The effect of seasonal birth pulses on pathogen persistence in wild mammal populations.

The notion of a critical community size (CCS), or population size that is likely to result in long-term persistence of a communicable disease, has been developed based on the empirical observations of acute immunizing infections in human populations, and extended for use in wildlife populations. Seasonal birth pulses are frequently observed in wildlife and are expected to impact infection dynamics, yet their effect on pathogen persistence and CCS have not been considered. To investigate this issue theoretically, we use stochastic epidemiological models to ask how host life-history traits and infection parameters interact to determine pathogen persistence within a closed population. We fit seasonal birth pulse models to data from diverse mammalian species in order to identify realistic parameter ranges. When varying the synchrony of the birth pulse with all other parameters being constant, our model predicted that the CCS can vary by more than two orders of magnitude. Tighter birth pulses tended to drive pathogen extinction by creating large amplitude oscillations in prevalence, especially with high demographic turnover and short infectious periods. Parameters affecting the relative timing of the epidemic and birth pulse peaks determined the intensity and direction of the effect of pre-existing immunity in the population on the pathogen's ability to persist beyond the initial epidemic following its introduction.

Using quantitative disease dynamics as a tool for guiding response to avian influenza in poultry in the United States of America.

Wild birds are the primary source of genetic diversity for influenza A viruses that eventually emerge in poultry and humans. Much progress has been made in the descriptive ecology of avian influenza viruses (AIVs), but contributions are less evident from quantitative studies (e.g., those including disease dynamic models). Transmission between host species, individuals and flocks has not been measured with sufficient accuracy to allow robust quantitative evaluation of alternate control protocols. We focused on the United States of America (USA) as a case study for determining the state of our quantitative knowledge of potential AIV emergence processes from wild hosts to poultry. We identified priorities for quantitative research that would build on existing tools for responding to AIV in poultry and concluded that the following knowledge gaps can be addressed with current empirical data: (1) quantification of the spatio-temporal relationships between AIV prevalence in wild hosts and poultry populations, (2) understanding how the structure of different poultry sectors impacts within-flock transmission, (3) determining mechanisms and rates of between-farm spread, and (4) validating current policy-decision tools with data. The modeling studies we recommend will improve our mechanistic understanding of potential AIV transmission patterns in USA poultry, leading to improved measures of accuracy and reduced uncertainty when evaluating alternative control strategies.

Ecology of zoonotic infectious diseases in bats: current knowledge and future directions.

Bats are hosts to a range of zoonotic and potentially zoonotic pathogens. Human activities that increase exposure to bats will likely increase the opportunity for infections to spill over in the future. Ecological drivers of pathogen spillover and emergence in novel hosts, including humans, involve a complex mixture of processes, and understanding these complexities may aid in predicting spillover. In particular, only once the pathogen and host ecologies are known can the impacts of anthropogenic changes be fully appreciated. Cross-disciplinary approaches are required to understand how host and pathogen ecology interact. Bats differ from other sylvatic disease reservoirs because of their unique and diverse lifestyles, including their ability to fly, often highly gregarious social structures, long lifespans and low fecundity rates. We highlight how these traits may affect infection dynamics and how both host and pathogen traits may interact to affect infection dynamics. We identify key questions relating to the ecology of infectious diseases in bats and propose that a combination of field and laboratory studies are needed to create data-driven mechanistic models to elucidate those aspects of bat ecology that are most critical to the dynamics of emerging bat viruses. If commonalities can be found, then predicting the dynamics of newly emerging diseases may be possible. This modelling approach will be particularly important in scenarios when population surveillance data are unavailable and when it is unclear which aspects of host ecology are driving infection dynamics.

Quantification of heterosubtypic immunity between avian influenza subtypes H3N8 and H4N6 in multiple avian host species.

