Estimating the human health risk from possible BSE infection of the British sheep flock

Following the controversial failure of a recent study and the small numbers of animals yet screened for infection, it remains uncertain whether bovine spongiform encephalopathy (BSE) was transmitted to sheep in the past via feed supplements and whether it is still present. Well grounded mathematical and statistical models are therefore essential to integrate the limited and disparate data, to explore uncertainty, and to define data-collection priorities. We analysed the implications of different scenarios of BSE spread in sheep for relative human exposure levels and variant Creutzfeldt-Jakob disease (vCJD) incidence. Here we show that, if BSE entered the sheep population and a degree of transmission occurred, then ongoing public health risks from ovine BSE are likely to be greater than those from cattle, but that any such risk could be reduced by up to 90% through additional restrictions on sheep products entering the food supply. Extending the analysis to consider absolute risk, we estimate the 95% confidence interval for future vCJD mortality to be 50 to 50,000 human deaths considering exposure to bovine BSE alone, with the upper bound increasing to 150,000 once we include exposure from the worst-case ovine BSE scenario examined.

Quantification of intrinsic residual viral replication in treated HIV-infected patients

The intrinsic rate of viral replication in HIV-infected patients treated with antiretroviral combination therapy is estimated by using a mathematical model of viral dynamics. This intrinsic replication is found to be episodic, varying considerably in quantity between patients (even among those achieving long-term undetectable levels of viremia) and is always reduced by increasing the potency of the antiviral drug regimen. The analysis reveals that even in conditions of perfect patient adherence and drug penetration a substantial level of residual viral replication is expected. The rate of evolution in the viral quasispecies, and thus also the probability of new drug-resistant viral strains being created, is proportional to the total amount of residual viral replication. Under most circumstances, the viral population continues to turn over rapidly during therapy, albeit at a much reduced level.

The BMP antagonists Chordin and Noggin have essential but redundant roles in mouse mandibular outgrowth

Here we investigate the roles of the Bone Morphogenetic Protein (BMP) antagonists Chordin and Noggin in development of the mandible, which is derived from the first branchial arch (BA1). Both genes are expressed in the pharynx during early mandibular outgrowth and later in the mandibular process. Mice mutant for either Nog or Chd have only mild mandibular defects; however, pups of the genotype Chd(-/-);Nog(+/-) exhibit a range of mandibular truncation phenotypes, from normal to agnathia. A few embryos homozygous null for both genes survive to late gestation; many are agnathic, though a few have significant mandibular outgrowth. In mandibular explants, ectopic BMP4 rapidly induces expression of both Chd and Nog, consistent with results obtained in vivo with mutant embryos. Previous work has shown that FGF8 is a survival factor for cells populating the mandibular bud. We find that excess BMP4 represses Fgf8 transcription in mandibular explants. Embryos lacking these BMP antagonists often show a strong reduction in Fgf8 expression in the pharyngeal ectoderm, and increased cell death in the mandibular bud. We suggest that the variable mandibular hypoplasia in double mutants involves increased BMP activity downregulating Fgf8 expression in the pharynx, decreasing cell survival during mandibular outgrowth.

Surrogate markers for disease progression in treated HIV infection

OBJECTIVE

To characterize the relationships among highly active antiretroviral therapy (HAART), HIV-1 RNA levels, immune system markers, and clinical outcome in a cohort of HIV-1-infected homosexual men.

PATIENTS

A total of 123 men enrolled in the Amsterdam cohort study of HIV-1 infection and AIDS with a documented seroconversion for HIV-1 antibodies and known date of seroconversion were included in this study.

METHODS

CD4 + /CD8 + T-cell counts and HIV-1 RNA levels in plasma were measured approximately every 6 months. Dates of starting and stopping antiretroviral therapy were also recorded. The relationship between HIV-1 RNA in plasma, CD4 + /CD8 + T-cell counts and HAART and their influence on clinical outcome were examined using a graphical chain modeling approach. Generalized estimating equations were used to examine correlations among the three disease markers. Hazards models with time-dependent covariates were used to examine the influence of HAART and the disease markers on progression to AIDS.

