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

The effect of neonatal vaccination for bovine respiratory disease in the face of a dual challenge with bovine viral diarrhea virus and Mannheimia hemolytica

Bovine respiratory disease is the greatest threat to calf health. In this study, colostrum-fed dairy X beef calves were vaccinated at ∼30 days of age with an adjuvanted parenteral vaccine containing modified live bovine viral diarrhea virus (BVDV) type 1 and type 2, bovine herpesvirus 1 (BHV-1), bovine parainfluenza type 3 virus (PI3V) and bovine respiratory syncytial virus (BRSV) andM. haemolyticatoxoid (Group 1), or intranasal temperature-sensitive BHV-1, BRSV and PI3V concurrently witha parenteral vaccine containing modified live BVDV type 1 and type 2 andM. haemolyticatoxoid (Group 2) or a placebo (Group 3). The calves were challenged ∼150 days post vaccination intranasally with BVDV 1b and then 7 days later intratracheally withM. haemolytica. The calves wereeuthanized 6 days after theM. haemolyticachallenge. Clinical signs following BVDV infection were similar in all groups. There was increased rectal temperatures in the Groups 2 and 3 on day 3 and in Group 3 on days 8-13. Group 1 animals had a slight leukopenia following BVDV infection while Groups 2 and 3 had greater leukopenia. BVDV type 1 and 2 serum titers increased in Group 1 following vaccination while these titers waned in Groups 2 and 3. There were higher levels of BVDV in the buffy coats and nasal samples in Group 2 and Group 3 versus Group 1 (p < 0.01). Interferon-gamma response was higher (p < 0.01) in Group 1 animals than Groups 2 and 3. Group 1 had the lowest percent pneumonic tissue (1.6%) while Group 2 vaccinates had 3.7% and the control Group 3 was 5.3%. Vaccination in the face of maternal antibody with a parenteral adjuvanted vaccine resulted in better protection than the regimen of an intranasal vaccine anda parenteral adjuvanted BVDV andM haemolyticacombination vaccine in a BVDV-M. haemolyticadual challenge.

NASYM, a live intranasal vaccine, protects young calves from bovine respiratory syncytial virus in the presence of maternal antibodies

BACKGROUND

Bovine respiratory syncytial virus (BRSV) is a major problem for cattle worldwide during their first year of life. The aim of the present study was to evaluate efficacy and longevity of immunity of a live vaccine (NASYM, HIPRA) in the presence of maternally derived antibodies (MDA).

METHOD

Calves (36) were distributed in four groups, based on MDA status and treatment. They received NASYM or a placebo at an early age (less than two weeks) by intranasal route. Eight weeks later, animals were challenged with the Asquith strain of BRSV. Efficacy was assessed by monitoring clinical signs and mortality, PaO₂ , virus shedding and lung lesions. The immunological response was evaluated by measuring IgG in serum and IgA in nasal secretions.

RESULTS

A reduction of mortality, lung lesions, shedding and a higher PaO₂ was achieved in NASYM vaccinated groups, independently of MDA status. An anamnestic IgG response was observed after challenge in vaccinated animals, both in MDA+ and MDA- groups. An IgA response was also observed in vaccinated animals after vaccination and challenge.

CONCLUSION

NASYM protected newborn calves with MDAs during the first 10 weeks of life, against a very virulent challenge that caused extensive pulmonary lesions and deaths in control animals, with just a single intranasal dose.

Bovine Respiratory Disease: Looking Back and Looking Forward, What Do We See?

Changes in cattle feeding in the twentieth century led to the "Golden Age of Cattle Feeding" on the US High Plains; this was accompanied by recognition that bovine respiratory disease (BRD) is the leading cause of feedlot morbidity and mortality. Decades of research have illuminated the multiple viruses and bacteria that contribute to BRD, which led to vaccines and antimicrobials to prevent, treat, and control BRD. Despite these discoveries, feedlot BRD morbidities do not appear to have changed substantially over this time. New technologies are being developed that have the potential to improve accuracy of BRD detection.

Pathological and virological features of skin lesions caused by BVDV in cattle

Dermatitis might occur in mucosal disease (MD) caused by bovine viral diarrhea virus (BVDV). This study describes the pathological and virological features of skin lesions associated with BVDV infection in four persistently infected (PI) cattle. Skin samples were reprocessed for histopathology and IHC. BVDV isolates were obtained and were genetically characterized. In addition to upper alimentary system ulcerative lesions, all cattle (one outbreak and three individual cases) presented focal crusty and ulcerative lesions affecting the mucocutaneous and skin-horn junctions, interdigital clefts, pastern, and areas surrounding the dewclaws and diffuse thickened skin within 7-20 days of infection. Microscopic analysis revealed parakeratotic hyperkeratosis and single-cell keratinocyte death, accompanied by ballooning degeneration and spongiosis in the epidermis, as well as intraepithelial and subcorneal pustules. IHC showed BVDV antigen in the cytoplasm of keratinocytes undergoing individual cell death. Phylogenetic analysis revealed that the isolates from cattle #1, #2, and #4 belonged to BVDV-1a, whereas that from cattle #3 belonged to BVDV-1d. Cytopathic BVDV was isolated from cattle #2 and #3 (MD), and non-cytopathic BVDV was isolated from cattle #1 and #4. Thus, BVDV infection might cause acute disease, characterized by skin and upper alimentary system ulcerative lesions, in both MD and PI cattle.

Mucosal disease-like lesions caused by HoBi-like pestivirus in Brazilian calves in 2010-2011: Clinical, pathological, immunohistochemical, and virological characterization

A HoBi-like pestivirus was first described in 2004 in a Brazilian fetal bovine serum that was exported to Germany. Nevertheless, it is believed that the virus had been present since the 1990's, when it was detected in buffalos of Brazilian origin. Reproductive and respiratory diseases have been reported since 2001 in cattle, and more recently, diseases accompanied by a clinical presentation of mucosal disease-like (MD-like lesions have been reported as well. In the present study, the authors reported the oldest case of MD--like in cattle, associated with a HoBi-like pestivirus infection. Diarrhea, anorexia, nasal discharge, hypersalivation, and weakness were observed in 20 calves. For two of the animals, clinical follow-ups were performed. Following their death, necropsy was performed on these two calves. The main gross alterations observed were ulcers and erosions in the upper and lower digestive tract and interdigital dermatitis. Clinical history, gross findings, histopathological examination, immunohistochemistry, RT-PCR, and virus isolation were determined as suitable tools for the diagnosis of a MD-like outbreak, caused by a HoBi-like pestivirus.

