Reducing Campylobacter and Salmonella infection: two studies of the economic cost and attitude to adoption of on-farm biosecurity measures.

To date there has been little research in the UK on farmer adoption of biosecurity measures to control food-borne zoonoses that have little or no impact on animal health or production but which threaten public health. Campylobacteriosis and salmonellosis are the two most common causes of food-borne infectious intestinal disease in people in Great Britain, causing approximately 57,000 and 13,000 reported cases in 2007 respectively (Anon 2008a) with an important cost to society. Poultry are an important source of both infections, while pigs may also contribute to human salmonellosis. However, these infections in poultry and pigs seldom cause disease. Research has shown that improved farm biosecurity may reduce the prevalence of these infections in livestock and if the majority of farmers were prepared to enhance biosecurity then there could be an important impact on public health. This article reports on the findings of two studies of farmer attitudes to and cost of the adoption of on-farm biosecurity measures to reduce the risk of animal diseases and therefore enhance food safety. One study, of Campylobacter infection among broiler flocks, is based on a survey of farmers faced with a hypothetical biosecurity intervention, while the other study, of Salmonella infection among pigs, is based on the participation of a group of farmers in an intervention study. In both cases, the results show a clear inverse relationship between the willingness of farmers to adopt a biosecurity measure and its estimated cost. This finding has implications for the success of on-farm biosecurity-enhancement policies based on voluntary adoption by farmers. In particular, financial inducements or penalties to farmers could be necessary to facilitate adoption of these measures.

Analysis of human megakaryocytic cells using dual-color immunofluorescence labeling.

BACKGROUND: Megakaryocytes are classically identified by their cellular morphology and expression of platelet glycoproteins. METHODS: In this study, the expression of GPIIIa (CD61) on hemopoietic cells was analyzed by dual-fluorescence flow cytometry. RESULTS: All monocytic cells (CD14+) were shown to coexpress CD61. As the expression of platelet protein on these monocytic cells cannot be reduced by treating the cells with anticoagulant (ethlyenediaminetetraacetic acid [EDTA]), this observation is not simply due to platelet adhesion. When sorted CD61(lo)CD14+ cells were studied by light and electron microscopy, platelets or platelet fragments could not be detected on the cell surface. These cells were found to have typical monocytic morphology but no megakaryocytic characteristics. CONCLUSIONS: This finding demonstrates that without careful definition, the quantitation of megakaryocytic cells will be inappropriately high. A clear and unambiguous criteria for the identification of megakaryocytic cells is described based on the high expression of platelet glycoprotein (e.g., CD61(hi) or CD41(hi)) but not the monocyte marker (CD14(neg)).

Modified thrombopoietic response to 5-FU in mice following transplantation of Lin-Sca-1+ bone marrow cells.

An experimental murine model of bone marrow transplantation (BMT) has been used to study the mechanisms of platelet production following transplantation. A defined primitive population of hematopoietic bone marrow cells (1000 Lin-Sca-1+) was isolated and transplanted into lethally irradiated (13 Gy) syngeneic recipient mice. Platelet counts, but neither red nor white blood cell (WBC) counts, were low 30 days after transplantation. By 90 days, platelet levels had normalized in transplanted mice, but this occurred from a reduced megakaryocyte progenitor (CFU-Mk) pool, implying that altered bone marrow control was involved in platelet production. To assess the capacity of the bone marrow of these compensated mice to sustain platelet production, the rate and degree of recovery were examined following administration of 150 mg/kg of 5-fluorouracil (5-FU) 90 days after transplantation. Transplanted mice showed a delay, both in platelet recovery and rebound thrombocytosis, after 5-FU administration when compared to normal littermates treated with 5-FU. The regeneration and expansion of bone marrow CFU-Mk and mature megakaryocytes was retarded in the transplanted mice and explained the altered platelet kinetics. The onset of increased platelet and mature megakaryocyte size, however, was not different between the two groups, indicating that the transplanted mice responded normally to the mechanisms controlling megakaryocyte development and platelet formation. The data suggest that following BMT a limitation in the proliferative capacity of primitive hematopoietic cells results in a smaller pool of megakaryocyte precursors. Compensatory adjustment within the megakaryocyte lineage, nevertheless, results in normalization of megakaryocyte and platelet number. The ability of transplanted mice to sustain platelet production when challenged with increased platelet demand is not limited by megakaryocytic maturation but by a restriction in proliferation or differentiation from the stem cell pool.

Compensatory mechanisms in platelet production: lack of a paracrine response in W/Wv mice treated with 5-fluorouracil.

