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Results for “Basic Reproduction Number”

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PubMed2006

Sperm motility parameters to evaluate the seminal quality of Boa constrictor occidentalis, a threatened snake species.

Semen quality analysis constitutes a powerful tool to evaluate the fertility potential of males in threatened species. The Argentine boa constrictor or lampalagua (Boa constrictor occidentalis) is a threatened snake species and has been included in Appendix I of CITES. The objective of this work is to characterize the sperm of B. c. occidentalis on the bases of dynamic parameters to improve this species conservation. Dynamic parameters were measured in sperm samples using videomicroscopy and image analysis software. The sperm population showed a high degree of heterogeneity in velocity parameter values and 95% of the cells showed a linear pattern of movement. Studies in other species indicate that the number of motile spermatozoa and their movement speed is directly correlated with fertilization success. This work will help to establish basic parameter values for the evaluation of the reproductive potential of populations of B. c. occidentalis and to resolve questions referred to its reproductive strategies.

Animals↗

PubMed1997

Dynamics of Forest Insect Density: Bifurcation Approach

Six basic phase portraits differing in character and in the number of their equilibrium behaviour regimes were suggested in the classification of forest insect population dynamics. The portraits graphically illustrate six types of dynamic behaviour of numbers of the system "phytophage-entomophage": two types of stable equilibrium dynamics (stationary and oscillatory) and four types corresponding to outbreaks of mass reproduction-fixed, permanent, reversive and true outbreaks, respectively. In this paper we consider the single parameter model, with its parametric domains realizing a wide spectrum of phase dynamics, both basic and transitional. The changes in the phase portraits are accompanied by the bifurcations in the model. The results of these analyses are in agreement with the "stability principle of mobile ecological systems" and may supply its parameter substantiation at the model level. Copyright 1997 Academic Press Limited

Journal Article↗

PubMed2005

A two-generation reproductive toxicity study of 2,4-dichlorophenol in rats.

A two-generation reproductive toxicity study was conducted with 2,4-dichlorophenol (2,4-DCP), an agent suspected of exerting endocrine disrupting effects. Wistar-Hannover rats, 24/sex/group, were given diet containing 2,4-DCP at dose levels of 0, 500, 2000 or 8000 ppm to examine the potential effects of the test substance on parental animals and their offspring over 2 successive generations. Neither clear systemic nor reproductive toxicity of 2,4-DCP was apparent in the 500 ppm group. In the 2000 ppm group, mean body weight gain and food consumption of females were lowered significantly during the treatment period. Effects on body weights and food consumption were more serious in the 8000 ppm group, both males and females being significantly affected. Reproductive effects of the test substance were also observed in the 2000 and 8000 ppm groups dose-dependently. Observations included significantly increased uterine weights of F1 and/or F2 female weanlings and reduced numbers of implantation sites and live births of F1 parental females. These results suggest that 2,4-DCP has weak reproductive toxicity, possibly based on endocrine activity. However, the basic mechanisms for apparent estrogenic effects of 2,4-DCP remain to be elucidated.

Administration, Oral↗

PubMed1981

Social rank and darwinian fitness in a multimale group of Barbary macaques (Macaca sylvana Linnaeus, 1758). Dominance reversals and male reproductive success.

In a 5-year study data were compared on rank and reproductive success of 3 mature males in a group of barbary macaques who had sired 32 infants on 14 females. The results indicate that the absolute number of offspring as well as the proportion of offspring from higher-ranking females is a function of the male's rank. Asymmetrical access to receptive females was produced by either a high basic rank or by the formation of a coalition, or both of these, which resulted in at least partial exclusion of competitors from reproduction. Rank reversals in basic rank was preceded by severe fights between the opponents involving deep wounds or loss of canine teeth. When such fights occurred they reaped benefits in each case for the challenger, which were measurable in terms of reproductive success.

Animals↗

PubMedDate not supplied

Birds as long-lived animal models for the study of aging.