Comparison of Tests for Detection of Bovine Viral Diarrhea Virus in Diagnostic Samples

Currently, a variety of tests are used to detect bovine viral diarrhea virus (BVDV) in persistently infected (PI) cattle. These tests include immunohistochemical staining (IHC), antigen capture enzyme-linked immunosorbent assay (ACE), virus isolation (VI), and reverse transcription-polymerase chain reaction (RT-PCR). However, a lack of methods standardization could compromise the ability to consistently identify animals infected with BVDV. This study evaluated the diagnostic proficiency of current methods for detecting BVDV in infected cattle using intra- and interlaboratory comparisons. Samples were collected from 4 animals more than 7 months of age (2 BVDV negative animals, a PI animal, and a PI animal that previously lacked detectable virus in serum as determined by VI). Samples were submitted to 23 participating diagnostic laboratories using the respective laboratory's standard submission protocol. Samples collected for submission included: 1) serum for ACE, RT-PCR, and VI; 2) whole blood for RT-PCR and VI; and 3) skin biopsies for ACE and IHC. The ACE performed on skin provided the greatest consistency in detecting positive samples and a perfect level of agreement among laboratories. Reverse transcription-polymerase chain reaction and IHC performed well by correctly identifying ≤85% of samples positive for BVDV. Virus isolation performed on serum yielded the lowest consistency in detecting positive samples and the lowest level of agreement. The level of agreement between laboratories for detecting BVDV in persistently infected cattle ranged from perfect to less than expected by chance. The variation between laboratories suggests a need for training opportunities in standardized laboratory protocols and proficiency testing.

Clinical disease and lung lesions in calves experimentally inoculated with Histophilus somni five days after metaphylactic administration of tildipirosin or tulathromycin

OBJECTIVE

To compare clinical disease and lung lesions in calves experimentally inoculated with Histophilus somni 5 days after metaphylactic administration of tildipirosin or tulathromycin. ANIMALS Twenty-four 3-month-old Holstein and Holstein-crossbreed steers.

PROCEDURES

Calves were randomly allocated to 3 groups of 8 calves. On day 0, calves in group 1 received tildipirosin (4 mg/kg, SC), calves in group 2 received tulathromycin (2.5 mg/kg, SC), and calves in group 3 received isotonic saline (0.9% NaCl) solution (1 mL/45 kg, SC; control). On day 5, calves were inoculated with 10 mL of a solution containing H somni strain 7735 (1.6 × 10(9) CFUs/mL, intrabronchially; challenge). Calves were clinically evaluated on days 5 through 8 and euthanized on day 8. The lungs were grossly evaluated for evidence of pneumonia, and bronchial secretion samples underwent bacteriologic culture.

RESULTS

The mean clinical score for each group was significantly increased 12 hours after challenge, compared with that immediately before challenge, and was significantly lower for tildipirosin-treated calves on days 6, 7, and 8, compared with those for tulathromycin-treated and control calves. The mean percentage of lung consolidation for tildipirosin-treated calves was significantly lower than those for tulathromycin-treated and control calves. Histophilus somni was isolated from the bronchial secretions of some tulathromycin-treated and control calves but was not isolated from tildipirosin-treated calves.

CONCLUSIONS AND CLINICAL RELEVANCE

Results indicated that metaphylactic administration of tildipirosin to calves 5 days prior to H somni challenge prevented subsequent culture of the pathogen from bronchial secretions and was more effective in minimizing clinical disease and lung lesions than was metaphylactic administration of tulathromycin.

Transmission of Bovine Viral Diarrhea Virus to Adult Goats from Persistently Infected Cattle

The transmission of bovine viral diarrhea virus (BVDV) from persistently infected (PI) heifers to adult seronegative goats was examined in this study. Ten seronegative adult goats were exposed to 4 PI heifers. None of the goats developed any clinical signs but all goats seroconverted by 42 days after exposure to the PI cattle. Results indicate that goats are susceptible to BVDV infection when housed with PI cattle.

Distribution and Cellular Heterogeneity of Bovine Viral Diarrhea Viral Antigen Expression in the Brain of Persistently Infected Calves: A New Perspective

Persistent infection following in utero exposure to bovine viral diarrhea virus (BVDV) early in gestation is a serious cause of morbidity and mortality in cattle industries worldwide. The brain is a primary target of persistent infection. In the current study, the types of cells infected and topography of viral antigen expression were examined in brain sections from 9 BVDV persistently infected crossbred calves, all less than 1 year of age, by immunohistochemical staining using the 15C5 primary monoclonal antibody. BVDV antigen was detected in the brains of all persistently infected calves. A variety of cell types was infected, including neurons, astrocytes, oligodendroglia, blood vessel-associated cells (pericytes, perivascular macrophages, smooth muscle cells), and cells in the leptomeninges (blood vessel-associated cells). Conclusive demonstration of viral antigen in vascular endothelial cells was elusive. The intensity and distribution of viral antigen staining in neurons were highly variable. Viral antigen staining was most consistent and intense in thalamic nuclei, most notably in dorsal and medial nuclear groups, followed by the hippocampus, entorhinal cortex, basal nuclei, and piriform cortex. Staining in other brain areas was often less intense and inconsistent. The variability in the intensity and topography of viral antigen in the brain may explain the heterogeneity in the clinical manifestations of BVDV-induced disease. Additionally, infection of the brain in persistently infected calves may underlie or at least contribute to endocrine disturbances and immunologic deficits that are protean manifestations of BVDV-induced disease.

Viral Antigen Distribution in the Respiratory Tract of Cattle Persistently Infected with Bovine Viral Diarrhea Virus Subtype 2a

Tissues were obtained at necropsy from the nasal vestibule, turbinates, nasopharynx, trachea, tracheobronchial bifurcation, and lung from each of 10 clinically healthy calves persistently infected (PI) with bovine viral diarrhea virus (BVDV) serotype 2a. Tissues from the nasal vestibule were obtained by biopsy from five additional PI calves. Formalin-fixed tissues were processed for immunohistochemistry to localize the distribution of BVDV throughout the respiratory tract. Antigen distribution and intensity were subjectively evaluated. Throughout the respiratory tract, mononuclear leukocytes, vascular smooth muscle, and endoneural and perineural cells had BVDV immunoreactivity (BVDV-IR). Multifocally, squamous and ciliated columnar epithelium throughout the respiratory tract contained weak to moderate BVDV antigen. Viral antigen was not seen in goblet cells. BVDV-IR in mixed tubuloalveolar glands of the nasal cavity was weak to strong in serous secretory cells and ductular epithelium. Chondrocytes of the concha often contained BVDV antigen diffusely. Nasal mucus-secreting and tracheobronchial glands multifocally contained weak viral signal. In all cases, alveolar macrophages had moderate to strong BVDV-IR, whereas BVDV-IR in alveolar epithelial cells was weak to moderate. BVDV was present in interalveolar leukocytes and mesenchymal cells. Results indicate that serous secretions of the nasal cavity, productive viral infection of epithelium, and infected leukocytes in respiratory secretions are likely major sources of infectious BVDV from PI calves. The presence of BVDV antigen in respiratory epithelium is, at least, indirect support for the notion that this virus predisposes PI cattle to secondary microbial infections.

