A model of animal-human brucellosis transmission in Mongolia

Human Brucellosis Trends: Re-emergence and Prospects for Control Using a One Health Approach in Azerbaijan (1983-2009)

Brucellosis is one of the most common and widely spread zoonotic diseases in the world. Control of the disease in humans is dependent upon limiting the infection in animals through surveillance and vaccination. Given the dramatic economic and political changes that have taken place in the former Soviet Union, which have limited control, evaluating the status of human brucellosis in former Soviet states is crucial. We assessed annual spatial and temporal trends in the epidemiology of human brucellosis in Azerbaijan, 1983-2009, in conjunction with data from a livestock surveillance and control programme (2002-2009). To analyse trends, we used a combination of segmented regression and spatial analysis. From 1983 to 2009, a total of 11 233 cases of human brucellosis were reported. Up to the mid-1990s, the incidence of human brucellosis showed a pattern of re-emergence, increasing by 25% annually, on average. Following Soviet governance, the incidence rates peaked, increasing by 1.8% annually, on average, and subsequently decreasing by 5% annually, on average, during the period 2002-2009. Despite recent national declines in human incidence, we identified geographic changes in the case distribution characterized by a geographic expansion and an increasing incidence among districts clustered in the south-east, compared to a decrease of elsewhere in the country. Males were consistently, disproportionately afflicted (71%) and incidence was highest in the 15 to 19 age group (18.1 cases/100 000). During the period 2002-2009, >10 million small ruminants were vaccinated with Rev1. Our findings highlight the improving prospects for human brucellosis control following livestock vaccination; however, the disease appears to be re-emerging in south-eastern Azerbaijan. Sustained one health measures are needed to address changing patterns of brucellosis in Azerbaijan and elsewhere in the former Soviet Union.

Human brucellosis occurrences in inner mongolia, China: a spatio-temporal distribution and ecological niche modeling approach

BACKGROUND

Brucellosis is a common zoonotic disease and remains a major burden in both human and domesticated animal populations worldwide. Few geographic studies of human Brucellosis have been conducted, especially in China. Inner Mongolia of China is considered an appropriate area for the study of human Brucellosis due to its provision of a suitable environment for animals most responsible for human Brucellosis outbreaks.

METHODS

The aggregated numbers of human Brucellosis cases from 1951 to 2005 at the municipality level, and the yearly numbers and incidence rates of human Brucellosis cases from 2006 to 2010 at the county level were collected. Geographic Information Systems (GIS), remote sensing (RS) and ecological niche modeling (ENM) were integrated to study the distribution of human Brucellosis cases over 1951-2010.

RESULTS

Results indicate that areas of central and eastern Inner Mongolia provide a long-term suitable environment where human Brucellosis outbreaks have occurred and can be expected to persist. Other areas of northeast China and central Mongolia also contain similar environments.

CONCLUSIONS

This study is the first to combine advanced spatial statistical analysis with environmental modeling techniques when examining human Brucellosis outbreaks and will help to inform decision-making in the field of public health.

MODELING THE TRANSMISSION DYNAMICS OF DAIRY CATTLE BRUCELLOSIS IN JILIN PROVINCE, CHINA

Dairy cattle brucellosis is a chronic bacterial disease, which is caused by Brucella abortus and mainly characterized by abortion in dairy cattle. With the rapid development of breeding industry of milk cows in China, the infectious cases of dairy cattle brucellosis show an increasing trend. Particularly in Jilin province, the annual number of the positive cases of dairy cattle was only 3 cows in 1987, and went up to 168 cows in 2005. Based on the situation of the brucellosis infection in Jilin province, we propose an Susceptible-Exposed-Infected-Virus (SEIV) dynamical model with outside transferred amount to describe the transmission of brucellosis amongst dairy cattle in this paper. We calculate the basic reproduction number R0 and prove that the equilibria are globally stable. Moreover, using the real data of nearly 20 years in Jilin province, we estimate the parameter values in the system. As a result, we can predict the number of infections as time increases. According to the prediction for the next 30 years, we can conclude that the disease will persist if we just take existing measures. If culling, sterilizing and decreasing the number of outer importing are used together, dairy cattle brucellosis will be well controlled.

