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Results for “Basic Reproduction Number”

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PubMed2004

Wildlife conservation and reproductive cloning.

Reproductive cloning, or the production of offspring by nuclear transfer, is often regarded as having potential for conserving endangered species of wildlife. Currently, however, low success rates for reproductive cloning limit the practical application of this technique to experimental use and proof of principle investigations. In this review, we consider how cloning may contribute to wildlife conservation strategies. The cloning of endangered mammals presents practical problems, many of which stem from the paucity of knowledge about their basic reproductive biology. However, situations may arise where resources could be targeted at recovering lost or under-represented genetic lines; these could then contribute to the future fitness of the population. Approaches of this type would be preferable to the indiscriminate generation of large numbers of identical individuals. Applying cloning technology to non-mammalian vertebrates may be more practical than attempting to use conventional reproductive technologies. As the scientific background to cloning technology was pioneered using amphibians, it may be possible to breed imminently threatened amphibians, or even restore extinct amphibian species, by the use of cloning. In this respect species with external embryonic development may have an advantage over mammals as developmental abnormalities associated with inappropriate embryonic reprogramming would not be relevant.

Animals↗

PubMed2003

The contribution of genetic diversity to the spread of infectious diseases in livestock populations.

This article uses stochastic simulations with a compartmental epidemic model to quantify the impact of genetic diversity within animal populations on the transmission of infectious disease. Genetic diversity is defined by the number of distinct genotypes in the population conferring resistance to microparasitic (e.g., viral or bacterial) infections. Scenarios include homogeneous populations and populations composed of few (finite-locus model) or many (infinitesimal model) genotypes. Genetic heterogeneity has no impact upon the expected value of the basic reproductive ratio (the primary description of the transmission of infection) but affects the variability of this parameter. Consequently, increasing genetic heterogeneity is associated with an increased probability of minor epidemics and decreased probabilities of both major (catastrophic) epidemics and no epidemics. Additionally, heterogeneity per se is associated with a breakdown in the expected relationship between the basic reproductive ratio and epidemic severity, which has been developed for homogeneous populations, with increasing heterogeneity generally resulting in fewer infected animals than expected. Furthermore, increased heterogeneity is associated with decreased disease-dependent mortality in major epidemics and a complex trend toward decreased duration of these epidemics. In summary, more heterogeneous populations are not expected to suffer fewer epidemics on average, but are less likely to suffer catastrophic epidemics.

Animal Diseases↗

PubMed1990

[Effect of glycosides of Tripterygium wilfordii Hook on the reproductive system and major organs of male rats].

Spermatogenesis and turnover of basic nuclear protein synthesis in late elongated spermatids of rat testis were found to be significantly inhibited by glycosides of Tripterygium wilfordii Hook (T II) at a daily dosage of 10 mg/kg for 7 or 13 weeks and 20 mg/kg for 4 or 10 weeks. The number of spermatozoa in the epididymis was found to be reduced and the remaining spermatozoa deformed, showing head swelling, head and tail separation and severe curling of the middle piece. These changes differed from those effected by gossypol treatment. The formazan deposits of sperm mitochondrial enzyme reactions were also reduced. Activities of several enzymes in the heart, liver and kidney were not obviously affected, except for an enhancement of SDH activity in tissues of all 3 organs and ALP in renal tubules, with a slight decrease of ALP in the brush-borders of proximal renal tubules arising as an adaptation to T II toxicity.

Animals↗

PubMed2004

[Ten years follow-up of medically assisted procreation in Belgium].

Since 1989, the data concerning medically assisted procreation (MAP) in Belgium have been registered through the BELRAP association (Belgian Register for Assisted Procreation). In 1999, the national College of Physicians in Reproductive Medicine has been installed and given the mission to carry out the quality controls and the registration of MAP activities in our country. In 2001, a new on line system of registration of all treatment cycles was started, the basic structure of the corresponding data base having undergone a series of changes along the years. Although the number of MAP trials has considerably increased in our country, mainly because of the introduction of new techniques such as intracytoplasmic injection of sperm (ICSI), the success rate per trial has remained almost unchanged, becoming stabilized around 18.8% of ongoing pregnancies per initiated cycle. The main modification that occurred during the analyzed period has been the reduction of the number of embryos transferred at each trial, being first reduced from 3 to 2 to evolve more recently towards the replacement of only one embryo per trial. Multiple pregnancies are indeed the chief complication of MAP and in order to avoid it Belgian centers have been among the first to reduce drastically the number of transferred embryos. In 2003, legal rules were enacted, fixing the number of replacable embryos in accordance to the patient's age and to the rank of trial, while also solving the problem of the long-awaited reimbursement of MAP by our national social security system.