Comparison of Ear Notch Immunohistochemistry, Ear Notch Antigen-Capture ELISA, and Buffy Coat Virus Isolation for Detection of Calves Persistently Infected with Bovine Viral Diarrhea Virus

Two techniques performed on skin biopsy samples (ear notches), immunohistochemistry (IHC) and antigen-capture ELISA (AgELISA), were compared for detection of bovine viral diarrhea virus (BVDV) persistent infection (PI) in 559 Angus calves between the ages of 1 and 5 months. The calves also were tested for BVDV infection using virus isolation (VI) and reverse transcription (RT)-PCR on buffy coat samples and for antibodies to BVDV types 1a and 2 by serum neutralization (SN). Sixty-seven of 559 (12.0%) calves tested positive at initial screening by IHC, AgELISA, or VI, and all 67 were kept for a minimum of 3 months and retested monthly by IHC, AgELISA, VI, RT-PCR, and SN. Of the calves positive at initial screening, 59/67 (88.1%) were determined PI and 8/67 (11.9%) were determined acutely infected. Both IHC and AgELISA detected 100% of PI calves; however, IHC and AgELISA also detected 6 and 8 acutely infected calves, respectively, at initial screening. Furthermore, IHC and AgELISA continued to detect 3 and 4 acutely infected calves, respectively, 3 months after initial screening. Three acutely infected calves had IHC staining indistinguishable from PI calves at initial screening. Both IHC and AgELISA are accurate at detecting BVDV-infected calves, but veterinarians and producers should be advised that both tests detect some calves acutely infected with BVDV in addition to PI animals. Repeat testing using VI or RT-PCR on buffy coat samples should be performed at 30 days after initial screening to conclusively discriminate between acute and PI.

Effects of Delayed or Prolonged Fixation on Immunohistochemical Detection of Bovine Viral Diarrhea Virus Type I in Skin of Two Persistently Infected Calves

The effects of delayed or prolonged fixation on immunohistochemical detection of bovine viral diarrhea virus (BVDV) antigen were evaluated in skin. Ear-notch specimens from 2 calves persistently infected with BVDV type 1 were handled in 1 of 3 ways: 1) fixed in formalin promptly and processed for immunohistochemistry (IHC) after 3–176 days; 2) held at 3–4°C in plastic bags up to 10 days, then fixed in formalin for 2–5 days before processing; or 3) exposed to room air and temperature for 1–5 days before formalin fixation. Immunohistochemical staining intensity was evaluated without the knowledge of specimen handling. Staining of specimens that had been promptly fixed in formalin was moderate to strong at all fixation periods through 36 days, weak or no staining was evident in specimens fixed for 176 days. Refrigerated specimens typically had moderate to strong immunohistochemical staining. Even after 10 days of refrigeration before fixation, all immunohistochemical reactions were positive. However, no immunohistochemical staining was detected in any specimen that was exposed to room air. Results indicate that prompt formalin fixation is optimal for BVDV IHC. Samples can be held in formalin at least 36 days, without loss of reactivity. A 1-day delay in fixation caused no loss of reactivity, provided the specimen was refrigerated and protected from desiccation.

Comparison of Five Diagnostic Methods for Detecting Bovine Viral Diarrhea Virus Infection in Calves

Five diagnostic techniques performed on skin biopsies (shoulder region) and/or serum were compared for detection of bovine viral diarrhea virus infection in 224 calves 0–3 months of age, 23 calves older than 3 months but younger than 7 months, and 11 cattle older than 7 months. The diagnostic methods used were immunohistochemistry (IHC), 2 commercial antigen ELISAs, 1 commercial antibody ELISA, and realtime RT-PCR. Results of 249 out of 258 skin and serum samples were identical and correlated within the 3 antigen detection methods and the real-time RT-PCR used. Twenty-six of these 249 samples were BVDV-positive with all antigen detection methods and the real-time RT-PCR. Nine out of 258 samples yielding discordant results were additionally examined by RT-PCR, RT-PCR Reamplification (ReA), and antigen ELISA I on serum and by immunohistochemistry on formalin fixed and paraffin-embedded skin biopsies. Virus isolation and genotyping was performed as well on these discordant samples. In 3 cases, transiently infected animals were identified. Two samples positive by real-time RT-PCR were interpreted as false positive and were ascribed to cross-contamination. The antigen ELISA II failed to detect 2 BVDV-positive calves due to the presence of maternal antibodies; the cause of 2 false-positive cases in this ELISA remained undetermined. Only persistently infected animals were identified in skin samples by IHC or antigen ELISA I. The 3 antigen detection methods and the real-time RT-PCR used in parallel had a high correlation rate (96.5%) and similar sensitivity and specificity values.

A Comparison of Polymerase Chain Reaction with and without RNA Extraction and Virus Isolation for Detection of Bovine Viral Diarrhea Virus in Young Calves

Previously, the authors described a multiplex reverse transcriptase–polymerase chain reaction (PCR) assay for detection and typing of bovine viral diarrhea virus (BVDV) from blood of persistently infected (PI) cattle that could be used with or without RNA extraction. In the present study, the PCR assay was evaluated for its ability to detect BVDV in young calves as a screening tool for detection of persistent infections. Both methods, PCR after RNA extraction (rPCR) and the direct method without RNA extraction (dPCR) were applied and compared with virus isolation (VI) with diagnostic specimens. From 450 whole blood samples from Ontario calves, 47 and 39 samples were positive by rPCR and VI, respectively. From the 47 samples positive by rPCR, 45 (96%) also were positive by dPCR when samples were tested both undiluted and diluted 1:10. In comparison to VI, the relative sensitivities of both PCR assays were 100%. Examination of the results indicates that both PCR assays can be used for screening calves for persistent infection with BVDV.

Assessment of a Bovine Viral Diarrhea Virus Antigen Capture ELISA and a Microtiter Virus Isolation ELISA Using Pooled Ear Notch and Serum Samples

To reduce the cost of whole herd screening for bovine viral diarrhea virus persistently infected animals, the sensitivity and specificity of an antigen-capture enzyme-linked immunosorbent assay (AC-ELISA) and a microtiter virus isolation ELISA using saline from ear notch samples or pooled serum was determined. Pooled saline from ear notch samples, assayed by AC-ELISA, gave a sensitivity and specificity of 98% and 94%, respectively, for pools containing 2 samples and 72% and 100%, respectively, for pools of 5. The sensitivity of pooled ear notch or serum samples for bovine viral diarrhea virus detection by microtiter virus isolation (sensitivity < 5%) or serum samples for detection by AC-ELISA (sensitivity < 15%) is too low to be used for whole herd screening. Pooling saline from ear notch samples from 2 animals tested by AC-ELISA, however, could provide a less expensive, reliable method for whole herd screening for bovine viral diarrhea virus.

Evaluation of Antigen-Capture ELISA and Immunohistochemical Methods for Avian Surveillance of West Nile Virus

Accurate detection of West Nile virus (WNV) in corvids is essential for monitoring the spread of virus during the mosquito season. Viremia in corvids is very high, with titers approaching 108 viral particles/ml. In the presence of such marked viremia, the sensitivity of real-time reverse transcription-polymerase chain reaction (RT-PCR) analysis is unnecessary, and more cost-effective methods should be assessed. To this end, antigen-capture ELISA (ACE) and immunohistochemical (IHC) assays were evaluated. Skin, cloacal swab specimens, and feathers from corvids were tested by use of ACE, and results were compared with results obtained from use of real-time RT-PCR analysis. Of the 3 sample types, skin gave the best sensitivity (98%) and specificity (100%). Skin, brain, kidney, and spleen from corvids were analyzed by IHC, and results were compared with real-time RT-PCR results. Kidney and spleen were more often positive by use of IHC than were brain and skin tissue; however, IHC did not perform as well as ACE in the identification of virus-positive birds. Results of this study support the use of a skin sample in an ACE format as an effective surveillance method for corvids.