Prediction and control of brucellosis transmission of dairy cattle in Zhejiang Province, China

Brucellosis is a bacterial disease caused by brucella; mainly spread by direct contact transmission through the brucella carriers, or indirect contact transmission by the environment containing large quantities of bacteria discharged by the infected individuals. At the beginning of 21st century, the epidemic among dairy cows in Zhejiang province, began to come back and has become a localized prevalent epidemic. Combining the pathology of brucellosis, the reported positive data characteristics, and the feeding method in Zhejiang province, this paper establishes an dynamic model to excavate the internal transmission dynamics, fit the real disease situation, predict brucellosis tendency and assess control measures in dairy cows. By careful analysis, we give some quantitative results as follows. (1) The external input of dairy cows from northern areas may lead to high fluctuation of the number of the infectious cows in Zhejiang province that can reach several hundreds. In this case, the disease cannot be controlled and the infection situation cannot easily be predicted. Thus, this paper encourages cows farms to insist on self-supplying production of the dairy cows. (2) The effect of transmission rate of brucella in environment to dairy cattle on brucellosis spreading is greater than transmission rate of the infectious dairy cattle to susceptible cattle. The prevalence of the epidemic is mainly aroused by environment transmission. (3) Under certain circumstances, the epidemic will become a periodic phenomenon. (4) For Zhejiang province, besides measures that have already been adopted, sterilization times of the infected regions is suggested as twice a week, and should be combined with management of the birth rate of dairy cows to control brucellosis spread.

Transmission dynamics and control for a brucellosis model in Hinggan League of Inner Mongolia, China

Brucellosis is one of the major infectious and contagious bacterial diseases in Hinggan League of Inner Mongolia, China. The number of newly infected human brucellosis data in this area has increased dramatically in the last 10 years. In this study, in order to explore effective control and prevention measures we propose a deterministic model to investigate the transmission dynamics of brucellosis in Hinggan League. The model describes the spread of brucellosis among sheep and from sheep to humans. The model simulations agree with newly infected human brucellosis data from 2001 to 2011, and the trend of newly infected human brucellosis cases is given. We estimate that the control reproduction number Rc is about 1.9789 for the brucellosis transmission in Hinggan League and compare the effect of existing mixed cross infection between basic ewes and other sheep or not for newly infected human brucellosis cases. Our study demonstrates that combination of prohibiting mixed feeding between basic ewes and other sheep, vaccination, detection and elimination are useful strategies in controlling human brucellosis in Hinggan League.

Representative seroprevalences of human and livestock brucellosis in two Mongolian provinces

Mongolia implemented a brucellosis livestock mass vaccination campaign from 2000 to 2009. However, the number of human cases did not decline since 2004 and the current epidemiological situation in Mongolia was uncertain. The objective of this study was to estimate the representative seroprevalences of humans and livestock in two provinces in view of their comparison with officially reported data. A representative cross-sectional study using cluster sampling proportional to size in humans, sheep, goats, cattle, yaks, horses, camels and dogs was undertaken to assess the apparent seroprevalence in humans and animals. A total of 8054 livestock and dog sera and 574 human sera were collected in Sukhbaatar and Zavkhan provinces. Human and animal sera were tested with the Rose Bengal and ELISA tests. The overall apparent seroprevalence of brucellosis was 27.3% in humans (95% CI 23.7-31.2%), 6.2% (95% CI 5.5-7.1%) in sheep, 5.2% (95% CI 4.4-5.9%) in goats, 16.0% (95% CI 13.7-18.7%) in cattle, 2.5% (95% CI 0.8-7.6%) in camels, 8.3 (95% CI 6.0-11.6%) in horses and 36.4% (95% CI 26.3-48.0%) in dogs. More women than men were seropositive (OR = 1.7; P < 0.0014). Human seroprevalence was not associated with small ruminant and cattle seroprevalence at the nomadic camp (hot ail) level. Annual incidence of clinical brucellosis, inferred from the seroprevalence using a catalytic model, was by a factor of 4.6 (1307/280) in Sukhbaatar and by a factor of 59 (1188/20) in Zavkhan. This represents a 15-fold underreporting of human brucellosis in Mongolia. The lack of access to brucellosis diagnostic testing at the village level hinders rural people from receiving appropriate treatment. In conclusion, this study confirms the high seroprevalence of human and livestock brucellosis in Mongolia. Stringent monitoring and quality control of operational management of a nationwide mass vaccination of small and large ruminants is warranted to assure its effectiveness. More research is needed to understand the complex animal-human interface of brucellosis transmission at different scales from farm to provincial level.

