I am a biological anthropologist with research interests in human ecology, demography and life history theory, and the ecology and evolutionary biology of infectious disease. A sampling of current projects includes: (1) human dimensions of primate retroviral transmission, (2) the impact of mobility and social contacts on the spillover and transmission of avian influenza, (3) the demography of residential mobility among Hadza hunter-gatherers, (4) fertility change, economic shocks, and reproductive decisions.
Post-Doc, University of Washington, Center for AIDS and STD, Center for Statistics and the Social Sciences, Center for Studies in Demography and Ecology (2003)
Ph.D., Harvard University, Anthropology (2000)
Current Research and Scholarly Interests
I am a biological anthropologist with primary research interests in evolutionary demography and life history theory. In addition these fundamental interests in the evolution of human life histories, I work at the intersection of disease ecology, the analysis of dynamical systems, and social network analysis. My work combines the formalisms of population biology, statistics, and social network analysis to address fundamental problems in biodemography, epidemiology, and human decision-making in variable environments.
Adaptation to Arid Climates, Climate Change, and Mobility in a Rural Nomadic Population
Climate change is expected to alter the geographical range, severity, and dynamics of infectious diseases. The existing body of research on pathogen dynamics and climate change largely focuses on environmentally transmitted, vector-borne, and zoonotic pathogens, the exposure to which is immediately tied to climate. However, climate change will have profound effects on human behavior, suggesting that there may be substantial downstream effects on directly transmitted infections, including sexually transmitted infections (STIs). This project will investigate study the regional effects on an epidemiological system, as mediated by adaptive (and other) human responses to changing environmental, economic, and social conditions, in the context of unexpected and potentially cascading consequences of global climate change.
- Mary-Ashley Hazel, Postdoctoral Research Fellow, Earth System Science, School of Earth, Energy & Environmental Sciences
The Most Rational People in the World
This is a book project exploring rationality, uncertainty, and the evolution of human behavior. It takes as its launching point a paradox which has only recently become apparent. By almost any measure, Homo sapiens is a spectacularly successful species. From humble origins approximately two million years ago, humans have grown to a population that exceeds seven billion and have colonized – and come to dominate – nearly every terrestrial biome. This phenomenal growth suggests that, on average, our ancestors made very good decisions. Yet a surging tide of work from psychology and economics makes the argument that the decision-making software that our brains run is profoundly flawed — that we are, in a word, irrational. How is it possible that a species apparently so defective in its ability to generate sound decisions can be so spectacularly successful?
Individual Decisions and Emergent Aggregate Patterns: Kin Co-residence among Hadza Hunter-Gatherers
The goal of this project is to investigate the individual and family-level decisions that lead to emergent patterns of kin coresidence among Hadza hunter-gatherers of northern Tanzania.
Comparative Ethnographic Networks
Using relational data gathered from a variety of field contexts (Uganda, Bangladesh, Namibia), we are investigating the properties of sampled social networks, with an eye toward infectious disease transmission dynamics. Topics include: scale-up to landscape-level networks from egocentric samples, missing data models, and integrating spatial and relational dependencies.
Biological and Human Determinants of Primate Retroviral Transmission
The goal of this project is to understand the early evolution of HIV-1 using red colobus monkey metapopulations in the Kibale Forest, Uganda.
Kibale National Park, Uganda
Comparative Spillover Dynamics of Avian Influenza in Endemic Countries
The goal of this project is to develop models of spillover and transmission dynamics of avian influenza in a variety of localities where it is endemic in wild waterfowl.
- Community Leadership
ESS 135 (Aut, Win, Spr)
- Demography and Life History Theory
ESS 163, ESS 363 (Win)
- Environmental Change and Emerging Infectious Diseases
ANTHRO 177, ANTHRO 277, HUMBIO 114 (Win)
- Topics in Earth System Science
ESS 301 (Aut)
Independent Studies (17)
- Directed Individual Study
ANTHRO 451 (Win, Spr)
- Directed Individual Study
ANTHRO 96 (Win, Spr, Sum)
- Directed Individual Study in Earth System Science
ESS 292 (Win)
- Directed Individual Study in Earth Systems
EARTHSYS 297 (Aut, Win, Spr)
- Directed Reading in Environment and Resources
ENVRES 398 (Aut, Win, Spr, Sum)
- Directed Research
EARTHSYS 250 (Aut, Win, Spr)
- Directed Research in Environment and Resources
ENVRES 399 (Aut, Win, Spr, Sum)
- Directed Study in Honors and Senior Papers
ANTHRO 95B (Win, Spr, Sum)
- Graduate Internship
ANTHRO 452 (Win, Spr, Sum)
- Graduate Research
ESS 400 (Aut, Win, Spr)
- Internship in Anthropology
ANTHRO 97 (Win, Spr, Sum)
- Master's Research Thesis
ANTHRO 441 (Win, Spr)
- Qualifying Examination: Area
ANTHRO 401B (Win, Spr)
- Qualifying Examination: Topic
ANTHRO 401A (Win, Spr)
- Research Apprenticeship
ANTHRO 450 (Win, Spr)
- Research in Anthropology
ANTHRO 95 (Win, Spr, Sum)
- Teaching Assistantship
ANTHRO 440 (Win, Spr)
- Directed Individual Study
Prior Year Courses
- Community Leadership
ESS 135 (Aut, Win, Spr)
- Demography and Life History Theory
ESS 363 (Win)
- Social Structure and Social Networks
ESS 360 (Spr)
- Topics in Earth System Science
ESS 301 (Aut)
- Community Leadership
ESS 135 (Aut, Win, Spr)
- Data Analysis for Quantitative Research
ANTHRO 304 (Win)
- EcoGroup: Current Topics in Ecological, Evolutionary, and Environmental Anthropology
ANTHRO 364 (Win)
- Social Structure and Social Networks
ANTHRO 360 (Aut)
- The Most Rational People in the World
ANTHRO 186N (Win)
- Community Leadership
Contact structure, mobility, environmental impact and behaviour: the importance of social forces to infectious disease dynamics and disease ecology
PHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY B-BIOLOGICAL SCIENCES
2017; 372 (1719)
Human factors, including contact structure, movement, impact on the environment and patterns of behaviour, can have significant influence on the emergence of novel infectious diseases and the transmission and amplification of established ones. As anthropogenic climate change alters natural systems and global economic forces drive land-use and land-cover change, it becomes increasingly important to understand both the ecological and social factors that impact infectious disease outcomes for human populations. While the field of disease ecology explicitly studies the ecological aspects of infectious disease transmission, the effects of the social context on zoonotic pathogen spillover and subsequent human-to-human transmission are comparatively neglected in the literature. The social sciences encompass a variety of disciplines and frameworks for understanding infectious diseases; however, here we focus on four primary areas of social systems that quantitatively and qualitatively contribute to infectious diseases as social-ecological systems. These areas are social mixing and structure, space and mobility, geography and environmental impact, and behaviour and behaviour change. Incorporation of these social factors requires empirical studies for parametrization, phenomena characterization and integrated theoretical modelling of social-ecological interactions. The social-ecological system that dictates infectious disease dynamics is a complex system rich in interacting variables with dynamically significant heterogeneous properties. Future discussions about infectious disease spillover and transmission in human populations need to address the social context that affects particular disease systems by identifying and measuring qualitatively important drivers.This article is part of the themed issue 'Opening the black box: re-examining the ecology and evolution of parasite transmission'.