Bovine viral diarrhea virus outbreak in a beef cow herd in South Dakota

CASE DESCRIPTION

136 pregnant beef cows were purchased in the fall of 2003. The following spring, 128 cows calved as expected; 8 cows were believed to have aborted with the fetuses unavailable for evaluation. Of the 128 calves born, 8 died within 2 weeks after birth and 9 were born with congenital abnormalities.

CLINICAL FINDINGS

Cows and their calves were evaluated for bovine viral diarrhea virus (BVDV) infection. Forty-four of 120 calves, but 0 cows, tested positive for BVDV antigen by immunohistochemical staining of ear notch specimens.

TREATMENT AND OUTCOME

Five BVDV test-positive calves died shortly after weaning, and the remaining 39 BVDV test-positive calves were moved to an isolated feedlot and retested for BVDV at 5 to 6 months of age; 36 had positive results, which indicated that they were persistently infected (PI) with BVDV, whereas 3 had negative results, which indicated that they were transiently infected with BVDV at the time of the first test. All PI calves were infected with the same BVDV type 2a strain. As yearlings, 17 of the 36 PI calves died peracutely with lesions consistent with mucosal disease, 6 died without gross lesions, and 2 were euthanized because of chronic ill thrift. The remaining 11 PI calves appeared healthy and were sold for slaughter. Screening of the following year's calf crop for BVDV by use of immunohistochemical staining of ear-notch specimens yielded negative results for all calves.

CLINICAL RELEVANCE

Introduction of BVDV into a naïve cow herd resulted in a loss of 44% of the calf crop subsequent to reproductive loss, poor thrift, and mucosal disease.

Transmission of border disease virus from a persistently infected calf to seronegative heifers in early pregnancy

Background

This study describes the transmission of border disease virus (BDV) from a persistently infected calf to seronegative heifers in early pregnancy, resulting in persistently infected fetuses. On day 50 of pregnancy (= day 0 of the infection phase), six heifers were co-housed in a free stall with a bull calf persistently infected with BDV (pi BVD) for 60 days. The heifers underwent daily clinical examination, and blood samples were collected regularly for detection of pestiviral RNA and anti-pestivirus antibodies. After day 60 (= day 110 of pregnancy), the heifers were slaughtered, and the fetuses and placentae underwent post-mortem and immunohistochemical examination and RT-PCR for viral RNA detection.

Results

Three heifers had mild viraemia from day 8 to day 14, and by day 40 all heifers had pestivirus antibodies identified as anti-BDV antibodies in the serum neutralisation test. The placenta of the three viraemic heifers had histological evidence of inflammation, and fetal organs from these heifers were positive for pestivirus antigen by immunohistochemical examination and for BD viral RNA by RT-PCR and sequencing. Thus, co-housing of heifers in early pregnancy with a pi-BDV calf led to seroconversion in all heifers and persistent fetal infection in three.

Conclusions

Considering that pi-BDV cattle can infect other cattle and lead to persistent infection of the fetus in pregnant cows, BDV should not be ignored in the context of the mandatory BVDV eradication and monitoring program. This strongly suggests that BDV should be taken into account in BVD eradication and control programs.

Duration of immunity to experimental infection with bovine respiratory syncytial virus following intranasal vaccination of young passively immune calves

OBJECTIVE

To determine whether a combination modified-live bovine respiratory syncytial virus (BRSV) vaccine could stimulate protective immunity in young BRSV-seropositive calves following intranasal administration and determine the duration of clinical immunity.

DESIGN

Controlled challenge study. Animals-84 dairy calves (3 to 11 days old).

PROCEDURES

Responses to BRSV challenge of seronegative calves vaccinated under licensing trial conditions were compared with those of seropositive calves 2 times after vaccination. In experiment 1, young BRSV-seronegative calves were vaccinated intranasally with a minimum immunizing dose of BRSV and challenged with BRSV approximately 7 weeks later. In experiments 2 and 3, young BRSV-seropositive calves were vaccinated intranasally with a commercially available combination modified-live virus vaccine containing the commercial dose of the BRSV fraction and challenged with BRSV 9 weeks or approximately 14 weeks later, respectively.

RESULTS

In experiments 1 and 2, BRSV-vaccinated calves had significantly higher Pao2, significantly fewer lung lesions, and significantly lower mortality rate than did unvaccinated calves subsequent to BRSV challenge. In contrast, in experiment 3, there were no differences in Pao2, lung lesions, or mortality rate between vaccinated and control calves after BRSV challenge approximately 14 weeks after vaccination. Protected calves in experiment 1 consistently had significant anamnestic mucosal and systemic antibody responses after challenge, whereas in experiments 2 and 3, antibody responses after challenge were more variable.

CONCLUSIONS AND CLINICAL RELEVANCE

A combination BRSV vaccine administered intranasally to young calves induced protective immunity in the presence of maternal antibodies. The duration of immune responses induced by intranasal vaccination was short (≤ 4 months). Boosting immunity iatrogenically, or by natural exposure, is probably required to obtain optimal responses to neonatal intranasal vaccination.

Bovine Viral Diarrhea Virus Infections

Bovine viral diarrhea virus (BVDV) continues to be of economic significance to the livestock industry in terms of acute disease and fetal loss. Many of the lesions relating to BVDV infection have been well described previously. The virus is perpetuated in herds through the presence of calves that are persistently infected. Relationships between various species and biotypes of BVDV and host defenses are increasingly understood. Understanding of the host defense mechanisms of innate immunity and adaptive immunity continues to improve, and the effects of the virus on these immune mechanisms are being used to explain how persistent infection develops. The noncytopathic biotype of BVDV plays the major role in its effects on the host defenses by inhibiting various aspects of the innate immune system and creation of immunotolerance in the fetus during early gestation. Recent advances have allowed for development of affordable test strategies to identify and remove persistently infected animals. With these improved tests and removal strategies, the livestock industry can begin more widespread effective control programs.

Laboratory diagnosis of bovine viral diarrhea virus

The control and eventual eradication of bovine viral diarrhea virus (BVDV) have been defined as objectives to reduce the economic losses due to the presence of this virus in the cattle population. These goals could not be envisioned without the significant achievements in the diagnostic procedures employed to detect the infection in its various manifestations. The tests that are currently available are fully capable of supporting the ACVIM consensus statement for the control and eradication of BVDV. In point of fact diagnostic testing is the essential component of any control program. What is now currently lacking is full implementation of the ACVIM recommendations.