Changing patterns of human anthrax in Azerbaijan during the post-Soviet and preemptive livestock vaccination eras

We assessed spatial and temporal changes in the occurrence of human anthrax in Azerbaijan during 1984 through 2010. Data on livestock outbreaks, vaccination efforts, and human anthrax incidence during Soviet governance, post-Soviet governance, preemptive livestock vaccination were analyzed. To evaluate changes in the spatio-temporal distribution of anthrax, we used a combination of spatial analysis, cluster detection, and weighted least squares segmented regression. Results indicated an annual percent change in incidence of (+)11.95% from 1984 to 1995 followed by declining rate of -35.24% after the initiation of livestock vaccination in 1996. Our findings also revealed geographic variation in the spatial distribution of reporting; cases were primarily concentrated in the west early in the study period and shifted eastward as time progressed. Over twenty years after the dissolution of the Soviet Union, the distribution of human anthrax in Azerbaijan has undergone marked changes. Despite decreases in the incidence of human anthrax, continued control measures in livestock are needed to mitigate its occurrence. The shifting patterns of human anthrax highlight the need for an integrated "One Health" approach that takes into account the changing geographic distribution of the disease.

A brucellosis disease control strategy for the Kakheti region of the country of Georgia: an agent-based model

Brucellosis has been reported in livestock and humans in the country of Georgia with Brucella melitensis as the most common species causing disease. Georgia lacked sufficient data to assess effectiveness of the various potential control measures utilizing a reliable population-based simulation model of animal-to-human transmission of this infection. Therefore, an agent-based model was built using data from previous studies to evaluate the effect of an animal-level infection control programme on human incidence and sheep flock and cattle herd prevalence of brucellosis in the Kakheti region of Georgia. This model simulated the patterns of interaction of human-animal workers, sheep flocks and cattle herds with various infection control measures and returned population-based data. The model simulates the use of control measures needed for herd and flock prevalence to fall below 2%. As per the model output, shepherds had the greatest disease reduction as a result of the infection control programme. Cattle had the greatest influence on the incidence of human disease. Control strategies should include all susceptible animal species, sheep and cattle, identify the species of brucellosis present in the cattle population and should be conducted at the municipality level. This approach can be considered as a model to other countries and regions when assessment of control strategies is needed but data are scattered.

A review of Brucella seroprevalence among humans and animals in Bangladesh with special emphasis on epidemiology, risk factors and control opportunities

Brucellosis is a neglected bacterial zoonotic disease in many countries affecting both humans and animals. The aim of this paper is to review published reports of the seroprevalence of brucellosis in humans and animals (cattle, buffalo, sheep, goats and dogs) in Bangladesh. The prevalence studies are based primarily on the following serological tests: rose bengal plate agglutination test (RBT), plate agglutination test (PAT), tube agglutination test (TAT), mercaptoethanol agglutination test (MET), standard tube agglutination test (STAT), slow agglutination test (SAT), milk ring test (MRT), indirect enzyme-linked immunosorbant assay (I-ELISA), competitive ELISA (C-ELISA) and fluorescent polarization assay (FPA). Seroprevalences of brucellosis were found to be affected by the sensitivity and specificity of serological tests employed. Brucellosis prevalence varied based on occupations of people (2.5-18.6%) and species of animals (3.7% in cattle, 4.0% in buffalo, 3.6% in goats and 7.3% in sheep). The prevalence of brucellosis in humans was reported in livestock farmers (2.6-21.6%), milkers (18.6%), butchers (2.5%) and veterinarians (5.3-11.1%) who have direct contact with animal and its products or who consume raw milk. According to published reports brucellosis does affect people and livestock of Bangladesh. There is an immediate need for a concerted effort to control and eradicate brucellosis from domesticated animals in Bangladesh.

