Comparative Diagnostic Utility of SARS-CoV-2 Rapid Antigen and Molecular Testing in a Community Setting.

BACKGROUND: SARS-CoV-2 antigen-detection rapid diagnostic tests (Ag-RDTs) have become widely utilized but longitudinal characterization of their community-based performance remains incompletely understood. METHODS: This prospective longitudinal study at a large public university in Seattle, WA utilized remote enrollment, online surveys, and self-collected nasal swab specimens to evaluate Ag-RDT performance against real-time reverse transcription polymerase chain reaction (rRT-PCR) in the context of SARS-CoV-2 Omicron. Ag-RDT sensitivity and specificity within 1 day of rRT-PCR were evaluated by symptom status throughout the illness episode and Orf1b cycle threshold (Ct). RESULTS: From February to December 2022, 5757 participants reported 17 572 Ag-RDT results and completed 12 674 rRT-PCR tests, of which 995 (7.9%) were rRT-PCR positive. Overall sensitivity and specificity were 53.0% (95% confidence interval [CI], 49.6%-56.4%) and 98.8% (95% CI, 98.5%-99.0%), respectively. Sensitivity was comparatively higher for Ag-RDTs used 1 day after rRT-PCR (69.0%), 4-7 days after symptom onset (70.1%), and Orf1b Ct ≤20 (82.7%). Serial Ag-RDT sensitivity increased with repeat testing ≥2 (68.5%) and ≥4 (75.8%) days after an initial Ag-RDT-negative result. CONCLUSIONS: Ag-RDT performance varied by clinical characteristics and temporal testing patterns. Our findings support recommendations for serial testing following an initial Ag-RDT-negative result, especially among recently symptomatic persons or those at high risk for SARS-CoV-2 infection.

Systematic review: fetal death reporting and risk in Zika-affected pregnancies.

OBJECTIVES: Zika virus is linked to several adverse pregnancy outcomes. We assessed whether Zika infection during pregnancy is associated with increased risk of foetal death (miscarriage, stillbirth, abortion) and whether there is incomplete reporting of such deaths. METHODS: We searched PubMed, Embase, CINAHL, Web of Science and LILACS for studies reporting Zika-affected completed pregnancies (ending in foetal death or live birth), excluding studies whose aim required live birth. Studies 'allowed' foetal death if their populations were defined to encompass both live births and foetal deaths, regardless of whether deaths were actually found. Two authors independently extracted data and assessed study quality. Foetal death absolute and relative risks in Zika-affected vs. unaffected pregnancies were calculated. RESULTS: We found 108 reports including 24 699 completed, Zika-affected pregnancies. The median absolute risk in 37 studies of completed, Zika-affected pregnancies was 6.3% (IQR 3.2%, 10.6%) for foetal death and 5.9% (IQR 0%, 29.1%) for non-fatal adverse outcomes (e.g. microcephaly). More studies allowed non-fatal adverse outcomes (95%) than foetal death (58%). Of studies which allowed them, 94% found at least one foetal death. In 37% of reports, it was unknown whether foetal deaths were allowed. Only one study had sufficient data to estimate a foetal death relative risk (11.05, 95% CI 3.43, 35.55). CONCLUSIONS: Evidence was insufficient to determine whether foetal death risk is higher in Zika-affected pregnancies, but suggests quality of foetal death reporting should be improved, including stating whether foetal deaths were found, how many, and at what gestational ages, or justifying their exclusion.

