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Biological Warfare↗

Performance of open-fronted microbiological safety cabinets: the value of operator protection tests during routine servicing.

The performance of class I and II microbiological safety cabinets over 7 years, employed in a force-ventilated containment level 3 (CL-3) laboratory, is described. Operator Protection (OP) provided by the cabinets, assessed by still and latterly limited 'in-use' KI-Discus tests, showed no overall deterioration during the review period. Comparisons show that a selected class II unit, but not a second, and a new class II MSC in a recently commissioned, similar CL-3 facility, provide the same order of OP as a class I cabinet. From the experiences described, it is strongly recommended that OP tests (OPTs) should be part of the routine servicing regime to ensure that cabinets meet required performance levels, and additionally to allow detection and rectification of poor containment, particularly where induced by environmental factors. The value of OPTs is discussed with reference to certain national standards.

Containment of Biohazards↗

Application of biosafety principles in blood establishments.

In light of increasing public and employee concern over potential infectious hazards associated with blood and other body fluids, several government agencies (the Food and Drug Administration, the Centers for Disease Control, the Occupational Safety and Health Administration, the Environmental Protection Agency, the Health Care Financing Administration and the National Heart, Lung and Blood Institute) cosponsored a Biosafety Workshop in April 1988. The objective of the workshop was to identify appropriate biosafety practices and standard control procedures to protect workers involved in the collection, storage, and transportation of human blood donations with the least possible disruption of the nation's blood supply. Speakers focused on human immunodeficiency virus (HIV) and hepatitis B virus (HBV); however, the safety principles discussed were considered equally applicable to other known (e.g., non-A, non-B hepatitis and human T-lymphotropic virus type I (HTLV-1) blood-transmitted infections. The resulting consensus included the need for blood establishments to develop and apply thoughtful biosafety programs to address staff training, accident prevention, HBV vaccination, handling spills, managing contaminated waste and transporting blood specimens. There was lack of agreement, however, on the usefulness of gloves during the phlebotomy of healthy blood donors.

Acquired Immunodeficiency Syndrome↗

[Ebola and Marburg viruses: the humans strike back].

Ebola and Marburg viruses are the causative agents of rapidly progressive hemorrhagic fevers with high mortality rates. Pre- or post-exposure treatments against the diseases are currently not available for human use. In the field, establishment of strict quarantine measures preventing further virus transmission are still the only way to fight the infections. However, our knowledge of Ebola and Marburg viruses has markedly increased as a result of two recent discoveries discussed in this review. Chandran et al. have elucidated the mechanism by which Ebola GP is converted to a fusion-active form. Infectivity of Ebola virus was shown to be dependent on the cleavage of GP by cellular endosomal proteases, cathepsin B and L, thus opening new therapeutic approaches options. As for Jones SM et al., they have successfully vaccinated monkeys with recombinant vesicular stomatitis virus expressing Ebola or Marburg virus surface glycoprotein GP, a promising vaccine approach.

Africa, Central↗

Elimination of mouse allergens in the working environment: assessment of individually ventilated cage systems and ventilated cabinets in the containment of mouse allergens.

BACKGROUND: Laboratory animal allergy is an important occupational disease that is preventable by reduction of exposure to mammalian allergens. OBJECTIVE: The purpose of this investigation was to assess the efficacy of safety equipment in containing mouse urinary protein (MUP)--specifically, individually ventilated cage (IVC) systems and class I--type and class II ventilated cabinets. METHODS: Six IVC systems (which are used to house rodents) were operated at positive and negative pressure. Air samples (2 L/min) were collected at the cage front, cage back, air inlet, and air outlet, and the MUP was quantified by immunoassay. The background MUP of the IVC study room was compared with that of rooms where mice were housed conventionally or in isolators. Class I--type cabinets (n = 2) were tested during the disposal of soiled litter. Air samples were positioned on and behind the operator and inside the cabinet (n = 2). Personal samples were collected while scientific procedures were performed in a class II cabinet and in the open. RESULTS: All of the IVC systems contained MUP effectively (>250-fold) when operated at negative pressure. At positive pressure, the "unsealed" IVC racks leaked MUP (1- to 25-fold reduction) but the "sealed" IVC system did not. Class I--type cabinets reduced (10-fold) but did not eliminate exposure during "cleaning out." No MUP was detected when procedures were performed in class II cabinets (protection factor, >10-fold). CONCLUSION: Safety equipment can substantially reduce exposure to mouse allergen. Allergen exposure in holding rooms will be minimized if mice are housed in IVC systems operated at negative pressure or in "sealed" IVC systems at positive pressure. Respiratory protection should be used whenever "unsealed" IVC systems are operated at positive pressure or during "cleaning out" in class I--type cabinets.

Allergens↗

A new approach for containment of microorganisms: dual control of streptavidin expression by antisense RNA and the T7 transcription system.

The use of microorganisms in the open environment would be of less concern if they were endowed with programmed self-destruction mechanisms. Here, we propose a new genetic design to increase the effectiveness of cell suicide systems. It ensures very tight control of the derepression of cell death by the combination of the bacteriophage T7 RNA polymerase-lysozyme system and an inducible synthesis of antisense RNA and the Escherichia coli LacI repressor. Functionality of this regulatory concept was tested by applying it to containment of Gram-negative bacteria, based on the conditional expression of the lethal Streptomyces avidinii streptavidin gene. Toxicity of streptavidin is derived from its exceptionally high binding affinity for an essential prosthetic group, D-biotin. The entire construct was designed to allow the soil bacterium Pseudomonas putida to survive only in the presence of aromatic hydrocarbons and their derivatives which it can degrade. Under favorable growth conditions, clones escaping killing appeared at frequencies of only 10(-7)-10(-8) per cell per generation. The general requirement for biotin through the living world should make streptavidin-based conditional lethal designs applicable to a broad range of containment strategies.

Bacterial Proteins↗

Review of epidemiological surveys on the prevalence of contamination of healthy cattle with Escherichia coli serogroup O157:H7.

This paper gathers and critically analyses the results of 26 published epidemiological surveys on the prevalence of contamination of cattle with verocytotoxin-producing E. coli (VTEC) serogroup O157:H7. These surveys have been conducted since 1986 on farms in North America (10 studies), on farms in Europe (6 studies) and at slaughterhouses prior to or just after slaughter (7 studies) or after skinning and evisceration (3 studies). The purpose of this review is to understand the first stages of the epidemiology of the infection in animals and humans (the infection process being obscure in many points) and to prepare herd-based control measures to reduce the risk of O157:H7 human infection. The different statistical methods employed in these surveys, as well as the various laboratory screening methods used for detecting positive animals are presented. The observed frequencies of infected animals (animal prevalence) and herds (herd prevalence) are given as a function of localisation, year, type of industry (beef or dairy) and age. From these measured prevalence values, the risk of contamination of ground beef by E. coli O157:H7 in the first stages of the farm-to-fork continuum is assessed. First, we follow the evolution of contamination frequencies from the living animal on-farm to carcasses before transformation. Then, within each set of measurements (i.e., on farm or at slaughterhouse), we identify the effects of the following factors: target population, sampling strategies and laboratory procedures. We argue that the prevalence values inferred from these measurements are very likely underestimated, due to insufficient sampling and not enough sensitive laboratory procedures (one exception being the immunomagnetic bead separation technique). No firm conclusion can be drawn as to the effects of geographical localisation and season. In those surveys, the effect of hygiene level at slaughterhouse on prevalence values is not quantitatively assessed. In addition, there is growing evidence of other sources of E. coli O157:H7 than live cattle in the farm environment, such as feed, water and water-troughs.

Abattoirs↗