Despite their high lifetime energy expenditures, most birds can be characterized as long-lived homeotherms with moderately slow aging. A growing body of research confirms the prediction that birds have special adaptations for preventing aging-related oxidative and glycoxidative damage. Nonetheless, biogerontologists have been slow to develop avian laboratory models. A number of domestic poultry and cage bird species represent either established or very promising animal models for studies of basic aging processes and their prevention, including degenerative neurobiological, behavioral and reproductive processes. Several kinds of birds have also been used in studies of cellular resistance to oxidative stressors in vitro. Results of preliminary studies on chickens and quail suggest that caloric restriction may extend the reproductive life span of hens, but its long-term effects on life span remain unstudied. Birds' innate anti-aging mechanisms may actually make them more suitable in some respects as models of longevity than short-lived laboratory rodents, and bird studies may ultimately reveal routes for therapeutic intervention in diseases of human aging and infertility.

Aging↗

PubMed2006

Evolution of pathogens towards low R0 in heterogeneous populations.

Maximization of the basic reproduction ratio or R(0) is widely believed to drive the emergence of novel pathogens. The presence of exploitable heterogeneities in a population, such as high variance in the number of potentially infectious contacts, increases R(0) and thus pathogens that can exploit heterogeneities in the contact structure have an advantage over those that do not. However, exploitation of heterogeneities results in a more rapid depletion of the potentially susceptible neighbourhood for an infected host. Here a simple model of pathogen evolution in a heterogeneous environment is developed and placed in the context of HIV transmission. In this model, it is shown that pathogens may evolve towards lower R(0), even if this results in pathogen extinction. For sufficiently high transmissibility, two locally stable strategies exist for an evolving pathogen, one that exploits heterogeneities and results in higher R(0), and one that does not, and results in lower R(0). While the low R(0) strategy is never evolutionarily stable, invading strains with higher R(0) will also converge to the low R(0) strategy if not sufficiently different from the resident strain. Heterogenous transmission is increasingly recognized as fundamental to epidemiological dynamics and the evolution of pathogens; here, it is shown that the ability to exploit heterogeneity is a strategy that can itself evolve.

Disease Outbreaks↗

PubMed1999

The evolutionary biology and population genetics underlying fungal strain typing.

Strain typing of medically important fungi and fungal population genetics have been stimulated by new methods of tapping DNA variation. The aim of this contribution is to show how awareness of fungal population genetics can increase the utility of strain typing to better serve the interests of medical mycology. Knowing two basic features of fungal population biology, the mode of reproduction and genetic differentiation or isolation, can give medical mycologists information about the intraspecific groups that are worth identifying and the number and type of markers that would be needed to do so. The same evolutionary information can be just as valuable for the selection of fungi for development and testing of pharmaceuticals or vaccines. The many methods of analyzing DNA variation are evaluated in light of the need for polymorphic loci that are well characterized, simple, independent, and stable. Traditional population genetic and new phylogenetic methods for analyzing mode of reproduction, genetic differentiation, and isolation are reviewed. Strain typing and population genetic reports are examined for six medically important species: Coccidioides immitis, Histoplasma capsulatum, Candida albicans, Cryptococcus neoformans, Aspergillus fumigatus, and A. flavus. Research opportunities in the areas of genomics, correlation of clinical variation with genetic variation, amount of recombination, and standardization of approach are suggested.

Biological Evolution↗

PubMed1986

[Is the postmenopausal-age-at-death variable a fitness-maximizing reproductive strategy?].

On the basis of the complete 18th century vital statistics available for 811 women from Ostfriesland (Germany), an attempt is made to examine the relationship between the postmenopausal age at death and the reproductive behaviour (reproductive effort and reproductive management). Although reproductive activities appeared to have a basically life-shortening effect in the population under study, this was independent of the amount of reproductive effort. The positive correlation reported in the literature to exist between the number of (surviving) children and the age at death was confirmed in our analysis; and it can partly be explained by the interference of another relationship, i.e. between the age at the last parturition and longevity. This correlation is interpreted as an expression of fitness-maximizing reproductive management. To this belongs the idea that the existence of unmarried children, i.e. the sub-optimal social position of one's descendants, had a life-lengthening effect on the women investigated. Whereas the effects found are largely statistically significant, they are on the whole very minor, so that we may surmise that only a small part of the total variance of the postmenopausal age at death can be interpreted as an expression of an adaptive reproductive strategy.

