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Biomedical subjects

J C Baker

Publications and source records attributed to J C Baker.

At least 55 records · Page 3Linked to original sources
PubMed1995

Prevalence of cattle persistently infected with bovine viral diarrhea virus in 20 dairy herds in two counties in central Michigan and comparison of prevalence of antibody-positive cattle among herds with different infection and vaccination status.

All cattle in 20 dairy herds randomly selected from herds participating in the Dairy Herd Improvement Association program in 2 counties in central Michigan were tested for the presence of bovine viral diarrhea virus (BVDV). Virus-positive animals were retested to ascertain persistent infection with the virus. A total of 5,481 animals were tested for presence of BVDV. In 9 of the herds, all animals were also tested for virus neutralizing antibody titer. Based on infection and vaccination status, these 9 herds were divided into 3 different herd categories: A, 5 herds with currently no cattle persistently infected (PI) with BVDV and without any vaccination program against BVDV in recent years; B, 2 herds with no current PI cattle but using killed BVDV vaccines; and C, 2 herds with PI cattle. PI cattle were detected in 3 out of 20 herds (15%). A total of 7 of 5,481 animals (0.13%) were PI. The mean prevalences of antibody carriers in herd categories A, B, and C were 28.8%, 76.4% and 90.6%, respectively. For one herd in category A, antibody analyses indicated that mostly young stock was seropositive, suggested recent BVDV infection in a previously closed and naive herd. Cattle in category B herds were vaccinated with killed vaccine from the age of 15 months. These herds had several antibody negative animals among the younger cows, suggesting incomplete protection against BVDV infection. In the 3 herds in which PI animals were detected, all cattle had been vaccinated with killed vaccine. The antibody-positive animals had antibody titers that were significantly different both among herds and among herd categories.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗
PubMed1995

Application of antibody titers against bovine viral diarrhea virus (BVDV) as a measure to detect herds with cattle persistently infected with BVDV.

Based on the distribution of antibody titers against bovine viral diarrhea virus (BVDV) in 10 Michigan dairy herds, it was calculated that screening of 5 young stock for BVDV antibody titer could be used to distinguish herds with persistently infected (PI) animals from herds without such animals. The herds were selected to represent 3 different herd categories: A, herds without use of vaccination and without PI animals (5 herds); B, herds with use of killed vaccine but no PI animals (2 herds); C, herds with use of killed vaccine and presence of PI animals (3 herds). The animals were described as having high antibody titers (> or = 128) or low antibody titers (< or = 64). For animals from 9 to 18 months of age, the probability of obtaining at least 3 animals with high titers among a screening sample of 5 animals was calculated as < 0.001 for all herds in category A, < 0.01 for the 2 herds in category B, and > 0.99 for all herds in category C. Thus, among herds in this study, by categorizing 9-18-month-old animals as having high titers (> or = 128) or low titers (< or = 64), herds with PI cattle could be distinguished from other herds by testing only 5 animals.

Animals↗
PubMed1995

Comparison of the prevalence and incidence of infection with bovine virus diarrhoea virus (BVDV) in Denmark and Michigan and association with possible risk factors.

Based on 2 previous surveys on the occurrence of infection with bovine virus diarrhoea virus (BVDV) in Danish and Michigan dairy herds, the prevalence and incidence of the infection were compared. The presence of certain possible risk factors for the occurrence of infection in the 2 areas were summarized and it was investigated if any of these risk factors had significant effect on the presence of animals persistently infected (PI) with BVDV in the dairy herds. Information on the cattle population density in the 2 areas was obtained from statistical yearbooks. Further information for the individual farms on age distribution, housing of animals, herd size, pasturing and purchasing policy was gathered. The prevalence of PI animals was more than 10 times higher in Denmark as compared to Michigan. In herds without PI animals, the annual incidence of seroconversion as calculated from the age specific prevalence of antibody carriers varied in most age groups between 20-25% in Denmark and between 5-10% in Michigan. All investigated risk factors except for herd size were in favour of a lower prevalence of infection in Michigan. The use of having animals on pasture and at the same time having purchased more than 40 animals within recent 3 1/2-4 years were significantly associated with presence of PI animals in the dairy herds (p = 0.01) when tested by the Mantel-Haenszel chi 2. Using multivariable logistic regression, the occurrence of PI animals was found to be significantly related to the study area (Michigan and Denmark) as well as to herd size and purchase intensity.