OBJECTIFS: Le virus Zika est lié à plusieurs issues défavorables de la grossesse. Nous avons évalué si l'infection à Zika pendant la grossesse était associée à un risque accru de mort fœtale (fausse couche, mortinaissance, avortement) et s'il y avait une déclaration incomplète de ces décès. MÉTHODES: Nous avons recherché dans PubMed, EMBASE, Cinahl, Web of Science et LILACS des études rapportant des grossesses terminées touchées par le virus Zika (se terminant par une mort fœtale ou une naissance vivante), à l'exclusion des études dont l'objectif nécessitait une naissance vivante. Les études «autorisaient¼ la mort fœtale si leur population était définie comme englobant à la fois les naissances vivantes et les décès fœtaux, indépendamment du fait que des décès aient été effectivement constatés. Deux auteurs ont indépendamment extrait les données et évalué la qualité des études. Les risques absolus et relatifs de mortalité fœtale dans les grossesses affectées par Zika par rapport aux grossesses non affectées ont été calculés. RÉSULTATS: Nous avons trouvé 108 reports dont 24.699 grossesses terminées et affectées par le virus Zika. Le risque médian absolu dans 37 études portant sur des grossesses terminées affectées par Zika était de 6,3% (IQR 3,2%, 10,6%) pour la mort fœtale et de 5,9% (IQR 0%, 29,1%) pour les issues indésirables non mortelles (par exemple microcéphalie). Plus d'études ont «autorisé¼ des résultats indésirables non mortels (95%) que la mort fœtale (58%). Parmi les études qui les ont «autorisé¼, 94% ont trouvé au moins un décès fœtal. Dans 37% des rapports, il n'est pas indiqué si la mort fœtale avait été «autorisée¼. Une seule étude contenait des données suffisantes pour estimer un risque relatif de mort fœtale (11,05 ; IC95%: 3,43, 35,55). CONCLUSIONS: Les données étaient insuffisantes pour déterminer si le risque de mort fœtale est plus élevé dans les grossesses touchées par le virus Zika, mais suggèrent que la qualité des reports sur les décès fœtaux devrait être améliorée, notamment en indiquant si des décès fœtaux ont été constatés, combien et à quel âge gestationnel, ou justifiant leur exclusion.

Reportable Bacterial Infections among New York City-Born Infants, 2001-2009.

OBJECTIVE: To determine rates of reportable bacterial infections among infants in New York City and identify populations at risk and preventable causes of morbidity. STUDY DESIGN: This retrospective cohort study matched live births in New York City from 2001-2009 to reported cases of bacterial infections among infants less than 1 year of age. Characteristics recorded on birth certificates were compared between infants with bacterial enteric infection, bacterial nonenteric infection, and no reportable bacterial infection. Multinomial logistic regression and multivariable logistic regression were used to identify risk factors for infection. RESULTS: Bacterial infection was reported in 4.6 cases per 1000 live births. Of 4524 infants with a reportable infection, the majority (2880, 63%) had an enteric infection. Asian/Pacific Islanders in Brooklyn were the borough-level race/ethnic group with the highest enteric infection rate (8.5 per 1000 live births). Citywide, infants with enteric infections were disproportionately male, from higher poverty neighborhoods, born to foreign-born mothers, and enrolled in Special Supplemental Food Program for Women, Infants, and Children or Medicaid. In contrast, infants with nonenteric infections were more likely to have low birthweight and mothers characterized by US birth and black race or white Hispanic race/ethnicity. CONCLUSIONS: Distinct patterns of risk factors for enteric and nonenteric bacterial infections among infants were identified. The results suggest that infants born to Asian/Pacific Islander mothers residing in Brooklyn should be a focus of enteric disease prevention. More research is necessary to better understand what behaviors increase the risk of enteric disease in this population.

The reverse zoonotic potential of SARS-CoV-2.

There has been considerable emphasis recently on the zoonotic origins of emerging infectious diseases in humans, including the SARS-CoV-2 pandemic; however, reverse zoonoses (infections transmitted from humans to other animals) have received less attention despite their potential importance. The effects can be devastating for the infected species and can also result in transmission of the pathogen back to human populations or other animals either in the original form or as a variant. Humans have transmitted SARS-CoV-2 to other animals, and the virus is able to circulate and evolve in those species. As global travel resumes, the potential of SARS-CoV-2 as a reverse zoonosis threatens humans and endangered species. Nonhuman primates are of particular concern given their susceptibility to human respiratory infections. Enforcing safety measures for all people working in and visiting wildlife areas, especially those with nonhuman primates, and increasing access to safety measures for people living near protected areas that are home to nonhuman primates will help mitigate reverse zoonotic transmission.

Prediction and prevention of the next pandemic zoonosis.

Most pandemics--eg, HIV/AIDS, severe acute respiratory syndrome, pandemic influenza--originate in animals, are caused by viruses, and are driven to emerge by ecological, behavioural, or socioeconomic changes. Despite their substantial effects on global public health and growing understanding of the process by which they emerge, no pandemic has been predicted before infecting human beings. We review what is known about the pathogens that emerge, the hosts that they originate in, and the factors that drive their emergence. We discuss challenges to their control and new efforts to predict pandemics, target surveillance to the most crucial interfaces, and identify prevention strategies. New mathematical modelling, diagnostic, communications, and informatics technologies can identify and report hitherto unknown microbes in other species, and thus new risk assessment approaches are needed to identify microbes most likely to cause human disease. We lay out a series of research and surveillance opportunities and goals that could help to overcome these challenges and move the global pandemic strategy from response to pre-emption.

