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Results for “Basic Reproduction Number”

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PubMed1966

Use of oral contraception in the United States, 1965. In only 5 years oral contraception has become a major means of regulating fertility.

This is the first report from the Na-tional Fertility Study, 1965, a survey of the reproductive behavior of a national sample of married women, under the age of 55, living with their husbands. The report presents basic data on the use of oral contraception by women under the age of 45, in relation to age, parity, education, race, and religion. The study leads to certain conclusions, as follows. Present, past, and prospective use vary inversely with the age of the woman and directly with the number of years of schooling; the majority of young women with college training have already used the oral contraceptive. Use by Negroes is somewhat less extensive than use by whites, particularly for ages below 25; some of this difference is explainable by concomitant racial differences in educational level. Negroes seem less likely than whites to use oral contraception for timing early births, and more likely, when they do use it, to be attempting to terminate their fertility. The same observation holds for white Catholics in relation to white non-Catholics. Although the extent of use may be lower among Catholics than non-Catholics, the proportion of Catholics who report use is substantial indeed in view of the persisting theological controversy. The prospects for increased use of oral contraception seem very good at present, but they may be limited by further developments in the technology of fertility regulation. Meanwhile the birth rate has declined substantially. Although much sophisticated analysis of other data from the survey will be required to determine the extent of the contribution of oral contraception to this decline, the findings presented here suggest that the contribution is substantial for young married couples. The major effect on the couple's eventual number of children may be less than the effect on the time pattern of childbearing; in any event, both lower eventual parity and delayed fertility contribute to a decline in the numbers of births from year to year. Whatever the intent may be, it is apparent that young American couples have adopted a new means for achieving their reproductive goals.

Adolescent↗

PubMed2003

Neighbourhood control policies and the spread of infectious diseases.

We present a model of a control programme for a disease outbreak in a population of livestock holdings. Control is achieved by culling infectious holdings when they are discovered and by the pre-emptive culling of livestock on holdings deemed to be at enhanced risk of infection. Because the pre-emptive control programme cannot directly identify exposed holdings, its implementation will result in the removal of both infected and uninfected holdings. This leads to a fundamental trade-off: increased levels of control produce a greater reduction in transmission by removing more exposed holdings, but increase the number of uninfected holdings culled. We derive an expression for the total number of holdings culled during the course of an outbreak and demonstrate that there is an optimal control policy, which minimizes this loss. Using a metapopulation model to incorporate local clustering of infection, we examine a neighbourhood control programme in a locally spreading outbreak. We find that there is an optimal level of control, which increases with increasing basic reproduction ratio, R(0); moreover, implementation of control may be optimal even when R(0) < 1. The total loss to the population is relatively insensitive to the level of control as it increases beyond the optimal level, suggesting that over-control is a safer policy than under-control.

Animals↗

PubMed2002

Paying for reproductive health services in Bangladesh: intersections between cost, quality and culture.

In 1997 a consortium of non-governmental organizations (NGOs) in Bangladesh began to implement health sector reform measures intended to expand access to and improve the quality of family planning and other basic health services. The new service delivery model entails higher costs for clients and requires that they take greater initiative. Clients have to travel further to get certain services, and they have to pay more for them than they did under the previous door-to-door family planning model. This paper is based on findings from a qualitative study looking at client and community reactions to the programme changes. It examines a number of barriers to access and constraints to cost recovery, including gender, class and ideas about entitlements, the role of government and obligations among people. The NGOs want to maximize cost recovery while making the basic services they offer accessible to most people. The findings suggest that this requires more than the establishment of an appropriate pricing structure. Attitudes related to charging and paying for services must also change, along with the institutional policies and practices that support them.

Attitude to Health↗

PubMed2005

The evolution of reproductive systems and sex-determining mechanisms within rumex (polygonaceae) inferred from nuclear and chloroplastidial sequence data.

