Border disease of sheep--aspects for diagnostic and epidemiologic consideration.

Border Disease (BD) is a condition of newborn sheep that results from congenital infection by a non-cytopathic pestivirus, occurring during the first half of gestation. The variations in expression of the virus directly relate to the age of the fetus at the time of infection. There are four distinct disease syndromes: (1) early embryonic death, (2) abortion and stillbirth, (3) birth of lambs with malformations, and (4) birth of small, weak lambs, lacking characteristic clinical signs, but bearing features of immunosuppression. In the newborn, the BD virus may be recovered from all tissues and teratogenic lesions are found in the endocrine, nervous, skeletal, integumentary and immune systems. These effects of virus infection are manifest in the clinical signs characteristic of the disease, such as tremors, ataxia, hairy birthcoat, low birth weight, facial bone malformations, short-boxy stature, and eye abnormalities. The consequences of the BD compromised immune system is an increased susceptibility to infection, a failure to produce specific antibody to BD virus, and an inability to clear the virus; features characteristic of the immuno-tolerant state. The lifelong shedding and persistence of virus is of epidemiologic importance. The persistently infected BD ewe remains a source of infection for the flock both through horizontal transmission (virus shedding) and congenital transmission (a persistently infected ewe will always bear a BD lamb). Detection of persistently infected individuals within a flock is difficult: clinical signs abate with time and most frequently no antibody to BD is produced.

A nested PCR for detection of North American isolates of bluetongue virus based on NS1 genome sequence analysis of BTV-17.

A nested polymerase chain reaction (PCR)-based assay, for detection of bluetongue virus (BTV) ribonucleic acid in cell culture and tissue samples, was developed. Two pairs of oligonucleotide primers (BTV1 and BTV4 and BTV2 and BTV3), selected from non-structural protein 1 (NS1) gene of BTV-17, were used for the nested PCR in two amplification steps. First a 826-bp product was amplified using an outer primer pair BTV1 and BTV4. The second amplification, using nested or internal primer pair BTV2 and BTV3, produced a 517-bp PCR product. RNA from North American prototype serotypes 2, 10, 11, 13 and 17, propagated in cell cultures, were detected by this nested PCR-based assay. The nested primers BTV2 and BTV3 increased the sensitivity of the BTV PCR assay, and as little as 0.1 fg of BTV RNA (equivalent to 5 viral particles) could be detected. Amplification products were not detected when the PCR-based assay was applied to RNA from a closely related orbivirus, epizootic hemorrhagic disease virus (EHDV) prototype serotypes 1 and 2; total nucleic acid extracts from uninfected BHK-21 cells; or whole blood from calves and deer that were BTV-seronegative and virus isolation negative. Application of this nested BTV PCR-based assay to clinical samples resulted in detection of BTV RNA from a variety of tissues collected from calves and deer with natural and experimental BTV infections. The described BTV PCR-based assay provides a valuable tool to study the epidemiology of BTV infection in susceptible wild ruminants and domestic livestock.

The role of cell-mediated immunity in the pathogenesis of bluetongue virus serotype 11 in the experimental infection of vaccine/sensitized calves.

The cellular immune response of cattle to virulent and avirulent (inactivated) bluetongue virus (BTV) was studied. Each of three calves received three vaccinations (sensitizations) with binary ethyleneimine (BEI)-inactivated BTV, 3 weeks apart. The sensitized animals were challenged with BTV-11 strain UC8 3 weeks after the last vaccination. BTV-seropositive and BTV-seronegative calves were used as controls. The animals were bled weekly for virus isolation and for evidence of cell-mediated immunity (CMI) as determined by the lymphocyte stimulation test (LST). Peripheral blood mononuclear leukocytes (PBM L) cultures were induced with purified BTV antigen; the phytomitogens phytohemagglutinin (PHA), Concanavalin A (ConA) and pokeweed (PKW) mitogen, and combinations of phytomitogens and BTV antigen. LST data were analysed by ANOVA and reported as counts per minute (CPM) and stimulation index (SI). Following BTV challenge exposure, significant SI to mitogens were found in PBML cultures for all animals. BTV antigen induced a weak CMI response. There was evidence of perturbations in lymphocyte response as characterised by a sharp decrease in lymphocyte response to mitogens following combined BTV-antigen and mitogen PBML induction. The SI diminished in PBML cultures after a 4 day incubation period, except for ConA. These results provide evidence that the cell-mediated immune response could be affected by BTV and that inhibitory mediators might play an important role in the pathogenesis of BTV in cattle.

Human recombinant interleukin-2(125) induced in vitro proliferation of equine, caprine, ovine, canine and feline peripheral blood lymphocytes.

