Biomedical subjects
C B Thomas
Publications and source records attributed to C B Thomas.
Impact of a computer-based auto-tutorial program on parasitology test scores of four consecutive classes of veterinary medical students.
A "Hard and Soft Tick" auto-tutorial that integrates basic knowledge of the parasite biology with practical aspects of tick identification, clinical presentation, pathology, disease transmission, treatment, and control was developed at the University of Wisconsin-Madison School of Veterinary Medicine. The purpose of this study was to assess impact of the auto-tutorial on parasitology test scores in four classes (1999, 2000, 2001, and 2002) of veterinary students. The analysis revealed a small but significant increase (p = 0.054) in mean percentage examination scores for students who used the tutorial over those who did not.
Structure of RsrI methyltransferase, a member of the N6-adenine beta class of DNA methyltransferases.
DNA methylation is important in cellular, developmental and disease processes, as well as in bacterial restriction-modification systems. Methylation of DNA at the amino groups of cytosine and adenine is a common mode of protection against restriction endonucleases afforded by the bacterial methyltransferases. The first structure of an N:6-adenine methyltransferase belonging to the beta class of bacterial methyltransferases is described here. The structure of M. RSR:I from Rhodobacter sphaeroides, which methylates the second adenine of the GAATTC sequence, was determined to 1.75 A resolution using X-ray crystallography. Like other methyltransferases, the enzyme contains the methylase fold and has well-defined substrate binding pockets. The catalytic core most closely resembles the PVU:II methyltransferase, a cytosine amino methyltransferase of the same beta group. The larger nucleotide binding pocket observed in M. RSR:I is expected because it methylates adenine. However, the most striking difference between the RSR:I methyltransferase and the other bacterial enzymes is the structure of the putative DNA target recognition domain, which is formed in part by two helices on an extended arm of the protein on the face of the enzyme opposite the active site. This observation suggests that a dramatic conformational change or oligomerization may take place during DNA binding and methylation.
Comment on the critique of the published article by Visser et al. (Theriogenology. 1999; 51:689-697).
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Failure of antibiotics gentamicin, tylosin, lincomycin and spectinomycin (GTLS) to eliminate Mycoplasma bovis in artificially infected frozen bovine semen.
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Corrigendum to "A linear programming assessment of the profit from strategies to reduce the prevalence of Staphylococcus aureus mastitis" [Prev. Vet. Med. 33 (1998) 183-193].
We used a linear programming model to estimate the financial returns to a Staphylococcus aureus testing and control program over a 1-year period for a 100-cow herd, with a 8636kg rolling-herd average. Six tests, which vary in sensitivity from 0.80 to 0.98 and specificity of 0.99, were examined in simulated herds with 10, 20, and 30% prevalence of S. aureus infection. Sensitivity of these results to a range of assumptions regarding rolling-herd average, milk price, somatic cell-count premium, and cost and cure rate of dry treatment were examined to determine the profits from the program. The profits of a control program are most dependent upon prevalence and cell-count premium. In our simulation for a 100-cow herd, a testing and control program results in a profit ranging from US$1.50 to US$20 per cow per year, except under the lowest prevalence and most-adverse conditions (low yield or low SCC premium).
Green fluorescent protein as a quantitative reporter of relative promoter activity in E. coli.
Green fluorescent protein (GFP) has become a valuable tool for the detection of gene expression in prokaryotes and eukaryotes. To evaluate its potential for quantitation of relative promoter activity in E. coli, we have compared GFP with the commonly used reporter gene lacZ, encoding beta-galactosidase. We cloned a series of previously characterized synthetic E. coli promoters into GFP and beta-galactosidase reporter vectors. Qualitative and quantitative assessments of these constructs show that (a) both reporters display similar sensitivities in cells grown on solid or liquid media and (b) GFP is especially well suited for quantitation of promoter activity in cells grown on agar. Thus, GFP provides a simple, rapid and sensitive tool for measuring relative promoter activity in intact E. coli cells.
Total gene deletions and mutant frequency of the HPRT gene as indicators of radiation exposure in Chernobyl liquidators.