Bovine tuberculosis and brucellosis in traditionally managed livestock in selected districts of southern province of zambia

A study was performed in 2008 to estimate the prevalence of tuberculosis and brucellosis in traditionally reared cattle of Southern Province in Zambia in four districts. The single comparative intradermal tuberculin test (SCITT) was used to identify TB reactors, and the Rose Bengal test (RBT), followed by confirmation with competitive enzyme-linked immunosorbent assay (c-ELISA), was used to test for brucellosis. A total of 459 animals were tested for tuberculosis and 395 for brucellosis. The overall prevalence of BTB based on the 4 mm and 3 mm cutoff criteria was 4.8% (95% CI: 2.6–7.0%) and 6.3% (95% CI: 3.8–8.8%), respectively. Change in skin thickness on SCITT was influenced by initial skin-fold thickness at the inoculation site, where animals with thinner skin had a tendency to give a larger tuberculin response. Brucellosis seroprevalence was estimated at 20.7% (95% CI: 17.0–24.4%). Comparison between results from RBT and c-ELISA showed good agreement (84.1%) and revealed subjectivity in RBT test results. Differences in brucellosis and tuberculosis prevalence across districts were attributed to type of husbandry practices and ecological factors. High prevalence of tuberculosis and brucellosis suggests that control programmes are necessary for improved cattle productivity and reduced public health risk.

Spatio-temporal clusters of incident human brucellosis cases in Ecuador

This study aimed to determine whether variations in the incidence of reported cases of human brucellosis in Ecuador were clustered in space and time. In addition, the effects of cattle and small ruminant population density and other socio-economic factors on the incidence were investigated. Significant space-time clusters were found in the northern and southern highlands and parts of Ecuadorian Amazonia. Customs of people, cattle, goat and sheep population density appeared to influence the incidence of brucellosis. In this study, the incidence of reported cases of human brucellosis was found to be higher in the highlands (sierra) and in municipalities near Peru and Colombia. The results of this study highlight the need for prevention and control measures aimed at abating the incidence of brucellosis among livestock and humans.

Prevalence and risk factors for brucellosis in goats in areas of Mexico with and without brucellosis control campaign

Brucellosis is a major constraint for small-scale goat farming systems in Mexico. This study estimated the prevalence of testing positive to brucellosis and identified and quantified risk factors in goats from small-scale farms of Michoacán that had participated in a brucellosis campaign (i.e. vaccination, serological testing, culling and awareness) and of Jalisco that had negligible brucellosis campaign participation. A cross-sectional serological survey was conducted among 1,713 goats of 83 flocks. The prevalence of testing positive to brucellosis was higher (38%) in Jalisco than in Michoacán (11%). Logistic regression analysis indicated that goats from Michoacán had lower odds to test positive for brucellosis (odds ratio (OR) = 0.32, 95% confidence interval (CI) 0.21-0.48) compared to goats from Jalisco. Goats in zero-grazing systems had lower odds than goats in grazing systems (OR = 0.22, 95% CI 0.09-0.57). When goats were kept in pens with low density (0.002 to 0.22 goat/m(2)), odds was lower (OR = 0.44, 95% CI 0.28-0.67) compared to goats kept in pens with higher density (0.23 to 1 goat/m(2)). Odds was higher for testing positive when farmers bought goats from goat traders (OR = 1.82, 95% CI 1.15-2.87) compared to farmers who did not. If scavenger poultry had access to goat pens, the odds was half (OR = 0.52, 95% CI 0.33-0.83) of those where poultry had no access. Regular disinfection of the pen reduced the odds (OR = 0.66, 95% CI 0.44-0.99) compared to where disinfection was not regular. The brucellosis control campaign was effective in reducing brucellosis seropositivity.

Progress in Brucella vaccine development

Brucella spp. are zoonotic, facultative intracellular pathogens, which cause animal and human disease. Animal disease results in abortion of fetuses; in humans, it manifests flu-like symptoms with an undulant fever, with osteoarthritis as a common complication of infection. Antibiotic regimens for human brucellosis patients may last several months and are not always completely effective. While there are no vaccines for humans, several licensed live Brucella vaccines are available for use in livestock. The performance of these animal vaccines is dependent upon the host species, dose, and route of immunization. Newly engineered live vaccines, lacking well-defined virulence factors, retain low residual virulence, are highly protective, and may someday replace currently used animal vaccines. These also have possible human applications. Moreover, due to their enhanced safety and efficacy in animal models, subunit vaccines for brucellosis show great promise for their application in livestock and humans. This review summarizes the progress of brucellosis vaccine development and presents an overview of candidate vaccines.

