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M Artzrouni

Publications and source records attributed to M Artzrouni.

16 recordsLinked to original sources
PubMed2003

Estimating tsetse population parameters: application of a mathematical model with density-dependence.

A density-dependent model is used to describe the dynamics of an open population of tsetse flies (Diptera: Glossinidae). Immigration (or emigration) takes place when the total population is below (or above) a biologically determined threshold value. The population is also subjected to birth and death rates, as well as to the risk of being trapped (continuously or intermittently). During trapping the population decreases toward a 'low' equilibrium population and when trapping ceases the population starts recovering and increases toward a 'high' equilibrium. The model is fitted using data collected on trapped flies in four experiments. The first one was conducted with 'intermittent trapping' (i.e. several trapping-recovery cycles) on Glossina fuscipes fuscipes Newstead in the Central African Republic (Bangui area). In the other experiments, trapping data on Glossina palpalis palpalis (Robineau-Desvoidy) was collected in 'aggregate' form over several days at a time. Two of these were in Congo-Brazzaville (Bouenza area) and one in the Ivory Coast (Vavoua focus). Estimates are derived for the low and high equilibrium values as well as the trapping rate. The estimated effect of sustained trapping is to reduce the population to low equilibrium values that are 85-87% lower than the levels without trapping. The effects of the natural intrinsic growth and of the migration flows cannot be estimated separately because in the model they are mathematically indistinguishable.

Animal Migration↗
PubMed2001

A density-dependent model with reinvasion for estimating tsetse fly populations (Diptera: Glossinidae) through trapping.

A simple density-dependent reinvasion model is described and used to estimate tsetse fly populations on the basis of removal trapping experiments. The model was tested on Glossina fuscipes fuscipes Newstead in the Central African Republic and G. palpalis palpalis (Robineau-Desvoidy) in the Republic of Congo (Brazzaville). The density-dependence is modelled by postulating that the inflow of flies each day is proportional to the deficit relative to the equilibrium population. Non-linear least square techniques were used to estimate the following parameters: the daily capture rate, the strength of the density-dependence, and the equilibrium fly population, at the beginning and at the end of the trapping experiment. The model ignores birth and death rates of flies and is applicable only when a rapid decrease in population occurs over a short period (between 10 and 20 days). Over longer periods one could not ignore the natural growth of the populations as well as other more complex density-dependent mechanisms.

Animals↗
PubMed2001

A model of Gambian sleeping sickness with open vector populations.

A compartmental model of Gambian sleeping sickness is described that takes into account density-dependent migratory flows of infected flies. Equilibrium and stability theorems are given which show that with a basic reproduction number R0 below unity, then in the absence of reinvasion the disease goes to extinction. However, even a low prevalence rate among reinvading flies can then bring about significant equilibrium prevalence rates among humans. For a set of realistic parameter values we show that even in the case of a virulent parasite that keeps infected individuals in the first stage for as little as 4 or 8 months (durations for which there would be extinction with no infected reinvading flies) there is a prevalence rate in the range 13.0-36.9%, depending on whether 1 or 2% of reinvading flies are infected. A rate of convergence of the population dynamics is introduced and is interpreted in terms of a halving time of the infected population. It is argued that the persistence and/or extension of Gambian sleeping sickness foci could be due either to a continuous reinvasion of infected flies or to slow dynamics.

Animals↗
PubMed2000

[Persistence and resurgence of sleeping sickness caused by Trypanosoma brucei gambiense in historic foci. Biomathematical approach of an epidemiologic enigma].

Since the end of the 19th century, historic endemic foci of Trypanosoma brucei gambiense sleeping sickness have proven very persistent. A five-compartment mathematical model with open vector populations was developed in order to study the dynamics of this disease in Central Africa. Of particular interest is the rate at which the disease spreads or goes to extinction at the beginning of an epidemic outbreak. A measure of this rate is the initial halving/doubling time T(o) of the numbers infected; T(o) is a doubling time when the basic reproduction number Ro > 1 and a halving time when Ro < 1. For realistic parameter values, T(o) can be quite large (i.e. several years or even decades) which corresponds to a persistent low-level endemic brought about by an Ro either just above 1 (slow spread) or just below 1 (slow extinction). A resurgence of historical foci can then be caused by a small shift in parameter values that brings Ro well above 1 and decreases T(o). In addition, when Ro is less than 1 (in the absence of vector migrations), simulations show that a very small percentage of infected immigrant flies can bring about high prevalence rates in the human population. The model is validated with field data from historical Congolese, Central and West African foci of the past.

Africa, Central↗
PubMed1998

A two-patch model of Gambian sleeping sickness: application to vector control strategies in a village and plantations.

