Search PubMed⌕ Search

Biomedical subjects

F R Hall

Publications and source records attributed to F R Hall.

At least 19 recordsLinked to original sources
PubMed2001

Windbreaks as a pesticide drift mitigation strategy: a review.

The use of natural and artificial barriers to mitigate pesticide drift from agricultural and forest applications is discussed. This technique has been considered as an alternative to current methods at a time when environmental concerns are under great public scrutiny. There has been a variety of research experiments on this subject from New Zealand to The Netherlands which have documented reductions in spray drift of up to 80-90%. However, there are still enormous data gaps to utilize this method accurately. The aerodynamic factors of wind barriers and shelter effects on crop growth and yield have been well investigated. In contrast, some of the important aspects of drift mitigation, e.g. porosity and turbulence, have been difficult to obtain and no standard methodologies are currently available to evaluate and classify windbreaks and shelterbelts or to determine their efficiency in reducing drift. Thus there is a significant opportunity to incorporate windbreaks into the tool set of drift mitigation tactics. Government policies, initiatives, legislation, etc, which currently address water quality, BMP, stewardship, buffers, etc, are issues which so far have not included windbreaks as a valuable drift mitigation strategy.

Agriculture↗
PubMed2001

Longitudinal trends in the applicant pool for U.S. medical schools, 1974--1999.

PURPOSE: To examine the pool of applicants to U.S. medical schools from 1974--1999 for changes in size and demographics and to identify factors that may be associated with such changes. METHOD: Data on characteristics of the total applicant pools to U.S. medical schools for 1974--1999 were collected from the Association of American Medical Colleges' Data Warehouse. Data on undergraduates' receiving bachelor's degrees and unemployment rates were obtained from the National Center for Education Statistics and the U.S. Bureau of Labor Statistics, respectively. Variables such as race/ethnicity, gender, age, and first time or reapplicant status were compared across the study period. RESULTS: The percentage of women applicants increased from 20% of the pool in 1974 to 45% of the pool in 1999, while the percentage of men dropped from 80% to 55%. The number of underrepresented minority (URM) applicants increased 45% during the period, from 2,890 to 4,181, but URM applicants represented only 11% of the total applicant pool in 1999. Between 1974 and 1999, the number of URM men applying to medical school dropped by 18%, from 1,984 to 1,629, while the number of URM women nearly tripled, from 906 to 2,552. The number of Asian/Pacific Islander applicants increased dramatically, from 986 in 1974 to 7,622 in 1999, and they now represent a fifth of all applicants. The proportion of reapplicants grew when the applicant pool grew and it shrank when the applicant pool shrank. No relationship was found between the size of the applicant pool and economic indicators, age, or geographic origin. CONCLUSION: Changes in the proportions of women and Asian/Pacific Islander applicants were the driving force in the expansion of the applicant pool between 1974 and 1999.

Adult↗
PubMed1999

Contribution of aerosols generated during mixing and loading of pesticides to operator inhalation exposure.

The occupational exposure resulting from the application of crop protection agents continues to be of great interest for the purposes of identifying hazards or determining safer chemical handling methods. The purpose of the present study was to identify the potential respirator exposure of a mixer/loader to chlorothalonil, with the mixing and loading operation as the only source of aerosols (particles <13 microm diameter). Three worst-case mixing/loading scenarios were simulated in the lab: (1) a spill of undiluted chlorothalonil formulation onto a dry, horizontal metal surface; (2) a spill of undiluted chlorothalonil formulation onto a rapidly rotating shaft; and (3) pouring undiluted chlorothalonil formulation into a container of water. Aerosol generation from these scenarios was compared to that resulting from atomizing dilute chlorothalonil through hydraulic nozzles. Aerosols were captured with a cascade impactor, and quantified by gas chromatography. Results indicated that simulated spill scenarios generated aerosol concentrations between 2.1 and 5.3 ng/l, which were in the same order of magnitude as, and only marginally higher than, the detection threshold (1.7 ng/l) and background levels (2.2 ng/l). In comparison, atomization of dilute chlorothalonil through a hollow cone and flat fan nozzles resulted in airborne concentrations of 354 and 96 ng/l, respectively, related to the atomization characteristics of these nozzles. Measurement of the dimensions of the aerosol cloud indicated that aerosols resulting from a spill amounted to approximately 10(-5)% of the spilled chlorothalonil. It was estimated that a male worker respiring 29 l/min would inhale approximately 0.32-0.78 ng of chlorothalonil during a typical 30 s spill, assuming a 1% transfer efficiency between the spill site and the mixer/loader. These estimates were between 10000 and 480000 times less than literature data for respiratory exposure of chlorothalonil by applicators and harvesters, suggesting that inhalation of aerosols from mixing and loading represents a minor component of overall exposure.