The genus Rumex includes hermaphroditic, polygamous, gynodioecious, monoecious, and dioecious species, with the dioecious species being represented by different sex-determining mechanisms and sex-chromosome systems. Therefore, this genus represents an exceptional case study to test several hypotheses concerning the evolution of both mating systems and the genetic control of sex determination in plants. Here, we compare nuclear intergenic transcribed spacers and chloroplast intergenic sequences of 31 species of Rumex. Our phylogenetic analysis supports a systematic classification of the genus, which differs from that currently accepted. In contrast to the current view, this new phylogeny suggests a common origin for all Eurasian and American dioecious species of Rumex, with gynodioecy as an intermediate state on the way to dioecy. Our results support the contention that sex determination based on the balance between the number of X chromosomes and the number of autosomes (X/A balance) has evolved secondarily from male-determining Y mechanisms and that multiple sex-chromosome systems, XX/XY1Y2, were derived twice from an XX/XY system. The resulting phylogeny is consistent with a classification of Rumex species according to their basic chromosome number, implying that the evolution of Rumex species might have followed a process of chromosomal reduction from x = 10 toward x = 7 through intermediate stages (x = 9 and x = 8).

Base Sequence↗

PubMed1997

[Reconstruction of an ancient Egytian mouth-opening device. As early as 5000 years ago artificial respiration was basically possible].

Reproduction of an ancient Egyptian mouth-opening device raises certain technological and historical questions. The most effective variation has proven to be a device made of strip iron built exactly according to the proportions given in the Hunefer papyrus. This device allows quick and safe intubation of intubation dummy CLA 8 without a supplementary light source. Originally, the device was a metal instrument made of meteoric iron, apparently produced only in small numbers. To data, the form of production remains a mystery, since the smelting and processing of iron was totally uncommon in ancient Egypt. Based on the material structure of the device and certain portrayals in graves in Deir el-Medina, mouth-opening as it was actually performed reveals a methodology that can be reconciled with modern pre-clinical polytrauma management. In principle, this indicates that the introduction of artificial respiration thousands of years ago would have been possible.

Egypt, Ancient↗

PubMed2002

[Reforms and demographic crisis].

During reformation years all basic medical and demographic indices have undergone negative changes in Russia. Since 1992 there has been a steady-state decrease in the population due to the fact that mortality rates are extremely greater than birth ones. In 2001, the Russian population reduced in number by nearly a million. The birth rates are twice less than that requires for a simple reproduction of generations. Extremely high death rates remain among the population, in able-bodied males. The main reasons for the demographic crisis are the negative consequences of the implemented reforms rather than the transition from traditional to the new present-day reproduction of the population. It is problematic now to correct the situation via active migration of Russian-speaking persons. This requires enormous funds to provide comers with jobs and dwelling. It is unreal to diminish annual departure of 100 thousand persons, mainly young educated professionals from the country, though it is joust not only a demographic, but a strategic problem. In 2001 there was a some rise in birth rates. But this is the most illusive way of solving the demographic crisis. Just in the USSR, the high educational level of the population, the socioeconomic emancipation of females and progress in medicine gave rise to the transition to the present-day reproduction of the population, which is characterized by low birth and death rates. So the population is unlikely to be replenished by high birth rates. The main way of overcoming the demographic crisis is to reduce mortality and not to allow young people to die prematurely. For this it is necessary to know the biological mechanisms responsible for extremely high mortality. It is most likely to be due to breakdown in the dynamic stereotype of higher nervous performance, as stated by I. P. Pavlov. Today it is insufficient to control alcoholism, traumatism, and smoking by healthy lifestyle propaganda in order to reduce death rates in Russian. All these disasters took place after the Great Patriotic War, but an aspiration for long and happy life was prevalent in the consciousness of the people who has won the war. At present, neither the whole able-bodied population nor all young people have an internal aim at living long. To overcome this tragic gap in the consciousness requires primarily a great working motivation.

Attitude to Health↗

PubMed1976

Cytologic features of oocytes in the adult human ovary.

A broad survey of the cytologic features of follicular oocytes from sections of adult ovaries from donors with normal menstrual cycles, from patients with polycystic ovarian disease, and from patients treated with estrogen and progesterone for gynecologic disorders with no apparent ovarian pathology has been made in this study. On the basis of light microscopic observations, four basic types of oocytes could be recognized: (1) oocytes with nuclei containing diffused or filamentous chromatin, (2) oocytes with metaphase I chromosomes or an extruded polar body, (3) oocytes with nuclei possessing massive clumps of chromatin frequently associated with the nucleolus, and (4) degenerating oocytes with no distinguishing cytologic features. The numbers of oocytes in these different groups varied with the reproductive state of the donors: 34 to 35% were type 1 during proliferative and secretory phases; mature oocytes type 2 were 3.3%, and were found only during the late proliferative phase; and 41 to 46% were type 3 during both phases of the menstrucal cycle. Large numbers of oocytes from polycystic ovaries (77%) and from ovaries of patients treated with steroids (86%) were degenerating and frequently contained massive clumps of chromatin material associated with the nucleolus.

