introduced into an infectious clone of drug-sensitive wild-type (WT) BVDV-1, replication of the resulting virus was resistant to VP32947. The RNA-dependent RNA polymerase activity of the NS5B proteins derived from WT and DR viruses expressed and purified from recombinant baculovirus-infected insect cells confirmed the drug sensitivity of the WT enzyme and the drug resistance of the DR enzyme. This work formally validates NS5B as a target for antiviral drug discovery and development. The utility of VP32947 and similar compounds for the control of pestivirus diseases, and for hepatitis C virus drug discovery efforts, is discussed.

Identificação do vírus da Diarréia Viral Bovina tipo 2 (BVDV-2) no sul do Brasil

Amostras do vírus da Diarréia Viral Bovina (BVDV), denominadas de BVDV tipo 2 (BVDV-2), foram inicialmente identificadas em surtos de BVD aguda e enfermidade hemorrágica e têm sido isoladas predominantemente na América do Norte. O presente artigo descreve dois casos de enfermidade gastroentérica/respiratória seguidos de isolamento e identificação de amostras de BVDV tipo 2 no sul do Brasil. Os vírus foram isolados de duas novilhas de diferentes rebanhos. Um dos animais apresentou enfermidade aguda, cursando com anorexia, atonia ruminal, diarréia escura ou muco-sanguinolenta, tenesmo e descarga nasal muco-purulenta. O outro animal desenvolveu enfermidade de longa duração (7 meses), caracterizada por crescimento retardado, anorexia, quadros recorrentes de diarréia, dermatite interdigital, hemorragias digestivas e genitais ocasionais, conjuntivite, artrite e pneumonia crônica. Congestão disseminada das mucosas, ulcerações extensivas e profundas na língua, palato e esôfago, áreas necróticas na mucosa do rúmen, áreas de congestão e ulcerações cobertas com fibrina no intestino delgado foram os achados mais proeminentes. Antígenos do BVDV foram demonstrados por imunohistoquí-mica no epitélio da língua, nos pulmões e em linfonodos mesentéricos. Amostras não-citopáticas do BVDV foram isoladas em cultivo celular a partir de leucócitos e do baço dos animais afetados e identificadas por imunofluorescência. Caracterização antigênica e análise filogenética desses isolados, e de outras duas amostras de BVDV isoladas de fetos coletados em matadouros, revelou tratar-se de BVDV tipo 2. A presença do BVDV tipo 2 na população bovina do Brasil possui um significado epidemiológico importante e pode ter conseqüências para o diagnóstico, estratégias de imunização e produção de vacinas.

Diversidade antigênica de amostras do vírus da diarréia viral bovina isoladas no Brasil: implicações para o diagnóstico e estratégias de imunização

Seqüenciamento e análise filogenética de 17 amostras do vírus da diarréia viral bovina (BVDV) isoladas no Brasil identificaram quatro amostras (23,5%) do genótipo 1a (BVDV-1a), nove amostras (52,9%) do genótipo 1b (BVDV tipo 1b) e quatro amostras (23,5%) do genótipo 2 (BVDV tipo 2). As amostras brasileiras de BVDV tipo 2 apresentaram-se genotipicamente distintas dos BVDV tipo 2 até então identificados na América do Norte e Europa, sugerindo pertencerem a um novo subgenótipo. A caracterização antigênica dessas amostras por neutralização cruzada revelou reatividade sorológica muito reduzida com cepas vacinais do BVDV. O anti-soro produzido contra três cepas vacinais do BVDV apresentou atividade neutralizante muito reduzida contra várias amostras brasileiras de BVDV tipos 1 e 2. Diferenças de até 128 vezes nos títulos de anticorpos neutralizantes foram observadas entre cepas vacinais e amostras brasileiras do BVDV. Nos testes de soroneutralização (SN) contra o vírus dos tipos 1 e 2, de 1134 amostras testadas, 280 (24,7%) possuiam anticorpos neutralizantes anti-BVDV e dessas, 215 (76,8%) apresentaram atividade neutralizante contra ambos os vírus, 37 (13,2%) reagiram apenas contra o BVDV tipo 2 e 28 amostras (10%) foram positivas apenas contra o BVDV tipo 1. Esses resultados demonstram que testes de SN utilizando vírus de apenas um genótipo podem resultar em um número significativo de falsos-negativos e indica a necessidade da formulação de vacinas com amostras locais de BVDV e/ou contendo vírus dos dois genótipos.

Bovine viral diarrhea virus cytopathic and noncytopathic biotypes and type 1 and 2 genotypes in diagnostic laboratory accessions: clinical and necropsy samples from cattle

One hundred three bovine samples submitted to the Oklahoma Animal Disease Diagnostic Laboratory (OADDL) that were positive for bovine viral diarrhea virus (BVDV) were typed by a nested reverse transcription-polymerase chain reaction for BVDV genotypes. These BVDV samples included supernatants from virus isolation (79), serums (17), and buffy coats (7). The biotype, cytopathic (CP) or noncytopathic (NCP), was determined by cell culture virus isolation. Twenty-eight of 103 samples were submitted for herd screening for BVDV, 32 from OADDL necropsy cases, and 43 from live cattle with varied clinical conditions. Two samples contained 2 bands indicating presence of both BVDV types 1 and 2. Of the 105 BVDV samples, 26 were type 1 CP strains (24.8%), 38 were type 1 NCP strains (36.2%), 10 were type 2 CP strains (9.5%), and 31 were type 2 NCP strains (29.5%). From the 105 BVDV isolates, NCP biotypes were isolated more frequently (69, 65.7%) than CP biotypes (36, 34.3%), and type 1 genotypes were more frequently isolated (64, 61.00%) than type 2 genotypes (41, 39.0%). The NCP strains were more common than CP in herd screening samples. Cattle with respiratory disease history at time of sampling had more NCP than CP biotypes and more type 1 than type 2 genotypes. Of the necropsy cases, more were type 1 than type 2 genotypes for the respiratory cases with fibrinous pneumonia, more were type 1 than type 2 genotypes in cattle with enteritis/colitis without systemic lesions, and more were CP than NCP biotypes in cattle with enteritis/colitis with systemic lesions. No CP biotype was isolated from serum samples.