View details for DOI 10.1098/rstb.2016.0454
View details for Web of Science ID 000397800300016
View details for PubMedID 28289265
Minimally Symptomatic Infection in an Ebola 'Hotspot': A Cross-Sectional Serosurvey
PLOS NEGLECTED TROPICAL DISEASES
2016; 10 (11)
Evidence for minimally symptomatic Ebola virus (EBOV) infection is limited. During the 2013-16 outbreak in West Africa, it was not considered epidemiologically relevant to published models or projections of intervention effects. In order to improve our understanding of the transmission dynamics of EBOV in humans, we investigated the occurrence of minimally symptomatic EBOV infection in quarantined contacts of reported Ebola virus disease cases in a recognized 'hotspot.'We conducted a cross-sectional serosurvey in Sukudu, Kono District, Sierra Leone, from October 2015 to January 2016. A blood sample was collected from 187 study participants, 132 negative controls (individuals with a low likelihood of previous exposure to Ebola virus), and 30 positive controls (Ebola virus disease survivors). IgG responses to Ebola glycoprotein and nucleoprotein were measured using Alpha Diagnostic International ELISA kits with plasma diluted at 1:200. Optical density was read at 450 nm (subtracting OD at 630nm to normalize well background) on a ChroMate 4300 microplate reader. A cutoff of 4.7 U/mL for the anti-GP ELISA yielded 96.7% sensitivity and 97.7% specificity in distinguishing positive and negative controls. We identified 14 seropositive individuals not known to have had Ebola virus disease. Two of the 14 seropositive individuals reported only fever during quarantine while the remaining 12 denied any signs or symptoms during quarantine.By using ELISA to measure Zaire Ebola virus antibody concentrations, we identified a significant number of individuals with previously undetected EBOV infection in a 'hotspot' village in Sierra Leone, approximately one year after the village outbreak. The findings provide further evidence that Ebola, like many other viral infections, presents with a spectrum of clinical manifestations, including minimally symptomatic infection. These data also suggest that a significant portion of Ebola transmission events may have gone undetected during the outbreak. Further studies are needed to understand the potential risk of transmission and clinical sequelae in individuals with previously undetected EBOV infection.
View details for DOI 10.1371/journal.pntd.0005087
View details for Web of Science ID 000392154400022
View details for PubMedID 27846221
Measuring selective constraint on fertility in human life histories
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
2015; 112 (29): 8982-8986
Human life histories combine late age at first reproduction, long reproductive span, relatively high fertility, and substantial postreproductive survival. However, even among the most fecund populations, human fertility falls far below its theoretical maximum. The extent of parental care required for successful offspring recruitment and widespread fertility decline under proper economic conditions suggest that selection on fertility is constrained by trade-offs with recruitment. Here we measure the trade-offs between life history traits under selection by approximating the slope of the selective constraint curve on two traits at the observed values. Using a selection of populations that span human demographic space, we find that the substitution elasticity of fertility for infant survival shows age-related patterns, with minimum substitution elasticities ranging from 14 to 22 for the four populations. The age of this minimum occurs earlier in the high-mortality populations relative to generation time than it does in the low-mortality populations. The human curves are qualitatively similar to one of two comparable nonhuman primate age-specific substitution elasticity curves. The curve for rhesus macaques has a similar shape but is shifted down, meaning that the threshold for switching from investing in survival to fertility is lower at all ages. The magnitude of the substitution elasticities is similar between chimpanzees and humans but the shape is quite different, rising more slowly for a longer fraction of the chimpanzee life cycle. The steeply rising substitution elasticities with age in humans has clear implications for the evolution of reproductive senescence.
View details for DOI 10.1073/pnas.1422037112
View details for Web of Science ID 000358225100062
View details for PubMedID 26150499
The evolutionary dynamics of timing of maternal immunity: evaluating the role of age-specific mortality.
Journal of evolutionary biology
If a female survives an infection, she can transfer antibodies against that particular pathogen to any future offspring she produces. The resulting protection of offspring for a period after their birth is termed maternal immunity. Because infection in newborns is associated with high mortality, the duration of this protection is expected to be under strong selection. Evolutionary modeling structured around a trade-off between fertility and duration of maternal immunity has indicated selection for longer duration of maternal immunity for hosts with longer life-spans. Here we use a new modeling framework to extend this analysis to consider characteristics of pathogens (and hosts) in further detail. Importantly, given the challenges in characterising trade-offs linked to immune function empirically, our model makes no assumptions about costs of longer-lasting maternal immunity. Rather, a key component of this analysis is variation in mortality over age. We found that the optimal duration of maternal immunity is shaped by the shifting balance of the burden of infection between young and old individuals. As age of infection depends on characteristics of both the host and the pathogen, both affect the evolution of duration of maternal immunity. Our analysis provides additional support for selection for longer duration of maternal immunity in long-lived hosts, even in the absence of explicit costs linked to duration of maternal immunity. Further, the scope of our results provides explanations for exceptions to the general correlation between duration of maternal immunity and life-span, as we found that both pathogen characteristics and trans-generational effects can lead to important shifts in fitness linked to maternal immunity. Finally, our analysis points to new directions for quantifying the trade-offs that drive the development of the immune system. This article is protected by copyright. All rights reserved.