Adult↗

PubMedDate not supplied

[Pregnancy, labor, and puerperium: concepts and practices of midwives in the state of Morelos].

In Mexico a combined type of care for the health-sickness phenomenon exists, where three systems interact: domestic, academic and traditional medicine. In relation to reproductive health, in the state of Morelos approximately 50 per cent of women in rural areas receive attention from traditional birth attendants, who make up one of the principal resources of traditional medicine. The goal of this study was to gather knowledge about and describe the concepts, resources and practices used by traditional birth attendants in their care during pregnancy, birth and puerperium; and likewise to determine their socio-demographic characteristics, their geographic distribution, their number and the level of training which they possess. A census based on three sources was carried out in which information about seven basic variables was sought. This information was completed with structured interviews with key informants which allowed the definition of a profile of the different types of traditional birth attendants according to the population they care for and the resources they use. The most relevant results indicate that 630 traditional birth attendants are distributed throughout the 32 municipalities of the state, with an average age of 52 years and 50 per cent having attended training courses. 17.5 per cent fall within the category of traditional birth attendant, 50 per cent are trained empiricists and 11.6 per cent are non-trained empiricists. The 20 per cent did not fit this typology. The strong social and cultural identification that exists between traditional birth attendants and their patients indicates the need to incorporate this valuable resource in rural reproductive health programs.

Adult↗

PubMed1999

[Assisted reproduction--present status and perspectives].

OBJECTIVE: To review the current status and new trends in assisted reproduction. DESIGN: The literature on intrauterine insemination, IVF, ICSI, MESA/TESE, preimplantation genetic diagnosis, cryopreservation, in vitro maturation, cloning and stem cells. SETTING: Assisted Reproduction Centre, Ist Medical Faculty of Charles University Prague and General Hospital Prague, Apolinárská 18, 128,00, Prague 2, Czech Republic. RESULTS: IUI, IVF, ICSI also in combination with MESA/TESE are widely used relatively high effective procedures. According to Czech Republic Assisted Reproduction Registry, the pregnancy rate per transfer using IVF, ICSI is 25%, 30% respectively. Cryopreservation of sperm and embryos is a basic part of assisted reproduction, the result with oocytes freezing are still not satisfactory. Preimplantation genetic diagnosis is performed in few countries only due to technical barriers and ethical restrictions. Other methods like cloning, nuclear transfer, embryotherapy or gene manipulation using embryonic stem cells are still only subjects of research. CONCLUSION: During the last ten years, assisted reproduction showed rapid development in a number of treated couples and the spectrum of used methods changed radically.

Czech Republic↗

PubMed2005

Walter Elsasser, prophet of biological complexity, seeker of simplifying rules.

Walter Elsasser was an eminent theoretical physicist who devoted much of his spare time for over half a century (approximately 1935-1987) to the development of a holistic theory of organisms. The three basic principles of his biological theory are a) order in the large which dominates heterogeneity in the small; b) creative selection of the relatively small number of cells and organisms in nature as compared with the immense number of potential molecular states allowed by quantum mechanics, based on the number of atoms, molecules and chemical bonds in a cell, and c) holistic memory in reproduction of cells and organisms, a process which is supplementary to, and fundamentally different in type from the information stored in DNA. His ideas have either been coolly received or ignored by biologists, at least partly because of their purely formal character, although that is considered the sine qua non for theories in physical science. I cite a variety of experiments at the cellular level that illustrate his principles. Those experiments add a concrete dimension to his abstractions that hopefully will promote a dialog between theory and practice to facilitate development of a non-reductionist biology.

Animals↗

PubMedDate not supplied

[The validity of "number repetition" in the aged].

The subtest Digit Span (Wechsler, 1945) is revealed as a frequently applied, standardized test procedure in the assessment of memory in the aged. A lot of studies show high degrees of age-dependence of the Digit Span task. Visually presented digits lead to a more distinct age-decline in reproduction. Practise effects can be observed even in old subjects with pathological symptoms. The hypothesis that the Digit Span score represents a basic intellectual function, which constitutes a prior condition for different other intellectual areas, is rejected. Memory span measured by the Digit Span task represents an independent component of cognitive functioning in old age. The Digit backwards task includes encoding procedures, which are not necessary for the Digit forwards task. A major problem in memory span research is that there are only a few longitudinal studies, which are concerned with this topic and enable conclusions for the underlying processes of a declining capacity of the short-term memory.