Apoptosis in Bovine viral diarrhea virus (BVDV)-induced mucosal disease lesions: a histological, immunohistological, and virological investigation

Cattle persistently infected with a noncytopathic Bovine viral diarrhea virus (BVDV) are at risk of developing fatal "mucosal disease" (MD). The authors investigated the role of various apoptosis pathways in the pathogenesis of lesions in animals suffering from MD. Therefore, they compared the expression of caspase-3, caspase-8, caspase-9, and Bcl-2L1 (Bcl-x) in tissues of 6 BVDV-free control animals, 7 persistently infected (PI) animals that showed no signs of MD (non-MD PI animals), and 11 animals with MD and correlated the staining with the localization of mucosal lesions. Caspase-3 and -9 staining were markedly stronger in MD cases and were associated with mucosal lesions, even though non-MD PI animals and negative controls also expressed caspase-9. Conversely, caspase-8 was not elevated in any of the animals analyzed. Interestingly, Bcl-x also colocalized with mucosal lesions in the MD cases. However, Bcl-x was similarly expressed in tissues from all 3 groups, and thus, its role in apoptosis needs to be clarified. This study clearly illustrates ex vivo that the activation of the intrinsic, but not the extrinsic, apoptosis pathway is a key element in the pathogenesis of MD lesions observed in cattle persistently infected with BVDV. However, whether direct induction of apoptosis in infected cells or indirect effects induced by the virus are responsible for the lesions observed remains to be established.

Aspectos clínicos, patológicos, imuno-histoquímicos e virológicos em cinco bezerros persistentemente infectados com o vírus da diarreia viral bovina em uma propriedade do Rio Grande do Sul

O vírus da diarreia viral bovina (BVDV) é responsável por diferentes síndromes que afetam bovinos em todo o mundo, causando grandes perdas econômicas. O presente trabalho analisou as características clínicas, patológicas e imuno-histoquímicas e virais de cinco bovinos persistentemente infectados pelo BVDV de uma mesma propriedade, localizada no Município de Viamão, Rio Grande do Sul. Dentre os sinais clínicos verificados destacaram-se subdesenvolvimento, secreções nasais e oculares, além de catarata congênita unilateral em dois bovinos. As principais lesões observadas durante a necropsia consistiram de aumento dos linfonodos mesentéricos, evidenciação das placas de Peyer e pododermatite e lesões crostosas no plano nasal e na região periocular em um animal. Os achados microscópicos caracterizavam-se, principalmente, por infiltrado mononuclear na lâmina do intestino delgado e rarefação linfoide com infiltrado histiocitário nos centrofoliculares de linfonodos e nas placas de Peyer. Antígenos virais foram detectados por imuno-histoquímica principalmente em queratinócitos da epiderme, no epitélio de folículos pilosos e células mononucleares da derme de orelhas e pele; histiócitos e em linfócitos dos linfonodos; células foliculares da tireoide; no citoplasma de neurônios e, em menor escala, em células da micróglia no córtex cerebral e no hipocampo. O isolamento viral de amostras de sangue e órgãos dos animais confirmou a presença de BVDV não citopático. Também foi possível detectar a presença do genoma viral por RT-PCR no soro dos animais. A análise filogenética do fragmento parcial da região 5' não traduzida do genoma viral permitiu a classificação da amostra viral como BVDV tipo 2b. O presente estudo reforça a necessidade de investigar e caracterizar surtos de BVD e descrever suas diferentes for-mas de apresentação.

The diagnosis and prevalence of persistent infection with bovine viral diarrhoea virus in South African feedlot cattle

Bovine viral diarrhoea virus (BVDV) infection is an important viral infection affecting the cattle industry today. The prevalence of this infection in South African feedlots is unknown. Ear notch biopsies were collected from chronic poor doers and animals that appeared unthrifty upon entering feedlots, as well as animals entering the hospital pen with respiratory disease for the first time. A total of 1690 samples were collected: 1074 from the former category and 616 from the latter. A routine immunohistochemistry staining protocol showed that 49 animals tested positive, of which 43 (4%) came from the feedlot entry group and six (1%) from the hospitalised group. The prevalence of persistently infected cattle from this selected, nonrandom sample entering six large South African feedlots was found to be 2.9%, which is higher than the international rule of thumb that 0.5% of all cattle entering feedlots are persistently infected. There was no clear correlation between persistent infection and respiratory disease. Serum samples were also collected when possible and 10 positive cases were found. Results from enzyme-linked immunosorbent assays for antigen and antibody performed on these sera correlated well with those from the immunohistochemistry staining method in six cases, but in four cases the animals tested falsely positive owing to nonspecific staining. Immunohistochemistry staining on ear notch biopsies is thus a reliable diagnostic method to identify persistently infected animals with BVDV, but the pathologist should be aware of nonspecific positive staining.

Keratinocytes are cell targets of West Nile virus in vivo

West Nile virus (WNV) replicates in the skin; however, cell targets in the skin have not been identified. In the current studies, WNV infected the epidermis and adnexal glands of mouse skin, and the epidermal cells were identified as keratinocytes by double labeling for WNV antigen and keratin 10. Inoculation of mice with WNV replicon particles resulted in high levels of replication in the skin, suggesting that keratinocytes are an initial target of WNV. In addition, primary keratinocytes produced infectious virus in vitro. In conclusion, keratinocytes are cell targets of WNV in vivo and may play an important role in pathogenesis.

A Simulation Model to Quantify the Value of Implementing Whole-Herd Bovine Viral Diarrhea Virus Testing Strategies in Beef Cow–Calf Herds

Although numerous diagnostic tests are available to identify cattle persistently infected (PI) with Bovine viral diarrhea virus (BVDV) in cow–calf herds, data are sparse when evaluating the economic viability of individual tests or diagnostic strategies. Multiple factors influence BVDV testing in determining if testing should be performed and which strategy to use. A stochastic model was constructed to estimate the value of implementing various whole-herd BVDV cow–calf testing protocols. Three common BVDV tests (immunohistochemistry, antigen-capture enzyme-linked immunosorbent assay, and polymerase chain reaction) performed on skin tissue were evaluated as single- or two-test strategies. The estimated testing value was calculated for each strategy at 3 herd sizes that reflect typical farm sizes in the United States (50, 100, and 500 cows) and 3 probabilities of BVDV-positive herd status (0.077, 0.19, 0.47) based upon the literature. The economic value of testing was the difference in estimated gross revenue between simulated cow–calf herds that either did or did not apply the specific testing strategy. Beneficial economic outcomes were more frequently observed when the probability of a herd being BVDV positive was 0.47. Although the relative value ranking of many testing strategies varied by each scenario, the two-test strategy composed of immunohistochemistry had the highest estimated value in all but one herd size–herd prevalence permutation. These data indicate that the estimated value of applying BVDV whole-herd testing strategies is influenced by the selected strategy, herd size, and the probability of herd BVDV-positive status; therefore, these factors should be considered when designing optimum testing strategies for cow–calf herds.

Comparison of Detection of Bovine Virus Diarrhea Virus Antigen in Various Types of Tissue and Fluid Samples Collected from Persistently Infected Cattle

Bovine viral diarrhea viruses are economically important pathogens of cattle. Most infections in susceptible animals are acquired from animals persistently infected with the virus. Surveillance programs rely on skin biopsies of persistently infected (PI) cattle to detect the infection. The purpose of this study was to compare antigen capture enzyme-linked immunosorbent assay (ACE) testing results using different types of samples from PI animals. The intent was to determine comparative detection rates in types of samples that are frequently submitted to diagnostic laboratories for evaluation of cases of unknown etiology or samples that could be easily collected for Bovine viral diarrhea virus (BVDV) screening. Eight types of samples were collected from 40 PI animals. The sample types were ear notches, serum, nasal swabs, conjunctival swabs, oral swabs, rectal swabs, vaginal/preputial swabs, and a tail skin fold biopsy. Each type of sample ( n = 8) for each animal ( n = 40) was evaluated with a commercial ACE kit. When using ACE, tail-skin fold and nasal swab samples were 100% sensitive compared with results using ear notches. Sensitivity using other samples was as follows: serum and vaginal/preputial swabs, 92%; conjunctival swabs, 64%; rectal swabs, 10%; oral swabs, 8%. Testing of tail skin fold biopsies, nasal swabs, and ear notch samples resulted in reliable results. In contrast, other sample types were unreliable for diagnosis of persistent infection in calves.