Adult↗
PubMed1999

Innate and adaptive immune responses co-operate to protect cattle against Theileria annulata.

For many years it was assumed that Theileria annulata resembled T. parva, parasitizing lymphocytes and causing lymphoproliferative disease, with the two species being controlled by similar protective immune responses. Patricia Preston et al. here review the evidence that has led to a different view of T. annulata. It is now thought that the schizonts of T. annulata inhabit macrophages and B cells, and that tropical theileriosis is not a lymphoproliferative disease. Both innate and adaptive responses contribute to recovery from infection and resistance to challenge and cytokines produced by infected and uninfected cells influence the outcome of infection. Partial protection has been stimulated recently by defined recombinant antigens; efficacy depended upon the delivery system.

Animals↗
PubMed1999

Tissue damage in cattle infected with Theileria annulata accompanied by metastasis of cytokine-producing, schizont-infected mononuclear phagocytes.

The distribution of schizont-infected cells in six calves undergoing acute, lethal sporozoite-induced infections with Theileria annulata was examined, the calves being killed in the early, middle or late stages of disease. A combination of histological and immunocytochemical techniques showed that schizont-infected cells became disseminated rapidly through the lymphoid tissues from the prescapular lymph node draining the site of inoculation to distant lymph nodes (e.g., precrural, mesenteric and mediastinal) and to the spleen and thymus. The parasitized cells also spread rapidly into non-lymphoid organs, being found in the liver, kidney, lung, abomasum, adrenal glands and pituitary gland by day 7, in the brain by day 12 and in the heart by day 14 after infection. As infection progressed, the schizonts differentiated into merozoites. By the late stages of disease, the cells containing merozoites greatly out-numbered schizont-infected cells. The parasitized mononuclear cells were labelled by antibodies to bovine interferon-alpha1 and tumour necrosis factor-alpha and, during the later stages of the disease, contained erythrocytes parasitized by piroplasms. The results suggested that the parasitized mononuclear cells themselves played a role in the development of clinical disease and in tissue damage. These findings provide new evidence that tropical theileriosis can no longer be viewed as a lymphoproliferative disease resulting from the uncontrolled multiplication and metastasis of lymphoid cells infected with T. annulata schizonts, but is caused by a parasite that lives in, and is disseminated by, cytokine-secreting, proliferating mononuclear phagocytes.

Animals↗
PubMed1998

Different vaccine strategies used to protect against Theileria annulata.

SPAG-1, a sporozoite surface antigen of T. annulata, has previously been shown to elicit partial protection when used, as an hepatitis B core antigen fusion, to immunize cattle. The objective of this study was to try and improve the protective capacity of this antigen by enlisting different vaccine strategies. Cattle were immunized with SPAG-1, as a fusion protein with a His6 tag, either incorporated into ISCOMs, with or without the merozoite antigens TAMS 1-1 and 1-2, or with RWL as adjuvant three times at monthly intervals. Another group of cattle were immunized with p67, the T. parva sporozoite antigen, in RWL to assess whether any cross-protection could be induced. The animals were then challenged with an estimated LD50 of T. annulata sporozoites, and their ability to resist the infection was investigated. Serum responses and T-cell proliferative responses were analyzed throughout the trial. Post-challenge analyses included lymph node biopsies and blood smears to check for the presence of parasites, routine hematological parameters, and observation for clinical manifestations of the disease. The results of this trial will be discussed.