This study was conducted to determine the utility of deletion spectrum and mutant frequency (MF) of the hypoxanthine phosphoribosyl transferase gene (HPRT) as indicators of radiation exposure in Russian Liquidators who served in 1986 or 1987 in the clean up effort following the nuclear power plant accident at Chernobyl. HPRT MF was determined using the cloning assay for 117 Russian Controls and 122 Liquidators whose blood samples were obtained between 1991 and 1998. Only subjects from whom mutants were obtained for deletion analysis are included. Multiplex PCR analysis was performed on cell extracts of 1080 thioguanine resistant clones from Controls and 944 clones from Liquidators. Although the deletion spectra of Liquidators and Controls were similar overall, the Liquidator deletion spectrum was heterogeneous over time. Most notable, the proportion of total gene deletions was higher in 1991-1992 Liquidators than in Russian Controls (chi 2 = 10.5, p = 0.001) and in 1993-1994 Liquidators (chi 2 = 8.3, p = 0.004), and was marginally elevated relative to 1995-1996 Liquidators (chi 2 = 3.3, p = 0.07). This type of mutations has been highly associated with radiation exposure. Total gene deletions were not increased after 1992. Band shift mutations were also increased in the 1991-1992 Liquidators but were associated with increased MF of both Liquidators and Controls (p = 0.009), not with increased MF in 1991-1992 Liquidators (p = 0.7), and hence are not believed to be associated with radiation exposure. Regression analysis demonstrated that relative to Russian Controls HPRT MF was elevated in Liquidators overall when adjusted for age and smoking status (37%, p = 0.0001), and also was elevated in Liquidators sampled in 1991-1992 (72%, p = 0.0076), 1993-1994 (22%, p = 0.037), and 1995-1996 (62%, p = 0.0001). In summary, HPRT MF was found to be the more sensitive and persistent indicator of radiation exposure, but the specificity of total gene deletions led to detection of probable heterogeneity of radiation exposure within the exposed population.
Elevated frequencies of hypoxanthine phosphoribosyltransferase lymphocyte mutants are detected in Russian liquidators 6 to 10 years after exposure to radiation from the Chernobyl nuclear power plant accident.
This study was conducted to determine whether the frequency of hypoxanthine phosphoribosyltransferase (HPRT) deficient lymphocyte mutants would detect an effect of radiation exposure in a population of Russians who were exposed to low levels of radiation while working in 1986 and 1987 as liquidators cleaning up after the Chernobyl nuclear power reactor accident. The HPRT lymphocyte cloning assay was performed on peripheral blood lymphocytes collected between 1992 and 1996 from 142 liquidators and 66 Russian controls, and between 1989 and 1993 from 231 American controls. Russian and American controls were not significantly different for either cloning efficiency or mutant frequency (MF); inclusion of both sets of controls in the analysis increased the ability to detect a Chernobyl exposure effect in the liquidators. After adjusting for age and smoking, the results revealed no significant difference in cloning efficiency of Chernobyl liquidators relative to Russian controls but a significant, 24% increase in liquidator HPRT mutant frequency over Russian controls (90% confidence interval was 7% to 45% increase). The analytical method also accounted for differences in precision of the individual estimates of log CE and log MF and accommodated for outliers. The increase in HPRT mutant frequency of liquidators is an attribute of the exposed population as a whole rather than of individuals. These results demonstrate that, under appropriate circumstances, the HPRT specific locus mutation assay of peripheral blood lymphocytes can be used to detect a semi-acute, low dose radiation exposure of a population, even 6 to 10 years after the exposure.
Effect of intracameral administration of carbachol on the postoperative increase in intraocular pressure in dogs undergoing cataract extraction.