Modeling the transmission dynamics of sheep brucellosis in Inner Mongolia Autonomous Region, China

Brucellosis is one of the major zoonotic diseases in China, especially in Inner Mongolia where occurs the largest number of human brucellosis cases of Mainland China, which can be attributed to the large number of sheep kept there, since at least 90% of the human brucellosis cases are caused by sheep. Therefore, given the characteristics of the brucellosis infection in Inner Mongolia Autonomous Region, we propose a dynamic model for the sheep-human transmission of brucellosis, involving sheep population, human population and brucella in the environment. We first determine the basic reproduction number R(0) and analyze the global stability of the disease-free and endemic equilibrium. Secondly, using the reported human brucellosis data, we carry out numerical simulations and make sensitivity analysis of the basic reproduction number in terms of some parameters. The results show that brucellosis cannot be eradicated even though disinfection rate and vaccination rate of adult sheep are 100%. By investigating and comparing the effect of vaccination, disinfection and eliminating strategies, we find that vaccinating and disinfecting both young and adult sheep are appropriate and effective strategies to control brucellosis in Inner Mongolia of China.

Modeling of wildlife-associated zoonoses: applications and caveats

Wildlife species are identified as an important source of emerging zoonotic disease. Accordingly, public health programs have attempted to expand in scope to include a greater focus on wildlife and its role in zoonotic disease outbreaks. Zoonotic disease transmission dynamics involving wildlife are complex and nonlinear, presenting a number of challenges. First, empirical characterization of wildlife host species and pathogen systems are often lacking, and insight into one system may have little application to another involving the same host species and pathogen. Pathogen transmission characterization is difficult due to the changing nature of population size and density associated with wildlife hosts. Infectious disease itself may influence wildlife population demographics through compensatory responses that may evolve, such as decreased age to reproduction. Furthermore, wildlife reservoir dynamics can be complex, involving various host species and populations that may vary in their contribution to pathogen transmission and persistence over space and time. Mathematical models can provide an important tool to engage these complex systems, and there is an urgent need for increased computational focus on the coupled dynamics that underlie pathogen spillover at the human-wildlife interface. Often, however, scientists conducting empirical studies on emerging zoonotic disease do not have the necessary skill base to choose, develop, and apply models to evaluate these complex systems. How do modeling frameworks differ and what considerations are important when applying modeling tools to the study of zoonotic disease? Using zoonotic disease examples, we provide an overview of several common approaches and general considerations important in the modeling of wildlife-associated zoonoses.

Analyzing the spatial and temporal distribution of human brucellosis in Azerbaijan (1995 - 2009) using spatial and spatio-temporal statistics

Background

Human brucellosis represents a significant burden to public and veterinary health globally, including the republic of Azerbaijan. The purpose of this study was to examine and describe the spatial and temporal aspects of the epidemiology of human brucellosis in Azerbaijan from 1995 to 2009.

Methods

A Geographic information system (GIS) was used to identify potential changes in the spatial and temporal distribution of human brucellosis in Azerbaijan during the study period. Epidemiological information on the age, gender, date, and location of incident cases were obtained from disease registries housed at the Republican Anti-Plague station in Baku. Cumulative incidences per 100,000 populations were calculated at the district level for three, 5-year periods. Spatial and temporal cluster analyses were performed using the Local Moran’s I and the Ederer-Myer-Mantel (EMM) test.

Results

A total of 7,983 cases of human brucellosis were reported during the 15-year study period. Statistically significant spatial clusters were identified in each of three, five year time periods with cumulative incidence rates ranging from 101.1 (95% CI: 82.8, 124.3) to 203.0 (95% CI; 176.4, 234.8). Spatial clustering was predominant in the west early in the study during period 1 and then in the east during periods 2 and 3. The EMM test identified a greater number of statistically significant temporal clusters in period 1 (1995 to 1999).

Conclusion

These results suggest that human brucellosis persisted annually in Azerbaijan across the study period. The current situation necessitates the development of appropriate surveillance aimed at improving control and mitigation strategies in order to help alleviate the current burden of disease on the population. Areas of concern identified as clusters by the spatial-temporal statistical analyses can provide a starting point for implementing targeted intervention efforts.

A one health framework for estimating the economic costs of zoonotic diseases on society

This article presents an integrated epidemiological and economic framework for assessing zoonoses using a "one health" concept. The framework allows for an understanding of the cross-sector economic impact of zoonoses using modified risk analysis and detailing a range of analytical tools. The goal of the framework is to link the analysis outputs of animal and human disease transmission models, economic impact models and evaluation of risk management options to gain improved understanding of factors affecting the adoption of risk management strategies so that investment planning includes the most promising interventions (or sets of interventions) in an integrated fashion. A more complete understanding of the costs of the disease and the costs and benefits of control measures would promote broader implementation of the most efficient and effective control measures, contributing to improved animal and human health, better livelihood outcomes for the poor and macroeconomic growth.