Aged↗

PubMed2006

Subthreshold and superthreshold coexistence of pathogen variants: the impact of host age-structure.

It is well known that in the most general epidemic models with multiple pathogen variants a competitive exclusion principle is valid, such that the variant with the highest reproduction number eliminates the rest. Mechanisms such as super-infection, coinfection, and cross-immunity can lead to pathogen polymorphism where multiple strains coexist. It is also known that variability of infectivity with host age can destabilize the endemic equilibrium and cause oscillations. In this article we show that the hosts' chronological age can itself lead to coexistence of microparasites in the most basic model where competitive exclusion will occur without the age structure. Moreover, the host age-structure leads to multiple subthreshold dominance equilibria, and both weakly and strongly subthreshold coexistence. We find that the two pathogens cannot cooperate to persist subthreshold if neither one of them can persist subthreshold by itself. If, however, one of them can persist subthreshold by itself, it can cause the two pathogens to coexist in a strongly subthreshold equilibrium. The second strain that persists subthreshold through the mediation of the first always has a lower virulence. Our results show that age structure in infectivity can permit the coexistence of competing pathogens when the incidence is of proportionate mixing type (frequency-dependent transmission) and at least one of the strains is virulent.

Age Factors↗

PubMed2001

Activation of follicle development: the primordial follicle.

Investigations of primordial follicle formation and growth are fundamental to our understanding of female gamete production. In all mammalian females the full complement of oocytes is established during fetal development. This store of primordial follicles is not renewable and serves the entire reproductive life span of the adult. The correct programming of fetal ovarian development and the number of primordial follicles formed will therefore limit the fecundity of the ovary. Primordial follicles are characterized by the presence of a single oocyte surrounded by a varying number of pregranulosa cells. The relatively small size, undifferentiated status and large numbers of primordial follicles make them prime candidates for use in basic and applied research in animal production, gene transfer and cloning. Furthermore, the development of cell culture systems that use primordial follicles as a source of oocytes for in vitro growth and maturation will enable us to maximize the potential of high genetic merit females and to shorten generation intervals. Despite these possibilities, primordial follicles are the least understood of all stages of follicle development. The factor(s) responsible for maintaining the primordial pool or, conversely, for activating primordial follicle growth remain elusive.

Animals↗

PubMed2004

Histological organization of roe deer testis throughout the seasonal cycle: variable and constant components of tubular and interstitial compartment.

Seasonally regulated breeding in roe deer, Capreolus capreolus, is associated with significant changes in testis mass, structure and function. This study has quantified seasonal changes of morphometric parameters and cellular composition in roe deer testis parenchyma. Tissue samples were collected bimonthly during a complete annual cycle. Morphometric parameters of seminiferous tubules were measured and the number of different cell types was counted using a computer-aided image-analyzing system. A scheme of eight tubular epithelium stages for active spermatogenesis was devised according to the spermatid development. Stage I is characterized by the occurrence of new round spermatids, stage IV by spermiation and stage VIII by the meiotic division of spermatocytes. The average diameter of seminiferous tubules varied between 88.4+/-3.6 micro m (February) and 216.8+/-9.2 micro m (June). Also numbers of spermatogonia, spermatocytes and spermatids per tubule cross-section showed considerable seasonal changes. In December and February the germinative epithelium mainly consists of Sertoli cells and spermatogonia. In February, the first differentiated spermatogonia enter meiosis, and in April even spermatids occasionally occur, which reach their highest numbers during the rut in August. Both the expansion and the proportion of tubular and interstitial compartment change seasonally and result in differing cell densities. Assuming numerically constant populations of Sertoli cells and interstitial cells during the entire year, the hypothetical cell numbers per mm(2) of the tubular and interstitial areas were calculated for the seasonally variable total areas of tissue cross-sections. The concordance of these theoretical values with measured cell densities provided evidence that the total numbers of Sertoli cells, as well as interstitial cells, remain really constant throughout the seasonal cycle. The exact quantification of variable and constant components provides basic data for characterization of cell type and stage-specific processes of spermatogenesis.

Animals↗

PubMed2000

Modeling and analysis of stochastic invasion processes.

