Human benefits of animal interventions for zoonosis control

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.

Brucellosis in low-income and middle-income countries

PURPOSE OF REVIEW

Human brucellosis is a neglected, underrecognized infection of widespread geographic distribution. It causes acute febrile illness and a potentially debilitating chronic infection in humans, and livestock infection has substantial socioeconomic impact. This review describes new information regarding the epidemiology of brucellosis in the developing world and advances in diagnosis and treatment.

RECENT FINDINGS

The highest recorded incidence of human brucellosis occurs in the Middle East and Central Asia. Fever etiology studies demonstrate brucellosis as a cause of undifferentiated febrile illness in the developing world. Brucellosis is a rare cause of fever among returning travelers, but is more common among travelers returning from the Middle East and North Africa. Sensitive and specific rapid diagnostic tests appropriate for resource-limited settings have been validated. Randomized controlled trials demonstrate that optimal treatment for human brucellosis consists of doxycycline and an aminoglycoside. Decreasing the burden of human brucellosis requires control of animal brucellosis, but evidence to inform the design of control programs in the developing world is needed.

SUMMARY

Brucellosis causes substantial morbidity in human and animal populations. While improvements in diagnostic options for resource-limited settings and stronger evidence for optimal therapy should enhance identification and treatment of human brucellosis, prevention of human disease through control in animals remains paramount.

Serological investigation of bovine brucellosis in three cattle production systems in Yewa Division, south-western Nigeria

Limited data are available on the risk factors responsible for the occurrence of brucellosis amongst different cattle production systems in Nigeria despite its significant impact on livestock production. Consequently, a cross-sectional study was conducted to determine the prevalence of bovine brucellosis in three cattle production systems in Yewa Division of Ogun State, south-western Nigeria. A total of 279 blood samples (sedentary = 88; transhumance = 64; trade = 127) were examined for antibodies to Brucella sp. using the Rose Bengal test (RBT) and competitive enzyme-linked immunosorbent assay (cELISA). Overall, 24 (8.6%) and 16 (5.7%) of the animals tested seropositive for Brucella using RBT and cELISA, respectively. The herd seroprevalences based on RBT and cELISA were 31.6% and 15.8%, respectively. The results using cELISA reveal higher seroprevalence in the trade cattle (7.9%; confidence intervals [CI] = 3.2% - 12.6%) and those in a sedentary system (5.7%; CI = 0.9% - 10.5%) than in cattle kept under a transhumant management system (1.6%; CI = 1.5% - 4.7%). Age (> 3 years; p = 0.043) and breed (Djali; p = 0.038) were statistically significant for seropositivity to brucellosis based on cELISA, but sex (female, p = 0.234), production system (trade and sedentary; p = 0.208) or herd size (> 120; p = 0.359) was not. Since breeding stock is mostly sourced from trade and sedentary cattle, it is important that routine serological screening should be conducted before introducing any animal into an existing herd.

Public health ethics and a status for pets as person-things : revisiting the place of animals in urbanized societies

Within the field of medical ethics, discussions related to public health have mainly concentrated on issues that are closely tied to research and practice involving technologies and professional services, including vaccination, screening, and insurance coverage. Broader determinants of population health have received less attention, although this situation is rapidly changing. Against this backdrop, our specific contribution to the literature on ethics and law vis-à-vis promoting population health is to open up the ubiquitous presence of pets within cities and towns for further discussion. An expanding body of research suggests that pet animals are deeply relevant to people's health (negatively and positively). Pet bylaws adopted by town and city councils have largely escaped notice, yet they are meaningful to consider in relation to everyday practices, social norms, and cultural values, and thus in relation to population health. Nevertheless, not least because they pivot on defining pets as private property belonging to individual people, pet bylaws raise emotionally charged ethical issues that have yet to be tackled in any of the health research on pet ownership. The literature in moral philosophy on animals is vast, and we do not claim to advance this field here. Rather, we pragmatically seek to reconcile philosophical objections to pet ownership with both animal welfare and public health. In doing so, we foreground theorizations of personhood and property from sociocultural anthropology.

Detection of Brucella abortus DNA and RNA in different stages of development of the sucking louse Haematopinus tuberculatus

Background

Brucellosis is considered the world’s most widespread zoonotic infection. It causes abortion and sterility in livestock leading to serious economic losses and has even more serious medical impact in humans, since it can be a trigger to more than 500,000 infections per year worldwide. The aim of this study was to evaluate the role of Haematopinus tuberculatus, a louse that can parasitize several ruminants, as a new host of brucellosis. Louse specimens were collected from seropositive and seronegative water buffaloes and divided in 3 developmental stages: adults, nymphs and nits. All samples were separately screened for Brucella spp. DNA and RNA detection by Real Time PCR. In particular, primers and probes potentially targeting the 16S rRNA and the Brucella Cell Surface 31 kDalton Protein (bcsp31) genes were used for Real Time PCR and buffalo β actin was used as a housekeeping gene to quantify host DNA in the sample. A known amount of B. abortus purified DNA was utilized for standard curve preparation and the target DNA amount was divided by the housekeeping gene amount to obtain a normalized target value. A further molecular characterization was performed for Brucella strain typing and genotyping by the Bruce-ladder, AMOS-PCR and MLVA assays. Data were statistically analysed by ANOVA.

Results

Brucella abortus DNA and RNA were detected in all developmental stages of the louse, suggesting the presence of viable bacteria. Data obtained by MLVA characterization support this finding, since the strains present in animals and the relative parasites were not always identical, suggesting bacterial replication. Furthermore, the detection of Brucella DNA and RNA in nits samples demonstrate, for the first time, a trans-ovarial transmission of the bacterium into the louse.