Female↗

PubMed2006

Adherence to antiretroviral HIV drugs: how many doses can you miss before resistance emerges?

The question of determining how many doses may be skipped before HIV treatment response is adversely affected by the emergence of drug-resistance is addressed. Impulsive differential equations are used to develop a prescription to minimize the emergence of drug-resistance for protease-sparing regimens. A threshold for the maximal number of missable doses is determined. If the number of missed doses is below this threshold, then resistance levels are negligible and dissipate quickly, assuming perfect adherence subsequently. If the number of missed doses exceeds this threshold, even for 24h, resistance levels are extremely high and will not dissipate for weeks, even assuming perfect adherence subsequently. After this interruption, the minimum number of successive doses that should be taken is determined. Estimates are provided for all protease-sparing drugs approved by the US Food and Drug Administration. Estimates for the basic reproductive ratios for the wild-type and mutant strains of the virus are also calculated, for a long-term average fractional degree of adherence. There are regions within this fraction of adherence where the outcome is not predictable and may depend on a patient's entire history of drug-taking.

Anti-HIV Agents↗

PubMed2003

A case/comparison study in the Eastern Region of Ghana on the effects of incorporating selected reproductive health services on family planning services.

OBJECTIVE: to assess the impact on the provision of family planning (FP) services when FP providers were also trained to provide additional, selected, reproductive health services. DESIGN: case/comparison study. PARTICIPANTS AND SETTINGS: twenty-four FP service delivery points in which training in sexually transmitted infection prevention and control services or post-abortion care services had been initiated (case facilities), were compared to 19 control facilities in which similar provider training had not yet been targeted. All settings were located in the Eastern Region of Ghana. MEASUREMENTS: service statistics for three study years (1996-1998) were reviewed. Structured interviews with providers, managers and clients provided qualitative data concerning impact and satisfaction. FINDINGS: case facilities which had integrated these additional reproductive health (RH) services experienced consistently higher numbers of clients and the total number of clients receiving FP services increased over time. There was also a statistically significant increase in continuing FP clients within case facilities. In contrast, the number of FP clients serviced in the comparison area remained basically unchanged over time. KEY CONCLUSIONS: interviews conducted with providers and managers in both types of settings indicated strong support for receipt of training to provide these integrated services and a request for additional training in an even broader array of RH and adult/child services. Clients also perceived the benefit of additional RH services and perceived these services to be of high quality. IMPLICATIONS FOR PRACTICE: expanding the repertoire of clinical skills of FP providers, enabling these practitioners to render RH services that augment basic FP services, has the potential to increase the number of new and continuing FP clients, and increases the satisfaction of both providers and consumers with respect to these services.

Abortion, Induced↗

PubMed2001

Approximating the long-term behaviour of a model for parasitic infection.

In a companion paper two stochastic models, useful for the initial behaviour of a parasitic infection, were introduced. Now we analyse the long term behaviour. First a law of large numbers is proved which allows us to analyse the deterministic analogues of the stochastic models. The behaviour of the deterministic models is analogous to the stochastic models in that again three basic reproduction ratios are necessary to fully describe the information needed to separate growth from extinction. The existence of stationary solutions is shown in the deterministic models, which can be used as a justification for simulation of quasi-equilibria in the stochastic models. Host-mortality is included in all models. The proofs involve martingale and coupling methods.

Animals↗

PubMed1994

The computation of R0 for discrete-time epidemic models with dynamic heterogeneity.