RESULTS

HAART was significantly associated with reduced disease progression (relative hazard [RH] of AIDS, 0.20;, 95% confidence interval [CI], 0.05-0.85). The most recent HIV-1 RNA measurement and CD4 + T-cell count are independently associated with disease progression (adjusted RH for HIV-1 RNA 1.8 per log 10 increase; 95% CI, 1.2-2.6, p =.002; adjusted RH for CD4 + 0.48 per 100 x 10(6)/L increase; 95% CI, 0.40-0.58; p <.001). Depending on these measurements, HAART was no longer significantly associated with AIDS (adjusted RH, 0.81; 95% CI, 0.18-3.6; p =.78).

CONCLUSIONS

HIV-1 RNA levels in plasma and CD4 + T-cell counts are currently considered as effective surrogate markers for the effect of HAART on disease progression in this cohort.

The role of antigenic stimulation and cytotoxic T cell activity in regulating the long-term immunopathogenesis of HIV: mechanisms and clinical implications

This paper develops a predictive mathematical model of cell infection, host immune response and viral replication that reproduces observed long-term trends in human immunodeficiency virus (HIV) pathogenesis. Cell activation induced by repeated exposure to many different antigens is proposed as the principal mechanism of providing target cells for HIV infection and, hence, of CD4+ T cell depletion, with regulation of the overall T cell pool size causing concomitant CD8 pool increases. The model correctly predicts the cross-patient variability in disease progression, the rate of which is found to depend on the efficacy of anti-HIV cytotoxic T lymphocyte responses, overall viral pathogenicity and random effects. The model also predicts a variety of responses to anti-viral therapy, including episodic residual viral replication and discordant responses and we find that such effects can be suppressed by increasing the potency of treatment.

Transmission intensity and impact of control policies on the foot and mouth epidemic in Great Britain

The foot and mouth disease (FMD) epidemic in British livestock remains an ongoing cause for concern, with new cases still arising in previously unaffected areas. Epidemiological analyses have been vital in delivering scientific advice to government on effective control measures. Using disease, culling and census data on all livestock farms in Great Britain, we analysed the risk factors determining the spatiotemporal evolution of the epidemic and of the impact of control policies on FMD incidence. Here we show that the species mix, animal numbers and the number of distinct land parcels in a farm are central to explaining regional variation in transmission intensity. We use the parameter estimates thus obtained in a dynamical model of disease spread to show that extended culling programmes were essential for controlling the epidemic to the extent achieved, but demonstrate that the epidemic could have been substantially reduced in scale had the most efficient control measures been rigorously applied earlier.

Persistence patterns of scrapie in a sheep flock

The epidemiology and transmission dynamics of sheep scrapie is as yet poorly understood. Here we present a theoretical analysis of the transmission dynamics within a sheep flock, concentrating on how persistence properties depend on transmission scenario and flock size. Patterns of disease persistence and extinction are studied analytically using branching-process approximations and numerically using stochastic model simulations. For a given basic reproduction number, disease extinction is most likely when late-stage infected animals are responsible for most of the transmission. This effect can be understood in terms of aggregation in the distribution of the number of secondary infections arising from a single primary infection. The presence of an environmental reservoir reduces the probability of extinction.

Comparison of the effectiveness of non-nucleoside reverse transcriptase inhibitor-containing and protease inhibitor-containing regimens using observational databases

OBJECTIVES

To compare the effectiveness of first protease inhibitor (PI)-containing and non-nucleoside reverse transcriptase inhibitor (NNRTI)-containing regimens.

METHODS

Data were analysed from three large HIV patient databases: Apache HIV Insight (APACHE), Target Management Services (TMS) and Clinical Partners (CP). The effectiveness of therapy was the time taken for HIV-1 RNA to fall below detectable levels on first highly active antiretroviral therapy regimen (PI- or NNRTI-containing) and the subsequent time to failure (two consecutive detectable measurements). Comparisons were made using proportional hazards models, adjusting for differences in age, sex, previous reverse transcriptase inhibitor use, calendar year and baseline viral load and CD4 T-cell count.

RESULTS

The type of regimen was not associated with time to undetectable viral load in any of the three databases, all of which had high power to detect a difference. PI-containing regimens were significantly less likely to fail after reaching undetectable viral loads for APACHE and CP patients (relative hazard, 1.7; 95% confidence interval, 1.3--2.1 and relative hazard, 1.6; 95% confidence interval, 1.0--2.5 respectively). These results remained significant after allowing for an unmeasured confounder with moderate effect on risk. No significant association between time to failure and regimen was found for TMS patients, possibly due to low power (67% to detect a relative hazard of 1.5). No difference was found between regimens in the time taken for an increase of > 100 x 10(9)cells/l in CD4 T-cell count. In the APACHE database, those on NNRTI-containing regimens were more likely to have a failing CD4 T-cell response.