Conclusions

These findings identified H. tuberculatus as a new host of brucellosis. Further studies are needed to establish the role of this louse in the epidemiology of the disease, such as vector or reservoir.

Brucellosis seroprevalence in Bali cattle with reproductive failure in South Sulawesi and Brucella abortus biovar 1 genotypes in the Eastern Indonesian archipelago

BACKGROUND

Brucellosis is a major cause of infertility and reproductive failure in livestock. While cattle in the Eastern Indonesian archipelago suffers from reproductive problems information on bovine brucellosis in the region is fragmentary. The control of brucellosis requires a major and prolonged effort and confirmation of the infection by isolation with detailed knowledge of the spread of the infection is essential when planning a control program.

RESULTS

Serological investigation of Brucella infection in beef cattle tended under extensive farming conditions revealed a high seroprevalence (19.3%; 95% CI, 17-22) in the compliment fixation tests. The results of a rapid and simple field test correlated well with the Rose Bengal test (kappa, 0.917) and indicated an acceptable sensitivity (87.5%) and specificity (98.1%) compared with the complement fixation test. Reproductive failure was reported for 39.0% of the cows with a loss of calves due to abortion or early death amounting to 19.3%. Past reproductive failure did not, however, correlate with seropositivity in the complement fixation test (RP = 1.21; P = 0.847). B. abortus biovar 1 was freshly isolated from the hygromas of two cows and together with thirty banked isolates collected since 1990 from different parts of Sulawesi and Timor eight related genotypes could be distinguished with one genotype being identical to that of an isolate (BfR91) from Switzerland. The Indonesian genotypes formed together with BfR91 and one African and one North American isolate a distinct branch on the B. abortus biovar 1 dendogram.

CONCLUSIONS

Bovine brucellosis appears to be widespread in the Eastern Indonesian archipelago and calls for urgent intervention. The fresh isolation of the pathogen together with the observed high seroprevalence demonstrates the presence and frequent exposure of cattle in the area to the pathogen. The application of a rapid and simple field test for brucellosis could be very useful for the quick screening of cattle at the pen side.

Identifying the public health benefits of livestock-dependent, agro-ecosystems under climate change

As the demand for meat continues to grow in South Asia and Africa and access to communal sources of water and forage shrinks, intensification of small-scale livestock systems in peri-urban areas is expected to expand. In South East Asia, smallholder transition to livestock intensification has been transformative, increasing economic opportunities while also introducing new disease risks. While we have an understanding of the emerging disease burden from livestock intensification; we have just begun to understand the possible public health benefits of sustainable landscapes and the potential health savings accrued from disease avoidance. To date, few studies have attempted to quantify the health benefits attributable to sustainable agro-ecosystems, especially in regard to livestock systems. In this paper, I will examine what is needed to measure and communicate the public health benefits and cost-savings (from disease avoidance) of sustainable agro-ecosystems.

Predicting the public health benefit of vaccinating cattle against Escherichia coli O157

Identifying the major sources of risk in disease transmission is key to designing effective controls. However, understanding of transmission dynamics across species boundaries is typically poor, making the design and evaluation of controls particularly challenging for zoonotic pathogens. One such global pathogen is Escherichia coli O157, which causes a serious and sometimes fatal gastrointestinal illness. Cattle are the main reservoir for E. coli O157, and vaccines for cattle now exist. However, adoption of vaccines is being delayed by conflicting responsibilities of veterinary and public health agencies, economic drivers, and because clinical trials cannot easily test interventions across species boundaries, lack of information on the public health benefits. Here, we examine transmission risk across the cattle-human species boundary and show three key results. First, supershedding of the pathogen by cattle is associated with the genetic marker stx2. Second, by quantifying the link between shedding density in cattle and human risk, we show that only the relatively rare supershedding events contribute significantly to human risk. Third, we show that this finding has profound consequences for the public health benefits of the cattle vaccine. A naïve evaluation based on efficacy in cattle would suggest a 50% reduction in risk; however, because the vaccine targets the major source of human risk, we predict a reduction in human cases of nearly 85%. By accounting for nonlinearities in transmission across the human-animal interface, we show that adoption of these vaccines by the livestock industry could prevent substantial numbers of human E. coli O157 cases.

Design and descriptive epidemiology of the Infectious Diseases of East African Livestock (IDEAL) project, a longitudinal calf cohort study in western Kenya

Background

There is a widely recognised lack of baseline epidemiological data on the dynamics and impacts of infectious cattle diseases in east Africa. The Infectious Diseases of East African Livestock (IDEAL) project is an epidemiological study of cattle health in western Kenya with the aim of providing baseline epidemiological data, investigating the impact of different infections on key responses such as growth, mortality and morbidity, the additive and/or multiplicative effects of co-infections, and the influence of management and genetic factors.

A longitudinal cohort study of newborn calves was conducted in western Kenya between 2007-2009. Calves were randomly selected from all those reported in a 2 stage clustered sampling strategy. Calves were recruited between 3 and 7 days old. A team of veterinarians and animal health assistants carried out 5-weekly, clinical and postmortem visits. Blood and tissue samples were collected in association with all visits and screened using a range of laboratory based diagnostic methods for over 100 different pathogens or infectious exposures.