Animals↗
PubMed1998

Phenotypic and genotypic alterations associated with the attenuation of a Theileria annulata vaccine cell line from Turkey.

Attenuated vaccines, produced by prolonged in vitro culture of the macroschizont stage of the life-cycle, are the main method of controlling Theileria annulata infections. Little is known about the mechanism(s) of attenuation. Here we present data from a Turkish cell line demonstrating that attenuation is associated with reduced ability to differentiate into microschizonts and a reduction in matrix metalloproteinase activity. We also show that attenuation results in a change in the structure of the parasite population. Using the technique of differential mRNA display, we demonstrate that gene expression profiles differ between non-attenuated and attenuated macroschizont infected leucocytes. One differentially expressed gene is of parasite origin. These data are discussed in the context of a multifactorial model for virulence.

Animals↗
PubMed1998

Metastasis of Theileria annulata macroschizont-infected cells in scid mice is mediated by matrix metalloproteinases.

Theileria annulata (Ta)-infected leucocytes are able to disseminate in scid mice. The dose of virulent parasites of the Ta-Ode line required to achieve quantifiable dissemination was found to be 2 x 10(6) cells given i.p. Dissemination was higher on day 11 post-inoculation than on day 18. The attenuated Ta-Ode cells were found to disseminate very poorly compared to their virulent progenitors, which correlates with a marked reduction in matrix metalloproteinase (MMP) expression. A daily i.p. injection of mice with BB94, a synthetic inhibitor of MMPs, almost completely ablated dissemination compared to controls. This provides strong evidence that metastasis of Theileria annulata macroschizont-infected host cells is mediated by host MMPs induced by the parasite. This has important implications for explaining a number of pathological features of tropical theileriosis in cattle.

Animals↗
PubMed1998

Spatial heterogeneity and insect adaptation to toxins.

Behavioral responses of insect herbivores to toxins are examined in managed and natural systems with reference to two important but largely ignored factors: heterogeneity in toxin distributions and the nature of the relationship between behavioral responses and physiological adaptation to the same toxins. Heterogeneous toxin distributions, which provide the opportunity for behavioral responses, are ubiquitous in managed and natural systems. Insect herbivores have evolved a wide variety of behavioral responses to such toxins. The nature of behavioral responses reflects toxin apparency, mode of action, and the extent to which sublethal effects influence behavior. The interaction between these behavioral responses to heterogeneously distributed toxins and physiological mechanisms of tolerance has influenced the evolution of insecticide resistance in managed systems and the evolution of plant defensive strategies in natural systems. An understanding of this interaction could lead to more evolutionarily stable methods of crop protection.

Journal Article↗
PubMed1996

Matrix metalloproteinases mediate the metastatic phenotype of Theileria annulata-transformed cells.

Theileria annulata infects and reversibly transforms bovine leucocytes. The parasite-transformed cells are immortalized, metastatic and express a number of metalloproteinases including matrix metalloproteinase 9 which they secrete. All the metalloproteinases observed on substrate gels are inhibited by tissue inhibitor of metalloproteinase 1 and 4 synthetic inhibitors BB94, GM6001, BRL29808AI and Ro31-4724. We have adapted an in vitro assay for metastatic behaviour that measures the ability of parasitized cells to cross reconstituted basement membrane, Matrigel. Using this we demonstrated that macroschizont-infected cells are invasive in vitro and that their invasive properties can be almost eliminated by the same specific inhibitors of metalloproteinases as used in the substrate gels. This demonstrates that the metastatic behaviour of the infected cells is due in part to metalloproteinase activity and strongly suggests a role for the metalloproteinases we observed on gels. This is further supported by the fact that an attenuated vaccine line which shows much reduced metalloproteinase activity also exhibits a marked reduction in metastatic behaviour. We suggest that these metalloproteinases are virulence factors mediating some pathological features of the disease and their loss in the vaccine line could provide an explanation for attenuation.

Animals↗
PubMed1994

Health policies and procedures for medical students at US medical schools: a progress report.

This paper presents the current status of school health policy at US medical schools and discusses implications for medical students with respect to physical health and occupational risks. The authors discuss the responsibility of schools to ensure that students are healthy and fit, both for their own benefit and to provide models of good health maintenance for their future patients. Schools have an obligation to monitor public safety issues, particularly in cases of chemical impairment, student mistreatment and infection control procedures.