A compartmental model is described for the spread of Gambian sleeping sickness in a spatially heterogeneous environment in which vector and human populations migrate between two "patches": the village and the plantations. The number of equilibrium points depends on two "summary parameters": gr the proportion removed among human infections, and R0, the basic reproduction number. The origin is stable for R0 < 1 and unstable for R0 > 1. Control strategies are assessed by studying the mix of vector control between the two patches that bring R0 below 1. The results demonstrate the importance of vector control in the plantations. For example if 20 percent of flies are in the village and the blood meal rate in the village is 10 percent, then a 20 percent added vector mortality in the village must be combined with a 9 percent added mortality in the plantations in order to bring R0 below 1. The results are quite insensitive to the blood meal rate in the village. Optimal strategies (that minimize the total number of flies trapped in both patches) are briefly discussed.

Communicable Disease Control↗
PubMed1996

Control strategies for sleeping sickness in Central Africa: a model-based approach.

Vector control and the detection (followed by treatment) of infected individuals are the two methods currently available for the control of sleeping sickness. The basic reproduction rate of a compartmental model is used to analyse and compare the two strategies. The efficiency of each strategy will depend on two epidemiologic parameters; the intrinsic contamination rate Q (closely related to the index of new contaminations) that captures the potential spread of the disease, and the intrinsic removal rate from the first stage (intrinsic to the particular trypanosome strain and to the population's susceptibility). The model shows that when the intrinsic removal rate is low (that is, when there is a long first stage characteristic of an endemic situation) the detection of sick individuals is more efficient than vector control. The situation is reversed when the removal rate is high (in an epidemic situation). The conclusions of the analysis are shown to be in general agreement with results obtained in two different sleeping sickness foci of Central Africa.

Africa, Central↗
PubMed1996

[Is vector control needed in the fight against sleeping sickness? A biomathematical approach].

Vector control and the detection (followed by treatment) of infected individual are the two methods currently available for the control of sleeping sickness. The basic reproduction rate of a compartmental model (Kermack and McKendrick) is used to analyze and compare the two strategies. The model shows that when there is a long first stage characteristic of an endemic situation, the detection of sick individuals is more efficient than vector control. This higher efficiency of detection decreases in a epidemic situation. In this case vector control in the form of a decrease in vector density and/or an increase in vector mortality is relatively more efficient than detection. Because it is squared in the basic reproduction rate, the probability of a tsetse blood meal on humans is an important and sensitive parameter in the study of control strategies. This sensitivity has been observed previously and empirically by field workers. When the probability of a tsetse blood meal on humans is above a certain value, vector control becomes warranted or even necessary.

Animals↗
PubMed1992

A modeled time-varying density function for the incubation period of AIDS.

Building on the Weibull distribution, we develop a modeled time-varying density function of the incubation time between exposure to HIV infection and full-blown AIDS. This approach leads to a series of cohort-specific density functions that take into account the increasing impact of new therapies such as zidovudine (AZT). The resulting modeled density functions are studied in detail, particularly with regard to their modes and medians. The mode is sensitive to changes in the period incubation time distribution, with even a possibility of a bimodal distribution for certain combinations of the parameters that determine the rate at which the period median incubation time changes. An important substantive result is that when a period median incubation period slowly increases to some leveling off value, say m(xc), then it is surprisingly early on that cohorts of infected individuals have a median incubation period very close to that ultimate value m(xc).

Acquired Immunodeficiency Syndrome↗
PubMed1990

Projections of the HIV/AIDS epidemic for homosexual/bisexual men in France, the Federal Republic of Germany and the United Kingdom.

Projections of the spread of the acquired immunodeficiency syndrome (AIDS) and of its etiologic agent, the human immunodeficiency virus (HIV), are presented for homosexual/bisexual men in the three European countries with the largest caseloads. The results suggest that the HIV epidemic for French, German, and British homosexual/bisexual men has peaked around 1985 and declined rapidly thereafter. By the end of the century, and for a median incubation period of AIDS equal to 8 years, the total numbers infected in these groups are predicted to be about 31,200, 10,400 and 9,800, respectively. (These estimates more than double if the median incubation period is 12 years). In all cases the annual incidence of AIDS will reach its maximum in the early to mid-1990s. However, the AIDS epidemic will be protracted because of the long incubation period.

Acquired Immunodeficiency Syndrome↗
PubMed1990

On transient effects in the HIV/AIDS epidemic.

During the initially exponential spread of the human immunodeficiency virus (HIV--the causative agent of AIDS) the growth rate of the number of AIDS cases decreased from plus infinity to the growth rate of HIV infections. A sensitivity analysis shows that for all reasonable values of the parameters of the HIV epidemic (incubation period, initial doubling time, etc.) the effect of this positive transient becomes negligible when the annual number of AIDS cases reaches a few dozen. Necessary and sufficient conditions are given for the growth rate of the number of AIDS cases to be monotonically decreasing during the positive transient. A mildly pathological density function for the incubation period of AIDS provides an example of a growth rate of AIDS that does not decrease monotonically, even though HIV is spreading exponentially. A negative transient occurs when the growth rate of HIV begins to decrease. In this context a somewhat surprising result emerges under the assumption that the growth rate of HIV is non-increasing: the growth rate of AIDS is at all times larger than the growth rate of HIV. A logistic HIV epidemic illustrates this result, and implications for the growth of the HIV epidemic in the United States and Europe are discussed. In particular, it is shown that the positive transient must have passed by 1982 in the United States and by 1986 or 1987 for the five European countries with the largest caseloads.