Results

The study followed the 548 calves over the first 51 weeks of life or until death and when they were reported clinically ill. The cohort experienced a high all cause mortality rate of 16% with at least 13% of these due to infectious diseases. Only 307 (6%) of routine visits were classified as clinical episodes, with a further 216 reported by farmers. 54% of calves reached one year without a reported clinical episode. Mortality was mainly to east coast fever, haemonchosis, and heartwater. Over 50 pathogens were detected in this population with exposure to a further 6 viruses and bacteria.

Conclusion

The IDEAL study has demonstrated that it is possible to mount population based longitudinal animal studies. The results quantify for the first time in an animal population the high diversity of pathogens a population may have to deal with and the levels of co-infections with key pathogens such as Theileria parva. This study highlights the need to develop new systems based approaches to study pathogens in their natural settings to understand the impacts of co-infections on clinical outcomes and to develop new evidence based interventions that are relevant.

Epidemiology of brucellosis and q Fever in linked human and animal populations in northern togo

Background

Although brucellosis (Brucella spp.) and Q Fever (Coxiella burnetii) are zoonoses of global importance, very little high quality data are available from West Africa.

Methods/Principal Findings

A serosurvey was conducted in Togo’s main livestock-raising zone in 2011 in 25 randomly selected villages, including 683 people, 596 cattle, 465 sheep and 221 goats. Additionally, 464 transhumant cattle from Burkina Faso were sampled in 2012. The serological analyses performed were the Rose Bengal Test and ELISA for brucellosis and ELISA and the immunofluorescence assay (IFA) for Q Fever Brucellosis did not appear to pose a major human health problem in the study zone, with only 7 seropositive participants. B. abortus was isolated from 3 bovine hygroma samples, and is likely to be the predominant circulating strain. This may explain the observed seropositivity amongst village cattle (9.2%, 95%CI:4.3–18.6%) and transhumant cattle (7.3%, 95%CI:3.5–14.7%), with an absence of seropositive small ruminants. Exposure of livestock and people to C. burnetii was common, potentially influenced by cultural factors. People of Fulani ethnicity had greater livestock contact and a significantly higher seroprevalence than other ethnic groups (Fulani: 45.5%, 95%CI:37.7–53.6%; non-Fulani: 27.1%, 95%CI:20.6–34.7%). Appropriate diagnostic test cut-off values in endemic settings requires further investigation. Both brucellosis and Q Fever appeared to impact on livestock production. Seropositive cows were more likely to have aborted a foetus during the previous year than seronegative cows, when adjusted for age. This odds was 3.8 times higher (95%CI: 1.2–12.1) for brucellosis and 6.7 times higher (95%CI: 1.3–34.8) for Q Fever.

Conclusions

This is the first epidemiological study of zoonoses in Togo in linked human and animal populations, providing much needed data for West Africa. Exposure to Brucella and C. burnetii is common but further research is needed into the clinical and economic impact.

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.

Review of rabies epidemiology and control in South, South East and East Asia: past, present and prospects for elimination

Rabies is a serious public health problem in Asia. It causes substantial animal welfare, economic and human health impacts, with approximately 39,000 human deaths each year. Domestic dogs are the main reservoir and source of rabies in Asia. Common constraints for the control of rabies in the countries of Asia include inadequate resources; lack of political commitment to control programs; lack of consensus on strategy; weak intersectoral coordination and inadequate management structure; insensitive surveillance systems; limited accessibility to modern rabies vaccine and supply problems; lack of public awareness and public cooperation; and the existence of myths and religious issues. In this review, we summarize the epidemiology of rabies in both human and animals in each South and South East Asian country, the past and current approaches to control and the prospect for rabies elimination. We conclude that defining the cost of rabies to society and communicating this to decisionmakers might be the key to achieving such an advance.

Rabies in Iraq: trends in human cases 2001-2010 and characterisation of animal rabies strains from Baghdad

Control of rabies requires a consistent supply of dependable resources, constructive cooperation between veterinary and public health authorities, and systematic surveillance. These are challenging in any circumstances, but particularly during conflict. Here we describe available human rabies surveillance data from Iraq, results of renewed sampling for rabies in animals, and the first genetic characterisation of circulating rabies strains from Iraq. Human rabies is notifiable, with reported cases increasing since 2003, and a marked increase in Baghdad between 2009 and 2010. These changes coincide with increasing numbers of reported dog bites. There is no laboratory confirmation of disease or virus characterisation and no systematic surveillance for rabies in animals. To address these issues, brain samples were collected from domestic animals in the greater Baghdad region and tested for rabies. Three of 40 brain samples were positive using the fluorescent antibody test and hemi-nested RT-PCR for rabies virus (RABV). Bayesian phylogenetic analysis using partial nucleoprotein gene sequences derived from the samples demonstrated the viruses belong to a single virus variant and share a common ancestor with viruses from neighbouring countries, 22 (95% HPD 14-32) years ago. These include countries lying to the west, north and east of Iraq, some of which also have other virus variants circulating concurrently. These results suggest possible multiple introductions of rabies into the Middle East, and regular trans-boundary movement of disease. Although 4000 years have passed since the original description of disease consistent with rabies, animals and humans are still dying of this preventable and neglected zoonosis.