Belgium↗

PubMed1991

Model fitting and projection of the AIDS epidemic.

Previously it was possible to fit detailed models to incidence data (for example, of AIDS) only by trial and error and good judgment; the large number of parameters obstructed optimization of, for example, the (approximate) likelihood. Here, we analyze a model for the spread of AIDS in a homosexual population and identify a minimal set of primary components that dictate the dynamics of the Model: the initial growth rate theta, the basic reproductive ratio R0, and the heterogeneity coefficient S. It is then shown that it is sufficient to maximize the likelihood over these three primary components; further maximization over the remaining secondary parameters does not produce a significant improvement in the fit or affect the projection of the epidemic. This method also allows construction of confidence limits for the projected incidence curve, allowing us to quantify the uncertainties associated with such model fitting procedures. The method is tested on simulation data to analyze how the accuracy of estimates and projections changes as we gain more data.

Acquired Immunodeficiency Syndrome↗

PubMed1977

Numbers and diameters of motoneurons and myelinated axons in the facial nucleus and nerve of the albino rat.

The number and diameter of the motoneurons in serial sections of the facial nucleus in the albino rat were estimated using a photograph-camera lucida technique for counting and measuring cells in conjunction with a systematic section method for sampling the population. The mean diameter of facial motoneuron nucleoli was also estimated. Total cell counts were estimated using two formulas, one a basic count and the other the basic count corrected for split nucleoli errors. The mean motoneuron diameter is 33-93 micronm (+/- 6-18 micronm S.D.). The number and diameter of myelinated axons in both the facial nerve and its cutaneous auricular branch at the level of the stylomastoid foramen were estimated. There are 5353 myelinated axons in the facial nerve, with a mean diameter of 2-74 micronm, and 627 myelinated axons in the cutaneous auricular branch with a mean diameter of 1-47 micronm. The accuracy and reproductibility of results using the photograph-camera lucida technique for counting and measuring cells and the systematic section method of sampling are compared with those of the methods used by previous investigators. The accuracy of results obtained for estimates of the total cell count using the formulas for the basic count and the basic count corrected for split nucleoli are also compared.

Animals↗

PubMed2003

Linear models for assessing mechanisms of sperm competition: the trouble with transformations.

Although sperm competition is a pervasive selective force shaping the reproductive tactics of males, the mechanisms underlying different patterns of sperm precedence remain obscure. Parker et al. (1990) developed a series of linear models designed to identify two of the more basic mechanisms: sperm lotteries and sperm displacement; the models can be tested experimentally by manipulating the relative numbers of sperm transferred by rival males and determining the paternity of offspring. Here we show that tests of the model derived for sperm lotteries can result in misleading inferences about the underlying mechanism of sperm precedence because the required inverse transformations may lead to a violation of fundamental assumptions of linear regression. We show that this problem can be remedied by reformulating the model using the actual numbers of offspring sired by each male, and log-transforming both sides of the resultant equation. Reassessment of data from a previous study (Sakaluk and Eggert 1996) using the corrected version of the model revealed that we should not have excluded a simple sperm lottery as a possible mechanism of sperm competition in decorated crickets, Gryllodes sigillatus.

Animals↗

PubMed2001

Basic fibroblast growth factor induces primordial follicle development and initiates folliculogenesis.

The recruitment of primordial follicles to initiate folliculogenesis determines the population of developing follicles available for ovulation and directly regulates female reproductive efficiency. In the current study, a floating organ culture system was used to examine the progression of primordial (stage 0) follicles to developing (stages 1-4) follicles in 4-day-old pre-pubertal rat ovaries. Basic fibroblast growth factor (bFGF) was found to induce primordial follicle development similar to what has been demonstrated for kit ligand/stem cell factor (KL). The bFGF-treated ovaries contained 85% developing follicles compared with 50% developing follicles for control untreated organ cultures. Correspondingly, the number of primordial follicles in bFGF-treated ovaries decreased to 15% of the total compared with 45% for controls. A bFGF neutralizing antibody was found to decrease the small amount of spontaneous follicle development that occurs during the organ culture. Basic FGF was localized to primordial and early developing follicles by immunocytochemistry and was primarily observed in the oocytes. Treatment of bovine ovarian theca cells and stroma cells with bFGF was found to promote cell growth. Basic FGF produced by the oocyte in early stage follicles appears to act on adjacent somatic cells to promote cell growth and development. Basic FGF, like KL, appears to be a primordial follicle-inducing factor. In summary, bFGF can regulate primordial follicle development that directly influences female reproductive efficiency.

