Identification and eradication of bovine viral diarrhea virus in a persistently infected dairy herd.

A milking herd consisting of 55 Holstein cows had experienced abortions in several cows, as well as congenital malformations in 1 newborn calf. Bovine viral diarrhea virus was isolated from blood mononuclear cell samples obtained from several cattle, documenting 1 acute infection and 8 persistently infected carriers identified by clinical appearance and laboratory testing. Initial suspicion of persistently infected status in some, but not all animals, was facilitated by poor growth rates in some calves. Virus isolation was performed on transtracheal wash fluid obtained from acutely and persistently infected cattle with respiratory tract infection. We describe the measures taken to identify and characterize the infecting virus strain, and the series of actions taken to identify and eliminate persistently infected carriers in a herd experiencing several related problems that were shown to be caused by bovine viral diarrhea virus.     

Bovine virus diarrhoea virus: detection of Danish dairy herds with persistently infected animals by means of a screening test of ten young stock

In each of 42 Danish dairy herds, ten young stock aged 8–18 months were tested for antibodies against bovine virus diarrhoea virus (BVDV). At the same time a bulk milk sample from each herd was examined for antibodies against BVDV.

The herds could be divided into two distinct groups: (1) Group A (24 herds) had three or less antibody carriers among the ten young stock sampled from each herd and were considered ‘slightly infected’; (2) Group B (18 herds) had eight or more antibody carriers in the ‘spot’ sample and were therefore considered ‘heavily infected’. Persistently infected animals were not found in two Group A herds studied by a subsequent total herd blood test but were detected in five Group B herds in which all animals in the herds were subsequently tested.

Bulk milk titers were generally higher in Group B than in Group A herds. However, there was considerable variation, and in most cases it was not possible to distinguish the two herd categories from one another by means of bulk milk titers.     

Identification of herds with cattle persistently infected with bovine viral diarrhea virus by virological evaluation of three calves

For the identification of herds with cattle persistently infected (PI) with bovine viral diarrhea virus, 1,272 animals from 20 herds were subjected to serum neutralizing (SN) test using the Nose strain and virus isolation. Eighteen PI cattle were detected from 5 herds. On the phylogenetic tree based on the nucleotide sequences of the 5' untranslated region, the isolates from the PI cattle were classified into genotypes-1a or -1b. Of 3 unvaccinated calves aged 6 to 12 months selected from each herd, the probabilities of obtaining 2 or more non-PI cattle with SN antibody titers of 64 or more (P(SN)), one or more PI cattle (P(VI)), and either of the conditions (P(Total)) were calculated using the hypergeometric probability model. P(Total) for the 5 herds with PI cattle was 1.000. P(SN) for 3 herds with many PI cattle within the selected age group was as low as 0.500 or less, and P(VI) was as high as 0.886 or more. P(SN) in the 2 other herds with few PI cattle was 1.000, and P(VI) was as low as 0.375 or less. P(Total) in 13 of 15 herds without PI cattle was 0.000, and was 0.714 or 0.774 for the 2 other herds. These results suggest that herds with PI cattle can be predicted with high accuracy when both SN test and virus isolation are performed on only 3 unvaccinated calves aged 6 to 12 months selected from a herd.     

Leukocyte profile of cattle persistently infected with bovine viral diarrhea virus

Animals acutely infected with bovine viral diarrhea virus (BVDV) exhibit transient immunosuppression as a result of the virus' predilection for cells that play critical roles in the host immune system. Acute BVDV infections have major effects on thymic and follicular T-lymphocytes, as well as follicular B-lymphocytes, often resulting in severe reduction in circulating numbers of lymphocytes and suppression of functional activities of these cells. Granulocytes and monocytes are equally susceptible to BVDV infections with reduction in numbers and suppression functions. However, there is limited information on the leukocyte profile of cattle persistently infected (PI) with BVDV. This study reports on phagocytic activities of granulocytes and monocytes as well as immunophenotyping by flow cytometric analysis of leukocytes isolated from healthy non-PI (NPI) and PI animals. No significant differences were found between the leukocyte profiles and the phagocytic activities of PI animals when compared to a group of healthy NPI animals.     