Lipopolysaccharide as a target for brucellosis vaccine design

The gram-negative bacteria of the genus Brucella are facultative intracellular parasites that cause brucellosis, a world wide-distributed zoonotic disease that represents a serious problem for animal and human health. There is no human-to-human contagion and, since there is no human vaccine, animal vaccination is essential to control brucellosis. However, current vaccines (all developed empirically) do not provide 100% protection and are infectious in humans. Attempts to generate new vaccines by obtaining mutants lacking the lipopolysaccharide O-polysaccharide, in purine metabolism or in Brucella type IV secretion system have not been successful. Here we propose a new approach to develop brucellosis vaccines based on the concept that Brucella surface molecules evade efficient detection by innate immunity, thus delaying protective Th1 responses and opening a time window to reach sheltered intracellular compartments. We showed recently that a branch of the core oligosaccharide section of Brucella lipopolysaccharide hampers recognition by TLR4-MD2. Mutation of glycosyltransferase WadC, involved in the synthesis of this branch, results in a lipopolysaccharide that, while keeping the O-polysaccharide essential for optimal protection, shows a truncated core, is more efficiently recognized by MD2 and triggers an increased cytokine response. In keeping with this, the wadC mutant is attenuated in dendritic cells and mice. In the mouse model of brucellosis vaccines, the Brucella abortus wadC mutant conferred protection similar to that provided by S19, the best cattle vaccine available. The properties of the wadC mutant provide the proof of concept for this new approach and open the way for more effective brucellosis vaccines.

Development of a curriculum for training in One Health analytical epidemiology at the University of Zambia

Recently, the world has witnessed emergence of novel diseases such as avian influenza, HIV and AIDS, West Nile Virus and Ebola. The evolution of these pathogens has been facilitated mainly by a constantly evolving animal-human interface. Whilst infectious disease control was previously conceptualised as either public health or animal health related issues, the distinction between disciplinary foci have been blurred by multiple causal factors that clearly traverse traditional disciplinary divides. These multiple evolutionary pressures have included changes in land use, ecosystems, human-livestock-wildlife interactions and antibiotic use, representing novel routes for pathogen emergence. With the growing realisation that pathogens do not respect traditional epistemological divides, the ‘One Health’ initiative has emerged to advocate for closer collaboration across the health disciplines and has provided a new agenda for health education. Against this background, the One Health Analytical Epidemiology course was developed under the auspices of the Southern African Centre for Infectious Diseases Surveillance by staff from the University of Zambia with collaborators from the London School of Hygiene and Tropical Medicine and the Royal Veterinary College in London. The course is aimed at equipping scientists with multidisciplinary skill sets to match the contemporary challenges of human, animal and zoonotic disease prevention and control. Epidemiology is an important discipline for both public and animal health. Therefore, this two-year programme has been developed to generate a cadre of epidemiologists with a broad understanding of disease control and prevention and will be able to conceptualise and design holistic programs for informing health and disease control policy decisions.

Economic benefits or drivers of a 'One Health' approach: why should anyone invest?

One Health concepts and ideas are some of the oldest in the health discipline, yet they have not become main stream. Recent discussions of the need for One Health approaches require some reflection on how to present a case for greater investments. The paper approaches this problem from the perspective of the control and management of resources for health in general. It poses the following questions, (1) where do we need extra resources for One Health, (2) where can we save resources through a One Health approach and (3) who has control of the resources that do exist for One Health? In answering these questions three broad areas are explored, (1) The management and resources allocated for diseases, (2) The isolation of parts of the society that require human and animal health services and (3) The use of resources and skills that are easily transferable between human and animal health.The paper concludes that One Health approaches are applicable in many scenarios. However, the costs of getting people from different disciplines to work together in order to achieve a true One Health approach can be large. To generate tangible benefits requires careful management of specialist skills, knowledge and equipment, which can only be achieved by a greater openness of the human and animal health disciplines. Without this openness, policy makers will continue to doubt the real value of One Health. In summary the future success of One Health is about people working in the research, education and provision of health systems around the world embracing and managing change more effectively.

Acellular vaccines for ovine brucellosis: a safer alternative against a worldwide disease

Ovine brucellosis is a very contagious zoonotic disease distributed worldwide and constitutes a very important zoosanitary and economic problem. The control of the disease includes animal vaccination and slaughter of infected flocks. However, the commercially available vaccine in most countries is based on the attenuated strain Brucella melitensis Rev 1, which presents important safety drawbacks. This review is focused on the most recent and promising acellular vaccine proposals.

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.

Human and animal rabies prevention and control cost in Bhutan, 2001-2008: the cost-benefit of dog rabies elimination

The objective of this study was to estimate the cost of various interventions and to quantify the economic impacts of rabies in Bhutan. Cost-benefit of dog rabies elimination versus human post exposure treatment cost was also assessed. The average direct medical cost of human post-exposure treatment (using rabies vaccine only) was estimated to be Nu. 1615 (US$ 35.65) per 5-dose Essen regimen per patient. The cost would increase to Nu. 2497 (US$ 55.13) and Nu. 19,633 (US$ 433.41) per patient when one dose of either equine rabies immunoglobulin (ERIG) or human rabies immunoglobulin (HRIG) is administered, respectively. The societal cost (direct medical and indirect patient expenses) per patient was estimated to be Nu. 2019 (US$ 45), Nu. 2901 (US$ 64) and Nu. 20,037 (US$ 442) using vaccine only, vaccine with ERIG and vaccine with HRIG, respectively. The average cost per dog vaccination and sterilization were estimated to be Nu. 75 (US$ 1.66) and Nu. 288 (US$ 6.36), respectively. The total direct cost of rabies and various interventions between 2001 and 2008 was estimated to be Nu. 46.95 million (US$ 1.03 million). The direct cost for intensified human PET was estimated to be Nu. 5.85 million (US$ 0.11 million) per year with a cumulated estimated costs of Nu. 35.10 million (US$ 0.70 million) while the cost of mass dog vaccination with at least 70% coverage is estimated to be approximately Nu. 10.31 million (US$ 0.21 million) at the end of 6 years. The combined cost of mass dog vaccination and human PET was estimated to be greater than the cost of human PET alone during the first 2 years of the campaign, and then would be lower than human PET cost alone after the 5th year of the campaign. The total cumulated cost of the combined strategy was estimated to be Nu. 34.14 million (US$ 0.73 million) and would be lower than the cumulated cost of human PET alone (Nu. 35.10 million, US$ 0.77 million) at the end of 6 years. Rabies represents a substantial economic impact to the Bhutanese society. Well-planned and implemented mass dog vaccination would result in elimination of rabies reservoirs in the domestic dog population and would eliminate human rabies cases. It would also reduce the recurrent expenditure on human post-exposure treatment.