Animals↗

PubMed1987

Mechanisms regulating the ovarian cycle in the frog Rana cyanophlyctis: effect of unilateral ovariectomy, season, feeding, human chorionic gonadotrophin, and estradiol-17 beta.

Effects of 30-day unilateral ovariectomy (ULO) on compensatory ovarian hypertrophy (COH) was studied in adult frog Rana cyanophlyctis in relation to reproductive phase/season, feeding, and treatment with human chorionic gonadotrophin (HCG) or estradiol-17 beta. Compensatory growth of the remaining ovary was assessed in terms of weight as well as changes in the dynamics of the pool sizes of different oocytes viz., first growth phase (FGP), medium-sized second growth phase (MSGP), large-sized second growth phase (LSGP), and atretic oocytes. The frogs were fed with live guppies 6 days a week. The effect of underfeeding on COH was studied in the frogs fed once a week. The ovaries removed at operation and those of the sham-operated frogs were used for comparison (controls). COH occurred in both pre- and postbreeding phases (February and November, respectively). In both instances follicular atresia was greatly reduced. In February, COH was due to recruitment of both MSGP and LSGP oocytes. The number of these oocytes increased significantly over controls, and the ovarian weight nearly doubled. However, in November COH occurred because of an increase in FGP oocytes and therefore total oocytes, but there were no changes in the ovarian weights. Administration of 20 IU HCG (6 days a week) had no influence on the basic pattern of COH-response exhibited by the remaining ovary in relation to reproductive phase/season, but it increased the recruitment of oocytes, i.e., FGP oocytes in November and SGP oocytes in February. Follicular atresia was drastically reduced with HCG. Underfeeding or treatment with estradiol-17 beta abolished the COH in both February and November.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed2005

Can farm animals help to study endocrine disruption?

The phenomenon of endocrine disruption can be regarded as part of the disciplines of toxicology and environmental toxicology. These two disciplines have generated guideline protocols on how various effects of chemicals should be tested as a basis for regulatory decisions. These protocols almost exclusively involve laboratory rodents and the data obtained are then used for human risk assessment. Would it be justifiable, then, to introduce or promote the use of other species in these test protocols? There are, at any rate rationales for studying effects in species other than laboratory rodents: (1) other species may better mimic the human system; (2) they may in some cases be more useful for studying a certain mechanism or phenomenon; (3) they may highlight the diversity of effects or sensitivity between species. However, there are at least two basic criteria that must be met for a species before it can be introduced in this context: (a) we must have a good understanding of the physiological system to be studied; and (b) we must have a number of tools to study effects on this system. When it comes to the reproductive system--regarding which most endocrine disruption has been reported--farm animals are second only, or in some respects superior, to laboratory rodents with respect to these criteria. This review gives examples of how farm animals can be of use in the study of endocrine disruption with a focus on the author's own data from studies in the pig.

Animals↗

PubMed1988

Population dynamics of mosquito-borne disease: persistence in a completely heterogeneous environment.

We investigate the persistence of a mosquito-borne disease (malaria) in a system where mosquitoes and hosts are grouped in patches containing any number of individuals. A mosquito from any one of vector patches can bite, and take blood meals, in any one of m host patches. We confirm our earlier result (C. Dye and G. Hasibeder, 1986, Trans. R. Soc. Trop. Med. Hyg. 80, 69-77) that nonhomogeneous host selection by mosquitoes leads to basic reproductive rates (which measure the persistence of infection in the system) greater than or equal to those obtained under uniform host selection. We find, in addition, that strong associations between particular groups of mosquitoes and hosts lead to still higher basic reproductive rates. Exacting fieldwork would be required to find out how much higher.

Animals↗

PubMed1992

Estimation of the dynamics and rate of transmission of classical swine fever (hog cholera) in wild pigs.