View details for DOI 10.1111/jeb.12583
View details for PubMedID 25611057
- Resource Transfers and Human Life-History Evolution ANNUAL REVIEW OF ANTHROPOLOGY, VOL 44 2015; 44: 513-531
- The marginal valuation of fertility EVOLUTION AND HUMAN BEHAVIOR 2014; 35 (1): 65-71
A meta-analysis suggesting that the relationship between biodiversity and risk of zoonotic pathogen transmission is idiosyncratic
2013; 16 (5): 679-686
Zoonotic pathogens are significant burdens on global public health. Because they are transmitted to humans from non-human animals, the transmission dynamics of zoonoses are necessarily influenced by the ecology of their animal hosts and vectors. The 'dilution effect' proposes that increased species diversity reduces disease risk, suggesting that conservation and public health initiatives can work synergistically to improve human health and wildlife biodiversity. However, the meta-analysis that we present here indicates a weak and highly heterogeneous relationship between host biodiversity and disease. Our results suggest that disease risk is more likely a local phenomenon that relies on the specific composition of reservoir hosts and vectors, and their ecology, rather than patterns of species biodiversity.
View details for DOI 10.1111/ele.12101
View details for Web of Science ID 000318077200014
View details for PubMedID 23489376
The role of social sciences in predicting and responding to emerging zoonotic diseases
2012; 380 (9857): 1884-1886
View details for DOI 10.1016/S0140-6736(12)61725-5
Primates and the Evolution of Long, Slow Life Histories
2011; 21 (18): R708-R717
Primates are characterized by relatively late ages at first reproduction, long lives and low fertility. Together, these traits define a life-history of reduced reproductive effort. Understanding the optimal allocation of reproductive effort, and specifically reduced reproductive effort, has been one of the key problems motivating the development of life-history theory. Because of their unusual constellation of life-history traits, primates play an important role in the continued development of life-history theory. In this review, I present the evidence for the reduced reproductive effort life histories of primates and discuss the ways that such life-history tactics are understood in contemporary theory. Such tactics are particularly consistent with the predictions of stochastic demographic models, suggesting a key role for environmental variability in the evolution of primate life histories. The tendency for primates to specialize in high-quality, high-variability food items may make them particularly susceptible to environmental variability and explains their low reproductive-effort tactics. I discuss recent applications of life-history theory to human evolution and emphasize the continuity between models used to explain peculiarities of human reproduction and senescence with the long, slow life histories of primates more generally.
View details for DOI 10.1016/j.cub.2011.08.025
View details for Web of Science ID 000295423400015
View details for PubMedID 21959161
A high-resolution human contact network for infectious disease transmission
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
2010; 107 (51): 22020-22025
The most frequent infectious diseases in humans--and those with the highest potential for rapid pandemic spread--are usually transmitted via droplets during close proximity interactions (CPIs). Despite the importance of this transmission route, very little is known about the dynamic patterns of CPIs. Using wireless sensor network technology, we obtained high-resolution data of CPIs during a typical day at an American high school, permitting the reconstruction of the social network relevant for infectious disease transmission. At 94% coverage, we collected 762,868 CPIs at a maximal distance of 3 m among 788 individuals. The data revealed a high-density network with typical small-world properties and a relatively homogeneous distribution of both interaction time and interaction partners among subjects. Computer simulations of the spread of an influenza-like disease on the weighted contact graph are in good agreement with absentee data during the most recent influenza season. Analysis of targeted immunization strategies suggested that contact network data are required to design strategies that are significantly more effective than random immunization. Immunization strategies based on contact network data were most effective at high vaccination coverage.
View details for DOI 10.1073/pnas.1009094108
View details for Web of Science ID 000285521800019
View details for PubMedID 21149721
View details for PubMedCentralID PMC3009790
Plague outbreaks in prairie dog populations explained by percolation thresholds of alternate host abundance
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
2010; 107 (32): 14247-14250
Highly lethal pathogens (e.g., hantaviruses, hendra virus, anthrax, or plague) pose unique public-health problems, because they seem to periodically flare into outbreaks before disappearing into long quiescent phases. A key element to their possible control and eradication is being able to understand where they persist in the latent phase and how to identify the conditions that result in sporadic epidemics or epizootics. In American grasslands, plague, caused by Yersinia pestis, exemplifies this quiescent-outbreak pattern, because it sporadically erupts in epizootics that decimate prairie dog (Cynomys ludovicianus) colonies, yet the causes of outbreaks and mechanisms for interepizootic persistence of this disease are poorly understood. Using field data on prairie community ecology, flea behavior, and plague-transmission biology, we find that plague can persist in prairie-dog colonies for prolonged periods, because host movement is highly spatially constrained. The abundance of an alternate host for disease vectors, the grasshopper mouse (Onychomys leucogaster), drives plague outbreaks by increasing the connectivity of the prairie dog hosts and therefore, permitting percolation of the disease throughout the primary host population. These results offer an alternative perspective on plague's ecology (i.e., disease transmission exacerbated by alternative hosts) and may have ramifications for plague dynamics in Asia and Africa, where a single main host has traditionally been considered to drive Yersinia ecology. Furthermore, abundance thresholds of alternate hosts may be a key phenomenon determining outbreaks of disease in many multihost-disease systems.