CONCLUSIONS

PI-containing regimens have a lower risk of treatment failure than NNRTI-containing regimens.

The foot-and-mouth epidemic in Great Britain: pattern of spread and impact of interventions

We present an analysis of the current foot-and-mouth disease epidemic in Great Britain over the first 2 months of the spread of the virus. The net transmission potential of the pathogen and the increasing impact of control measures are estimated over the course of the epidemic to date. These results are used to parameterize a mathematical model of disease transmission that captures the differing spatial contact patterns between farms before and after the imposition of movement restrictions. The model is used to make predictions of future incidence and to simulate the impact of additional control strategies. Hastening the slaughter of animals with suspected infection is predicted to slow the epidemic, but more drastic action, such as "ring" culling or vaccination around infection foci, is necessary for more rapid control. Culling is predicted to be more effective than vaccination.

A rural HIV epidemic in Zimbabwe? Findings from a population-based survey

The aim of the study was to use population-based data from 689 adults to describe the socio-demographic, behavioural and biomedical correlates of HIV infection and aid identification of effective HIV control strategies for rural Zimbabwe. Dried blood spot and urine samples were collected for HIV and sexually transmitted disease (STD) testing and participants were interviewed on socio-demographic characteristics, sexual behaviour and experience of STD symptoms. HIV seroprevalence was 23.3% and was higher in females, divorcees, widows, working men, estate residents, and respondents reporting histories of STD symptoms. Female HIV seroprevalence rises sharply at ages 16-25. A third of sexually-active adults had experienced STD-associated symptoms but there were delays in seeking treatment. Herpes simplex virus type 2 (HSV-2) and Trichomonas vaginalis are more common causes than syphilis, gonorrhoea, and chlamydia, and are strongly associated with HIV infection. Local programmes promoting safer sexual behaviour and fast and effective STD treatment among young women, divorcees and working men could reduce the extensive HIV transmission in rural communities.

Using decision analysis to choose phosphorus targets for Lake Erie

Lake Erie water quality has improved dramatically since the degraded conditions of the 1960s. Additional gains could be made, but at the expense of further investment and reductions in fishery productivity. In facing such cross-jurisdictional issues, natural resource managers in Canada and the United States must grapple with conflicting objectives and important uncertainties, while considering the priorities of the public that live in the basin. The techniques and tools of decision analysis have been used successfully to deal with such decision problems in a range of environmental settings, but infrequently in the Great Lakes. The objective of this paper is to illustrate how such techniques might be brought to bear on an important, real decision currently facing Lake Erie resource managers and stakeholders: the choice of new phosphorus loading targets for the lake. The heart of our approach is a systematic elicitation of stakeholder preferences and an investigation of the degree to which different phosphorus-loading policies might satisfy ecosystem objectives. Results show that there are potential benefits to changing the historical policy of reducing phosphorus loads in Lake Erie.

Viral dynamics and anti-viral pharmacodynamics: rethinking in vitro measures of drug potency

Most current assays used to quantitate the pharmacodynamic effect of anti-viral agents measure the net inhibitory effect of a drug on virus replication over several days in an in vitro cell culture. Such endpoint experiments give cumulative measures of inhibition that vary with the assay used and therefore provide suboptimal information on likely in vivo drug performance. We argue that instantaneous inhibition (proportion of cell infection prevented at a point in time) is a more robust pharmacodynamic measure, and propose techniques to estimate this quantity from endpoint data. Implications for the quantification of drug interactions are discussed.

The effectiveness of HIV prevention and the epidemiological context

Planning an intervention to prevent infections with the human immunodeficiency virus (HIV) should be guided by local epidemiological and socioeconomic conditions. The socioeconomic setting and existing public service capacity determine whether an intervention can have a significant outcome in terms of a reduction in a defined risk. The epidemiological context determines whether such risk reduction translates into a measurable impact on HIV incidence. Measurement of variables describing the epidemiological context can be used to determine the local suitability of interventions, thereby guiding planners and policy-makers in their choice of intervention. Such measurements also permit the retrospective analysis of the impact of interventions where HIV incidence was not recorded. The epidemiological context is defined for four different categories of intervention, shown to be effective in lower-income countries by randomized controlled trials. Appropriate indicators for the epidemiological context and methodological guidelines for their measurement are proposed. Their use in the transfer of a successful intervention from one context to another and in scaling up the effort to control HIV infection is explored. These indicators should provide a useful resource for those involved in planning HIV prevention interventions.