Stability of Bovine viral diarrhea virus antigen in ear punch samples collected from bovine fetuses

Fourteen first-calf heifers were tested free of antibodies against Bovine viral diarrhea viruses (BVDV) by serum neutralization and free of BVDV by polymerase chain reaction. Twelve were exposed to BVDV-1b strain CA0401186a at 84-86 days of gestation, and 2 were exposed to mock inoculum and served as negative controls. Fetuses were harvested by cesarean section at 115-117 days of gestation. The 12 fetuses removed from the BVDV-exposed heifers were BVDV positive based on virus isolation from kidney, thymus, cerebellum, and spleen. It can be assumed that these fetuses would have developed into persistently infected calves had they been allowed to go to term. Virus was not isolated from the fetuses of control animals. Ear punch samples were collected from all fetuses at time of harvest. Antigen capture enzyme-linked immunosorbent assay (ACE), using a commercial kit, was performed on ear punch samples that were frozen within 5 hr of collection and stored at -20 degrees C until tested, tested after storage for 7 days at room temperature (18-25 degrees C), or tested after storage for 7 days at 37 degrees C. Samples stored for 7 days at room temperature or 37 degrees C lost an average of 34% of their starting weight. All samples from BVDV isolation-positive fetuses tested positive by ACE, whereas samples from nonexposed fetuses tested negative, regardless of storage conditions. These results suggest that ACE testing of skin samples collected from aborted fetuses and stillborn calves found in the field may represent a practical surveillance method for BVDV-induced reproductive disease.

Evidence for persistent Bovine viral diarrhea virus infection in a captive mountain goat (Oreamnos americanus)

Bovine viral diarrhea (BVD) viruses are pestiviruses that have been isolated from domestic and wild ruminants. There is serologic evidence of pestiviral infection in more than 40 species of free-range and captive mammals. Vertical transmission can produce persistently infected animals that are immunotolerant to the infecting strain of Bovine viral diarrhea virus (BVDV) and shed virus throughout their lives. Seven species (white-tailed deer, mouse deer, eland, domestic cattle, alpaca, sheep, and pigs) have been definitively identified as persistently infected with BVDV. This study provides serological, molecular, immunohistochemical, and histological evidence for BVDV infection in 2 captive mountain goats from a zoological park in Idaho. The study was triggered by isolation of BVDV from tissues and immunohistochemical identification of viral antigen within lesions of a 7-month-old male mountain goat (goat 1). Blood was collected from other mountain goats and white-tailed and mule deer on the premises for BVDV serum neutralization, viral isolation, and reverse transcription polymerase chain reaction. One 3-month-old mountain goat (goat 2) was antibody negative and BVDV positive in serum samples collected 3 months apart. This goat subsequently died, and though still antibody negative, BVDV was isolated from tissues and identified by immunohistochemistry within lesions. Sequencing and phylogenetic analysis identified the isolates as BVDV-2. These findings provide evidence of persistent infection in a mountain goat, underscoring the need for pestivirus control strategies for wild ruminants in zoological collections.

Systemic reactive angioendotheliomatosis-like syndrome in a steer presumed to be persistently infected with bovine viral diarrhea virus

Unusual proliferative intravascular lesions were seen in multiple organs of a 2-year-old Corriente steer presumed to be persistently infected with bovine viral diarrhea virus (BVDV), based on widespread immunohistochemical detection of BVDV antigen. Proliferations of spindle cells, which were immunohistochemically positive for von Willebrand factor-related antigen, partially-to-completely occluded vessel lumens and were supported by cells that were immunohistochemically positive for smooth muscle actin. Distribution and character of the intraluminal proliferations are strikingly similar to those described in feline systemic reactive angioendotheliomatosis, a rare entity of unknown cause. The presence of occasional intravascular thrombi suggests that the proliferative vasculopathy was associated with an underlying thrombotic process with immunohistochemical similarities to thrombotic thrombocytopenic purpura of humans. Death of the steer was due to hemorrhage from a castration wound, which may indicate thrombocytopenia or platelet dysfunction. The role of persistent BVDV infection in the formation of the intravascular lesions is unknown.

Persistent Bovine viral diarrhea virus infection in wild cervids of Colorado

Bovine viral diarrhea virus (BVDV) is a significant viral pathogen of domestic cattle. Worldwide, there is evidence of BVDV exposure and infection in wild ungulates; however, the frequency and significance of such events are unknown. To determine the prevalence and distribution of Colorado deer, elk, and moose persistently infected (PI) with BVDV, a cross-sectional study was conducted using full-thickness ear tissue samples collected from animals presented to the Colorado Division of Wildlife for chronic wasting disease surveillance in the 2005-2006 hunting season. Tissue from 5,597 harvested animals (2,934 mule deer, 2,516 elk, 141 white-tailed deer, and 6 moose) was paraffin-embedded and stained for BVDV using immunohistochemistry. A single adult male mule deer had BVDV antigen in the skin; staining distribution was consistent with that seen in PI cattle. Skin and lymph node were also positive for viral RNA by polymerase chain reaction, and the virus was determined to be a type 1. The prevalence of BVDV PI cervids in Colorado is very low. However, the identification of a naturally infected adult PI animal in the wild suggests that the virus infects free-ranging populations. The source of the BVDV is unknown and is assumed to be spillover from cattle or maintenance within wildlife populations. Consideration of a potential wild animal reservoir is important in the design and implementation of BVDV management practices in cattle.

Serological Evaluation of Precolostral Serum Samples to Detect Bovine Viral Diarrhea Virus Infections in Large Commercial Dairy Herds

The authors propose that screening newborn calves for Bovine viral diarrhea virus (BVDV) antibody prior to colostrum feeding is a useful strategy to detect herds with endemic BVDV infection. In the current study, precolostral serum samples of newborn calves in 2 Minnesota and 2 California dairy farms were examined. Precolostral BVDV antibodies were detected by serum neutralization and enzyme-linked immunosorbent assay in 7.4% (33/446) and 6.2% (32/515) of newborn calves in the California and Minnesota herds, respectively. The serum samples were also tested by reverse transcription polymerase chain reaction (RT-PCR), and BVDV was detected in 1.6% (7/446) and 3.5% (18/515) of newborn calves in the California and Minnesota herds, respectively. The primary advantages of precolostral testing are that calves congenitally infected with BVDV and seropositive at birth represent a larger percentage of calves born than BVDV-viremic calves and that fewer animals would need to be tested with an antibody test than a RT-PCR or antigen detection test to detect endemic BVDV infections at the herd level. Testing for BVDV antibody in calves prior to colostrum feeding detects fetal infections in both late-gestating cows and nonlactating heifers. Precolostral serum antibody detection is not confounded by vaccination and may be a more sensitive screening method than bulk milk RT-PCR and nonvaccinated sentinel calf strategies in large dairy herds.