View details for DOI 10.1073/pnas.1002826107
View details for Web of Science ID 000280767700050
View details for PubMedID 20660742
Dynamics and Control of Diseases in Networks with Community Structure
PLOS COMPUTATIONAL BIOLOGY
2010; 6 (4)
The dynamics of infectious diseases spread via direct person-to-person transmission (such as influenza, smallpox, HIV/AIDS, etc.) depends on the underlying host contact network. Human contact networks exhibit strong community structure. Understanding how such community structure affects epidemics may provide insights for preventing the spread of disease between communities by changing the structure of the contact network through pharmaceutical or non-pharmaceutical interventions. We use empirical and simulated networks to investigate the spread of disease in networks with community structure. We find that community structure has a major impact on disease dynamics, and we show that in networks with strong community structure, immunization interventions targeted at individuals bridging communities are more effective than those simply targeting highly connected individuals. Because the structure of relevant contact networks is generally not known, and vaccine supply is often limited, there is great need for efficient vaccination algorithms that do not require full knowledge of the network. We developed an algorithm that acts only on locally available network information and is able to quickly identify targets for successful immunization intervention. The algorithm generally outperforms existing algorithms when vaccine supply is limited, particularly in networks with strong community structure. Understanding the spread of infectious diseases and designing optimal control strategies is a major goal of public health. Social networks show marked patterns of community structure, and our results, based on empirical and simulated data, demonstrate that community structure strongly affects disease dynamics. These results have implications for the design of control strategies.
View details for DOI 10.1371/journal.pcbi.1000736
View details for Web of Science ID 000278125300012
View details for PubMedID 20386735
Increased mortality and AIDS-like immunopathology in wild chimpanzees infected with SIVcpz
2009; 460 (7254): 515-519
African primates are naturally infected with over 40 different simian immunodeficiency viruses (SIVs), two of which have crossed the species barrier and generated human immunodeficiency virus types 1 and 2 (HIV-1 and HIV-2). Unlike the human viruses, however, SIVs do not generally cause acquired immunodeficiency syndrome (AIDS) in their natural hosts. Here we show that SIVcpz, the immediate precursor of HIV-1, is pathogenic in free-ranging chimpanzees. By following 94 members of two habituated chimpanzee communities in Gombe National Park, Tanzania, for over 9 years, we found a 10- to 16-fold higher age-corrected death hazard for SIVcpz-infected (n = 17) compared to uninfected (n = 77) chimpanzees. We also found that SIVcpz-infected females were less likely to give birth and had a higher infant mortality rate than uninfected females. Immunohistochemistry and in situ hybridization of post-mortem spleen and lymph node samples from three infected and two uninfected chimpanzees revealed significant CD4(+) T-cell depletion in all infected individuals, with evidence of high viral replication and extensive follicular dendritic cell virus trapping in one of them. One female, who died within 3 years of acquiring SIVcpz, had histopathological findings consistent with end-stage AIDS. These results indicate that SIVcpz, like HIV-1, is associated with progressive CD4(+) T-cell loss, lymphatic tissue destruction and premature death. These findings challenge the prevailing view that all natural SIV infections are non-pathogenic and suggest that SIVcpz has a substantial negative impact on the health, reproduction and lifespan of chimpanzees in the wild.
View details for DOI 10.1038/nature08200
View details for Web of Science ID 000268257000039
View details for PubMedID 19626114
- Assessing Commitment and Reporting Fidelity to a Text Message-Based Participatory Surveillance in Rural Western Uganda PLOS ONE 2016; 11 (6)
Assessing Commitment and Reporting Fidelity to a Text Message-Based Participatory Surveillance in Rural Western Uganda.
2016; 11 (6)
Syndromic surveillance, the collection of symptom data from individuals prior to or in the absence of diagnosis, is used throughout the developed world to provide rapid indications of outbreaks and unusual patterns of disease. However, the low cost of syndromic surveillance also makes it highly attractive for the developing world. We present a case study of electronic participatory syndromic surveillance, using participant-mobile phones in a rural region of Western Uganda, which has a high infectious disease burden, and frequent local and regional outbreaks. Our platform uses text messages to encode a suite of symptoms, their associated durations, and household disease burden, and we explore the ability of participants to correctly encode their symptoms, with an average of 75.2% of symptom reports correctly formatted between the second and 11th reporting timeslots. Concomitantly we identify divisions between participants able to rapidly adjust to this unusually participatory style of data collection, and those few for whom the study proved more challenging. We then perform analyses of the resulting syndromic time series, examining the clustering of symptoms by time and household to identify patterns such as a tendency towards the within-household sharing of respiratory illness.
View details for DOI 10.1371/journal.pone.0155971
View details for PubMedID 27281020
In-Transitivity: Network Patterns of Female Sex Workers (FSWs) in China
2016; 75 (4): 358-370
View details for Web of Science ID 000393024100008
- Human Social Behavior and Demography Drive Patterns of Fine-Scale Dengue Transmission in Endemic Areas of Colombia PLOS ONE 2015; 10 (12)
- Beyond Bushmeat: Animal Contact, Injury, and Zoonotic Disease Risk in Western Uganda ECOHEALTH 2015; 11 (4): 534-543
- Pursuit: A Foraging Simulation Tool for Research and Teaching EVOLUTIONARY PSYCHOLOGY 2015; 13 (4)
- Public health perspective on patterns of biodiversity and zoonotic disease PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA 2015; 112 (46): E6261-E6261
Genomic Resources Notes Accepted 1 December 2014-31 January 2015
MOLECULAR ECOLOGY RESOURCES
2015; 15 (3): 684-684
This article documents the public availability of (i) transcriptome sequence data and assembly for the rostrum dace (Leuciscus burdigalensis) naturally infected by a copepod ectoparasite (Tracheliastes polycolpus) and (ii) SNPs identified and validated from RAD sequencing for the Ugandan red colobus (Procolobus rufomitratus tephrosceles) using RAD sequencing.
View details for DOI 10.1111/1755-0998.12388
View details for Web of Science ID 000352653700020
View details for PubMedID 25857929
- Gender inequality and HIV transmission: a global analysis JOURNAL OF THE INTERNATIONAL AIDS SOCIETY 2014; 17
Gender inequality and HIV transmission: a global analysis.
Journal of the International AIDS Society
2014; 17: 19035-?