An explicit algorithm is given for the computation of the basic reproduction ratio R0 (or the net reproduction ratio R in the case of a not wholly susceptible population) for a class of discrete-time epidemic models. These models allow for a finite number of different individual types, type changes at fixed type-dependent intervals, arbitrary contact intensity between individuals of the various types, and variable infectivity. The models reflect the situation where an infectious disease spreads in a population of animals that are reared in different stables on farms. In addition, it is shown analytically that the reproduction ratio depends, for any given type, on the product of the susceptibility and the total infectivity of that type and not on these factors separately. We call this product the transmission weight of the type. The maximum overall transmission weight gives an upper bound for the reproduction ratio, irrespective of the particular submodels for type change and contact structure. Reduction of all transmission weights below 1, by vaccination or some other control measure, will result in R < 1 and will hence lead to eradication of the disease.

Algorithms↗

PubMed2001

Effects of Oxyrrhis marina (Dinoflagellata), bacteria and vitamin D(2) on population dynamics of Tisbe holothuriae (Copepoda).

Laboratory experiments were performed to determine which food combinations had the most favorable effect on population dynamics of the harpacticoid copepod Tisbe holothuriae. In addition to basic diets of TetraMin (T), rice (R) or a mixture of both (T+R), supplements consisting of the following were given: the heterotrophic dinoflagellate Oxyrrhis marina, a bacterial suspension and vitamin D(2). Results show a beneficial effect of bacteria at a given concentration on T. holothuriae, which is enhanced in combination with vitamin D(2). A higher concentration of bacteria together with vitamin D(2), however, has a reverse effect leading to greater mortality, lower sex ratio and number of ovigerous females, and a dramatic decrease in production of eggs, regardless of the basic diet. We conclude that different concentrations of a given bacterial community may have variable effects on the reproduction of harpacticoid copepods and that, in addition to the bacteria, vitamin D(2) may also play a role in invertebrate nutrition.

Journal Article↗

PubMed1992

Cell lineages, developmental timing, and spatial pattern formation in embryos of free-living soil nematodes.

From soils of various origins we have isolated a number of nematode strains and cultured them on agar plates. We have analyzed their anatomy, reproduction, and particularly their pattern of embryogenesis. With respect to early cleavage we can define six different classes. The basic scheme of embryogenesis is similar in all strains but considerable differences were observed in detail. Embryogenesis is more than five times longer in the slowest strain than in the fastest. The following general correlation was found: The slower embryogenesis proceeds in a strain, the relatively earlier the cleavage of germline cells occurs. In the fastest strain the primordial germ cell P4 is present at the 24-cell stage, while in the slowest strain it is already generated in the 5-cell stage. We hypothesize that germline cleavages have to occur within a certain time limit to preserve germline quality. The typical reversal of cleavage polarity in the division of the germline cell P2 is absent in the slowest, on other grounds apparently more primitive strain. This results in an unusual spatial arrangement of cells transiently. However, prior to gastrulation as a consequence of compensatory cell migrations (which may indicate the necessity for cell interactions), the pattern becomes very similar to that in the other strains. We propose that a standard cellular configuration is required at the beginning of gastrulation to ensure normal further development. Early cell interactions might be necessary to achieve this standard pattern. In about half of the analyzed strains cellular structures can be marked with an antibody raised against germline-specific granules of Caenorhabditis elegans. Our results do not support the notion that the staining pattern for P granules is a useful indicator for phylogenetic relationship.

Animals↗

PubMed1985

[The involutional age from the viewpoint of the gynecologist].