Acquired Immunodeficiency Syndrome↗
PubMed1990

Mathematical investigations of the escape from the Malthusian trap.

"We present a simulation model that synthesizes Malthusian and Boserupian notions of the way population growth and economic development were intertwined. The non-linear stochastic model consists of a system of equations whose dynamics culminate in an industrial revolution after hundreds of iterations. The Industrial Revolution [in Europe] can thus be conceptualized as a permanent 'escape' from the Malthusian trap that occurs once the economy is capable of permanently sustaining an ever growing population. We investigate the conditions for such an escape and their sensitivity to the parameters of the model.... Our results show that the likelihood of an escape is sensitive to the savings rate and to the output elasticities of the two sectors of the economy. When not in a subsistence crisis, the chances that an escape will occur increase for larger values of the ratio of the savings rate to the growth rate of the population. The chances of an escape also increase substantially for larger values of the output elasticities of labor." (SUMMARY IN FRE)

Demography↗
PubMed1988

Contact tracing to identify human immunodeficiency virus infection in a rural community.

This report describes a contact investigation conducted in rural South Carolina to identify, counsel, and educate persons infected with or exposed to the human immunodeficiency virus (HIV). Starting with one HIV antibody-positive man and his 19 sex contacts, we identified 83 sex contacts of HIV antibody-positive men. Of these, 64 were residents of the county and 63 (98%) agreed to be tested for evidence of HIV infection. Eight (13%) were HIV antibody positive. Thirty-six initially HIV antibody-negative men were reevaluated at a six-month follow-up visit, and three had seroconverted during this time. Of 25 men who reported practicing anal receptive intercourse, 13 (52%) were HIV antibody positive vs none of 43 men who reported strictly anal insertive intercourse. Comparing reported numbers of sexual contacts for the six-month periods before and after our initial investigation, the mean numbers of named sex contacts decreased by 82% for antibody-positive men and 54% for antibody-negative men. None of the men reported using condoms before entering the study; at the six-month follow-up visit, four (80%) of five of the antibody-positive men and 25 (69%) of 36 of the antibody-negative men reported using condoms at least some of the time.

Acquired Immunodeficiency Syndrome↗
PubMed1986

The rate of convergence of a generalized stable population.

In an age-structured population that grows exponentially, each age group pi(t) at period t is asymptotically equivalent to x0t for some positive number x0. In this paper we show that the speed at which the ith age group reaches its exponential state of equilibrium can be measured by the rate at which the ratio vi(t) = pi(t)/pi(t-1) converges to x0. The age specific rate of convergence is determined by considering a quantity r satisfying [vi(t)-x0] less than or equal to rt when t is large; Ri = Inf r (over all initial populations, r satisfying the above inequality) is the R-factor used in numerical analysis to measure the rate at which the sequence vi(t) converges to x0; Si = -1n Ri is then defined as the rate of convergence to stability of the ith age group. The case of constant net maternity rates is studied in detail; in this context S0 is compared to the population entropy H, which was proposed by Tuljapurkar (1982) as a measure of the rate of convergence to stability.

Age Factors↗
PubMed1985

Generalized stable population theory.

In generalizing stable population theory we give sufficient, then necessary conditions under which a population subject to time dependent vital rates reaches an asymptotic stable exponential equilibrium (as if mortality and fertility were constant). If chi 0 (t) is the positive solution of the characteristic equation associated with the linear birth process at time t, then rapid convergence of chi 0 (t) to chi 0 and convergence of mortality rates produce a stable exponential equilibrium with asymptotic growth rate chi 0-1. Convergence of chi 0 (t) to chi 0 and convergence of mortality rates are necessary. Therefore the two sets of conditions are very close. Various implications of these results are discussed and a conjecture is made in the continuous case.

Age Factors↗
PubMedDate not supplied

Population growth through history and the escape from the Malthusian trap: a homeostatic simulation model.

"A Malthusian simulation model is proposed to describe the growth of human population from the Neolithic through the Industrial Revolution. The economy is composed of a subsistence sector and a capital-producing sector. Our model captures the 'incessant contest' between population growth and the means of subsistence. When the per capita agricultural output falls below a biological minimum, the growth rate of the population is subject, in a random fashion, to perturbations that can take on disastrous proportions." It is suggested that "the slow accumulation of capital (and the buildup of the population of the capital-producing sector) eventually enables the population to overcome the constraints of the hostile economic environment. Our simulations (complete with confidence intervals) yield numerically realistic estimates of the population that eventually escapes from the Malthusian menace and grows unhindered during the Industrial Revolution." (summary in FRE, ITA)

Conservation of Natural Resources↗