The HIV pandemic disproportionately impacts young women. Worldwide, young women aged 15-24 are infected with HIV at rates twice that of young men, and young women alone account for nearly a quarter of all new HIV infections. The incommensurate HIV incidence in young - often poor - women underscores how social and economic inequalities shape the HIV epidemic. Confluent social forces, including political and gender violence, poverty, racism, and sexism impede equal access to therapies and effective care, but most of all constrain the agency of women.HIV prevalence data was compiled from the 2010 UNAIDS Global Report. Gender inequality was assessed using the 2011 United Nations Human Development Report Gender Inequality Index (GII). Logistic regression models were created with predominant mode of transmission (heterosexual vs. MSM/IDU) as the dependent variable and GII, Muslim vs. non-Muslim, Democracy Index, male circumcision rate, log gross national income (GNI) per capita at purchasing power parity (PPP), and region as independent variables.There is a significant correlation between having a predominantly heterosexual epidemic and high gender inequality across all models. There is not a significant association between whether a country is predominantly Muslim, has a high/low GNI at PPP, has a high/low circumcision rate, and its primary mode of transmission. In addition, there are only three countries that have had a generalized epidemic in the past but no longer have one: Cambodia, Honduras, and Eritrea. GII data are available only for Cambodia and Honduras, and these countries showed a 37 and 34% improvement, respectively, in their Gender Inequality Indices between 1995 and 2011. During the same period, both countries reduced their HIV prevalence below the 1% threshold of a generalized epidemic. This represents limited but compelling evidence that improvements in gender inequality can lead to the abatement of generalized epidemics.Gender inequality is an important factor in the maintenance - and possibly in the establishment of - generalized HIV epidemics. We should view improvements in gender inequality as part of a broader public health strategy.
View details for DOI 10.7448/IAS.17.1.19035
View details for PubMedID 24976436
View details for PubMedCentralID PMC4074603
Beyond Bushmeat: Animal Contact, Injury, and Zoonotic Disease Risk in Western Uganda.
Zoonotic pathogens cause an estimated 70% of emerging and re-emerging infectious diseases in humans. In sub-Saharan Africa, bushmeat hunting and butchering is considered the primary risk factor for human-wildlife contact and zoonotic disease transmission, particularly for the transmission of simian retroviruses. However, hunting is only one of many activities in sub-Saharan Africa that bring people and wildlife into contact. Here, we examine human-animal interaction in western Uganda, identifying patterns of injuries from animals and contact with nonhuman primates. Additionally, we identify individual-level risk factors associated with contact. Nearly 20% (246/1,240) of participants reported either being injured by an animal or having contact with a primate over their lifetimes. The majority (51.7%) of injuries were dog bites that healed with no long-term medical consequences. The majority (76.8%) of 125 total primate contacts involved touching a carcass; however, butchering (20%), hunting (10%), and touching a live primate (10%) were also reported. Red colobus (Piliocolobus rufomitratus tephrosceles) accounted for most primate contact events. Multivariate logistic regression indicated that men who live adjacent to forest fragments are at elevated risk of animal contact and specifically primate contact. Our results provide a useful comparison to West and Central Africa where "bushmeat hunting" is the predominant paradigm for human-wildlife contact and zoonotic disease transmission.
View details for DOI 10.1007/s10393-014-0942-y
View details for PubMedID 24845574
Metapopulation Dynamics Enable Persistence of Influenza A, Including A/H5N1, in Poultry
2013; 8 (12)
Highly pathogenic influenza A/H5N1 has persistently but sporadically caused human illness and death since 1997. Yet it is still unclear how this pathogen is able to persist globally. While wild birds seem to be a genetic reservoir for influenza A, they do not seem to be the main source of human illness. Here, we highlight the role that domestic poultry may play in maintaining A/H5N1 globally, using theoretical models of spatial population structure in poultry populations. We find that a metapopulation of moderately sized poultry flocks can sustain the pathogen in a finite poultry population for over two years. Our results suggest that it is possible that moderately intensive backyard farms could sustain the pathogen indefinitely in real systems. This fits a pattern that has been observed from many empirical systems. Rather than just employing standard culling procedures to control the disease, our model suggests ways that poultry production systems may be modified.
View details for DOI 10.1371/journal.pone.0080091
View details for Web of Science ID 000327944500010
View details for PubMedID 24312455
Interactions between Social Structure, Demography, and Transmission Determine Disease Persistence in Primates
2013; 8 (10)
Catastrophic declines in African great ape populations due to disease outbreaks have been reported in recent years, yet we rarely hear of similar disease impacts for the more solitary Asian great apes, or for smaller primates. We used an age-structured model of different primate social systems to illustrate that interactions between social structure and demography create 'dynamic constraints' on the pathogens that can establish and persist in primate host species with different social systems. We showed that this varies by disease transmission mode. Sexually transmitted infections (STIs) require high rates of transmissibility to persist within a primate population. In particular, for a unimale social system, STIs require extremely high rates of transmissibility for persistence, and remain at extremely low prevalence in small primates, but this is less constrained in longer-lived, larger-bodied primates. In contrast, aerosol transmitted infections (ATIs) spread and persist at high prevalence in medium and large primates with moderate transmissibility;, establishment and persistence in small-bodied primates require higher relative rates of transmissibility. Intragroup contact structure - the social network - creates different constraints for different transmission modes, and our model underscores the importance of intragroup contacts on infection prior to intergroup movement in a structured population. When alpha males dominate sexual encounters, the resulting disease transmission dynamics differ from when social interactions are dominated by mother-infant grooming events, for example. This has important repercussions for pathogen spread across populations. Our framework reveals essential social and demographic characteristics of primates that predispose them to different disease risks that will be important for disease management and conservation planning for protected primate populations.
View details for DOI 10.1371/journal.pone.0076863
View details for Web of Science ID 000326029300057
View details for PubMedID 24204688
To kill a kangaroo: understanding the decision to pursue high-risk/high-gain resources.
Proceedings. Biological sciences / The Royal Society
2013; 280 (1767): 20131210-?
In this paper, we attempt to understand hunter-gatherer foraging decisions about prey that vary in both the mean and variance of energy return using an expected utility framework. We show that for skewed distributions of energetic returns, the standard linear variance discounting (LVD) model for risk-sensitive foraging can produce quite misleading results. In addition to creating difficulties for the LVD model, the skewed distributions characteristic of hunting returns create challenges for estimating probability distribution functions required for expected utility. We present a solution using a two-component finite mixture model for foraging returns. We then use detailed foraging returns data based on focal follows of individual hunters in Western Australia hunting for high-risk/high-gain (hill kangaroo) and relatively low-risk/low-gain (sand monitor) prey. Using probability densities for the two resources estimated from the mixture models, combined with theoretically sensible utility curves characterized by diminishing marginal utility for the highest returns, we find that the expected utility of the sand monitors greatly exceeds that of kangaroos despite the fact that the mean energy return for kangaroos is nearly twice as large as that for sand monitors. We conclude that the decision to hunt hill kangaroos does not arise simply as part of an energetic utility-maximization strategy and that additional social, political or symbolic benefits must accrue to hunters of this highly variable prey.