Report of the health care delivery work group: behavioral research related to the establishment of a chronic disease model for diabetes care

As one of four work groups for the November 1999 conference on Behavioral Science Research in Diabetes, sponsored by the National Institute on Diabetes and Digestive and Kidney Diseases, the health care delivery work group evaluated the status of research on quality of care, patient-provider interactions, and health care systems' innovations related to improved diabetes outcomes. In addition, we made recommendations for future research. In this article, which was developed and modified at the November conference by experts in health care delivery, diabetes and behavioral science, we summarize the literature on patient-provider interactions, diabetes care and self-management support among underserved and minority populations, and implementation of chronic care management systems for diabetes. We conclude that, although the quality of care provided to the vast majority of diabetic patients is problematic, this is principally not the fault of either individual patients or health care professionals. Rather, it is a systems issue emanating from the acute illness model of care, which still predominates. Examples of proactive population-based chronic care management programs incorporating behavioral principles are discussed. The article concludes by identifying barriers to the establishment of a chronic care model (e.g., lack of supportive policies, understanding of population-based management, and information systems) and priorities for future research in this area needed to overcome these barriers.

Slower decline of plasma HIV-1 RNA following highly suppressive antiretroviral therapy in primary compared with chronic infection

OBJECTIVES

To study the effect of highly suppressive antiretroviral therapy on the slopes of HIV-1 RNA decline in primary compared with chronic HIV-1 infection.

METHODS

Slopes of HIV-1 RNA decline in plasma were compared before and after the start of highly suppressive antiretroviral therapy from five acutely infected patients who started treatment 2 to 5 weeks following the onset of clinical symptoms. Slopes of decline after the initiation of therapy were also compared with those found in 12 chronically infected individuals on the same therapy. Numbers and percentages of activated CD4 and CD8 T cells at baseline were compared as well.

RESULTS

The pre-treatment slopes of HIV-1 RNA decline in the acutely infected individuals increased significantly (P = 0.0001) after the start of anti-retroviral therapy. However, these post-treatment slopes were lower than those found in the chronically infected individuals (P= 0.012). Slopes were inversely correlated (P= 0.012) with baseline HIV-1 RNA. Although the number of CD38+HLA-DR+ CD4 cells was higher in primary infection (P= 0.02), the percentage did not differ between primary and chronic infection.

CONCLUSIONS

These findings indicate that antiretroviral therapy contributes significantly to the clearance of HIV-1 during primary infection. Based on the mathematical model the less steep RNA slope following the start of treatment in primary infection can be predicted to be the result of lower clearance of productively infected cells and higher burst size per cell per unit time. This may indicate a growing immune response to HIV-1 in this very early stage of infection.

The transmission dynamics of the aetiological agent of scrapie in a sheep flock

We formulate and investigate the properties of a model framework to mimic the transmission dynamics of the aetiological agent of scrapie in a sheep flock. We derive expressions for summary parameters that characterize transmission scenarios, notably the basic reproduction number R(0) and the mean generation time T(g). The timescale of epidemic outbreaks is expressed in terms of R(0) and cumulants of the generation time distribution. We discuss the relative contributions to the overall rate of transmission of horizontal and vertical routes during invasion and in endemicity. Simplified models are used to obtain analytical insight into the characteristics of the endemic state.

Mathematical models of the transmission and control of sexually transmitted diseases

BACKGROUND

The development of mathematical models to describe and interpret the epidemiology of sexually transmitted infections has involved the incremental addition of various forms of biological and behavioral complexity to simple mathematical templates.

GOAL

To review simple and complex models used in study of observed epidemiologic pattern.

STUDY DESIGN

An overview of modeling in sexually transmitted disease epidemiology identifies the function of different types of models.

RESULTS

Simple models have the advantage of transparency and analytical tractability and can illustrate the relative merits of different intervention options. However, real life is replete with complexities that can have effects that are difficult to predict in the absence of a mathematical framework.

CONCLUSIONS

Research should increasingly be based on robust parameterization of model structures and try to capture individual behaviors. Progress will be most rapid by interdisciplinary work where the clinician, epidemiologist, and mathematician work collaboratively to help improve our knowledge of how to best control infection and disease.

