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Biomedical subjects

T E Awerbuch

Publications and source records attributed to T E Awerbuch.

10 recordsLinked to original sources
PubMed1992

A comprehensive multiple matrix model representing the life cycle of the tick that transmits the agent of Lyme disease.

An extension of Leslie matrix methodology was developed to describe the life cycle of Ixodes dammini, the tick that transmits the agent of Lyme disease in eastern North America. Thereby, we described the seasonally changing pattern of interactions of the tick with its various hosts in a well-studied site on Nantucket Island, Massachusetts. Particular numerical values representing the site were estimated mainly on the basis of published values and interpreted on the basis of experience. The model was used to predict seasonal abundance and annual rate of increase of this vector tick. Although these ticks quest for hosts during two consecutive feeding seasons, all but a few feed during the first such season. The relative distribution of developmental stages of the tick stabilized after 35 years. Abundance of the simulated population increased exponentially and doubled every 6 years. The simulations produced realistic seasonal feeding distributions of the ticks in its various developmental stages.

Animals↗
PubMed1992

It takes two to tango but one to infect (on the underestimation of the calculated risk for infection with HIV in sexual encounters, arising from nondisclosure of previous risk behavior or seropositivity).

The effects of nondisclosure of either HIV seropositivity or previous engagement in risk behavior on the estimation of risk in sexual intercourse is studied through the use of a probability model. Equations are utilized to derive an Underestimation Factor for three cases, which is shown to range from 2 to 20 in the case of insertive anal intercourse between an HIV+ and an HIV- man, and to 1 x 10(4) in a similar case of heterosexual insertive vaginal intercourse. This factor remains constant regardless of the number of sexual encounters between the same partners, and regardless of the protective measures as long as unawareness prevails. The discussion focuses on the implications of this formulation for education and social attitudes toward disclosure and nondisclosure in sexual encounters. It also raises the question of moral responsibility of sexual partners and some legal aspects of nondisclosure.

Attitude to Health↗
PubMed1989

Mathematical formulation and studies of the risk parameters involved in HIV transmission.

The probability of becoming infected with HIV is formulated in terms of the total number of sexual contacts (N), the probability that a sexual act is infectious (r) and the prevalence (p). Using the appropriate equations we studied the effect of reducing each of the risk factors on lowering the probability of infection. We show that for many realistic situations the probability of becoming infected by multiple partners is equal to the probability of becoming infected by one partner in a monogamous relationship given that the prevalence is the same in both cases; however if the multiple partners are chosen over time from a pool of a growing prevalence, then one is better off in a monogamous relationship where that partner is chosen early in the epidemic.

Acquired Immunodeficiency Syndrome↗
PubMed1987

A mathematical model for determining minimal inhibitory concentrations (MICs) via diffusion assays.

A mathematical model is presented for the description of inhibition zones in a diffusion bioassay. In such an experiment the drug is placed at the center of a Petri dish containing a bacterial lawn in an agar gel and after a certain incubation period one observes a concentric ring around the center marking the toxic area. From the knowledge of the radius rtox of the toxic zone, the lower limit ctox at which the inhibitory response is observed can be readily calculated. This quantity is very important in evaluating the sensitivity of microorganisms to toxic substances. The mathematical model of the assay is given by a two-dimensional diffusion equation describing the changes in drug concentration due to diffusion, decay of the chemical and consumption by bacteria. The diffusion equation being mildly non-linear is solved numerically with the aid of a computer. For this purpose a numerical solver was developed as well as a "best-fit" simulation program that fits the parameters for which experimental values could not be obtained. The method was tested with N-methyl-N'-nitro-N-nitrosoguanidine and ethylmethanesulfonate and was seen to be fast, efficient, and inexpensive. In principle it could be used for routine quantitative screening for toxicity of chemicals.

Diffusion↗
PubMed1987

A program which determines mutagenic concentrations of chemical carcinogens via a diffusion bioassay.

A computer program implementing a mathematical model for determining mutagenic concentrations of chemical carcinogens was developed. The mathematical model describes the experiment in which a droplet of a suspected carcinogen is put at the center of a petri dish containing a bacterial lawn in an agar gel. After a period of incubation during which the chemical diffuses outward, one observes a concentric ring of mutants around the center. The largest radius at which mutation occurs, r mut, corresponds to the lowest (threshold) concentration of the chemical sufficient to produce bacterial mutation. Given a series of initial concentrations of a chemical and the resulting r mut's, the program computes and reports the threshold concentration and the decay time of the chemical. The program is also used as a method to determine the lowest mutagenic concentration for a particular time of exposure.

Diffusion↗
PubMed1983

The effect of different genetic properties of Salmonella typhimurium on the determination of stabilities and mutagenic concentrations of chemical carcinogens using the diffusion bioassay.

The mathematical model used to calculate half-life and mutagenic concentrations of chemical carcinogens from the diffusion bioassay does not include any terms related to the nature of the microorganism used in the assay (Awerbuch et al., 1979; Awerbuch and Sinskey, 1980). In this work we tested the model with different strains of Salmonella typhimurium. These strains are auxotrophs for histidine and are sensitive to base-pair substitution. The half-life (tau 1/2) of N-methylN'-nitro-N-nitrosoguanidine (NG) was calculated by the diffusion assay, using strains hisG46, TA1950, TA1535 and TA100 as the bacterial indicators. For all strains tau 1/2 equalled 2.2 h; strain sensitivity for detecting threshold mutagenic concentrations of NG was essentially the same, except that hisG46 was slightly more sensitive.

Biological Assay↗
PubMed1980

Quantitative determination of half-lifetimes and mutagenic concentrations of chemical carcinogens using a diffusion bioassay.

It is possible to deduce quantitative information about the mutagenic concentrations of direct carcinogens and procarcinogens from the well-known experiment in which a droplet of a chemical is put at the center of a petri dish containing a bacterial lawn in an agar gel. The model employed relates the mutagenic action to the space-time concentration profile of the diffusing substances. The range of mutagenic concentrations, in particular the lower limit Cmut, at which mutations occur, can be calculated from knowledge of the radii of the mutagenic zone. The only parameters necessary for the calculation of Cmut are the diffusion coefficient, D, which can be calculated, and the half-lifetime of the mutagenic substance, tau 1/2, which can be obtained from the diffusion experiments. The system was tested with N-methyl-N'-nitro-N-nitrosoguanidine (NG), N-methyl-N-nitrosourea (MNU), ethyl methanesulfonate (EMS), and acetoxydimethylnitrosoamine (AcDMN), which are direct carcinogens, and with nitrosomorpholine (NM) and nitrosopyrrolidine (NP), which are procarcinogens. As a consistency check, homogeneous experiments (dose-response curves) at low concentrations of the chemicals were also conducted. However, the statistical analysis of the results showed that the homogeneous assay is not adequate for determining threshold concentrations. Using the concept of the threshold to rank the tested chemicals according to mutagenic potency, the ranking is: NG greater than NP greater than MNU greater than AcDMN greater than EMS.

Carcinogens↗
PubMed1979

Plate diffusion assay as a rapid method for dosimetry of mutagens.

This paper presents a method for determining mutagenic concentrations of chemicals by using an agar diffusion assay. The method is based on the linear relationship between the amount of chemical placed at the center of the dish and the radius of the mutagenic zone. A brief theoretical discussion and experimental data confirming this relationship are given. Alkylating agents and mycotoxins were used to test the system. This method can be used to follow up decreased mutagenic potencies of solutions of unstable mutagens and to follow the production of mutagenic substances throughout fermentation.

Biological Assay↗