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.

Seroepidemiological study of livestock brucellosis in a pastoral region

A seroepidemiological study of Brucella infections in multiple livestock species in the Borana pastoral system of Ethiopia was performed between December 2007 and October 2008. A cross-sectional multi-stage sampling technique was employed to select 575 cattle, 1073 camels and 1248 goats from the target populations. Sera were collected from the animals, and serially tested using Rose Bengal test and complement fixation test. Overall prevalence and prevalence with respect to explanatory variables were established, and potential risk factors for seropositivity were analysed using a multivariable logistic regression. The results showed that 8·0% (95% CI 6·0–10·6), 1·8% (95% CI 1·1–2·8) and 1·6% (95% CI 1·0–2·5) of the tested cattle, camels and goats, respectively, had antibodies to Brucella antigen. Positive reactors were found in 93·8% of the villages with more frequent detection of positive cattle (93·3%) than camels (56·3%) and goats (37·5%). Risk factors identified for cattle were: keeping more livestock species at household level (OR 4·1, 95% CI 1·9–8·9), increasing age of the animal (OR 2·8, 95% CI 1·3–6·0) and wet season (OR 3·3, 95% CI 1·6–6·9). Increase in household-level species composition (OR 4·1, 95% CI 1·2–14·2) and wet season (OR 3·7, 95% CI 1·5–9·1) were found to be risk factors for seropositivity in camels and goats, respectively. Existence of more than one seroreactor animal species in most villages and association of increased livestock species composition with seropositivity may add more credence to the possibility of cross-species transmission of Brucella infections. Although no attempt to isolate Brucella spp. was made, our results suggest that cattle are more likely maintenance hosts of Brucella abortus which has spread to goats and camels. This should be substantiated by further isolation and identification of Brucella organisms to trace the source of infection and transmission dynamics in various hosts kept under mixed conditions. In conclusion, the present study suggests the need for investigating a feasible control intervention and raising public awareness on prevention methods of human exposure to brucellosis.

Renewed global partnerships and redesigned roadmaps for rabies prevention and control

Canine rabies, responsible for most human rabies deaths, is a serious global public health concern. This zoonosis is entirely preventable, but by focusing solely upon rabies prevention in humans, this “incurable wound” persists at high costs. Although preventing human deaths through canine rabies elimination is feasible, dog rabies control is often neglected, because dogs are not considered typical economic commodities by the animal health sector. Here, we demonstrate that the responsibility of managing rabies falls upon multiple sectors, that a truly integrated approach is the key to rabies elimination, and that considerable progress has been made to this effect. Achievements include the construction of global rabies networks and organizational partnerships; development of road maps, operational toolkits, and a blueprint for rabies prevention and control; and opportunities for scaling up and replication of successful programs. Progress must continue towards overcoming the remaining challenges preventing the ultimate goal of rabies elimination.

Brucellosis at the animal/ecosystem/human interface at the beginning of the 21st century

Following the recent discovery of new Brucella strains from different animal species and from the environment, ten Brucella species are nowadays included in the genus Brucella. Although the intracellular trafficking of Brucella is well described, the strategies developed by Brucella to survive and multiply in phagocytic and non-phagocytic cells, particularly to access nutriments during its intracellular journey, are still largely unknown. Metabolism and virulence of Brucella are now considered to be two sides of the same coin. Mechanisms presiding to the colonization of the pregnant uterus in different animal species are not known. Vaccination is the cornerstone of control programs in livestock and although the S19, RB51 (both in cattle) and Rev 1 (in sheep and goats) vaccines have been successfully used worldwide, they have drawbacks and thus the ideal brucellosis vaccine is still very much awaited. There is no vaccine available for pigs and wildlife. Animal brucellosis control strategies differ in the developed and the developing world. Most emphasis is put on eradication and on risk analysis to avoid the re-introduction of Brucella in the developed world. Information related to the prevalence of brucellosis is still scarce in the developing world and control programs are rarely implemented. Since there is no vaccine available for humans, prevention of human brucellosis relies on its control in the animal reservoir. Brucella is also considered to be an agent to be used in bio- and agroterrorism attacks. At the animal/ecosystem/human interface it is critical to reduce opportunities for Brucella to jump host species as already seen in livestock, wildlife and humans. This task is a challenge for the future in terms of veterinary public health, as for wildlife and ecosystem managers and will need a "One Health" approach to be successful.