Prevalence of calves persistently infected with bovine viral diarrhea virus in beef cow-calf herds enrolled in a voluntary screening project

OBJECTIVE: To report the prevalence of bovine viral diarrhea virus (BVDV) in calves and calf groups (ie, calves from the same farm) in beef breeding herds and evaluate the ability of biosecurity risk assessment questionnaires to identify calf groups with positive results for BVDV. DESIGN: Nonrandom survey. ANIMALS: 12,030 calves born in spring from 102 operations. PROCEDURES: Cow-calf producers that voluntarily enrolled in a screening project submitted ear notch specimens from calves and answered a 29-question survey instrument. Ear notch specimens were tested for BVDV with an antigen-capture ELISA (ACE), and ear notch specimens with positive ACE results for BVDV were immediately retested by performing immunohistochemistry (IHC). Follow-up testing, 3 to 4 weeks after initial positive ACE results, was done by use of a second IHC test and virus isolation on a subsequently submitted ear notch specimen from the same calves to identify those that were persistently infected (PI). RESULTS: 102 producers submitted ear notch specimens for BVDV screening. Initially, 24 of 12,030 calves had positive ACE results for BVDV. A second ear notch specimen was submitted for 20 of these 24 calves. Of 20 retested calves, 12 had positive ICH results for BVDV, confirming PI status. The 12 PI calves came from 4 calf groups (3 singletons and 1 calf group with 9 PI calves). CONCLUSIONS AND CLINICAL RELEVANCE: Prevalence of BVDV in calf groups was low, and questions designed to identify high-risk biosecurity behaviors had little value in identifying calf groups with positive results for BVDV.     

Serologic evaluation of five unvaccinated heifers to detect herds that have cattle persistently infected with bovine viral diarrhea virus

OBJECTIVE: To determine whether serologic evaluation of 5 unvaccinated 6- to 12-month-old heifers is a valid method for identifying herds that contain cattle persistently infected (PI) with bovine viral diarrhea virus (BVDV). ANIMALS: 14 dairy herds with a history of BVDV infection, with health problems consistent with BVDV infection, or at risk for contracting BVDV infection. PROCEDURE: 5 unvaccinated 6- to 12-month-old heifers were randomly selected from each herd. Neutralizing antibody titers for type-I and -II BVDV were determined. A herd was classified as likely to contain PI cattle when at least 3/5 heifers had antibody titers > or = 128. Virus isolation was performed on all cattle to identify PI cattle. Genotype of isolated viruses was determined by nested multiplex polymerase chain reaction. RESULTS: 6 of 14 herds contained PI cattle. Sensitivity and specificity of serologic evaluation of 5 heifers for identifying these herds were 66 and 100%, respectively. In herds that contained PI cattle, the predominant BVDV titer in the tested heifers corresponded to the genotype of the isolated virus. CONCLUSIONS AND CLINICAL RELEVANCE: Serologic evaluation of unvaccinated 6- to 12- month-old heifers is an accurate method for identifying herds containing PI cattle. Both type-I and -II BVDV antibody titers should be determined to prevent herd misclassification. The genotype of BVDV found in PI cattle can be predicted by the predominant neutralizing antibody titers found in tested heifers. Serologic evaluation of 5 unvaccinated heifers can be used to determine whether a herd is likely to contain PI cattle.     

Reproductive performance of apparently healthy cattle persistently infected with bovine viral diarrhea virus.