Besides the normal aging processes, which affect all human beings, regardless of their gender the involutional years of women have a number of special characteristics. These are based on the fact, that one group of organs-the reproductive system - hold their function earlier than the others. Because of this fact the involution of women ist basically different from that of men. During these years she often require therapeutic help by a physician not only for drug therapy but also psychologically. The drug-therapy seems to be relatively simple: balance of the oestrogen deficit. But today the oestrogen therapy became more difficult and has to be adjusted individually. The decision has to be made in regard to the type of hormone, the dose, the time sequence, the question of the gestagen component, the risk for malignancy, the effect on clothing and vessels etc. Old and new types of therapy including diet, tea, climate and bathing cures, tranquilizers, drugs for the autonomic nervous system, homeopathic therapy, acupuncture etc. also have their place. We will discuss these questions in the afternoon session extensively since the involutional years of women from the view of the gynaecologists are a very interesting and important field of medicine still for therapy and research.

Blood Pressure↗

PubMed2005

Qualitative research in fertility and reproduction: Does it have any value?

Quantitative researchers may argue that a finding or result is more likely to be accepted as a fact if it is quantified (expressed in numbers), than if it is not (Black, 1994). 'There is little or no scientific evidence, for example to support the well-known "fact" that one couple in 10 is infertile, yet most of us are happy to accept uncritically such simplified, reductionist, and blatantly incorrect statements, so long as they contain at least one number' (Greenhalgh & Taylor, 1997, p. 740). Interest in qualitative methods and their wider exposure in health care has led to necessary scrutiny of this type of research (Mays & Pope, 2000). This article compares the basic purpose and focus of quantitative and qualitative research, and draws attention to the relative lack of qualitative research in fertility and reproduction compared to quantitative methods. The authors highlight the strengths and weaknesses of both methods and promote qualitative methods as a valuable tool in fertility and reproduction related studies.

Embryo Transfer↗

PubMed2002

Diverse realities: sexually transmitted infections and HIV in India.

There are many features that make India a vulnerable country as far as a sexually transmitted infection (STI)/HIV epidemic is concerned. These include the lack of a strong evidence base on which to formulate decision making, a pluralistic and often unregulated health sector, and a highly vulnerable population. Nonetheless, India has shown strong commitment to other areas of a comprehensive reproductive health care programme, and may be able to do so in the field of STI/HIV control. Vast numbers of people in India are severely disadvantaged in terms of income, education, power structures, and gender. Addressing these basic issues of human rights lies at the core of achieving better health outcomes.

Developing Countries↗

PubMed2005

Molecular analysis of KAL-1, GnRH-R, NELF and EBF2 genes in a series of Kallmann syndrome and normosmic hypogonadotropic hypogonadism patients.

We report the results of molecular analysis in a series of twelve Kallmann syndrome (KS) and five normosmic hypogonadotropic hypogonadism (nHH) Brazilian patients. Kallman syndrome 1 (KAL-1) gene analysis was performed in all patients and the gonadotrophin releasing hormone receptor (GnRH-R) gene was investigated in nHH patients using PCR analysis with exon-flanking primers followed by automated sequencing techniques. Two-point mutations at the KAL-1 locus were found in two KS patients. One case exhibited a novel C deletion (del1956C) in exon 12 leading to a premature stop codon at position 617. The second case, a C to T transition at exon 5, showed a stop codon at aminoacid 191 (Arg191X). Renal agenesis and bimanual synkinesis, which are frequently found in patients with the KAL-1 mutation, were observed in these cases. Among the KS patients, two previously reported cases had intragenic deletions of exons 5-10, while a third patient had a KAL-1 gene microdeletion detected by fluorescence in situ hybridization. For the nHH patients, no abnormalities were observed at the exonic and flanking sequences of the KAL-1 or GnRH-R genes. Nasal embryonic LHRH factor (NELF) and early B-cell factor 2 (EBF2) exons were evaluated in KAL-1/GnRH-R mutation-negative cases (seven KS and five nHH) by sequence analysis but no mutations were identified in the coding regions in these patients. In conclusion, this report includes the description of a novel point mutation of the KAL-1 gene and suggests that the KAL-1 mutations and deletions might be more prevalent in KS Brazilian patients than previously described in other series. NELF and EBF2 genes have been considered good candidates for HH and a large number of patients need to be studied to assess their contribution to reproductive function.

Amino Acids↗