Human rabies post exposure prophylaxis in Bhutan, 2005-2008: trends and risk factors

The aim of this study was to understand the use and distribution of human rabies post exposure prophylaxis (PEP) vaccine in Bhutan and to identify risk factors for receiving an incomplete course of the vaccine. We analyzed post exposure treatment records from 28 medical hospitals from 2005 to 2008. Males (59%) accounted for significantly more PEP events than females (41%) across all age groups (P<0.001). Children - particularly 5-9 years of age - received more rabies PEP than other age groups. Animal bite and non-bite accounted for 27% (n=2239) and 16% (n=1303) of rabies PEP, respectively, whilst 57% (n=4773) of the PEP events had no recorded information about the reasons for post exposure treatment. Post exposure treatment was provided throughout the year with a higher number during the winter and spring months. The number of PEP events significantly (P<0.001) increased between 2005 and 2008, from <1000 to >2800 events, respectively. Significantly (P<0.001) more PEP events were reported from the southern parts of Bhutan that are endemic for rabies or those areas in eastern Bhutan that have reported rabies outbreaks than other parts of Bhutan. Forty percent (n=3360) of the patients received an incomplete course of vaccine (<5-doses of vaccine intramuscular). Results suggest that patients with animal bite injury were less likely to receive an incomplete vaccine course than non-bite recipients, and patients presented to hospitals in rabies endemic or outbreak areas were less likely to receive an incomplete course than in non-rabies areas or rabies free areas. Similarly, patients presenting to hospitals for PEP during spring and summers months were less likely to receive an incomplete vaccine course than those during other seasons. Public education campaigns need to be conducted in Bhutan to reduce dog bite incidents and also to prevent mass exposures to rabies. A thorough assessment of each individual case based on the WHO guidelines would reduce unnecessary PEP (and therefore costs) in Bhutan.

Zoonotic emerging infectious disease in selected countries in Southeast Asia: insights from ecohealth

Most emerging diseases of humans originate in animals, and zoonotic emerging infectious diseases (EIDs) threaten human, animal, and environment health. We report on a scoping study to assess actors, linkages, priorities, and needs related to management of these diseases from the perspective of key stakeholders in three countries in Southeast Asia. A comprehensive interview guide was developed and in-depth interviews completed with 21 key stakeholders in Vietnam, Lao People's Democratic Republic, and Cambodia. We found numerous relevant actors with a predominance of public sector and medical disciplines. More capacity weaknesses than strengths were reported, with risk analysis and research skills most lacking. Social network analysis of information flows showed policy-makers were regarded as mainly information recipients, research institutes as more information providers, and universities as both. Veterinary and livestock disciplines emerged as an important "boundary-spanning" organization with linkages to both human health and rural development. Avian influenza was regarded as the most important zoonotic EID, perhaps reflecting the priority-setting influence of actors outside the region. Stakeholders reported a high awareness of the ecological and socioeconomic drivers of disease emergence and a demand for disease prioritization, epidemiological skills, and economic and qualitative studies. Evaluated from an ecohealth perspective, human health is weakly integrated with socioeconomics, linkages to policy are stronger than to communities, participation occurs mainly at lower levels, and equity considerations are not fully considered. However, stakeholders have awareness of ecological and social determinants of health, and a basis exists on which transdisciplinarity, equity, and participation can be strengthened.

Ruminant brucellosis in the Kafr El Sheikh Governorate of the Nile Delta, Egypt: prevalence of a neglected zoonosis

Background

Brucellosis is a neglected tropical zoonosis allegedly reemerging in Middle Eastern countries. Infected ruminants are the primary source of human infection; consequently, estimates of the frequency of ruminant brucellosis are useful elements for building effective control strategies. Unfortunately, these estimates are lacking in most Middle East countries including Egypt. Our objectives are to estimate the frequency of ruminant brucellosis and to describe its spatial distribution in Kafr El Sheikh Governorate, Nile Delta, Egypt.

Methodology/Principal Findings

We conducted a cross-sectional study in which 791 sheep, 383 goats, 188 cattle milk tanks and 173 buffalo milk tanks were randomly selected in 40 villages and tested for the presence of antibodies against Brucella spp. The seroprevalence among different species was estimated and visualized using choropleth maps. A spatial scanning method was used to identify areas with significantly higher proportions of seropositive flocks and milk tanks. We estimated that 12.2% of sheep and 11.3% of goats in the study area were seropositive against Brucella spp. and that 12.2% and 12% of cattle and buffalo milk tanks had antibodies against Brucella spp. The southern part of the governorate had the highest seroprevalence with significant spatial clustering of seropositive flocks in the proximity of its capital and around the main animal markets.

Conclusions/ Significance

Our study revealed that brucellosis is endemic at high levels in all ruminant species in the study area and questions the efficacy of the control measures in place. The high intensity of infection transmission among ruminants combined with high livestock and human density and widespread marketing of unpasteurized milk and dairy products may explain why Egypt has one of the highest rates of human brucellosis worldwide. An effective integrated human-animal brucellosis control strategy is urgently needed. If resources are not sufficient for nationwide implementation, high-risk areas could be prioritized.

Brucellosis is a zoonosis of mammals caused by bacteria of the genus Brucella. It is responsible for a vast global burden imposed on human health through disability and on animal productivity. In humans brucellosis causes a range of flu-like symptoms and chronic debilitating illness. In livestock brucellosis causes economic losses as a result of abortion, infertility and decreased milk production. The main routes for human infection are consumption of contaminated dairy products and contact with infected ruminants. The control of brucellosis in humans depends on its control in ruminants, for which accurate estimates of the frequency of infection are very useful, especially in areas with no previous frequency estimates. We studied the seroprevalence of brucellosis and its geographic distribution among domestic ruminants in one governorate of the Nile Delta region, Egypt. In the study area, the seroprevalence of ruminant brucellosis is very high and has probably increased considerably since the early 1990s. The disease is widespread but more concentrated around major animal markets. These findings question the efficacy of the control strategy in place and highlight the high infection risk for the animal and human populations of the area and the urgent need for an improved control strategy.