OBJECTIVE: To determine whether intracameral injection of carbachol at the completion of phacoemulsification in dogs would prevent the increase in intraocular pressure (i.o.p) that can develop during the first 24 hours after surgery. DESIGN: Randomized controlled trial. ANIMALS: 32 adult dogs undergoing elective unilateral or bilateral phacoemulsification. PROCEDURE: Dogs were randomly assigned to 1 of 4 groups with 8 dogs/group: phacoemulsification and intracameral administration of 0.5 ml of 0.01% carbachol at the end of surgery; phacoemulsification, intraocular lens implantation, and intracameral administration of 0.5 ml of 0.01% carbachol; phacoemulsification and intracameral administration of 0.5 ml of balanced salt solution; and phacoemulsification, intraocular lens implantation, and intracameral administration of 0.5 ml of balanced salt solution. Intraocular pressure was measured at 3 and 6 hours and the morning after surgery. Aqueous flare was also measured 6 hours and the morning after surgery. RESULTS: None of the dogs treated with carbachol developed postoperative ocular hypertension (i.e., IOP > 27 mm of Hg), whereas 12 of 16 control dogs had ocular hypertension 3 hours after surgery. Intraocular pressure 3 hours after surgery was not significantly associated with phacoemulsification time or phacoemulsification power or with whether the dog received an intraocular lens implant. Severity of aqueous flare was similar for treated and control dogs. CLINICAL IMPLICATIONS: Results suggested that intracameral administration of 0.01% carbachol at the end of surgery was a safe and efficacious method of preventing the postoperative increase in IOP associated with phacoemulsification in dogs.
Human in vivo somatic mutation measured at two loci: individuals with stably elevated background erythrocyte glycophorin A (gpa) variant frequencies exhibit normal T-lymphocyte hprt mutant frequencies.
A survey of glycophorin A (gpa) in vivo somatic cell mutation in a population of 394 healthy people from 8 to 77 years of age (mean age +/- SD 41 +/- 15 years) revealed a subset of 37 individuals with stably elevated allele-loss and/or allele-loss with duplication variant erythrocyte frequencies (Vf) exceeding 30 x 10(-6). These 37 individuals with gpa outlier Vf are significantly older (P < 0.001) than the remainder of the larger study population from which they were drawn reflecting a highly significant increase in the prevalence of these individuals in the population beyond age 40 years. A study of hpt mutant frequencies (Mf) in the peripheral blood T-lymphocytes of 27 of these individuals, together with 15 matched control individuals with unremarkable gpa Vf, was undertaken to determine if these subjects also displayed elevated mutation frequencies at this independent locus indicative of globally elevated somatic mutation. The hprt Mf in these 27 subjects (geometric mean 11.5 x 10(-6)(dispersion interval 5.8 x 10(-6) to 22.8 x 10(-6)) was not significantly different from that observed in the 15 controls (geometric mean 12.1 x 10(-6)(dispersion interval 5.7 x 10(-6) to 25.5 x 10(-6)). These Mf are higher than typically reported values reflecting the older age distribution of these individuals (arithmetic mean age +/- SD 53 +/- 12 and 50 +/- 16 years for the subjects and controls, respectively). Taken together, these data suggest that several genetic mechanisms may be responsible for producing the gpa outlier Vf observed in these subjects. The observation that hprt Mf were not increased indicates that the majority did not arise by a genome-wide increased rate of somatic mutation detectable at both loci. The fixation and subsequent expansion of 'jackpot' mutations at the gpa locus occurring early in embryonic/fetal development also does not appear to be a predominant mechanism. Some cases may result from a stable over-representation of gpa variant cells, perhaps associated with a marked age-dependent decrease in the number of contributing erythroid stem cells in the bone marrow. The subset that displays elevated allele-loss with duplication Vf involving both gpa alleles may represent individuals with increased rates of somatic recombination. Elevations arising by this mechanism are not detected in the hprt assay, but could be confirmed using a autosomal locus in vivo somatic cell mutation endpoint such as the hla-a assay. Of primary biological significance, these results demonstrate that genetics/stochastic processes leading to the loss of heterozygosity of somatic cells occur ubiquitously in humans and in some individuals this level of somatic mosaicism can approach a frequency of 10(-3) at the gpa locus in erythroid lineage cells.
A linear programming assessment of the profit from strategies to reduce the prevalence of Staphylococcus aureus mastitis.