Herpetiform genital lesions in a heifer with mucosal disease

A 14-month-old heifer with a 17-day history of unresponsive bloody diarrhea was necropsied. There were focal, pink-red erosions of the nares and hard palate; ulcers and fissures of the tongue; and multiple ulcerative lesions of the alimentary canal. Interdigital skin of both rear limbs was ulcerated and bleeding; and the margins of the vulva contained punctiform red ulcers. The gross lesions were consistent with mucosal disease. Histopathology and laboratory testing ruled out rinderpest, foot-and-mouth disease, and vesicular stomatitis, and identified bovine virus diarrhea virus to be the cause of this disease. Lesions of the vulva similar to those seen in some stages of infectious pustular vulvovaginitis were negative for bovine herpesvirus-1 and tested positive for bovine viral diarrhea virus antigen by immunohistochemistry.

Evaluation of Hunter-Harvested White-Tailed Deer for Evidence of Bovine Viral Diarrhea Virus Infection in Alabama

Bovine viral diarrhea virus (BVDV) is one of the most relevant pathogens affecting today's cattle industries. Although great strides have been made in understanding this virus in cattle, little is known about the role of wildlife in the epidemiology of BVDV. While persistently infected cattle are the most important reservoir, free-ranging ungulates may become infected with BVDV as demonstrated by serosurveys and experimental infections. Therefore, free-ranging wildlife may maintain BVDV as the result of an independent cycle and may serve as a reservoir for the virus. Systematic studies on prevalence of BVDV-specific antibodies or frequency of persistent BVDV infection in North American wildlife are sparse, and no information is available from the southeastern United States. The objective of this study was to evaluate blood and skin samples from hunter-harvested white-tailed deer (Odocoileus virginianus) for evidence of BVDV infection. Virus-neutralizing antibodies were detected in 2 of 165 serum samples. Skin biopsy immunohistochemistry (IHC) was performed on samples from 406 deer using a BVDV-specific monoclonal antibody (MAb) (15c5), and BVDV antigen was detected in one sample. A similar IHC staining pattern was obtained using a second BVDV MAb (3.12F1). Viral antigen distribution in the skin sample of this deer resembled that found in persistently infected cattle and in a previously described persistently infected white-tailed deer; thus, the deer was presumed to be persistently infected. Evidence of BVDV infection in free-ranging white-tailed deer should encourage further systematic investigation of the prevalence of BVDV in wildlife.

Reverse transcription-polymerase chain reaction on pooled samples to detect bovine viral diarrhea virus by using fresh ear-notch-sample supernatants

Ear-notch samples from 3,599 yearling heifers were collected to detect persistently infected (PI) animals with suspect bovine viral diarrhea virus (BVDV). Individual immunohistochemistry (IHC), individual antigen-capture enzyme-linked immmunosorbent assay (AC-ELISA), and reverse transcription-polymerase chain reaction (RT-PCR) tests with pooled ear-notch supernatants were compared with samples from 3,016 heifers, whereas RT-PCR ear-notch pools and individual AC-ELISA tests were compared with samples from all 3,599 heifers. Four heifers were identified positive by both IHC and AC-ELISA, whereas the remaining heifers were identified negative by both tests. When supernatant from ear notches from 100 animals was randomly pooled and RT-PCR was accomplished on each pool, RT-PCR identified 2 pools that contained 1 positive AC-ELISA sample and 1 pool that contained 2 positive AC-ELISA samples. Further evaluation of the pooled RT-PCR ear-notch supernatant detected 100% (n = 36) samples spiked with supernatant from a single randomly selected positive AC-ELISA ear notch. Although follow-up confirmatory tests were not completed, all 3 methods correlated 100% in detecting suspect PI animals, with a kappa value of 1. The use of RT-PCR on pooled ear-notch supernatant could provide an initial, rapid, cost-effective method of screening cattle herds for BVDV PI animals. Subsequent serial testing with an AC-ELISA to evaluate individual samples included in the positive pool could minimize the length of time other animals are exposed to the virus.

Diseases and pathogens associated with mortality in Ontario beef feedlots

This study determined the prevalence of diseases and pathogens associated with mortality or severe morbidity in 72 Ontario beef feedlots in calves that died or were euthanized within 60 days after arrival. Routine pathologic and microbiologic investigations, as well as immunohistochemical staining for detection of bovine viral diarrhea virus (BVDV) antigen, were performed on 99 calves that died or were euthanized within 60 days after arrival. Major disease conditions identified included fibrinosuppurative bronchopneumonia (49%), caseonecrotic bronchopneumonia or arthritis (or both) caused by Mycoplasma bovis (36%), viral respiratory disease (19%), BVDV-related diseases (21%), Histophilus somni myocarditis (8%), ruminal bloat (2%), and miscellaneous diseases (8%). Viral infections identified were BVDV (35%), bovine respiratory syncytial virus (9%), bovine herpesvirus-1 (6%), parainfluenza-3 virus (3%), and bovine coronavirus (2%). Bacteria isolated from the lungs included M. bovis (82%), Mycoplasma arginini (72%), Ureaplasma diversum (25%), Mannheimia haemolytica (27%), Pasteurella multocida (19%), H. somni (14%), and Arcanobacterium pyogenes (19%). Pneumonia was the most frequent cause of mortality of beef calves during the first 2 months after arrival in feedlots, representing 69% of total deaths. The prevalence of caseonecrotic bronchopneumonia caused by M. bovis was similar to that of fibrinosuppurative bronchopneumonia, and together, these diseases were the most common causes of pneumonia and death. M. bovis pneumonia and polyarthritis has emerged as an important cause of mortality in Ontario beef feedlots.

Evaluation of two commercial enzyme-linked immunosorbent assays for detection of bovine viral diarrhoea virus in serum and skin biopsies of cattle

AIM

To assess the ability of two commercial bovine viral diarrhoea (BVD) virus (BVDV) antigen-capture enzyme-linked immunosorbent assays (ELISAs) to detect virus in serum and skin biopsies.

METHODS

Thirty cattle persistently infected (PI) with BVDV were identified using routine diagnostic laboratory testing. Additional ear-notch skin biopsies and blood samples were collected from these animals to confirm the diagnosis, and from 246 cohorts, to determine their BVDV status. Skin biopsies were soaked overnight in buffer and the eluate collected. All sera and eluate were tested using two commercially available ELISAs for detecting BVDV antigen, and a subsample of positive and negative sera was tested using a polymerase chain reaction (PCR) test. A study was also performed to ascertain the risk of cross contamination occurring during the collection and processing of skin biopsies.

RESULTS

Both serum and skin samples tested using either ELISA resulted in the detection of all cattle identified as PI and no non-infected cattle were incorrectly classified as infected using either method. Agreement between all assays (ELISAs, whether performed on serum or skin, and PCR) was 100%. No cross-contamination of skin samples between animals was evident using routine biopsy methods.