Animals↗
PubMed1993

Imaging fluid/solid interactions in hydrocarbon reservoir rocks.

The environmental scanning electron microscope (ESEM) has been used to image liquid hydrocarbons in sandstones and oil shales. Additionally, the fluid sensitivity of selected clay minerals in hydrocarbon reservoirs was assessed via three case studies: HCl acid sensitivity of authigenic chlorite in sandstone reservoirs, freshwater sensitivity of authigenic illite/smectite in sandstone reservoirs, and bleach sensitivity of a volcanic reservoir containing abundant secondary chlorite/corrensite. The results showed the suitability of using ESEM for imaging liquid hydrocarbon films in hydrocarbon reservoirs and the importance of simulating in situ fluid-rock interactions for hydrocarbon production programmes. In each case, results of the ESEM studies greatly enhanced prediction of reservoir/borehole reactions and, in some cases, contradicted conventional wisdom regarding the outcome of potential engineering solutions.

Aluminum Silicates↗
PubMed1993

Hemorrhagic diathesis associated with a hereditary platelet disorder in Simmental cattle.

A severe bleeding disorder in Simmental cattle has been described in widespread locations in the USA and Canada. The clinical findings are consistent with a hemophilia-like disease or, more precisely, a hereditary hemorrhagic diathesis and include spontaneous epistaxis, hematuria, and excessive bleeding associated with trauma or standard management procedures such as tattooing, ear tagging, and castration. A preliminary investigation of this defect showed that blood-platelet numbers and coagulation profiles of affected cattle were normal. Affected animals have a marked dysfunction of platelets (thrombopathy), termed Simmental hereditary thrombopathy. The defect is very similar or identical to that described in the same breed by 2 other laboratories.

Animals↗
PubMed1992

Identification of subgroups of bovine respiratory syncytial virus.

The occurrence of antigenic variation among nine isolates of bovine respiratory syncytial virus (BRSV) was determined by examining their reaction patterns to human respiratory syncytial virus (HRSV) subgroup A and B monoclonal antibodies (MAbs) by enzyme immunoassay and radioimmunoprecipitation with fractionation by sodium dodecyl sulfate-polyacrylamide gel electrophoresis by using MAbs and polyclonal antisera to HRSV and BRSV. Shared epitopes were demonstrated on four of five structural proteins between BRSV and both subgroups A and B of HRSV. The nine isolates of BRSV showed different patterns of reactivity in enzyme immunoassays with panels of MAbs to HRSV subgroups A and B. Major variations in the molecular weights of the P (phosphoprotein) and F (fusion protein) proteins were demonstrated among the BRSV isolates tested. These results suggest that BRSV belongs to a different antigenic grouping than HRSV and that BRSV is composed of two distinct subgroups.

Animals↗
PubMed1992

Pharmacokinetic evaluation of ceftiofur in serum, tissue chamber fluid and bronchial secretions from healthy beef-bred calves.

Ceftiofur is a new broad spectrum cephalosporin marketed for the treatment of acute bovine respiratory disease. In this investigation ceftiofur was administered by intramuscular injection, at 24 h intervals, to healthy beef-bred calves for four days at dosages of 2.2 and 4.4 mg/kg of body weight, with 4 wk intervals between dosing regimens. Serum, tissue chamber fluid (TCF), and bronchial secretion (BS) concentrations of ceftiofur were measured by microbiological assay after the first and fourth dose of each dosing regimen. Peak serum concentrations (Cmax) of 8.8 micrograms/mL and 17.3 micrograms/mL were obtained approximately 2 h (Tmax), the time of mean peak concentration) after single injections of 2.2 mg/kg and 4.4 mg/kg, respectively. The Cmax was increased approximately twofold following multiple doses of 2.2 mg/kg (Cmax = 13.1 micrograms/mL) and 4.4 mg/kg (Cmax = 24.1 micrograms/mL). Ceftiofur accumulated slowly into TCF and peak concentrations were found to be approximately 14% of those observed in serum after the first dose and approximately 24% after multiple dosing. Concentrations of ceftiofur in BS were obtained rapidly with peak concentrations reaching 45% of the serum Cmax after the first dose. After multiple dosing the Cmax for BS was approximately 25% of the serum Cmax. This study found that both the 2.2 mg/kg and 4.4 mg/kg dosing regimens resulted in continuous serum, TCF and BS concentrations of ceftiofur that exceeded the minimal concentration required to inhibit the bacteria most frequently isolated from calves with acute bovine respiratory disease.