Equine, caprine, ovine, canine and feline peripheral blood lymphocytes were evaluated in a short term dose-response study for their in vitro blastogenic responsiveness to human recombinant interleukin-2(125) (HrIL-2(125] alone or in combination with phytohemagglutinin-P, concanavalin-A, and pokeweed mitogen. HrIL-2(125) induced lymphocyte proliferation in all of the animals tested. The magnitude of the proliferative response varied among the species of animal tested. In all cases the proliferative response was dependent on the concentration of HrIL-2(125). HrIL-2(125) at a minimum concentration of 10(2) Cetus Units (CU)/ml produced a significant proliferative response in isolated horse, goat and sheep lymphocytes. In cat and dog lymphocytes, a concentration of 10(3) CU/ml was necessary to induce a significant proliferative response. Maximal lymphocyte proliferation was reached in horses and sheep at a concentration of 10(4) CU/ml of HrIL-2(125). In goats, cats, and dogs a maximum proliferative response was found to be at a concentration equal to or greater than 10(4) CU/ml of HrIL-2. Co-stimulation of lymphocytes with mitogens and submaximal concentrations of HrIL-2(125) (10 CU/ml) induced a synergistic proliferative response which in nearly all cases was significantly greater (P less than 0.05) than the arithmetic sum of the responses induced by the same concentration of the mitogens and HrIL-2(125) alone. The two exceptions were co-stimulation of feline lymphocytes with concanavalin-A and co-stimulation of canine lymphocytes with pokeweed mitogen.

Prevalence of group A and group B rotaviruses in the feces of neonatal dairy calves from California.

136 fecal samples, collected from 47 dairy calves on a calf ranch and in a dairy herd in California, were tested for the presence of group A and group B rotaviruses by reverse transcription-polymerase chain reaction (RT-PCR). Samples were collected from each calf at days 1, 7 and 14. Within the 14 day period, 44 calves (94%) were positive for group A rotavirus and an unexpectedly high number of calves (38 calves, 81%) were positive for group B rotavirus. When these samples were examined by polyacrylamide gel electrophoresis (PAGE), rotavirus was found in 21 calves and all of them had group A electropherotype. Among 25 PAGE positive samples from 21 calves, 17 (68%) were of short electropherotype, 4 (28%) were of long electropherotype and 4 (28%) contained both short and long electropherotype rotaviruses. Group B and short and long electropherotype group A rotaviruses were found in both normal and diarrheic calves.

Lymphocyte blastogenesis in bluetongue virus or Mycobacterium bovis-inoculated bovine fetuses.

Bovine fetuses were inoculated with Mycobacterium bovis, bluetongue virus or placebo at approximately 125 days of gestation, and blastogenic responses of peripheral blood lymphocytes and lymph node cells were determined at various time intervals after inoculation. Lymphocytes from all fetuses were stimulated by phytohemagglutinin, concanavalin A, and pokeweed mitogen, and peripheral blood lymphocytes gave consistently greater stimulation indices than did prescapular lymph node cells. Bluetongue virus infection did not consistently suppress mitogen induced lymphocyte blastogenesis. Lymphocytes taken from fetuses at 20 or 50 days after Mycobacterium bovis inoculation were not stimulated by purified protein derivative (PPD), whereas lymphocytes taken from adult cattle at similar intervals after Mycobacterium bovis inoculation were stimulated by PPD. Although lymphocytes from bovine fetuses may be stimulated by mitogens, antigen specific blastogenesis to a known inducer of cellular immunity was not detected by 175 days of gestation.

Immune response of sheep to bluetongue virus: in vitro induced lymphocyte blastogenesis.

Sheep were inoculated with 2 ml of 10(7) plaque forming units per ml of purified prototypes of the four United States serotypes (10, 11, 13 and 17) of bluetongue virus. Nine weeks following the initial inoculation, a challenge inoculation with homologous virus was done. Animals were followed for virus isolation and evidence of cell-mediated immunity by weekly lymphocyte stimulation tests (LST). Two dilutions (10 micrograms/ml and 1 microgram/ml) of pure virus from each of the purified serotypes were used as antigen as were the phytomitogens phytohemagglutinin, Concanavalin A, and pokeweed mitogen. LST data were analyzed by the analysis of variance method and reported as counts per minute and stimulation index (SI). Significant SI were observed following primary and secondary challenge with both homologous and heterologous virus. There was evidence of lymphocyte perturbations characterized by a sharp decrease in response to mitogens following primary and secondary challenge lasting for one week followed by a significant increase in blastogenesis three to four weeks after inoculation of virus. These results provide evidence that cell-mediated immunity is evident in bluetongue infection, that there is cross reactivity between viral serotypes and that BTV infection leads to perturbations in lymphocyte function including suppression of responses. An increase in the blastogenic response to phytomitogens correlated with viral clearance.

Immune responses to Mycoplasma bovis vaccination and experimental infection in the bovine mammary gland.

This study characterized the immune responses in four vaccinated and four control cows in response to vaccination and experimental intramammary inoculation with Mycoplasma bovis. Specific antibody responses occurred in serum and milk in response to vaccination and experimental infection. Lymphocytes from peripheral blood, but not from the mammary gland of vaccinated cows had increased responsiveness to mitogens. No lymphocytes tested were responsive to M. bovis antigen. Both vaccination and experimental infection resulted in skin test reactivity. These results imply that vaccination results in immune responses which may alter the course of experimental M. bovis mastitis, but may contribute to cellular inflammation.