In this paper we derive spatially explicit equations to describe a stochastic invasion process. Parents are assumed to produce a random number of offspring which then disperse according to a spatial redistribution kernel. Equations for population moments, such as expected density and covariance averaged over an ensemble of identical stochastic processes, take the form of deterministic integro-difference equations. These equations describe the spatial spread of population moments as the invasion progresses. We use the second order moments to analyse two basic properties of the invasion. The first property is 'permanence of form' in the correlation structure of the wave. Analysis of the asymptotic form of the invasion wave shows that either (i) the covariance in the leading edge of the wave of invasion asymptotically achieves a permanence of form with a characteristic structure described by an unchanging spatial correlation function, or (ii) the leading edge of the wave has no asymptotic permanence of form with the length scales of spatial correlations continually increasing over time. Which of these two outcomes pertains is governed by a single statistic, phi which depends upon the shape of the dispersal kernel and the net reproductive number. The second property of the invasion is its patchy structure. Patchiness, defined in terms of spatial correlations on separate short (within patch) and long (between patch) spatial scales, is linked to the dispersal kernel. Analysis shows how a leptokurtic dispersal kernel gives rise to patchiness in spread of a population.

Animals↗

PubMed1999

Advanced semen analysis: a simple screening test to predict intrauterine insemination success.

OBJECTIVE: To determine if a simple screening test of sperm recovery through a density gradient preparation and sperm survival after a 24-hour incubation is predictive of IUI success. DESIGN: Prospective nonrandomized descriptive study. SETTING: Tertiary assisted reproductive technology center. PATIENT(S): Four hundred fourteen couples undergoing IUI for male factor and unexplained infertility. INTERVENTION(S): An advanced semen analysis, which consisted of a basic semen analysis, sperm processing through a density gradient preparation, and a 24-hour sperm incubation, was performed on all couples before beginning IUIs. MAIN OUTCOME MEASURE(S): Cumulative and per cycle pregnancy rates (PRs) were calculated for routine semen parameters, number of sperm processed through density gradient, and percent motile sperm after a 24-hour incubation. RESULT(S): None of the basic semen analysis parameters accurately predicted IUI success. When the processed total motile sperm available for insemination was > or = 10 x 10(6) and their 24-hour survival was > or = 70%, 89% (162 of 182) of couples achieved a pregnancy with a 21.4% (162 of 757) per cycle PR compared to a 2.8% (11 of 403) per cycle PR and 4.7% total PR when survival was <70%. With use of these cutoff values for the advanced semen analysis, the test had a sensitivity of 94% and specificity of 86%. CONCLUSION(S): The number of motile sperm available for insemination and especially their 24-hour survival are highly predictive of IUI success. This advanced semen analysis is an excellent screening test to evaluate couples considering IUI.

Cell Survival↗

PubMed1986

The invasion, persistence and spread of infectious diseases within animal and plant communities.

Recent theoretical and empirical studies of the population biology of infectious diseases have helped to improve our understanding of the major factors that influence the three phases of a successful invasion, namely initial establishment, persistence in the longer term and spread to other host communities. Of central importance in all three phases is the magnitude of the basic reproductive rate or transmission potential of the parasite. The value of this parameter is determined by a variety of biological properties of the association between an individual parasite and its host and the interaction between their populations. The recent epidemic of acquired immunodeficiency syndrome (AIDS) in North America and Europe is employed to illustrate the factors that promote disease establishment and spread. The frequency distribution of the number of different sexual partners per unit of time within homosexual communities is shown to be of central importance with respect to future trends in the incidence of AIDS. Broader aspects of pathogen invasion are examined by reference to simple mathematical models of three species associations, which mirror parasite introduction into resident predator-prey, host-parasite and competitive interactions. Many outcomes are possible, depending on the values of the numerous parameters that influence multi-species population interactions. Pathogen invasion is shown to have far-reaching implications for the structure and stability of ecological communities.

Acquired Immunodeficiency Syndrome↗

PubMedDate not supplied

Migration and stability.

"In this endeavor to incorporate net migration in a model of population growth, we have found that when net maternity rates are held constant, birth trajectories can be traced in several examples. We have basically experimented with (a) unchanging age-specific net migration rates and also with (b) constant number of net migrants with unchanging age composition. In most cases, the birth trajectory approaches an exponential pattern of growth with two interesting exceptions. When the intrinsic rate of growth is negative, the population approaches stationarity in the second example. Also a linear trend is found in the same example, when the net reproduction rate is equal to one." (SUMMARY IN FRE AND ITA)

Age Distribution↗