Representative seroprevalences of brucellosis in humans and livestock in Kyrgyzstan

Kyrgyzstan reported 77.5 new human brucellosis cases per 100,000 people in 2007, which is one of the highest incidences worldwide. In Kyrgyzstan, the currently used diagnostic tests in humans and animals are the Rose Bengal Test and the Huddleson test. A national representative cross-sectional study using cluster sampling proportional to size in humans, cattle, sheep, and goats was undertaken to assess the apparent seroprevalence in humans and animals. A total of 4,936 livestock sera and 1,774 human sera were tested in Naryn, Chuy, and Osh Oblasts. The overall apparent seroprevalences of brucellosis were 8.8% in humans (95% CI 4.5-16.5), 2.8% (95% CI 1.6-4.9%) in cattle, 3.3% (95% CI 1.5-6.9%) in sheep, and 2.5% (95% CI 1.4-4.5%) in goats. Naryn Oblast had the highest seroprevalences in humans and sheep. More men than women were seropositive (OR = 1.96; P < 0.001). Human seroprevalence was significantly associated with small ruminant seroprevalence but not with cattle seroprevalence. Annual incidence of human brucellosis exposure, measured by serological tests, was more than ten times higher than the annual incidence of reported clinical brucellosis cases. This indicates an under-reporting of human brucellosis cases, even if only a fraction of seropositive people have clinical symptoms. In conclusion, this study confirms the high seroprevalence of brucellosis in Kyrgyzstan and warrants rapid effective intervention, among others, by mass vaccination of sheep and goats but also of cattle.

Serological evidence for brucellosis in Bos indicus in Nigeria

PURPOSE

Nigeria is the largest cattle-rearing nation in Africa with most animals kept under traditional husbandry practices. While bovine brucellosis does not receive much attention, a relatively high seroprevalence is found in samples submitted for laboratory testing. The aim of the study was to provide serological evidence of brucellosis in cattle from some of the main cattle-rearing states of the country and to validate a simple and rapid field test for the serodiagnosis of bovine brucellosis.

METHOD

Serum samples collected in various states of Nigeria from cattle because of suspicion of brucellosis were investigated in the Rose Bengal plate test, and results were compared with a newly developed rapid field test for the detection of Brucella-specific antibodies.

RESULTS

Serological evidence for the presence of brucellosis in cattle was obtained for all states included in the study and a high herd prevalence was observed. The seroprevalence was also high among trade and slaughter animals. Results of a rapid field test for the serodiagnosis of bovine brucellosis correlated well with the Rose Bengal plate test (agreement, 95.7%; kappa value, 0.80).

CONCLUSIONS

The results indicate that bovine brucellosis is an important veterinarian problem in Nigeria. The easy-to-use and robust field test is most promising for field-based surveillance as it provides an immediate result allowing the prompt instigation of control measures.

A network control theory approach to modeling and optimal control of zoonoses: case study of brucellosis transmission in sub-Saharan Africa

Background

Developing control policies for zoonotic diseases is challenging, both because of the complex spread dynamics exhibited by these diseases, and because of the need for implementing complex multi-species surveillance and control efforts using limited resources. Mathematical models, and in particular network models, of disease spread are promising as tools for control-policy design, because they can provide comprehensive quantitative representations of disease transmission.

Methodology/Principal Findings

A layered dynamical network model for the transmission and control of zoonotic diseases is introduced as a tool for analyzing disease spread and designing cost-effective surveillance and control. The model development is achieved using brucellosis transmission among wildlife, cattle herds, and human sub-populations in an agricultural system as a case study. Precisely, a model that tracks infection counts in interacting animal herds of multiple species (e.g., cattle herds and groups of wildlife for brucellosis) and in human subpopulations is introduced. The model is then abstracted to a form that permits comprehensive targeted design of multiple control capabilities as well as model identification from data. Next, techniques are developed for such quantitative design of control policies (that are directed to both the animal and human populations), and for model identification from snapshot and time-course data, by drawing on recent results in the network control community.