Effects of prefrontal cortex microinjection of neurotensin-(8-13) on midbrain dopamine and non-dopamine cell firing

Effects of prefrontal cortex microinjections of 0.3 and 3 nmol/0.5 microl of neurotensin-(8-13) on the firing rate of midbrain dopamine and non-dopamine cells were studied in urethane-anesthetized rats. Neurotensin produced an increase in firing in 14 of 26 dopamine cells tested, an effect that peaked between 15 and 20 min after the injection at both doses. On the other hand, a majority of non-dopamine cells (7/10) tested with the higher dose of neurotensin showed a statistically significant decrease in firing when compared to saline, an effect that also peaked between 15 and 20 min. These results show that prefrontal cortex neurotensin can modulate both dopamine and non-dopamine neurotransmission in the ventral midbrain.

Compliance and adherence are dysfunctional concepts in diabetes care

Recognizing that adherence and compliance are dysfunctional concepts is not a passing fad or the latest trend in behavioral approaches to diabetes care and education. Shifting from the acute-care/compliance-focused paradigm to an empowerment/collaborative approach requires a new vision of diabetes education and a new definition and enactment of the roles of educators and patients. Our practice is always an expression of our vision; therefore, if our vision is transformed, our practice will most likely change to reflect our vision. Eliminating the concepts of adherence and compliance makes it possible for our patients to discover and actualize their personal responsibility for their diabetes self-management. Also, it helps us to practice diabetes education as win-win collaboration among equals.

The Diabetes Empowerment Scale: a measure of psychosocial self-efficacy

OBJECTIVE

The purpose of this study was to assess the validity, reliability, and utility of the Diabetes Empowerment Scale (DES), which is a measure of diabetes-related psychosocial self-efficacy.

RESEARCH DESIGN AND METHODS

In this study (n = 375), the psychometric properties of the DES were calculated. To establish validity, DES subscales were compared with 2 previously validated subscales of the Diabetes Care Profile (DCP). Factor and item analyses were conducted to develop subscales that were coherent, meaningful, and had an acceptable coefficient alpha.

RESULTS

The psychometric analyses resulted in a 28-item DES (alpha = 0.96) with 3 subscales: Managing the Psychosocial Aspects of Diabetes (alpha = 0.93), Assessing Dissatisfaction and Readiness To Change (alpha = 0.81), and Setting and Achieving Diabetes Goals (alpha = 0.91). Consistent correlations in the expected direction between DES subscales and DCP subscales provided evidence of concurrent validity.

CONCLUSIONS

This study provides preliminary evidence that the DES is a valid and reliable measure of diabetes-related psychosocial self-efficacy. The DES should be a useful outcome measure for various educational and psychosocial interventions related to diabetes.

Reduction of the HIV-1-infected T-cell reservoir by immune activation treatment is dose-dependent and restricted by the potency of antiretroviral drugs

BACKGROUND

Treatments combining T-cell activating agents and potent antiretroviral drugs have been proposed as a possible means of reducing the reservoir of long-lived HIV-1 infected quiescent CD4 T-cells.

OBJECTIVE

To analyse the effect of such therapies on HIV-1 dynamics and T-cell homeostasis.

DESIGN AND METHODS

A mathematical framework describing HIV-1 dynamics and T-cell homeostasis was developed. Three patients who were kept on a particularly potent course of highly active antiretroviral therapy (HAART) were treated with the anti-CD3 monoclonal antibody OKT3 and interleukin (IL)-2. Plasma HIV-RNA, and HIV-RNA and DNA in peripheral blood mononuclear cells and lymph node mononuclear cells were measured. These results and other published studies on the use of IL-2 alone were assessed using our mathematical framework.

RESULTS

We show that outcome of treatment is determined by the relative rates of depletion of the infected quiescent T-cell population by activation and of its replenishment through new infection. Which of these two processes dominates is critically dependent on both the potency of HAART and also the degree of T-cell activation induced. We demonstrate that high-level T-cell stimulation is likely to produce negative outcomes, both by failing to reduce viral reservoirs and by depleting the CD4 T-cell pool and disrupting CD4/CD8 T-cell homeostasis. In contrast, repeated low-level stimulation may both aid CD4 T-cell pool expansion and achieve a substantial reduction in the long-lived HIV-1 reservoir.

CONCLUSIONS

Our analysis suggests that although treatment that activates T-cells can reduce the long-lived HIV-1 reservoir, caution should be used as high-level stimulation may result in a negative outcome.