Education of veterinary medical and other public health providers: linking interventions with health outcomes

A systematic literature review was performed to summarize the nature, implementation, outcomes, and long-term impacts of previously instituted interventions and programs aimed at educating veterinary public health providers. A logic model was developed to direct the literature search strategy, provide a framework for evaluating the relationship between veterinary public health professional education and their associated population health outcomes, and guide future training development and recommendations for the education of veterinary health professionals. Our literature review indicates that there is a relative lack of published literature that connects veterinary public health educational interventions to population health outcomes. Reasons for the lack of evidence to connect educational programs and population health outcomes include the evaluation of outcomes on a short-term rather than intermediate- or long-term basis, a lack of experimental studies, and infrequent grounding in population health or educational theory. Future intervention recommendations as suggested in the reviewed articles are also summarized.

Milk producers' awareness of milk-borne zoonoses in selected smallholder and commercial dairy farms of Zimbabwe

A cross-sectional questionnaire-based study was conducted to assess milk producers' awareness of milk-borne zoonoses in selected smallholder and commercial dairy farms of Zimbabwe. The questionnaire was designed to obtain information on dairy breeds, milk production, dairy farmers' knowledge and awareness of zoonoses with particular emphasis on milk-borne zoonoses and farmers' behavioural practices that may lead to increased risk of milk-borne zoonoses transmission. A total of 119 dairy farmers were interviewed, and 41.5% were aware of milk-borne zoonoses with a significantly (P<0.01) higher percentage of commercial dairy farmers (65.0%) being aware compared to smallholder dairy farmers (36.7%). The behavioural practices of dairy farmers observed to increase the risk of milk-borne zoonoses transmission were; consumption of raw milk (68.1%), sale of raw milk to the local public (25.2%), lack of cooling facilities by smallholder farmers (98%), and no routine testing (84.9%) and medical check-ups (89.1%) for milk-borne zoonoses. General hygienic and disease control practices need to be integrated in the milk production process particularly at the smallholder level. Awareness, teaching and training programmes for smallholder dairy farmers can improve disease control in animals and reduce the public health risk of milk-borne zoonoses.

Towards improved diagnosis of zoonotic trematode infections in Southeast Asia

Humans in Southeast Asia are at risk for at least 70 species of food-borne and water-borne trematodes, including blood flukes, intestinal flukes, liver flukes and lung flukes, which are shared with a great variety of animals. Co-infection with several other zoonotic trematodes is pervasive, and hence differential diagnosis represents a major challenge. Many zoonotic trematodes are commonly overlooked, leading to unreliable prevalence data, underappreciation of their veterinary and public health burden and impact, and general neglect with respect to treatment and control. Additionally, many eggs are indistinguishable by microscopy. For example, failure to address this diagnostic dilemma has resulted in overestimation of Clonorchis sinensis prevalence and underestimation of minute intestinal flukes. Test insensitivity is becoming a problem of prime interest as surveillance is gaining in importance and various control programmes now regularly register progress. Hence, the likelihood of underestimating the true burden of disease is growing in well-controlled areas when the faecal egg excretion among infected individuals approaches zero. While antibody testing has ultimate sensitivity, its use as a test of cure remains contentious. On the other hand, employing faecal egg detection as the diagnostic 'gold' standard makes many positive antibody test results (incorrectly) appear false. Polymerase chain reaction (PCR)-based diagnostics could solve this dilemma, but more experience is needed and costs must be brought down to permit large-scale use of this approach. The future development of virtual microscopy to be used for diagnosis of parasitic infections in the field could make ordinary microscopy obsolete by electronically capturing specimens at point-of-contact in remote areas.

Capacity building for zoonotic and foodborne diseases in the Mediterranean and Middle East regions (an intersectoral WHO/MZCP proposed strategy)

Epidemics and threats of epidemics are events of national and international public health importance. Zoonotic and foodborne disease management in the Mediterranean and the Middle East regions suffers from the inconsistent availability of accurate data at national and regional levels as well as difficulties in the timely recognition and containment of disease events. This situation mostly results from weak intersectoral national policies, strategies and programmes, together with a lack of education for professionals in crucial technical posts to help them provide effective management. There is urgent need for the development of a capacity-building strategy among human resources through specialised training in fields of major importance. The adoption of an expanded training strategy at national and inter-country level targeted at increasing the capability of professionals in sectors involved in zoonoses, foodborne diseases, food safety, the environment, emergencies, public health education and promoting intersectoral collaboration and coordination is proposed. Such a capacity-building strategy will need sustained political commitment for support and reform, together with sustained technical contributions and funds mobilisation by international organisations.