A Holstein-Friesian bull and three Holstein-Friesian cows were seronegative for bovine viral diarrhea (BVD) virus but were persistently infected with the virus. Virus was isolated from buffy coat cells and nasal and lacrimal secretions during their lifetime, and they remained free of clinical signs of BVD. The three cows were pregnant when purchased, and they gave birth to full-term calves. One calf lived only a few hours, one calf became ill and died within a few days, and one calf became ill and was euthanatized within a few weeks. One cow was then bred and became pregnant but aborted a 7-month fetus. A second cow was bred approximately 5 months after parturition but did not conceive. The third cow was necropsied 6 weeks after calving, because of loss of weight. Although the bull's semen contained BVD virus when seropositive cows were bred, normal calves were born. When seronegative heifers were bred, they became seropositive to BVD virus within two weeks, with higher titers in six weeks. On heifer conceived after one service but aborted a 6-month fetus. Three others continued to have estrous cycles until their titers rose to 1:128, then they conceived and gave birth to normal calves. Another heifer conceived on the first service, had a titer of 1:128 two weeks after breeding, and gave birth to a normal calf.     

Survivorship of animals persistently infected with bovine virus diarrhoea virus (BVDV)

The survivorship of animals persistently infected with bovine virus diarrhoea virus was studied in ten Danish dairy herds. The ages of 34 persistently infected animals were compared with the ages of non-persistently infected animals in the herds in a cross-sectional study in which the risk rate of removal of animals in the two groups within 1 year was estimated from an exponential probability function of the age. In a cohort study, the 34 persistently infected animals were followed from the date of the initial blood test and onwards and the risk rates of dying or being slaughtered due to unthriftiness or either of these events were calculated.

The attributable risk of leaving the herds within 1 year was 0.35 among persistently infected animals. The risk rate of dying or being slaughtered due to unthriftiness within 1 year was 0.28 and 0.31, respectively; the risk rate of either of these events was 0.5.     

Viral antigen distribution in the central nervous system of cattle persistently infected with bovine viral diarrhea virus

Distribution of viral antigens in the central nervous system of 25 cattle with a persistent bovine viral diarrhea virus (BVDV) infection was studied. Using a polyclonal antiserum produced in pigs and the direct immunofluorescence and immunoperoxidase technique, BVDV antigen was located exclusively in neurons. Predilection sites for viral persistence were cerebral cortex and hippocampus; in other areas of brain and spinal cord, viral antigens were in single neurons or small groups of neurons. There was no morphological evidence of cellular alteration due to viral persistence. Perivascular lymphocytic infiltrations were in affected nervous tissue. It is concluded that the central nervous system is an important location for persistence of BVDV.     

Serological analysis of a small herd sample to predict presence or absence of animals persistently infected with bovine viral diarrhoea virus (BVDV) in dairy herds.

In 10 herds containing animals persistently infected (PI) with bovine viral diarrhoea virus (BVDV) and nine herds without such animals the probabilities of obtaining at least two antibody-positive animals in a test sample of three or five animals selected among animals six to 18 months old were calculated. Among herds with PI animals these probabilities, with the exception of one herd, varied between 0.725 and 0.992 when samples of three animals were tested and between 0.977 and one when samples of five animals were tested. Among herds without PI animals the probabilities varied between 0 and 0.015 when samples of three animals were tested and between 0 and 0.048 when samples of five animals were tested. Thus, based upon a few blood samples, herds with PI animals and herds without PI animals could be distinguished with a high degree of accuracy.     

Severe clinical disease induced in cattle persistently infected with noncytopathic bovine viral diarrhea virus by superinfection with cytopathic bovine viral diarrhea virus

Eight healthy cattle that were persistently infected with noncytopathic bovine viral diarrhea virus (BVDV) were inoculated with cell culture fluids that contained noncytopathic or cytopathic BVDV. A severe disease occurred after inoculation with cytopathic BVDV. The clinical signs, lesions, and immune response were consistent with those of clinical BVDV infections.     