Low-pathogenicity avian influenza virus (LPAIV) can lead to epizootics that cause economic losses in poultry or the emergence of human-infectious strains. LPAIVs experience a complex immunity landscape as they are endemic in numerous host species, and many antigenically distinct strains co-circulate. Prevention and control of emergence of detrimental strains requires an understanding of infection/transmission characteristics of the various subtypes in different hosts, including interactions between subtypes. In order to develop analytical frameworks for examining control efficacy, quantification of heterosubtypic immunity interactions is fundamental. However, these data are scarce, especially for wild avian subtypes in natural hosts. Consequently, in this study, three host species (mallards, quail and pheasants) were infected with two LPAIV subtypes isolated from wild birds: H3N8 and H4N6. The recovered hosts were also reinfected with the alternate subtype to measure the effects of heterosubtypic immunity. Oropharyngeal and cloacal swabs were collected and viral RNA load was quantified by real-time RT-PCR. For secondary infections in recovered hosts, peak viral load was up to four orders of magnitude lower and shedding length was up to 4 days shorter. However, both the magnitude and presence of heterosubtypic immunity varied across specific host species/subtype combinations. Using a mathematical model of virus replication, the variation in virus replication dynamics due to host individuals was quantified. It was found that accounting for individual heterogeneity is important for drawing accurate conclusions about treatment effects. These results are relevant for developing epidemiological models to inform control practices and for analysing virus replication data.

The impact of nonacademic variables on performance at two medical schools.

Recent research shows that nonacademic variables must be taken into account when analyzing the indicators of medical student success. However, most previous studies have been limited to a single institution or population. This study investigated the relationship between nonacademic variables and performance at two very different medical schools. The Noncognitive Questionnaire was administered to 104 students at School A (predominantly white and historically oriented toward women) and 102 at School B (predominantly black). Correlation and multiple regression analyses were conducted to determine the relationship among nonacademic variables, undergraduate academic variables (Medical College Admission Test, undergraduate grade point average, and college quality), basic science grades, and US Medical Licensure Exam Step I (USMLE 1) scores. At School A, leadership/decisiveness, expected difficulty, and motivation predicted higher USMLE I scores and higher basic science grades each semester. At School B, expected difficulty was correlated with higher first semester grades only. For School A women, initiative/commitment was positively associated with both higher grades and higher USMLE scores. For black students of School B, expected difficulty was positively associated with higher grades. Identifying school-specific nonacademic variables of performance is critical to developing improved student support services.

Schizotypal and paranoid personality disorder in the relatives of patients with schizophrenia and affective disorders: a review.

This review considers the possible familial relationship of schizotypal and paranoid personality disorders (SPD, PPD) to schizophrenia (SCZ) and affective disorders (AD). There have been few controlled studies on familial risk of SPD and PPD based on direct semi-structured interviews of relatives, blind to proband diagnosis. Three of six studies reported increased familial risk of SPD for SCZ probands, but with considerable variability in estimates of this risk. None of four studies reported a significant relationship between AD and familial SPD. There is substantial but less consistent evidence for a familial relationship between PPD and SCZ: three of six studies supported such a relationship, but one large study reported increased familial risk of PPD for AD and not for SCZ probands. There is also some evidence that negative symptoms are most characteristic of SPD in relatives of SCZ probands. Also discussed are issues concerning the adequacy of current criteria for defining schizophrenia spectrum pathology, and of diagnostic methods in this area.

Relationship between locus of control and performance on the National Board of Medical Examiners, Part I, among black medical students.

Several investigators have recently suggested that nonacademic factors may be particularly important in the performance of minority medical students. This study examined the relationship between the personality variable of locus of control and black medical students' performance on the National Board of Medical Examiners I. Subjects included 50 third- and fourth-year medical students of African-American, Caribbean, and African backgrounds from 4 medical schools. An internal locus of control was correlated with test performance, whereas the more traditional index of the Medical College Admissions Test was not. Implications of these results for the preparation, admission, and training of black medical students are discussed.

Relationship between locus of control and performance on the national board of medical examiners, part 1, among black medical students

Several investigators have recently suggested that nonacademic factors may be particularly important in the performance of minority medical students. This study examined the relationship between the personality variable of locus of control and black medical students' performance on the National Board of Medical Examiners I. Subjects include 50 third - and fourth-year medical students of African-American, Caribbean, and African backgrounds from 4 medical schools. An internal locus of control was correlated with test performance, whereas the more traditional index of the Medical College Admissions Test was not. Implications of these results for the preparation, admission, and training of black medical students are discussed (AU)