Infectious diseases establish in a population of wildlife hosts when the number of secondary infections is greater than or equal to one. To estimate whether establishment will occur requires extensive experience or a mathematical model of disease dynamics and estimates of the parameters of the disease model. The latter approach is explored here. Methods for estimating key model parameters, the transmission coefficient (beta) and the basic reproductive rate (RDRS), are described using classical swine fever (hog cholera) in wild pigs as an example. The tentative results indicate that an acute infection of classical swine fever will establish in a small population of wild pigs. Data required for estimation of disease transmission rates are reviewed and sources of bias and alternative methods discussed. A comprehensive evaluation of the biases and efficiencies of the methods is needed.

Animals↗

PubMed1997

ACOG educational bulletin. Nutrition and women. Number 229, October 1996. Committee on Educational Bulletins of the American College of Obstetricians and Gynecologists.

Adoption by women of dietary practices that are based on Dietary Guidelines for Americans (8) can promote improved general and reproductive health and can help prevent chronic disease. Additional guidance is indicated for helping prevent neural tube defects, iron deficiency anemia, and osteoporosis. The obstetrician-gynecologist plays an important preventive role by providing basic nutritional assessment; nutrition education; counseling concerning diet, weight, and exercise; and referral for special nutritional care as needed. The physician needs to be especially alert for serious nutrition-related problems such as eating disorders that pose a serious health risk and to stress the importance of good nutrition particularly to adolescent and elderly patients.

Adolescent↗

PubMed1984

Neurological disorders with autosomal dominant transmission.

Neurofibromatosis, Huntington's disease, and myotonic dystrophy are three hereditary disorders affecting the nervous system. They have in common the basic principles of autosomal dominant inheritance: an affected individual has one parent with the disorder; the disorder affects males and females in approximately equal numbers; and an affected individual has a 50 percent risk of transmitting the disorder to every child. Furthermore, each of the three disorders have additional features that complicate genetic counseling and decisions about reproduction. Neurofibromatosis has an extremely variable expressivity, making the identification of affected individuals difficult and allowing for some reduction in the risk figures; although there is a 50 percent risk of a child inheriting the mutant gene, only one-fourth to one-third of these will experience serious consequences. Huntington's disease has a fairly typical course with degeneration occurring over 10 to 20 years. The frequent late onset of the disorder and the lack of any preclinical test for detecting carriers create problems for those at risk who wish to have children but do not want to pass the disorder to future generations. Both variable expressivity and variable onset are found in myotonic dystrophy. In addition, there is a risk of the severe early onset myotonic dystrophy when the mother is the affected parent. Genetic counseling should be available to patients and families with these three disorders. Nurses who have an understanding of the dynamics of these particular disorders can be empathetic to patients who face personal and family problems caused by the conditions. Alert nursing staff, in casual discussion with patients, may learn of hereditary disorders in a family or may notice symptoms that could lead to diagnosis of one of these disorders. Finally, nurses who are aware of the variations in genetic transmission of these disorders, may be in position to instruct and reinforce genetic counseling that the family has received.

Adult↗

PubMed2005

Number of offspring and maternal allergy.

The consistent association seen between family size and childhood allergy has led to the 'hygiene hypothesis', namely that a lower frequency of infections in early childhood is associated with an increased risk of asthma and hay fever. Maternal atopy, however, is a strong predictor of childhood asthma and hay fever. If maternal atopy is inversely related to the number of siblings then the role of siblings in the development of childhood atopy, the basic tenet of the 'hygiene hypothesis', is challenged. We evaluated the association between number of pregnancies and number of live births with lifetime occurrence of maternal wheeze, asthma, allergic rhinitis, and allergic conjunctivitis in a cross-sectional study in four areas in Italy. A total of 1755 (35-74 year old) nonsmoking women filled a questionnaire on reproductive history as well as on lifetime occurrence of symptoms/diseases. The number of live births was inversely related to lifetime allergic rhinitis (P-value for trend=0.031) and allergic conjunctivitis (P-value for trend=0.011). The odds ratios for those with 4+ children (in comparison with those having 0-1) were: 0.53 (95% CI: 0.27-1.04) and 0.42 (95% CI: 0.22-0.81), respectively. A similar trend was seen for number of pregnancies, although not statistically significant. No association was found between number of pregnancies and number of live births with wheeze or asthma. The results may be interpreted as an indication that maternal atopy influences pregnancy outcomes or that pregnancy itself has an effect on maternal atopy.

Adult↗

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↗