CONCLUSIONS

Viraemic cattle infected with BVDV were accurately identified using either of the two commercial ELISAs evaluated on either serum or skin samples.

CLINICAL RELEVANCE

Either skin biopsies or serum samples can be collected from cattle to determine their BVDV status. This should overcome problems in accurately identifying the infection status of young calves in which colostral antibodies might interfere with the antigen-capture ELISA.

Diagnostic efficacy of a reverse transcriptase–polymerase chain reaction assay to screen cattle for persistent bovine viral diarrhea virus infection

OBJECTIVE

To evaluate diagnostic efficacy of a reverse transcriptase-PCR assay performed on pooled supernatant from fresh tissue samples to screen cattle for persistent infection with bovine viral diarrhea virus (BVDV).

DESIGN

Cross-sectional study.

SAMPLE POPULATION

174 pooled supernatant samples representing 12,528 animals between 1 and 12 months old.

PROCEDURES

The supernatant was collected from fresh tissue samples suspended in phosphate-buffered saline solution that had been submitted for testing for BVDV infection. Supernatant samples were pooled, with pool size limited to < or = 100 samples, and assayed with a reverse transcriptase-PCR assay for BVDV. Results of the PCR assay were compared with results of an antigen-capture ELISA performed on individual tissue samples.

RESULTS

Results of the PCR assay were positive for 27 of the 174 pooled samples (mean pool size, 72 samples). For 23 of these 27 pooled samples, results of the ELISA were positive for 1 or more of the individual tissue samples represented in the pooled sample, whereas for 4 of these pooled samples, results of the ELISA were negative for all individual tissue samples represented in the pooled sample. Results of the ELISA were negative for all individual tissue samples represented in the 147 pooled samples with negative PCR assay results.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggested that the reverse transcriptase-PCR assay can be used to screen cattle for persistent BVDV infection, with calculated sensitivity of 100% (95% confidence interval, 85.2% to 100%) and calculated specificity of 97.5% (95% confidence interval, 93.4% to 99.3%).

Association between the existence of calves persistently infected with bovine viral diarrhea virus and commingling on pen morbidity in feedlot cattle

OBJECTIVE

To determine the association between the existence of a calf persistently infected (PI) with bovine viral diarrhea virus (BVDV) and pen morbidity.

ANIMALS

5,041 calves in 50 pens at a feedlot in Iowa.

PROCEDURE

In a longitudinal study, ear notches were collected from cattle and tested for BVDV antigen. Characteristics of each pen (owner, sex, disease rate, number of groups, and source) were recorded. The association between the existence of a BVDV-PI calf and morbidity in each pen was examined.

RESULTS

Commingling was associated with an increase in respiratory tract disease (odds ratio [OR], 3; 95% confidence interval [CI], 2.5 to 3.6). Ten BVDV-PI calves (10/5,041 [0.2%]) were identified in 8 of 50 pens. A BVDV-PI calf was associated with reduced pen-level respiratory tract disease (OR, 0.7; 95% CI, 0.5 to 0.9). Disease prevalence (mean +/- SD morbidity, 7.9 +/- 3.1%) was lowest in pens containing single-source cattle and a BVDV-PI calf (4 pens containing 302 cattle), compared with single-source cattle with no BVDV-PI calf (mean morbidity, 11.89 +/- 9.7%; 31 pens containing 3,093 cattle), commingled cattle with no BVDV-PI calf (mean morbidity, 29.3 +/- 16.22%; 11 pens containing 1,127 cattle), and commingled cattle with a BVDV-PI calf (mean morbidity, 28.6 +/- 10.1%; 4 pens containing 519 cattle).

CONCLUSIONS AND CLINICAL RELEVANCE

Commingling was the greatest risk factor associated with morbidity in each pen. A BVDV-PI calf in a pen was not associated with increased disease prevalence in commingled groups.

Bovine viral diarrhea virus in alpaca: abortion and persistent infection

An alpaca herd in eastern Ontario experienced vague signs of illness, including anorexia and lethargy in 9 animals, 2.5 months after the addition of a chronically ill cria and his dam to the farm. Subsequently 2 alpaca had early pregnancy loss; one aborted at 5.5 months gestation and the other at 7 months gestation. Seventeen were found to have serum antibody to bovine viral diarrhea virus (BVDV), with highest titers to BVDV type 1. The fetus that was aborted at 5.5 months gestation, 3 months after the clinical outbreak, was found to be positive for BVDV on immunohistochemical staining, and noncytopathic BVDV type 1b was isolated. Of the 13 cria born alive that season, a single male underweight alpaca cria, born 9 months after the clinical illnesses, was infected with BVDV type 1b. The cria was positive for BVDV at birth, at 3 and 26 days of age and continued to be positive for noncytopathic BVDV using virus isolation, nested reverse transcription PCR, antigen detection ELISA, and immunohistochemical staining until euthanasia at 46 days of age. The cria remained serum antibody negative to both BVDV type 1 and type 2. A diagnosis of persistent infection was made. This is the first report describing persistent infection with BVDV in an alpaca cria.

Evaluation of diagnostic tests used for detection of bovine viral diarrhea virus and prevalence of subtypes 1a, 1b, and 2a in persistently infected cattle entering a feedlot

OBJECTIVE

To evaluate diagnostic tests used for detection of bovine viral diarrhea virus (BVDV) and determine the prevalence of BVDV subtypes 1a, 1b, and 2a in persistently infected (PI) cattle entering a feedlot.

DESIGN

Prospective study.

ANIMALS

21,743 calves.

PROCEDURES

Samples were obtained from calves initially testing positive via antigen capture ELISA (ACE) performed on fresh skin (ear notch) specimens, and ACE was repeated. Additionally, immunohistochemistry (IHC) was performed on skin specimens fixed in neutral-buffered 10% formalin, and reverse transcriptase PCR (RT-PCR) assay and virus isolation were performed on serum samples. Virus was subtyped via sequencing of the 5' untranslated region of the viral genome.

RESULTS

Initial ACE results were positive for BVDV in 88 calves. After subsequent testing, results of ACE, IHC, RT-PCR assay, and viral isolation were positive in 86 of 88 calves; results of all subsequent tests were negative in 2 calves. Those 2 calves had false-positive test results. On the basis of IHC results, 86 of 21,743 calves were PI with BVDV, resulting in a prevalence of 0.4%. Distribution of BVDV subtypes was BVDV1b (77.9%), BVDV1a (11.6%), and BVDV2a (10.5%).

CONCLUSIONS AND CLINICAL RELEVANCE

Rapid tests such as ACE permit identification and segregation of PI cattle pending results of further tests, thus reducing their contact with the rest of the feedlot population. Although vaccines with BVDV1a and 2a components are given to cattle entering feedlots, these vaccines may not provide adequate protection against BVDV1b.

Immunohistochemistry: Forging the links between immunology and pathology

The technique of immunohistochemical staining allows the visualization of epitopes in situ in histological tissue sections. A series of innovations in the methods and reagents and the introduction of mechanization have enhanced the ease and technical reliability of this technique resulting in widespread application in veterinary diagnostics and research. This brief overview will highlight some of the applications for immunohistochemical staining with an emphasis on the use of the technique in diagnostic veterinary medicine, particularly for the detection of infectious disease agents.