The impact of COVID-19 on dental care in New York State and Georgia.

Introduction During the COVID-19 pandemic, there was an unprecedented and forced closure of dental offices worldwide. As American state recommendations differed considerably during this period, this research strives to better define the effects of this pause on dental care.Materials and methods A 16-question Qualtrics survey was sent to the membership of the New York State Dental Association (NYSDA) and Georgia Dental Association (GDA). Licenced, actively practising dental members of the NYSDA and GDA (n = 680) answered questions about their practice demographics, appointment cancellations, reopening times and the volume of individual dental procedures performed from 1 March through to 1 August 2020, compared to the same five-month period in 2019.Results Demographic characteristics of respondent NYSDA and GDA members were statistically similar. Nonetheless, NYSDA members reported significantly larger decreases in provision of all types of dental procedures, except for antibiotic prescription, including prophylaxis, elective care, emergency dental care and speciality procedures.Discussion and conclusions All dental procedures declined significantly during the COVID-19 pandemic, with greater decrease in New York than in Georgia. This study raises concerns about the negative impact of the pandemic on oral public health and mandates both further research and clinical strategies to mitigate against this future risk.

HIV Care Engagement Is Not Associated with COVID-19 Vaccination Hesitancy during the Initial Peak of the COVID-19 Pandemic among Black Cisgender Sexual Minority Men and Transgender Women in the N2 COVID Study.

BACKGROUND: Although there is limited literature on medication adherence (including HIV care engagement) and COVID-19 vaccine hesitancy in general populations (i.e., non-sexual or gender minority populations), even less is known about whether HIV care engagement correlates with COVID-19 vaccine hesitancy among sexual and gender minorities, especially those from intersectional backgrounds. The objective of the current study was to examine if an association exists between HIV status neutral care (i.e., current pre-exposure prophylaxis [PrEP] or antiretroviral therapy [ART] use) and COVID-19 vaccination hesitancy among Black cisgender sexual minority men and transgender women at the initial peak of the pandemic. METHODS: We conducted the N2 COVID Study in Chicago from 20 April 2020 to 31 July 2020 (analytic n = 222), including Black cisgender sexual minority men and transgender women who were vulnerable to HIV as well as those who were living with HIV. The survey included questions regarding HIV care engagement, COVID-19 vaccination hesitancy and COVID-19 related socio-economic hardships. Multivariable associations estimated adjusted risk ratios (ARRs) using modified Poisson regressions for COVID vaccine hesitancy adjusting for baseline socio-demographic characteristics and survey assessment time period. RESULTS: Approximately 45% of participants reported COVID-19 vaccine hesitancy. PrEP and ART use were not associated with COVID-19 vaccine hesitancy when examined separately or combined (p > 0.05). There were no significant multiplicative effects of COVID-19 related socio-economic hardships and HIV care engagement on COVID-19 vaccine hesitancy. CONCLUSIONS: Findings suggest no association between HIV care engagement and COVID-19 vaccine hesitancy among Black cisgender sexual minority men and transgender women at the initial peak of the pandemic. It is therefore essential that COVID-19 vaccine promotion interventions focus on all Black sexual and gender minorities regardless of HIV care engagement and COVID-19 vaccine uptake is likely related to factors other than engagement in HIV status neutral care.

Delays in Diagnosis and Treatment of Bacterial Meningitis in NYC: Retrospective Cohort Analysis.