View details for DOI 10.1098/rspb.2013.1210
View details for PubMedID 23884091
- To kill a kangaroo: understanding the decision to pursue high-risk/high-gain resources. Proceedings. Biological sciences / The Royal Society 2013; 280 (1767): 20131210-?
Prevalences of sexually transmitted infections in young adults and female sex workers in Peru: a national population-based survey
LANCET INFECTIOUS DISEASES
2012; 12 (10): 765-773
We assessed prevalences of seven sexually transmitted infections (STIs) in Peru, stratified by risk behaviours, to help to define care and prevention priorities.In a 2002 household-based survey of the general population, we enrolled randomly selected 18-29-year-old residents of 24 cities with populations greater than 50 000 people. We then surveyed female sex workers (FSWs) in these cities. We gathered data for sexual behaviour; vaginal specimens or urine for nucleic acid amplification tests for Neisseria gonorrhoeae, Chlamydia trachomatis, and Trichomonas vaginalis; and blood for serological tests for syphilis, HIV, and (in subsamples) herpes simplex virus 2 (HSV2) and human T-lymphotropic virus. This study is a registered component of the PREVEN trial, number ISRCTN43722548.15 261 individuals from the general population and 4485 FSWs agreed to participate in our survey. Overall prevalence of infection with HSV2, weighted for city size, was 13·5% in men, 13·6% in women, and 60·6% in FSWs (all values in FSWs standardised to age composition of women in the general population). The prevalence of C trachomatis infection was 4·2% in men, 6·5% in women, and 16·4% in FSWs; of T vaginalis infection was 0·3% in men, 4·9% in women, and 7·9% in FSWs; and of syphilis was 0·5% in men, 0·4% in women, and 0·8% in FSWs. N gonorrhoeae infection had a prevalence of 0·1% in men and women, and of 1·6% in FSWs. Prevalence of HIV infection was 0·5% in men and FSWs, and 0·1% in women. Four (0·3%) of 1535 specimens were positive for human T-lymphotropic virus 1. In men, 65·0% of infections with HIV, 71·5% of N gonorrhoeae, and 41·4% of HSV2 and 60·9% of cases of syphilis were in the 13·3% who had sex with men or unprotected sex with FSWs in the past year. In women from the general population, 66·7% of infections with HIV and 16·7% of cases of syphilis were accounted for by the 4·4% who had been paid for sex by any of their past three partners.Defining of high-risk groups could guide targeting of interventions for communicable diseases-including STIs-in the general Peruvian population.Wellcome Trust-Burroughs Wellcome Fund Infectious Disease Initiative and US National Institutes of Health.
View details for DOI 10.1016/S1473-3099(12)70144-5
View details for Web of Science ID 000309631200024
View details for PubMedID 22878023
Phenotypic quality influences fertility in Gombe chimpanzees
JOURNAL OF ANIMAL ECOLOGY
2010; 79 (6): 1262-1269
1. Fertility is an important fitness component, but is difficult to measure in slowly reproducing, long-lived animals such as chimpanzees (Pan troglodytes). 2. We measured fertility and the effect of measured covariates on fertility in a 43-year sample of birth intervals of chimpanzees from the Gombe National Park, Tanzania using Cox proportional hazards regression with individual-level random effects. 3. The birth hazard declined with mothers' age at a rate of 0·84 per year following age at first reproduction. This value is somewhat stronger than previous estimates. 4. Loss of the infant that opened the birth interval increased the birth hazard 134-fold. 5. Birth intervals following the first complete birth interval were shorter than this first interval, while sex of the previous infant had no significant effect. 6. Maternal dominance rank was significant at the P < 0·1 level when coded as high/middle/low but was highly significant when we simply considered high rank vs. others. 7. Individual heterogeneity had a substantial impact on birth interval duration. We interpret this individual effect as a measure of phenotypic quality, controlling for the measured covariates such as dominance rank. This interpretation is supported by the correlation of individual heterogeneity scores with similar independent measures of body mass.
View details for DOI 10.1111/j.1365-2656.2010.01687.x
View details for Web of Science ID 000283074000013
View details for PubMedID 20412347
Impact of Simian Immunodeficiency Virus Infection on Chimpanzee Population Dynamics
2010; 6 (9)
Like human immunodeficiency virus type 1 (HIV-1), simian immunodeficiency virus of chimpanzees (SIVcpz) can cause CD4+ T cell loss and premature death. Here, we used molecular surveillance tools and mathematical modeling to estimate the impact of SIVcpz infection on chimpanzee population dynamics. Habituated (Mitumba and Kasekela) and non-habituated (Kalande) chimpanzees were studied in Gombe National Park, Tanzania. Ape population sizes were determined from demographic records (Mitumba and Kasekela) or individual sightings and genotyping (Kalande), while SIVcpz prevalence rates were monitored using non-invasive methods. Between 2002-2009, the Mitumba and Kasekela communities experienced mean annual growth rates of 1.9% and 2.4%, respectively, while Kalande chimpanzees suffered a significant decline, with a mean growth rate of -6.5% to -7.4%, depending on population estimates. A rapid decline in Kalande was first noted in the 1990s and originally attributed to poaching and reduced food sources. However, between 2002-2009, we found a mean SIVcpz prevalence in Kalande of 46.1%, which was almost four times higher than the prevalence in Mitumba (12.7%) and Kasekela (12.1%). To explore whether SIVcpz contributed to the Kalande decline, we used empirically determined SIVcpz transmission probabilities as well as chimpanzee mortality, mating and migration data to model the effect of viral pathogenicity on chimpanzee population growth. Deterministic calculations indicated that a prevalence of greater than 3.4% would result in negative growth and eventual population extinction, even using conservative mortality estimates. However, stochastic models revealed that in representative populations, SIVcpz, and not its host species, frequently went extinct. High SIVcpz transmission probability and excess mortality reduced population persistence, while intercommunity migration often rescued infected communities, even when immigrating females had a chance of being SIVcpz infected. Together, these results suggest that the decline of the Kalande community was caused, at least in part, by high levels of SIVcpz infection. However, population extinction is not an inevitable consequence of SIVcpz infection, but depends on additional variables, such as migration, that promote survival. These findings are consistent with the uneven distribution of SIVcpz throughout central Africa and explain how chimpanzees in Gombe and elsewhere can be at equipoise with this pathogen.