Education, Medical, Undergraduate↗
PubMed1994

Theileria annulata sporozoite targets.

Bovine peripheral blood mononuclear cells (PBM) infected in vitro with Theileria annulata sporozoites have previously been characterized as MHC class II+ mature macrophages. The ability of T. annulata sporozoites to infect different subpopulations of MHC class II+ bovine monocytes was investigated. Cells were labelled with monocyte specific monoclonal antibodies (MoAb) and isolated using magnetic cell sorting (MACS). Sporozoites infected both immature and mature monocytes, but more readily infected the mature population. A potential ligand for sporozoite entry is the elastin receptor which is expressed mainly on the immature population of monocytes and not on B cells or T cells. T. annulata sporozoites infected elastin receptor positive and negative cell populations equally well. Infected immature cells lost the expression of elastin receptors and the immature marker, subsequently expressing the mature marker. All monocytes lost the expression of CD14 (the LPS receptor) upon infection with sporozoites. The infection of specific populations and subsequent alterations in phenotype may alter the function of these cells and play an important role in disease pathogenesis.

Animals↗
PubMed1992

Correlating students' undergraduate science GPAs, their MCAT scores, and the academic caliber of their undergraduate colleges with their first-year academic performances across five classes at Dartmouth Medical School.

Reviewing the predictive validity of admission criteria to improve the selection process is important to a school in maintaining quality in the entering class. For this reason, the authors studied how the academic criteria used to select the 420 students who entered Dartmouth Medical School from 1982 to 1986 compared with the students' first-year academic performances. The criteria used were Medical College Admission Test scores, undergraduate science grade-point averages, and college selectivity (i.e., the academic caliber of the students' undergraduate colleges). Results showed that a combination of these criteria were useful in identifying the students who were successful in their first year. The authors suggest that their findings also demonstrate the ability to an admission committee to subjectively weigh these academic criteria with consistent results in student performance.

College Admission Test↗
PubMed1992

Relationship of medical students' admission interview scores to their dean's letter ratings.

The authors examined the relationship between the admission interview scores for 62 students in the 1986 entering class at Dartmouth Medical School and the students' dean's letter ratings given four years later; they found the relationship to be significant (V = .372, p = .014) and the interview scores to be better independent predictors of the ratings than were total Medical College Admission Test scores or science grade-point averages. Among the 17 students receiving "strong" admission interview scores, 53% received dean's letter ratings in the top one-third and 47% received ratings in the lower two-thirds. Of those 34 who received "medium" interview scores, 68% received ratings in the lower two-thirds; all 11 students who received "weak" interview scores received ratings in the lower two-thirds. The authors suggest (1) that admission interview scores help schools to identify more clearly those applicants most likely to become strong, competitive performers in residency and (2) that the significant relationship between interview scores and dean's letter ratings indicates a need to discover what qualities the interview actually measures and to consider the methods by which interviewers are trained, rather than to forsake the interview.

Interviews as Topic↗
PubMed1990

Theileria annulata: control measures, diagnosis and the potential use of subunit vaccines.

Theileria annulata is an important pathogen of domestic Bovidae across a broad region of the world with some 250 million cattle at risk. Our basic knowledge of the incidence and mortality is reviewed together with an outline of current control measures, including the use of acaricides, chemotherapy and attenuated cell line vaccines. The limitations and potential problems of these control measures are discussed and considered in relation to the use of a subunit vaccine. Research over the last ten years on the protective immune response to the disease in both laboratory and field studies suggests that a humoral immune response to the sporozoite could be protective although the primary protective response appears to be mediated by cytotoxic T-cells recognising the macroschizont-infected lymphocyte stage. Recent work on the study of protective antigens using recombinant DNA and hybridoma technologies is discussed together with the potential advantages and problems of such approaches. Possible future developments in our understanding of the immune response and the identification of the relevant antigens are considered in addition to the use of new techniques for diagnosis and the analysis of parasite diversity.

Animals↗