Community-acquired bacterial meningitis (CABM) morbidity and mortality remains high in those infected. Rapid diagnosis and treatment is paramount to reducing mortality and improving outcome. This retrospective cohort study aims to assess the time from presentation to diagnosis and treatment of vaccine preventable CABM as well as identify possible factors associated with delays in diagnosis and antibiotic administration. A retrospective chart review was conducted of individuals who presented to Columbia University Irving Medical Center (CUIMC), Children's Hospital of New York (CHONY), Mount Sinai Medical Center, and Weill Cornell Medical Center with BM due to Haemophilus influenzae type B, Streptococcus pneumoniae, and Neisseria meningitidis between January 1, 2012 and December 31, 2017. Diagnosis was delayed by more than 8 hours in 13 patients (36.1%) and 5 individuals (13.9%) had a delay of 4 hours or more from presentation to the administration of antibiotics with appropriate CNS coverage. All of these patients were also initially misdiagnosed at an outpatient clinic, outside hospital, or emergency department. This retrospective study identified febrile and/or viral infections not otherwise specified and otitis media as the most common misdiagnoses underlying delays from presentation to diagnosis and to antibiotic treatment in those with BM.

Impact of non-pharmaceutical interventions on URIs and influenza in crowded, urban households.

OBJECTIVES: We compared the impact of three household interventions-education, education with alcohol-based hand sanitizer, and education with hand sanitizer and face masks-on incidence and secondary transmission of upper respiratory infections (URIs) and influenza, knowledge of transmission of URIs, and vaccination rates. METHODS: A total of 509 primarily Hispanic households participated. Participants reported symptoms twice weekly, and nasal swabs were collected from those with an influenza-like illness (ILI). Households were followed for up to 19 months and home visits were made at least every two months. RESULTS: We recorded 5034 URIs, of which 669 cases reported ILIs and 78 were laboratory-confirmed cases of influenza. Demographic factors significantly associated with infection rates included age, gender, birth location, education, and employment. The Hand Sanitizer group was significantly more likely to report that no household member had symptoms (p < 0.01), but there were no significant differences in rates of infection by intervention group in multivariate analyses. Knowledge improved significantly more in the Hand Sanitizer group (p < 0.0001). The proportion of households that reported > or = 50% of members receiving influenza vaccine increased during the study (p < 0.001). Despite the fact that compliance with mask wearing was poor, mask wearing as well as increased crowding, lower education levels of caretakers, and index cases 0-5 years of age (compared with adults) were associated with significantly lower secondary transmission rates (all p < 0.02). CONCLUSIONS: In this population, there was no detectable additional benefit of hand sanitizer or face masks over targeted education on overall rates of URIs, but mask wearing was associated with reduced secondary transmission and should be encouraged during outbreak situations. During the study period, community concern about methicillin-resistant Staphylococcus aureus was occurring, perhaps contributing to the use of hand sanitizer in the Education control group, and diluting the intervention's measurable impact.

Low sensitivity of rapid diagnostic test for influenza.

The QuickVue Influenza A+B Test (Quidel) was used to test nasal swab specimens obtained from persons with influenza-like illness in 3 different populations. Compared with reverse-transcriptase polymerase chain reaction, the test sensitivity was low for all populations (median, 27%; range, 19%-32%), whereas the specificity was high (median, 97%; range, 96%-99.6%).

Using satellite images of environmental changes to predict infectious disease outbreaks.

Recent events clearly illustrate a continued vulnerability of large populations to infectious diseases, which is related to our changing human-constructed and natural environments. A single person with multidrug-resistant tuberculosis in 2007 provided a wake-up call to the United States and global public health infrastructure, as the health professionals and the public realized that today's ease of airline travel can potentially expose hundreds of persons to an untreatable disease associated with an infectious agent. Ease of travel, population increase, population displacement, pollution, agricultural activity, changing socioeconomic structures, and international conflicts worldwide have each contributed to infectious disease events. Today, however, nothing is larger in scale, has more potential for long-term effects, and is more uncertain than the effects of climate change on infectious disease outbreaks, epidemics, and pandemics. We discuss advances in our ability to predict these events and, in particular, the critical role that satellite imaging could play in mounting an effective response.

Effect of intensive education on knowledge, attitudes, and practices regarding upper respiratory infections among urban Latinos.