Conclusions/Significance

The modeling approach is shown to provide quantitative insight into comprehensive control policies for zoonotic diseases, and in turn to permit policy design for mitigation of these diseases. For the brucellosis-transmission example in particular, numerous insights are obtained regarding the optimal distribution of resources among available control capabilities (e.g., vaccination, surveillance and culling, pasteurization of milk) and points in the spread network (e.g., transhumance vs. sedentary herds). In addition, a preliminary identification of the network model for brucellosis is achieved using historical data, and the robustness of the obtained model is demonstrated. As a whole, our results indicate that network modeling can aid in designing control policies for zoonotic diseases.

Zoonotic diseases (ones that infect both animals and humans) exact a significant economic and human cost, especially in developing economies. Developing effective policies for mitigating zoonotic infections is often challenging, both because of the complexity of their spread and because very limited resources must be allocated among a range of control options. It is increasingly becoming clear that mathematical modeling, and in particular network modeling, of disease spread can aid in analyzing and mitigating these spreads. Here, we develop a network model for the spread and control of a zoonotic infection, focusing particularly on a case study of brucellosis transmission and control among wildlife, cattle herds, and human subpopulations in an agricultural community. After motivating and formulating the model, we introduce tools for 1) parameterization of the model from time-course and snapshot data, 2) simulation and analysis of the model, and 3) optimal design of control policies using the model. The study shows that the network model can inform design of heterogeneous control policies that mitigate zoonotic disease spread with limited resources.

From "one medicine" to "one health" and systemic approaches to health and well-being

Faced with complex patterns of global change, the inextricable interconnection of humans, pet animals, livestock and wildlife and their social and ecological environment is evident and requires integrated approaches to human and animal health and their respective social and environmental contexts. The history of integrative thinking of human and animal health is briefly reviewed from early historical times, to the foundation of universities in Europe, up to the beginning of comparative medicine at the end of the 19th century. In the 20th century, Calvin Schwabe coined the concept of “one medicine”. It recognises that there is no difference of paradigm between human and veterinary medicine and both disciplines can contribute to the development of each other. Considering a broader approach to health and well-being of societies, the original concept of “one medicine” was extended to “one health” through practical implementations and careful validations in different settings. Given the global health thinking in recent decades, ecosystem approaches to health have emerged. Based on complex ecological thinking that goes beyond humans and animals, these approaches consider inextricable linkages between ecosystems and health, known as “ecosystem health”. Despite these integrative conceptual and methodological developments, large portions of human and animal health thinking and actions still remain in separate disciplinary silos. Evidence for added value of a coherent application of “one health” compared to separated sectorial thinking is, however, now growing. Integrative thinking is increasingly being considered in academic curricula, clinical practice, ministries of health and livestock/agriculture and international organizations. Challenges remain, focusing around key questions such as how does “one health” evolve and what are the elements of a modern theory of health? The close interdependence of humans and animals in their social and ecological context relates to the concept of “human-environmental systems”, also called “social-ecological systems”. The theory and practice of understanding and managing human activities in the context of social-ecological systems has been well-developed by members of The Resilience Alliance and was used extensively in the Millennium Ecosystem Assessment, including its work on human well-being outcomes. This in turn entails systems theory applied to human and animal health. Examples of successful systems approaches to public health show unexpected results. Analogous to “systems biology” which focuses mostly on the interplay of proteins and molecules at a sub-cellular level, a systemic approach to health in social-ecological systems (HSES) is an inter- and trans-disciplinary study of complex interactions in all health-related fields. HSES moves beyond “one health” and “eco-health”, expecting to identify emerging properties and determinants of health that may arise from a systemic view ranging across scales from molecules to the ecological and socio-cultural context, as well from the comparison with different disease endemicities and health systems structures.

A model for ovine brucellosis incorporating direct and indirect transmission

In this work, we construct and analyse an ovine brucellosis mathematical model. In this model, the population is divided into susceptible and infected subclasses. Susceptible individuals can contract the disease in two ways: (i) direct mode - caused by contact with infected individuals; (ii) indirect mode - related to the presence of virulent organisms in the environment. We derive a net reproductive number and analyse the global asymptotic behaviour of the model. We also perform some numerical simulations, and investigate the effect of a slaughtering policy.

A mechanistic model of infection: why duration and intensity of contacts should be included in models of disease spread

BACKGROUND

Mathematical models and simulations of disease spread often assume a constant per-contact transmission probability. This assumption ignores the heterogeneity in transmission probabilities, e.g. due to the varying intensity and duration of potentially contagious contacts. Ignoring such heterogeneities might lead to erroneous conclusions from simulation results. In this paper, we show how a mechanistic model of disease transmission differs from this commonly used assumption of a constant per-contact transmission probability.