W/Wv mice maintain normal platelet levels despite having a reduced functional stem cell pool, indicating that platelet production in these mice is compensated by altered megakaryocytopoiesis. In this study the effect of 5-fluorouracil (5-FU) treatment on platelet production in W/Wv mice and their congenic normal littermates was assessed. Recovery of circulating platelet levels occurred 11 days after 5-FU administration in W/Wv mice and subsequently did not increase above control values. In contrast, normal littermates showed an increased platelet count by day 8 and significant thrombocytosis between days 11 and 14. Investigation of bone marrow megakaryocytopoiesis in W/Wv mice showed there was no recovery in the number of megakaryocyte progenitors (CFU-Meg) per femur between days 3 and 5, but control values were reached by day 10. In addition, by day 8 the number of mature megakaryocytes per unit volume of bone marrow in these mice had not returned to control values, although the megakaryocytes were of an increased size. In comparison, the number of CFU-Meg per femur in normal mice treated with 5-FU began to recover after day 3, returned to control values by day 8 and increased to supranormal levels by day 14. Bone marrow megakaryocyte concentration was increased 2-fold over the control by day 8 and an increase in mean megakaryocyte size was also observed. The data suggest that platelet production in mice is dependent on the rate of establishment of both the progenitor cell and megakaryocyte pools. The inability of W/Wv mice to enhance and accelerate progenitor cell levels led to a reduced bone marrow response and failure to produce a marked thrombocytosis.

Acquired amegakaryocytic thrombocytopaenia in a child.

A boy aged 5 years is described with amegakaryocytic thrombocytopaenia, which was associated with defective granulopoiesis and erythropoiesis, but did not evolve into marrow aplasia. Marrow cultures confirmed the presence of abnormalities in each of the haemopoietic lineages and identified defective maturation of megakaryocytic precursors. The was no evidence of a humoral inhibitor of megakaryopoiesis. The patient's blood cell counts responded to treatment with oxymetholone.

Acquired amegakaryocytic thrombocytopenia: report of a case and review of literature.

We describe a 55-year-old female with acquired amegakaryocytic thrombocytopenia who has been successfully treated with antithymocyte globulin. In-vitro studies assessing megakaryocytopoiesis in the presence of the patient's plasma and peripheral blood adherent cells showed normal or increased stimulation. This patient brings to 30 the number of adult cases of acquired amegakaryocytic thrombocytopenia now reported in the English literature. Review of this material suggests that it may be more common than has been appreciated. Several pathogenic mechanisms, especially immune mechanisms, have been identified; good, sustained remissions have been achieved in eight patients who were treated with immunosuppressive agents.

Generation of murine hematopoietic precursor cells from macrophage high-proliferative-potential colony-forming cells.

High-proliferative-potential colony-forming cells (HPP-CFC) have been described as primitive murine macrophage progenitors. We have previously demonstrated the existence of two populations of HPP-CFC: one population, termed HPP-CFC-1, is stimulated by the combination of macrophage colony-stimulating factor (CSF-1) plus haemopoietin-1 (H-1) and actively generates a second population of HPP-CFC, termed HPP-CFC-2. HPP-CFC-2 are stimulated by CSF-1 plus interleukin-3 and generate macrophage CFC that differentiate to form mature macrophages. In this study, we have demonstrated that HPP-CFC-1, when stimulated by CSF-1 plus H-1, generate colony-forming cells (CFC) for the megakaryocyte and granulocyte lineages in addition to HPP-CFC-2 and M-CFC. No CFC were detected with erythroid potential. In addition, HPP-CFC-1 generated cells that formed day-13 spleen colonies, cells that repopulated the bone marrow, cells with platelet-repopulating ability, and cells with erythroid-repopulating ability in lethally irradiated mice. These data support previous data that the HPP-CFC-1 represent a primitive hemopoietic cell population and demonstrate the multipotentiality but not totipotentiality of these cells.

Human megakaryocytes. IV. Growth and characterization of clonable megakaryocyte progenitors in agar.

Human megakaryocyte progenitors were cloned in semisolid agar from unfractionated bone marrow cells and recognized by their capability of producing discrete megakaryocyte colonies. Megakaryocyte colonies were identified in situ by immunofluorescence, using antibodies against platelet glycoproteins Ib, IIb, and IIIa, as well as von Willebrand factor (vWf), which are regarded as distinct protein markers for the megakaryocyte-platelet lineage. Megakaryocyte colonies typically contained 20-50 cells arranged in compact configurations, with high nuclear-cytoplasmic ratios, diameters between 10 and 14 micron, and round, oval, or indented nuclei. Colony numbers peaked at days 6 and 7, with a mean of 17.9 megakaryocyte colonies (range, 8-33) per 2 X 10(5) unseparated marrow cells. The in vitro growth characteristics and kinetics of megakaryocytes grown in agar are different from those described for the plasma clot and methylcellulose systems, which suggests selection of distinct progenitor subsets. Consequently, this assay may be a useful complement to other approaches in characterizing the megakaryocyte progenitor population.