BACKGROUND: Although upper respiratory infections (URIs) take a major social and economic toll, little research has been conducted to assess the impact of educational interventions on knowledge, attitudes, and practices of community members regarding prevention and treatment of URIs, particularly among recently immigrated urban Latinos who may not be reached by the mainstream healthcare system. OBJECTIVES: The objective of this study was to assess the impact of a culturally appropriate, home-based educational intervention on the knowledge, attitudes, and practices regarding prevention and treatment of URIs among urban Latinos. METHODS: Using a pretest-posttest design, Spanish-language educational materials available from sources such as the Centers for Disease Control and Prevention were adapted based on feedback from community focus groups and provided to households during an in-person home visit every 2 months (generally three to four visits). Outcome data regarding knowledge, attitudes, and practices were collected in home-based interviews using an 85-item instrument adapted and pilot tested from three other validated instruments. Nonparametric and multiple linear regression analyses were used to summarize data and identify predictors of knowledge scores. RESULTS: Four hundred twenty-two households had complete data at baseline and 6 months. Knowledge and attitude scores were improved significantly, and use of alcohol hand sanitizer and rates of influenza vaccine were increased significantly (all p <.01). DISCUSSION: Although this home-based educational intervention was successful in improving knowledge, attitudes, and self-reported practices among urban Latinos regarding prevention and treatment of URIs, further research is needed to determine the cost-effectiveness of such a person-intensive intervention, the long-term outcomes, and whether less intensive interventions might be equally effective.

What Have We Learned About Middle East Respiratory Syndrome Coronavirus Emergence in Humans? A Systematic Literature Review.

BACKGROUND: Middle East respiratory syndrome coronavirus (MERS-CoV) was first identified in humans in 2012. A systematic literature review was conducted to synthesize current knowledge and identify critical knowledge gaps. MATERIALS AND METHODS: We conducted a systematic review on MERS-CoV using PRISMA guidelines. We identified 407 relevant, peer-reviewed publications and selected 208 of these based on their contributions to four key areas: virology; clinical characteristics, outcomes, therapeutic and preventive options; epidemiology and transmission; and animal interface and the search for natural hosts of MERS-CoV. RESULTS: Dipeptidyl peptidase 4 (DPP4/CD26) was identified as the human receptor for MERS-CoV, and a variety of molecular and serological assays developed. Dromedary camels remain the only documented zoonotic source of human infection, but MERS-like CoVs have been detected in bat species globally, as well as in dromedary camels throughout the Middle East and Africa. However, despite evidence of camel-to-human MERS-CoV transmission and cases apparently related to camel contact, the source of many primary cases remains unknown. There have been sustained health care-associated human outbreaks in Saudi Arabia and South Korea, the latter originating from one traveler returning from the Middle East. Transmission mechanisms are poorly understood; for health care, this may include environmental contamination. Various potential therapeutics have been identified, but not yet evaluated in human clinical trials. At least one candidate vaccine has progressed to Phase I trials. CONCLUSIONS: There has been substantial MERS-CoV research since 2012, but significant knowledge gaps persist, especially in epidemiology and natural history of the infection. There have been few rigorous studies of baseline prevalence, transmission, and spectrum of disease. Terms such as "camel exposure" and the epidemiological relationships of cases should be clearly defined and standardized. We strongly recommend a shared and accessible registry or database. Coronaviruses will likely continue to emerge, arguing for a unified "One Health" approach.

Policy and Science for Global Health Security: Shaping the Course of International Health.

The global burden of infectious diseases and the increased attention to natural, accidental, and deliberate biological threats has resulted in significant investment in infectious disease research. Translating the results of these studies to inform prevention, detection, and response efforts often can be challenging, especially if prior relationships and communications have not been established with decision-makers. Whatever scientific information is shared with decision-makers before, during, and after public health emergencies is highly dependent on the individuals or organizations who are communicating with policy-makers. This article briefly describes the landscape of stakeholders involved in information-sharing before and during emergencies. We identify critical gaps in translation of scientific expertise and results, and biosafety and biosecurity measures to public health policy and practice with a focus on One Health and zoonotic diseases. Finally, we conclude by exploring ways of improving communication and funding, both of which help to address the identified gaps. By leveraging existing scientific information (from both the natural and social sciences) in the public health decision-making process, large-scale outbreaks may be averted even in low-income countries.

Inhalation anthrax: dose response and risk analysis.