METHODS

We present an exposure-based, mechanistic model of disease transmission that reflects heterogeneities in contact duration and intensity. Based on empirical contact data, we calculate the expected number of secondary cases induced by an infector (i) for the mechanistic model and (ii) under the classical assumption of a constant per-contact transmission probability. The results of both approaches are compared for different basic reproduction numbers R0.

RESULTS

The outcomes of the mechanistic model differ significantly from those of the assumption of a constant per-contact transmission probability. In particular, cases with many different contacts have much lower expected numbers of secondary cases when using the mechanistic model instead of the common assumption. This is due to the fact that the proportion of long, intensive contacts decreases in the contact dataset with an increasing total number of contacts.

CONCLUSION

The importance of highly connected individuals, so-called super-spreaders, for disease spread seems to be overestimated when a constant per-contact transmission probability is assumed. This holds particularly for diseases with low basic reproduction numbers. Simulations of disease spread should weight contacts by duration and intensity.

Linkages between animal and human health sentinel data

INTRODUCTION

In order to identify priorities for building integrated surveillance systems that effectively model and predict human risk of zoonotic diseases, there is a need for improved understanding of the practical options for linking surveillance data of animals and humans. We conducted an analysis of the literature and characterized the linkage between animal and human health data. We discuss the findings in relation to zoonotic surveillance and the linkage of human and animal data.

METHODS

The Canary Database, an online bibliographic database of animal-sentinel studies was searched and articles were classified according to four linkage categories.

RESULTS

465 studies were identified and assigned to linkage categories involving: descriptive, analytic, molecular, or no human outcomes of human and animal health. Descriptive linkage was the most common, whereby both animal and human health outcomes were presented, but without quantitative linkage between the two. Rarely, analytic linkage was utilized in which animal data was used to quantitatively predict human risk. The other two categories included molecular linkage, and no human outcomes, which present health outcomes in animals but not humans.

DISCUSSION

We found limited use of animal data to quantitatively predict human risk and listed the methods from the literature that performed analytic linkage. The lack of analytic linkage in the literature might not be solely related to technological barriers including access to electronic database, statistical software packages, and Geographical Information System (GIS). Rather, the problem might be from a lack of understanding by researchers of the importance of animal data as a 'sentinel' for human health. Researchers performing zoonotic surveillance should be aware of the value of animal-sentinel approaches for predicting human risk and consider analytic methods for linking animal and human data. Qualitative work needs to be done in order to examine researchers' decisions in linkage strategies between animal and human data.

The Global Burden of Disease assessments--WHO is responsible?

The Global Burden of Disease (GBD) concept has been used by the World Health Organization (WHO) for its reporting on health information for nearly 10 years. The GBD approach results in a single summary measure of morbidity, disability, and mortality, the so-called disability-adjusted life year (DALY). To ensure transparency and objectivity in the derivation of health information, WHO has been urged to use reference groups of external experts to estimate burden of disease. Under the leadership and coordination of WHO, expert groups have been appraising and abstracting burden of disease information. Examples include the Child Health Epidemiology Reference Group (CHERG), the Malaria Monitoring and Evaluation Reference Group (MERG), and the recently established Foodborne Disease Burden Epidemiology Reference Group (FERG). The structure and functioning of and lessons learnt by these groups are described in this paper. External WHO expert groups have provided independent scientific health information while operating under considerable differences in structure and functioning. Although it is not appropriate to devise a single "best practice" model, the common thread described by all groups is the necessity of WHO's leadership and coordination to ensure the provision and dissemination of health information that is to be globally accepted and valued.

Human benefits of animal interventions for zoonosis control

Although industrialized countries have been able to contain recent outbreaks of zoonotic diseases, many resource-limited and transitioning countries have not been able to react adequately. The key for controlling zoonoses such as rabies, echinococcosis, and brucellosis is to focus on the animal reservoir. In this respect, ministries of health question whether the public health sector really benefits from interventions for livestock. Cross-sectoral assessments of interventions such as mass vaccination for brucellosis in Mongolia or vaccination of dogs for rabies in Chad consider human and animal health sectors from a societal economic perspective. Combining the total societal benefits, the intervention in the animal sector saves money and provides the economic argument, which opens new approaches for the control of zoonoses in resource-limited countries through contributions from multiple sectors.