Animals↗
PubMed1991

An outbreak of fetal and neonatal losses associated with the diagnosis of bovine viral diarrhea virus.

A severe outbreak of dairy herd pregnancy wastage was investigated. At the beginning of the outbreak, a total of 121 lactating cattle were pregnant and considered to be at risk. Overall, 33.1% of the population at risk aborted, while 25.6% gave birth to calves that either died during the early neonatal period or demonstrated signs compatible with congenital defects (abnormal births). A laboratory diagnosis of bovine viral diarrhea virus (BVDV) infection was made in two surviving neonatal calves with symptoms of cerebellar hypoplasia and blindness. An on-farm investigation was conducted to determine if the abortions and abnormal births were associated with BVDV infection. The rate of abortions versus abnormal births was biphasic when graphed by the date of occurrence. The cases of abortion occurred early in the outbreak and were followed by the neonatal losses. Within the population at risk, the mean values for gestational age at the beginning of the outbreak were different between the subpopulations described by gestational outcome. The outcome of each pregnancy that existed at the beginning of the outbreak was determined. Classifications included normal birth (birth of a normal calf), abnormal birth (a neonatal loss of the type described above), abortion, and continued gestation (normal, uncompleted pregnancy). The average gestational age at the time of the index case (the first cases of pregnancy wastage) for these four pregnancy outcome classfications was 142.0, 106.2, 86.7 and 31.3 days, respectively. Reasons for assuming that this outbreak was related to BVDV are discussed.

Journal Article↗
PubMed1991

Experimental reproduction of respiratory tract disease with bovine respiratory syncytial virus.

An experiment was conducted to reproduce respiratory tract disease with bovine respiratory syncytial virus (BRSV) in one-month-old, colostrum-fed calves. The hypothesized role of viral hypersensitivity and persistent infection in the pathogenesis of BRSV pneumonia was also investigated. For BRSV inoculation a field isolate of BRSV, at the fifth passage level in cell culture, was administered by a combined respiratory tract route (intranasal and intratracheal) for four consecutive days. Four groups of calves were utilized as follows: Group I, 6 calves sham inoculated with uninfected tissue culture fluid and necropsied 21 days after the last inoculation; Group II, 6 calves inoculated with BRSV and necropsied at the time of maximal clinical response (4-6 days after the last inoculation); Group III, 6 calves inoculated with BRSV and necropsied at 21 days after the last inoculation; Group IV, 6 calves inoculated with BRSV, rechallenged with BRSV 10 days after initial exposure, and necropsied at 21 days after the initial inoculation. Clinical response was evaluated by daily monitoring of body temperature, heart rate, respiratory rate, arterial blood gas tensions, hematocrit, total protein, white blood cell count, and fibrinogen. Calves were necropsied and pulmonary surface lesions were quantitated by computer digitization. Viral pneumonia was reporduced in each principal group. Lesions were most extensive in Group II. Disease was not apparent in Group I (controls). Significant differences (p less than 0.05) in body temperature, heart rate, respiratory rate, arterial oxygen tension, and pneumonic surface area were demonstrated between control and infected calves. Results indicate that severe disease and lesions can be induced by BRSV in one-month-old calves that were colostrum-fed and seropositive to BRSV. BRSV rechallenge had minimal effect on disease progression. Based on clinical and pathological response, results did not support viral hypersensitivity or persistent infection as pathogenetic mechanisms of BRSV pneumonia.

Animals↗
PubMed1991

Human and bovine respiratory syncytial virus: immunopathologic mechanisms.

Human respiratory syncytial virus (HRSV) is the major respiratory tract pathogen of infants and young children. Bovine respiratory syncytial virus (BRSV) is recognised as an important cause of respiratory tract disease in calves. Both of these viruses and their respective diseases share many similarities. Immunopathologic mechanisms have been proposed to be involved in the pathogenesis of respiratory syncytial virus (RSV) infections. This review examines the current understanding of the role of immunopathologic mechanisms in RSV infections. The role of vaccines in inducing hypersensitivity is also examined. Additionally, non-immunopathogenic mechanisms involved in RSV infections are discussed.