View details for DOI 10.1371/journal.ppat.1001116
View details for Web of Science ID 000282373000015
View details for PubMedID 20886099
The Effect of the Civil War on Southern Marriage Patterns
JOURNAL OF SOUTHERN HISTORY
2010; 76 (1): 39-70
View details for Web of Science ID 000274306000002
Early Assessment of Anxiety and Behavioral Response to Novel Swine-Origin Influenza A(H1N1)
2009; 4 (12)
Since late April, 2009, a novel influenza virus A (H1N1), generally referred to as the "swine flu," has spread around the globe and infected hundreds of thousands of people. During the first few days after the initial outbreak in Mexico, extensive media coverage together with a high degree of uncertainty about the transmissibility and mortality rate associated with the virus caused widespread concern in the population. The spread of an infectious disease can be strongly influenced by behavioral changes (e.g., social distancing) during the early phase of an epidemic, but data on risk perception and behavioral response to a novel virus is usually collected with a substantial delay or after an epidemic has run its course.Here, we report the results from an online survey that gathered data (n = 6,249) about risk perception of the Influenza A(H1N1) outbreak during the first few days of widespread media coverage (April 28-May 5, 2009). We find that after an initially high level of concern, levels of anxiety waned along with the perception of the virus as an immediate threat. Overall, our data provide evidence that emotional status mediates behavioral response. Intriguingly, principal component analysis revealed strong clustering of anxiety about swine flu, bird flu and terrorism. All three of these threats receive a great deal of media attention and their fundamental uncertainty is likely to generate an inordinate amount of fear vis-a-vis their actual threat.Our results suggest that respondents' behavior varies in predictable ways. Of particular interest, we find that affective variables, such as self-reported anxiety over the epidemic, mediate the likelihood that respondents will engage in protective behavior. Understanding how protective behavior such as social distancing varies and the specific factors that mediate it may help with the design of epidemic control strategies.
View details for DOI 10.1371/journal.pone.0008032
View details for Web of Science ID 000272829000001
View details for PubMedID 19997505
- The force of selection on the human life cycle EVOLUTION AND HUMAN BEHAVIOR 2009; 30 (5): 305-314
- Demographic and Social Predictors of Intimate Partner Violence in Colombia HUMAN NATURE-AN INTERDISCIPLINARY BIOSOCIAL PERSPECTIVE 2009; 20 (2): 184-203
Demographic and social predictors of intimate partner violence in Colombia : a dyadic power perspective.
Human nature (Hawthorne, N.Y.)
2009; 20 (2): 184-203
Intimate partner violence (IPV) is a major health and human rights problem globally. However, empirical findings on the predictors of IPV cross-culturally are highly inconsistent, and the theory of IPV is underdeveloped. We propose a new analytical framework based on cooperative game theory in which IPV is a function of the power relations of the dyadic relationship, not simply the actors involved. Using data from the 2005 Colombian Demographic and Health Survey, we test the hypothesis that IPV is predicted by large asymmetries in dyadic power using a hierarchical generalized linear model. Results suggest that education, urban residence, age at sexual debut, whether the woman has other sexual partners, and the age difference between spouses have strong effects on the log-odds of a woman experiencing IPV. Cooperative game theory and social network analysis offer a general approach to the problem of intimate partner interactions which can be applied broadly cross-culturally.
View details for DOI 10.1007/s12110-009-9064-6
View details for PubMedID 25526957
The "fire stick farming" hypothesis: Australian Aboriginal foraging strategies, biodiversity, and anthropogenic fire mosaics
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
2008; 105 (39): 14796-14801
Aboriginal burning in Australia has long been assumed to be a "resource management" strategy, but no quantitative tests of this hypothesis have ever been conducted. We combine ethnographic observations of contemporary Aboriginal hunting and burning with satellite image analysis of anthropogenic and natural landscape structure to demonstrate the processes through which Aboriginal burning shapes arid-zone vegetational diversity. Anthropogenic landscapes contain a greater diversity of successional stages than landscapes under a lightning fire regime, and differences are of scale, not of kind. Landscape scale is directly linked to foraging for small, burrowed prey (monitor lizards), which is a specialty of Aboriginal women. The maintenance of small-scale habitat mosaics increases small-animal hunting productivity. These results have implications for understanding the unique biodiversity of the Australian continent, through time and space. In particular, anthropogenic influences on the habitat structure of paleolandscapes are likely to be spatially localized and linked to less mobile, "broad-spectrum" foraging economies.
View details for DOI 10.1073/pnas.0804757105
View details for Web of Science ID 000259840500012
View details for PubMedID 18809925
Aging and fertility patterns in wild chimpanzees provide insights into the evolution of menopause
2007; 17 (24): 2150-2156
Human menopause is remarkable in that reproductive senescence is markedly accelerated relative to somatic aging, leaving an extended postreproductive period for a large proportion of women. Functional explanations for this are debated, in part because comparative data from closely related species are inadequate. Existing studies of chimpanzees are based on very small samples and have not provided clear conclusions about the reproductive function of aging females. These studies have not examined whether reproductive senescence in chimpanzees exceeds the pace of general aging, as in humans, or occurs in parallel with declines in overall health, as in many other animals. In order to remedy these problems, we examined fertility and mortality patterns in six free-living chimpanzee populations. Chimpanzee and human birth rates show similar patterns of decline beginning in the fourth decade, suggesting that the physiology of reproductive senescence was relatively conserved in human evolution. However, in contrast to humans, chimpanzee fertility declines are consistent with declines in survivorship, and healthy females maintain high birth rates late into life. Thus, in contrast to recent claims, we find no evidence that menopause is a typical characteristic of chimpanzee life histories.