We used a linear programming model to estimate the financial returns to a Staphylococcus aureus testing and control program over a 1-year period for a 100-cow herd, with a 8636-kg rolling-herd average. Six tests, which vary in sensitivity from 0.80 to 0.98 and specificity of 0.99, were examined in simulated herds with 10, 20 and 30% prevalence of S. aureus infection. Sensitivity of these results to a range of assumptions regarding rolling-herd average, milk price, somatic cell-count premium, and cost and cure rate of dry treatment were examined to determine the profits from the program. The profits of a control program are most dependent upon prevalence, cell-count premium, and cost of dry treatment. In our simulation for a 100-cow herd, a testing and control program appears to cost less than US$10 per cow per year, and pays for itself within 1 yr, except under the lowest prevalence and most-adverse conditions (low yield, high cost of dry treatment, or low SCC premium.
Brain tissue response to Holmium:YAG laser irradiation.
OBJECTIVE: To evaluate the usefulness of pulsed infrared solid-state Holmium:Yttrium-Aluminum-Garnet (Ho:YAG) laser in neurosurgery, acute responses of brain tissue to Ho:YAG irradiation and to investigate the healing processes in rats and rabbits. METHODS: Animals were divided into groups according to different survival time and laser irradiation mode. Craniotomy was made and laser energy was delivered to the brain surface by two irradiation modes: 1) contact mode with the fiber in contact with the brain surface; and 2) non-contact mode with the fiber tip 5 mm above the brain surface. Gross observations were made and histological changes were studied. RESULTS: Acute responses were studied on rats' brain. The contact mode produced a crater lined with less than 1 mm thick thermally coagulated layer of brain tissue. The non-contact mode effectively vaporized the brain tissue even with water irrigation. Good homeostatic effect was achieved. The shock waves generated by the pulsed delivery of laser energy, however, impacted on the brain resulting in debris spreading and brain vibration. The healing processes were studied on rabbits' brain one day to six weeks after irradiation. The lesions produced by the contact mode were narrow and sharply defined. With the non-contact mode, the thickness of the coagulated layer at the bottom of the crater varied between 0.8 and 1.1 mm. CONCLUSIONS: Ho:YAG laser should be a clinically useful tool in neurosurgery because of its good ablation effect, shallow penetration and convenient optic fiber transmission system. Meanwhile, a continuously waved Ho:YAG laser is desired to reduce the shock wave impact.
Psychological precursors of disorders: a thought-provoking observation.
While still in medical school at The Johns Hopkins University, participants in the Precursors Study, a longitudinal study of the precursors of coronary artery disease and other disorders, were given the Rorschach test along with other psychological and physical tests. In the present study, we looked at a cohort of 41 participants who, 8 to 24 years after having finished medical school, could be classified into five disorder groups: coronary, hypertension, mental illness, suicide, or malignant tumor. Using stepwise discriminant analysis, we found that participants' Rorschach test scores differed significantly among disorder groups. Since the Rorschach scores considerably predated the appearance of the disorders, this finding implies that the Rorschach scores were predictive of the subsequent development of the various disorders. The Rorschach scores were especially good at predicting mental illness. If this finding is not spurious, it suggests that a given Rorschach profile would be predictive long before mental illness became apparent. Consequently, it offers the possibility that some intervention might be undertaken which could either result in mental illness not occurring or, at perhaps a minimum, lessen its severity. Since the Precursors Study results discussed in this paper are some years old, it is likely that another cohort of participants have developed the various disorders. Therefore, the authors recommend that the discriminant functions derived from this effort be validated with another cohort from that study who had not yet exhibited one of the five disorders when the current analysis was undertaken. Were that not possible, we would recommend that this study simply be replicated with another cohort.
Epidemiologic study of on-farm management practices associated with prevalence of Mycobacterium paratuberculosis infections in dairy cattle.