Animals↗
PubMed1991

The role of passive immunity in bovine respiratory syncytial virus-infected calves.

The role of passive immunity in bovine respiratory syncytial virus (BRSV) infections in neonatal calves was evaluated. Calves were divided into groups as follows: colostrum-deprived, sham-inoculated; colostrum-deprived, BRSV-inoculated; and colostrum-fed, BRSV-inoculated. Calves were inoculated with a low-passage field isolate of BRSV for 4 consecutive days by a combined respiratory tract route and were euthanized 6 days after receiving the last inoculation. Arterial oxygen tension (Pao2) decreased significantly over time in colostrum-deprived, BRSV-inoculated calves (P less than .01) and was significantly different among treatment groups (P less than .05). A significant decrease in arterial oxygen saturation was observed in this same group over time (P less than .01). Mean percentage of pneumonic lung volume (determined by computer data digitalization) was significantly greater in infected, colostrum-deprived calves compared with the other groups (P less than .01), and BRSV antigen was detected in these calves by avidin-biotin immunoperoxidase staining. Thus, passive immunity derived from colostrum feeding decreased the severity of BRSV infections in calves.

Analysis of Variance↗
PubMed1991

The severity of diabetes is a major determinant of myocardial damage in the rat.

The severity of insulin-dependent diabetes mellitus had a marked effect upon the development of myocardial sequelae in the rat. Even with the same degree of hyperglycemia, glycosuria, polydipsia, and polyuria, moderately diabetic animals did not develop the degenerative ultrastructural changes seen in myocardium from more severely diabetic rats. These included decreased cardiocyte size, loss and disorganization of myofibrils, and loss of sarcoplasmic reticulum and transverse tubules. Since hyperglycemia and glycosuria are frequently used as the primary, and often sole, criteria for identifying diabetes in experimental animals, this study demonstrates the need to more specifically define the severity of the disease in studies of the heart.

Animals↗
PubMed1991

Characterization of the alpha-2C adrenergic receptor subtype in the opossum kidney and in the OK cell line.

The alpha-2 adrenergic receptors have been subdivided into two pharmacological subtypes known as alpha-2A and alpha-2B. The OK cell, a cell line derived from an opossum kidney, expresses an alpha-2 adrenergic receptor which has pharmacological characteristics different from both the alpha-2A and alpha-2B subtypes, and thus may be a third subtype. To test this hypothesis, we compared the affinities (Ki values from radioligand binding) of 49 drugs in the OK cell with their affinity for the alpha-2A (HT-29 cells) and alpha-2B (neonatal rat lung) adrenergic receptor subtypes. Eight drugs (spiroxarine, prazosin, WY 27127, L-657,743, ARC 239, akuammigine, rauwolscine and oxymetazoline) were identified whose Ki differed by 10-fold or more between the OK cells and HT29 cells. Five drugs (BAM 1303, raubasine, WB 4101, akuammigine and rauwolscine) differentiated, by at least 10-fold, between OK cells and neonatal rat lung. Correlations of pKi values between the OK cell and tissues or cell lines expressing either the alpha-2A or alpha-2B subtypes were poor, confirming that the OK cell receptor could not be classified as either alpha-2A or alpha-2B. In contradistinction, there was a good correlation between pKi values for the OK cell line and opossum kidney showing that they express the same subtype. In addition, ratios of subtype-selective drug Ki values were similar for the OK cell and opossum kidney, but different from other tissues or cell lines expressing either the alpha-2A or alpha-2B subtypes. We conclude that the OK cell line and opossum kidney express a novel subtype of alpha-2 adrenergic receptor which we term the alpha-2C subtype.

Animals↗
PubMed1991

Effects of bovine respiratory syncytial virus on airway function in neonatal calves.