View details for DOI 10.1016/j.cub.2007.11.033
View details for Web of Science ID 000251852200028
View details for PubMedID 18083515
View details for PubMedCentralID PMC2190291
demogR: A package for the construction and analysis of age-structured demographic models in R
JOURNAL OF STATISTICAL SOFTWARE
2007; 22 (10): 1-28
View details for Web of Science ID 000252430400001
Interval estimates for epidemic thresholds in two-sex network models
THEORETICAL POPULATION BIOLOGY
2006; 70 (2): 125-134
Epidemic thresholds in network models of heterogeneous populations characterized by highly right-skewed contact distributions can be very small. When the population is above the threshold, an epidemic is inevitable and conventional control measures to reduce the transmissibility of a pathogen will fail to eradicate it. We consider a two-sex network model for a sexually transmitted disease which assumes random mixing conditional on the degree distribution. We derive expressions for the basic reproductive number (R(0)) for one and heterogeneous two-population in terms of characteristics of the degree distributions and transmissibility. We calculate interval estimates for the epidemic thresholds for stochastic process models in three human populations based on representative surveys of sexual behavior (Uganda, Sweden, USA). For Uganda and Sweden, the epidemic threshold is greater than zero with high confidence. For the USA, the interval includes zero. We discuss the implications of these findings along with the limitations of epidemic models which assume random mixing.
View details for DOI 10.1016/j.tpb.2006.02.004
View details for Web of Science ID 000239979000003
View details for PubMedID 16714041
The Marriage Squeeze in Colombia, 1973-2005: The Role of Excess Male Death
2006; 53 (3-4): 140-151
View details for DOI 10.1080/19485565.2006.9989123
Fetal programming: Adaptive life-history tactics or making the best of a bad start?
29th Annual Meeting of the Human-Biology-Association
WILEY-LISS. 2005: 22–33
Fetal programming is an ontogenetic phenomenon of increasing interest to human biologists. Because the downstream consequences of fetal programming have clear impacts on specific life-history traits (e.g., age at first reproduction and the general age-pattern of reproductive investments), a number of authors have raised the question of the adaptive significance of fetal programming. In this paper, I review in some detail several classical models in life-history theory and discuss their relative merits and weaknesses for human biology. I suggest that an adequate model of human life-history evolution must account for the highly structured nature of the human life cycle, with its late age at first reproduction, large degree of iteroparity, highly overlapping generations, and extensive, post-weaning parental investment. I further suggest that an understanding of stochastic demography is essential for answering the question of the adaptive significance of fetal programming, and specifically the finding of low birth weight on smaller adult body size and earlier age at first reproduction. Using a stage-structured stochastic population model, I show that the downstream consequences of early deprivation may be "making the best of a bad start" rather than an adaptation per se. When a high-investment strategy entails survival costs, the alternate strategy of early reproduction with relatively low investment may have higher fitness than trying to play the high-investment strategy and failing.
View details for DOI 10.1002/ajhb.20099
View details for Web of Science ID 000226105500003
View details for PubMedID 15611978
Likelihood-based inference for stochastic models of sexual network formation
THEORETICAL POPULATION BIOLOGY
2004; 65 (4): 413-422
Sexually-transmitted diseases (STDs) constitute a major public health concern. Mathematical models for the transmission dynamics of STDs indicate that heterogeneity in sexual activity level allow them to persist even when the typical behavior of the population would not support endemicity. This insight focuses attention on the distribution of sexual activity level in a population. In this paper, we develop several stochastic process models for the formation of sexual partnership networks. Using likelihood-based model selection procedures, we assess the fit of the different models to three large distributions of sexual partner counts: (1) Rakai, Uganda, (2) Sweden, and (3) the USA. Five of the six single-sex networks were fit best by the negative binomial model. The American women's network was best fit by a power-law model, the Yule. For most networks, several competing models fit approximately equally well. These results suggest three conclusions: (1) no single unitary process clearly underlies the formation of these sexual networks, (2) behavioral heterogeneity plays an essential role in network structure, (3) substantial model uncertainty exists for sexual network degree distributions. Behavioral research focused on the mechanisms of partnership formation will play an essential role in specifying the best model for empirical degree distributions. We discuss the limitations of inferences from such data, and the utility of degree-based epidemiological models more generally.
View details for DOI 10.1016/j.tpb.2003.09.006
View details for Web of Science ID 000221621800009
View details for PubMedID 15136015
An assessment of preferential attachment as a mechanism for human sexual network formation
PROCEEDINGS OF THE ROYAL SOCIETY B-BIOLOGICAL SCIENCES
2003; 270 (1520): 1123-1128
Recent research into the properties of human sexual-contact networks has suggested that the degree distribution of the contact graph exhibits power-law scaling. One notable property of this power-law scaling is that the epidemic threshold for the population disappears when the scaling exponent rho is in the range 2 < rho < or = 3. This property is of fundamental significance for the control of sexually transmitted diseases (STDs) such as HIV/AIDS since it implies that an STD can persist regardless of its transmissibility. A stochastic process, known as preferential attachment, that yields one form of power-law scaling has been suggested to underlie the scaling of sexual degree distributions. The limiting distribution of this preferential attachment process is the Yule distribution, which we fit using maximum likelihood to local network data from samples of three populations: (i) the Rakai district, Uganda; (ii) Sweden; and (iii) the USA. For all local networks but one, our interval estimates of the scaling parameters are in the range where epidemic thresholds exist. The estimate of the exponent for male networks in the USA is close to 3, but the preferential attachment model is a very poor fit to these data. We conclude that the epidemic thresholds implied by this model exist in both single-sex and two-sex epidemic model formulations. A strong conclusion that we derive from these results is that public health interventions aimed at reducing the transmissibility of STD pathogens, such as implementing condom use or high-activity anti-retroviral therapy, have the potential to bring a population below the epidemic transition, even in populations exhibiting large degrees of behavioural heterogeneity.
View details for DOI 10.1098/rspb.2003.2369
View details for Web of Science ID 000183400900003
View details for PubMedID 12816649
- Sexual contacts and epidemic thresholds NATURE 2003; 423 (6940): 605-606
The raw and the stolen - Cooking and the ecology of human origins
1999; 40 (5): 567-594
View details for Web of Science ID 000083794300001