Use of serologic evaluation for antibodies against bovine viral diarrhea virus for detection of persistently infected calves in beef herds

OBJECTIVE: To determine whether use of serologic evaluation of a sentinel sample of calves or cows for antibodies against bovine viral diarrhea virus (BVDV) would accurately predict whether an animal persistently infected with BVDV could be detected in beef herds. SAMPLE POPULATION: 27 cow-calf herds in which the status of persistently infected calves was not known and 11 herds known to have persistently infected calves. Procedure-Detection of persistently infected calves was determined through immunohistochemical testing of tissue obtained at necropsy of all calves that died during calving season and skin (ear notch) specimens obtained from all young stock in the fall of 2002. Serum samples were collected from 30 spring-born calves and 10 mature cows. RESULTS: Optimum serologic test performance at time of weaning was detected when 10 calves were evaluated. At least 3 of 10 randomly selected calves were likely to have a titer > 1:1000 against BVDV type I or II in 53% of herds in which a persistently infected calf was detected during that year (sensitivity, 53%). However, at least 3 of 10 randomly selected calves were also likely to have a titer > 1:1000 in 20% of herds that did not have a persistently infected calf detected during that year (specificity, 80%). CONCLUSIONS AND CLINICAL RELEVANCE: Despite the use of a number of various cutoff values and sample sizes, serologic evaluation of a small number of calves or cows could not be used to accurately predict the presence of persistently infected cattle in a herd.     

Lymphocyte blastogenesis and neutrophil function in cattle persistently infected with bovine viral diarrhea virus

Neutrophil function and mononuclear cell proliferative responses to mitogens were determined in healthy cattle and in cattle persistently infected with bovine viral diarrhea (BVD) virus. Uptake of [3H]thymidine by resting and mitogen-stimulated peripheral blood mononuclear cells was significantly lower in cattle persistently infected with BVD virus than in healthy cattle. Neutrophils from cattle persistently infected with BVD virus had significantly impaired capability to ingest Staphylococcus aureus, but were normal in respect to random migration under agarose, cytochrome C reduction, iodination, and antibody-dependent cell-mediated cytotoxicity. Impairment of neutrophil function in cattle persistently infected with BVD virus differs from impairment of neutrophil function reported in healthy cattle mounting an immune response to recent BVD virus infection.     

Study of cattle persistently infected with bovine viral diarrhea virus that lack detectable virus in serum

OBJECTIVE: To determine whether cattle persistently infected with bovine viral diarrhea virus (BVDV) that lack virus detectable in serum by use of the immunoperoxidase microtiter assay (IPMA) can transmit the virus to susceptible herdmates and determine prevalence of these cattle. DESIGN: Clinical trial and serologic survey. SAMPLE POPULATION: 2 cattle and 1,952 blood samples. PROCEDURE: A persistently infected cow in which virus could not be detected in serum was housed with a BVDV-seronegative steer. Blood and nasal swab specimens were tested via virus isolation and serum virus neutralization. Parallel WBC preparations and sera from blood samples of 1,952 adult cows were screened for BVDV by use of IPMA. RESULTS: The steer seroconverted to BVDV within 4 weeks of contact with the cow. Virus was detected in sera and WBC of 5 adult cows that were verified as persistently infected by retest 3 weeks later. Cattle persistently infected with BVDV in which virus could not be detected in both serum and WBC by use of IPMA were not found. CONCLUSION AND CLINICAL RELEVANCE: Cattle persistently infected with BVDV in which virus cannot be detected in serum by use of IPMA may serve as virus reservoirs for infecting susceptible cattle. Persistent infection was detected at a prevalence of 0.26%. Screening adult cattle by use of IPMA on serum samples appears to be a reliable means of detecting persistent infection with BVDV. Prevalence of cattle persistently infected with BVDV that have negative results of IPMA on serum is extremely low.     

Fatal trichuris spp. infection in a Holstein heifer persistently infected with bovine viral diarrhea virus

Whipworms (Trichuris spp.) were identified in the colon of a recently purchased, 10-month-old dairy heifer that died suddenly. A skin test was positive for bovine viral diarrhea virus (BVDV). Signs of BVDV occurred in other heifers in the group, but fecal flotations were negative for whipworm eggs.     

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.     

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.     

Prevalence of bovine viral diarrhea virus in dairy cattle herds in eastern China

Tropical Animal Health and Production - Bovine viral diarrhea virus (BVDV) is a worldwide spreading pestivirus affecting cattle and other ruminants; however, there have been few reports on...