The notion that inhalation of a single Bacillus anthracis spore is fatal has become entrenched nearly to the point of urban legend, in part because of incomplete articulation of the scientific basis for microbial risk assessment, particularly dose-response assessment. Risk analysis (ie, risk assessment, risk communication, risk management) necessitates transparency: distinguishing scientific facts, hypotheses, judgments, biases in interpretations, and potential misinformation. The difficulty in achieving transparency for biothreat risk is magnified by misinformation and poor characterization of both dose-response relationships and the driving mechanisms that cause susceptibility or resistance to disease progression. Regrettably, this entrenchment unnecessarily restricts preparedness planning to a single response scenario: decontaminate until no spores are detectable in air, water, or on surfaces-essentially forcing a zero-tolerance policy inconsistent with the biology of anthrax. We present evidence about inhalation anthrax dose-response relationships, including reports from multiple studies documenting exposures insufficient to cause inhalation anthrax in laboratory animals and humans. The emphasis of the article is clarification about what is known from objective scientific evidence for doses of anthrax spores associated with survival and mortality. From this knowledge base, we discuss the need for future applications of more formal risk analysis processes to guide development of alternative non-zero criteria or standards based on science to inform preparedness planning and other risk management activities.

BacCapSeq: a Platform for Diagnosis and Characterization of Bacterial Infections.

We report a platform that increases the sensitivity of high-throughput sequencing for detection and characterization of bacteria, virulence determinants, and antimicrobial resistance (AMR) genes. The system uses a probe set comprised of 4.2 million oligonucleotides based on the Pathosystems Resource Integration Center (PATRIC) database, the Comprehensive Antibiotic Resistance Database (CARD), and the Virulence Factor Database (VFDB), representing 307 bacterial species that include all known human-pathogenic species, known antimicrobial resistance genes, and known virulence factors, respectively. The use of bacterial capture sequencing (BacCapSeq) resulted in an up to 1,000-fold increase in bacterial reads from blood samples and lowered the limit of detection by 1 to 2 orders of magnitude compared to conventional unbiased high-throughput sequencing, down to a level comparable to that of agent-specific real-time PCR with as few as 5 million total reads generated per sample. It detected not only the presence of AMR genes but also biomarkers for AMR that included both constitutive and differentially expressed transcripts.IMPORTANCE BacCapSeq is a method for differential diagnosis of bacterial infections and defining antimicrobial sensitivity profiles that has the potential to reduce morbidity and mortality, health care costs, and the inappropriate use of antibiotics that contributes to the development of antimicrobial resistance.

Knowledge Management Framework for Emerging Infectious Diseases Preparedness and Response: Design and Development of Public Health Document Ontology.

BACKGROUND: There are increasing concerns about our preparedness and timely coordinated response across the globe to cope with emerging infectious diseases (EIDs). This poses practical challenges that require exploiting novel knowledge management approaches effectively. OBJECTIVE: This work aims to develop an ontology-driven knowledge management framework that addresses the existing challenges in sharing and reusing public health knowledge. METHODS: We propose a systems engineering-inspired ontology-driven knowledge management approach. It decomposes public health knowledge into concepts and relations and organizes the elements of knowledge based on the teleological functions. Both knowledge and semantic rules are stored in an ontology and retrieved to answer queries regarding EID preparedness and response. RESULTS: A hybrid concept extraction was implemented in this work. The quality of the ontology was evaluated using the formal evaluation method Ontology Quality Evaluation Framework. CONCLUSIONS: Our approach is a potentially effective methodology for managing public health knowledge. Accuracy and comprehensiveness of the ontology can be improved as more knowledge is stored. In the future, a survey will be conducted to collect queries from public health practitioners. The reasoning capacity of the ontology will be evaluated using the queries and hypothetical outbreaks. We suggest the importance of developing a knowledge sharing standard like the Gene Ontology for the public health domain.

Global hotspots and correlates of emerging zoonotic diseases.

Zoonoses originating from wildlife represent a significant threat to global health, security and economic growth, and combatting their emergence is a public health priority. However, our understanding of the mechanisms underlying their emergence remains rudimentary. Here we update a global database of emerging infectious disease (EID) events, create a novel measure of reporting effort, and fit boosted regression tree models to analyze the demographic, environmental and biological correlates of their occurrence. After accounting for reporting effort, we show that zoonotic EID risk is elevated in forested tropical regions experiencing land-use changes and where wildlife biodiversity (mammal species richness) is high. We present a new global hotspot map of spatial variation in our zoonotic EID risk index, and partial dependence plots illustrating relationships between events and predictors. Our results may help to improve surveillance and long-term EID monitoring programs, and design field experiments to test underlying mechanisms of zoonotic disease emergence.