Antiviral responses of bluetongue virus-inoculated bovine fetuses and their dams.

Antiviral responses of bovine fetuses to bluetongue virus (BTV) infection were determined. Fetuses inoculated with BTV at 125 days of gestation apparently had cleared all virus by the time of birth; however, the mechanism responsible for virus clearance was not determined. Interferon production and virus clearance were temporally unrelated. Cell-mediated responses to BTV antigens were not detected by the lymphocyte stimulation test using lymphocytes from infected fetuses or cows. Although virus clearance and fetal production of high titers of neutralizing antibody did coincide, it was considered unlikely that antibody alone was responsible for virus clearance. As congenital BTV infection did not lead to specific immunologic tolerance or postnatal persistance of virus, such animals would not be expected to have a major role in the dissemination of BTV.

Comparison of slot blot nucleic acid hybridization, immunofluorescence, and virus isolation techniques to detect bluetongue virus in blood mononuclear cells from cattle with experimentally induced infection.

A slot blot hybridization technique was applied for detection of bluetongue virus (BTV) in blood mononuclear cells (BMNC) obtained from cattle with experimentally induced infection. This technique lacked sensitivity to detect the viral nucleic acid directly in clinical specimens. When aliquots of mononuclear cells from these cattle were cultivated in vitro for 10 days to amplify virus titer, only 33.3% of the samples collected during viremia gave a positive signal in the slot blot hybridization format. By contrast, results for 34.3% of noncultured and 63.3% of cultured mononuclear cell samples collected during viremia were positive by immunofluorescence. The average number of infected cells, as detected by immunofluorescence in the noncultured mononuclear cell samples, was 1 to 5/300,000, and was usually > 10/300,000 in the cultured cell samples. Virus was isolated from all postinoculation blood samples obtained from 4 heifers that were seronegative at the time of inoculation, but was not isolated from any of the preinoculation samples, or from any of the postinoculation samples obtained from 2 heifers that were seropositive at the time of inoculation. When virus isolation was attempted from separated mononuclear cells in 2 heifers, 43.7% of the noncultured and 87.5% of the cultured samples had positive results.

Border disease in a flock of sheep: epidemiologic, laboratory, and clinical findings.

A flock of sheep in which border disease (BD) was enzootic was studied through a breeding season. At the beginning of the study (August 1981), 125 (82%) of 152 ewes were seropositive to the cross-reacting bovine viral diarrhea virus. Within 7 months, 3 (18%) of 17 seropositive ewes retested had reverted to seronegative. Of the remaining 21 ewes identified as seronegative, 7 (33%) converted to seropositive by the end of the study. Triplet lambs were born, 2 of which exhibited clinical signs of BD. The virus was isolated from blood lymphocytes from both of the affected lambs. The most severely affected lamb shed virus into the urine, saliva, and feces through 10 weeks of age. Lymphocyte stimulation tests indicated that the lymphocytes from the affected lambs had decreased function in months 4 through 7, but returned to normal function by the eighth month. Transmission of BD virus was investigated by exposing 5 seronegative ewes to the BD-infected lambs. Two of the contact ewes developed viremia and 3 converted to seropositive within the 13-week exposure period. Evidence from this and other studies supports a model of BD in gravid, nongravid, and persistently infected adult sheep.

PCR detection of North American and Central African isolates of epizootic hemorrhagic disease virus (EHDV) based on genome segment 10 of EHDV serotype 1.

PCR amplification technology for the detection of epizootic hemorrhagic disease virus (EHDV) ribonucleic acid in cell culture and clinical specimens was developed. With oligoribonucleotide primers selected from genome segment 10 of EHDV serotype 1 (EHDV-1), which codes for two nonstructural proteins (NS3 and NS3a), the PCR-based assay resulted in a 535-bp PCR product. RNAs from North American EHDV-1 prototype, EHDV-2 prototype, and a number of EHDV field isolates, including the Central African isolates of EHDV-5 and EHDV-318 propagated in cell cultures, were detected by this PCR-based assay. The specific 535-bp PCR products were visualized onto agarose gels, and the identity of the PCR products was confirmed by chemiluminescent hybridization with a 352-bp internal probe. The sensitivity of the EHDV PCR assay was increased by chemiluminescent hybridization; by this EHDV-NS3 PCR, 10 fg of EHDV RNA was detected (equivalent to 600 viral particles). Amplification product was not detected when the PCR-based assay was applied to RNAs from North American bluetongue virus prototype serotypes 2, 10, 11, 13, and 17; total nucleic acid extracts from uninfected BHK-21 cells; or unfractionated blood from calves and deer that were EHDV seronegative and virus isolation negative. The described EHDV PCR-based assay with primers derived from segment 10 of EHDV-1 resulted in detection of EHDV RNA from blood and tissues collected from calves and deer with natural and experimental EHDV infections and provides a valuable tool to study the epidemiology of EHDV infection in susceptible ruminants.