Experimental model of type II bovine viral diarrhea virus-induced thrombocytopenia in neonatal calves

Thrombocytopenia has been associated with type II bovine viral diarrhea virus (BVDV) infection in immunocompetent cattle, but the mechanism is unknown. The purpose of the present study was to develop and characterize a model of type II BVDV-induced thrombocytopenia. Colostrum-deprived Holstein calves were obtained immediately after birth, given a BVDV-negative and BVDV antibody-negative plasma transfusion, housed in an isolation facility, and randomly assigned to either control (n = 4) or infected (n = 5) groups. Infected calves were inoculated by intranasal instillation on day 3 of age with 10(7) TCID50 of the prototype type II isolate, BVDV 890, whereas control calves were sham inoculated. Blood counts and virus isolations from serum, white blood cells, and platelets were performed daily until day 12 after infection, at which time all experimental calves were euthanatized, and pathologic, virologic, and immunohistochemical examinations were performed. On physical examination, the control calves remained normal, but the infected calves developed pyrexia and diarrhea characteristic of type II BVDV infection. The platelet count decreased in all infected calves, and a statistically significant difference in the platelet count between control and infected calves was observed on days 7-12 after infection. In addition, the mean platelet volume and white blood cell counts also decreased. Examination of the bone marrow from the infected calves revealed immunohistochemical staining for BVDV antigen in megakaryocytes and evidence of concurrent megakaryocyte necrosis and hyperplasia.

Typing of bovine viral diarrhea viruses directly from blood of persistently infected cattle by multiplex PCR

A nested multiplex PCR was developed for genotyping of bovine viral diarrhea viruses (BVDVs). The assay could detect as little as 3 50% tissue culture infective doses of BVDV per ml and typed 42 out of 42 cell culture isolates. BVDV was also successfully typed, with or without RNA extraction, from all 27 whole-blood samples examined from 22 carriers or probable carriers and 5 experimentally infected cattle.

Experimental infection of calves with bovine viral diarrhea virus genotype II (NY-93)

To ascertain the virulence of bovine viral diarrhea virus (BVDV) genotype II, isolate NY-93 was inoculated intranasally into 3 calves, 2 of which were treated with a synthetic glucocorticoid prior to and after virus inoculation. Anorexia, fever (up to 42 C), dyspnea, and hemorrhagic diarrhea developed 6 days after intranasal inoculation with BVDV NY-93. The condition of all calves deteriorated further until the end of the study on day 14 postinoculation. The most significant postmortem macroscopic changes in all calves were limited to the gastrointestinal tract and consisted of moderate to severe congestion of the mucosa with multifocal hemorrhages. Microscopic lesions found in the gastrointestinal tract were similar to those observed in mucosal disease, including degeneration and necrosis of crypt epithelium and necrosis of lymphoid tissue throughout the ileum, colon, and rectum. The basal stratum of the epithelium of tongue, esophagus, and rumen had scattered individual necrotic cells. Spleen and lymph nodes had lymphocytolysis and severe lymphoid depletion. Severe acute fibrinous bronchopneumonia was present in dexamethasone-treated calves. Abundant viral antigen was detected by immunohistochemistry in the squamous epithelium of tongue, esophagus, and forestomachs. BVDV antigen was prominent in cells of the media of small arteries and endothelial cells. The presence of infectious virus in tissues correlated with an absence of circulating neutralizing antibodies. These findings highlight the potential of BVDV genotype II to cause severe disease in normal and stressed cattle.

Detection of bovine torovirus in fecal specimens of calves with diarrhea from Ontario farms

Breda virus (BRV), a member of the genus Torovirus, is an established etiological agent of disease in cattle. BRV isolates have been detected in the stools of neonatal calves with diarrhea in both Iowa and Ohio and in several areas of Europe. However, this virus has been reported only once in Canada. Therefore, a study was performed to determine the extent to which bovine torovirus is present in calves with diarrhea from farms in southern Ontario. A total of 118 fecal samples from symptomatic calves and 43 control specimens from asymptomatic calves were examined by electron microscopy (EM) and reverse transcription-PCR (RT-PCR) for the presence of torovirus. Torovirus RNA was detected in 43 of the 118 diarrheic samples (36.4%) by RT-PCR with primers designed in the conserved 3' end of the torovirus genome. By EM, torovirus particles were observed in 37 of the 118 specimens (31.4%). All but one of these samples were also positive by RT-PCR. The incidence of torovirus in the asymptomatic control specimens by RT-PCR was only 11.6%. To establish the identity of the particles observed in the diarrheic specimens, five of the amplicons from samples positive by both RT-PCR and EM were cloned and sequenced. Nucleotide sequence analysis revealed that the bovine torovirus found in southern Ontario manifests between 96 and 97% sequence identity to the BRV type 1 strain found in Iowa. This study shows that bovine torovirus is a common virus in the fecal specimens of calves with diarrhea from farms in southern Ontario and thus may be an important pathogen of cattle.