OBJECTIVE: To use an on-farm recording form to quantity the effect of specific management practices on apparent prevalence of Mycobacterium paratuberculosis in dairy cattle herds. DESIGN: Epidemiologic survey. ANIMALS: 26 commercial Wisconsin dairy farms. PROCEDURES: An instrument was developed on the basis of literature review and expert interviews to quantify on-farm management practices associated with increased apparent prevalence of M paratuberculosis. On-farm visits were conducted to assess how specific management practices were conducted. Apparent prevalence of M paratuberculosis infection was measured for all animals > 20 months old on all farms, using a commercial ELISA. Regression analysis was used to identify management variables that were significantly associated with apparent prevalence of M paratuberculosis. RESULTS: Regression analysis (R2 = 0.90) identified that high scores for environmental conditions, newborn calf care, grower calf care, bred heifer care, and manure handling were significantly associated with M paratuberculosis apparent prevalence in Wisconsin dairy herds. CLINICAL IMPLICATIONS: Environmental conditions, newborn calf care, grower calf management, bred heifer management, and manure handling factors may serve as a prioritized checklist for instructing owners and managers where to place emphasis in changing management practices to limit M paratuberculosis prevalence. Likewise, the factors identified as having low association with apparent prevalence may be de-emphasized in control programs, allowing dairy managers to focus time and finances on more effective components of an M paratuberculosis control program.
Exposure of wild waterfowl to Mycoplasma anatis.
We developed an ELISA procedure to assess the presence of M. anatis-specific serum antibody in ducks. Sera from exposed and unexposed Pekin ducks (Anas platyrhynchos) were used to standardize the ELISA and to establish reference ranges to classify ELISA results as exposed or not exposed. We conducted serological surveys of female waterfowl in the central and eastern United States between 1988 and 1992 to assess the frequency of exposure in wild waterfowl. Adult breeding mallards (Anas platyrhynchos), wintering mallards, and black ducks (Anas rubripes) had high prevalences of exposure to M. anatis (25% to > 80%). In comparison, none of the breeding adult canvasbacks (Aythya valisineria) had serum antibody levels indicating exposure. Approximately 50% of the juvenile mallards and black ducks were exposed to M. anatis by 8 months of age, indicating high transmission rates among wild birds.
Temporal stability of the virus load of cattle infected with bovine leukemia virus.
The relative virus load of bovine leukemia virus (BLV) infected cattle was measured by an immunoperoxidase infectivity assay (IPIA), and by immunoperoxidase staining of cultured leukocytes using a monoclonal antibody to the capsid protein (p24) of BLV. The results of paired sample data taken at different time points spanning 2-3 years show that BLV-infected cattle are stable regarding the amount of BLV produced by their peripheral blood mononuclear cells (PBMCs). Spearman's Rank Correlation demonstrated significant relationships between data from individual cattle taken at four different time points. In addition, this study documents the large range of variation in the virus load of individual cattle.
Impact of age and environment on somatic mutation at the hprt gene of T lymphocytes in humans.
Analysis of two human populations for dependence of somatic mutation on age has revealed both similarities and differences. The studies performed employed peripheral blood lymphocytes and measured the efficiency with which these cells form clones in vitro (cloning efficiency, CE) and the frequency of cells with inactivating mutations of the hypoxanthine phosphoribosyltransferase gene (mutant frequency, MF). The people studied were between 19 and 64 years of age. In one population, composed of 78 never smokers and 140 current smokers from the United States (US), both CE and MF were dependent on age: CE declined with age (p = 0.005); MF increased 0.15 per 10(6) cells per year of age for nonsmokers (p < 0.001) and at 1.3 times that rate for smokers (p = 0.01). In the second population, 80 people of unknown smoking status from Russia, the increase in MF per year was even greater, 2.5 times that of the US nonsmokers (p = 0.001) but the dependence of CE on age was the same as for the US population (p = 0.043). Because the increase of MF of the Russians with age is 2-fold greater than that of the US smokers, the intensity of smoking and/or other environmental exposures, or the susceptibility to these exposures, must account for the difference in age dependent MF increase, not the proportion of Russians that are smokers. Differences in the lymphocyte subpopulations that survived the longer transit from Russia may have contributed to the observed differences in MF. However, overall, the mutant frequency results suggest that the Russians were chronically exposed to higher levels of agents that induce somatic mutation and that, on an age adjusted basis, the Russia population studied is at increased risk for health consequences from accumulated genetic damage.