Respiratory syncytial virus (RSV) infection causes severe lower respiratory tract disease in infants and calves. Neonatal respiratory tract infection in children often produces persistent changes in lung function. The specific objective of this study was to determine whether neonatal calves have transient or persistent alterations in pulmonary function and airway reactivity following RSV infection. Six 2- to 3-day-old Holstein bull calves were inoculated with 10 ml of bovine respiratory syncytial virus (BRSV) inoculum (10(2.7) to 10(3.8) cell culture infective doses/ml) intranasally and 10 ml of BRSV inoculum (10(4.8) to 10(5.9) cell culture infective doses/ml) intratracheally for 4 consecutive days, and 5 other calves were sham-inoculated. Prior to inoculation (day 0) and on days 4, 14, and 30 after the last inoculation, body weight (kg), dynamic compliance (Cdyn), pulmonary resistance (RL), and 2 indices of airway reactivity (effective dose [ED] 65Cdyn and ED200RL) were measured. Control calves gained weight progressively throughout the study, whereas RSV-inoculated calves failed to gain weight for 14 days, but equaled control calf weight by 30 days after inoculation. The Cdyn of control calves increased significantly by 30 days, but did not in the RSV-infected calves. Pulmonary resistance was increased significantly at 4, 14, and 30 days, but was unaffected by sham inoculation. The ED65Cdyn and ED200RL indicated an age-dependent increase in reactivity to histamine and an increase in responsiveness in the infected group beginning at 14 days and persisting until the end of the study.(ABSTRACT TRUNCATED AT 250 WORDS)

Airway Resistance↗
PubMed1990

Clinical aspects of bovine virus diarrhoea virus infection.

Bovine virus diarrhoea virus (BVDV) infection of cattle results in a wide range of clinical manifestations. This article reviews the clinical responses associated with BVDV and discusses these diseases in terms of acute infection in immunocompetent cattle, fetal infection, infection in cattle immunotolerant to and persistently infected with BVDV and finally mucosal disease.

Acute Disease↗
PubMed1990

Granulocyte plasma membrane damage by leukotoxic supernatant from Pasteurella haemolytica A1 and protection by immune serum.

Bovine respiratory disease caused by Pasteurella haemolytica may be partially mediated by a leukotoxin secreted by the microorganism. We examined the effect of leukotoxic Pasteurella supernatants on leakage of the cytosol enzyme lactate dehydrogenase and the lysosomal enzyme arylsulfatase from bovine granulocytes. Lactate dehydrogenase release (94%) was much higher than arylsulfatase release (38%) over 30 minutes of incubation. The Pasteurella supernatants inhibited superoxide production by stimulated granulocytes at concentrations which also caused substantial cell death as measured by failure to exclude trypan blue. Both toxic effects were prevented by serum from aerosol-immunized calves, and protection appeared to be antibody-specific by comparison with fetal bovine serum or with serum absorbed against intact P. haemolytica. These findings suggest that the leukotoxin may selectively disrupt the granulocyte plasma membrane, and that antibody directed against a surface component of the microorganism is also capable of protecting against the leukotoxin effect.

Animals↗
PubMed1989

Calcium ion involvement in the action of Pasteurella haemolytica leukotoxin.

The influence of Ca2+ ions on the cytotoxic activity of Pasteurella haemolytica leukotoxin was investigated. The divalent cation influenced the cytotoxic effect of the leukotoxin for sensitive BL-3 target cells, but its absence did not eliminate cytotoxicity. In short-term 1-h assays using neutral red uptake as a measure of cell viability, depletion of Ca2+ either by exhaustive dialysis or by addition of the Ca2+ chelators EDTA and EGTA eliminated the cytolytic effect of low doses of the toxin. Addition of Ca2+ to target cell cultures depleted of the divalent cation restored the cytolytic effect of the leukotoxin. Prolonged exposure of the BL-3 cells to the toxin abrogated the protective effect of EDTA and EGTA. Cell death measured by uptake of neutral red, exclusion of trypan blue and 51Cr release indicated that protection observed in the absence of free Ca2+ was temporary. Toxin-induced cytolysis equivalent to that observed in the presence of Ca2+ occurred following the initial 2-h exposure. In addition, verapamil, a Ca2+ channel blocker, prevented cell death during 1-h cytotoxicity assays. The protection afforded by verapamil was dose-dependent and was influenced by the concentration of Ca2+ in the buffer medium. The results suggest that Ca2+ positively influences the rapid initial phase of cell death resulting from exposure to the toxin, but is not required for the entirety of the cytolytic process.

Animals↗