Emergence and re-emergence of viral diseases of the central nervous system

Neurologic disease is a major cause of disability in resource-poor countries and a substantial portion of this disease is due to infections of the CNS. A wide variety of emerging and re-emerging viruses contribute to this disease burden. New emerging infections are commonly due to RNA viruses that have expanded their geographic range, spread from animal reservoirs or acquired new neurovirulence properties. Mosquito-borne viruses with expanding ranges include West Nile virus, Japanese encephalitis virus and Chikungunya virus. Zoonotic viruses that have recently crossed into humans to cause neurologic disease include the bat henipaviruses Nipah and Hendra, as well as the primate-derived human immunodeficiency virus. Viruses adapt to new hosts, or to cause more severe disease, by changing their genomes through reassortment (e.g. influenza virus), mutation (essentially all RNA viruses) and recombination (e.g. vaccine strains of poliovirus). Viruses that appear to have recently become more neurovirulent include West Nile virus, enterovirus 71 and possibly Chikungunya virus. In addition to these newer challenges, rabies, polio and measles all remain important causes of neurologic disease despite good vaccines and global efforts toward control. Control of human rabies depends on elimination of rabies in domestic dogs through regular vaccination. Poliovirus eradication is challenged by the ability of the live attenuated vaccine strains to revert to virulence during the prolonged period of gastrointestinal replication. Measles elimination depends on delivery of two doses of live virus vaccine to a high enough proportion of the population to maintain herd immunity for this highly infectious virus.

Zoonotic tuberculosis and brucellosis in Africa: neglected zoonoses or minor public-health issues? The outcomes of a multi-disciplinary workshop

Late in 2007, veterinary, medical and anthropological professionals from Europe and Africa met in a 2-day workshop in Pretoria, South Africa, to evaluate the burden, surveillance and control of zoonotic tuberculosis and brucellosis in sub-Saharan Africa. Keynote presentations reviewed the burden of these diseases on human and livestock health, the existing diagnostic tools, and the available control methods. These presentations were followed by group discussions and the formulation of recommendations. The presence of Mycobacterium bovis and Brucella spp. in livestock was considered to be a serious threat to public health, since livestock and animal products are the only source of such infections in human beings. The impact of these pathogens on human health appears to be relatively marginal, however, when compared with Mycobacterium tuberculosis infections and drug resistance, HIV and malaria. Appropriate diagnostic tools are needed to improve the detection of M. bovis and Brucella spp. in humans. In livestock, the 'test-and-slaughter' approach and the pasteurization of milk, which have been used successfully in industrialized countries, might not be the optimal control tools in Africa. Control strategies should fit the needs and perceptions of local communities. Improved intersectoral and international collaboration in surveillance, diagnosis and control, and in the education of medical and veterinary personnel, are advocated.

Development of combined vaccines for rabies and immunocontraception

Rabies prevention and appropriate population management of free-ranging animals have an important role to play in the eventual elimination of rabies in dogs. An effective sterilant based on rabies vaccines has the potential to create a supportive measure of public acceptability and to reduce associated clinic visit costs. We inserted the coding sequence of gonadotropin-releasing hormone (GnRH) into different locations within the rabies virus ERA glycoprotein (G) gene, and demonstrated that the amino terminus (N), antigenic site IIa, and the junction between the ecto- and cytoplasmic domains (C) of the G were suitable sites for GnRH insertion. The rescued recombinant rabies viruses ERA-N-GnRH and ERA-C-GnRH grew as well as the parental ERA virus, reaching 1x10(9)ffu/ml in cell culture. Insertion and expression of the GnRH were stable in the viruses after multiple passages in vitro. To increase immunogenicity of the GnRH peptide, two copies of GnRH, aligned in tandem, were fused to the N terminus of the G. The recombinant rabies virus ERA-N-2GnRH was recovered and grown to high titers in cell culture. All GnRH-carrying rabies viruses induced antibodies against GnRH in immunized mice and protected 100% of the animals after rabies virus challenge. The recombinant viruses reacted strongly with the serum from a GonaCon-immunized animal. The GnRH-carrying rabies viruses have significant potential in rabies and animal population control.

Reemerging rabies and lack of systemic surveillance in People's Republic of China

Rabies is a reemerging disease in China. The high incidence of rabies leads to numerous concerns: a potential carrier-dog phenomenon, undocumented transmission of rabies virus from wildlife to dogs, counterfeit vaccines, vaccine mismatching, and seroconversion testing in patients after their completion of postexposure prophylaxis (PEP). These concerns are all scientifically arguable given a modern understanding of rabies. Rabies reemerges periodically in China because of high dog population density and low vaccination coverage in dogs. Mass vaccination campaigns rather than depopulation of dogs should be a long-term goal for rabies control. Seroconversion testing after vaccination is not necessary in either humans or animals. Human PEP should be initiated on the basis of diagnosis of biting animals. Reliable national systemic surveillance of rabies-related human deaths and of animal rabies prevalence is urgently needed. A laboratory diagnosis-based epidemiologic surveillance system can provide substantial information about disease transmission and effective prevention strategies.

Are we getting closer to the treatment of rabies?

Rabies is a top-ten infectious killer and is newly re-emergent worldwide. Focusing on the unique aspects of the pathophysiology and immunology of rabies, we improvised a strategy that led to the first survivor of rabies without rabies prophylaxis. Our data support the long-standing speculation that rabies is a disorder of neurotransmission. Improvements in human survival have better delineated the immune and metabolic responses to rabies. We anticipate a new generation of rabies biologicals in the very near future, as well as the more remote possibility of rescue monoclonal antibodies engineered from several recent survivors of human rabies. The general approach to rabies treatment serves as a model for a more complex, physiological approach to treating infectious neurological disorders.

Human rabies focusing on dog ecology-A challenge to public health in Sri Lanka

Sri Lanka is among the top ten countries in the world that report the highest rate of human rabies deaths (2.8 per 1,000,000 in 2007) and animal bites requiring anti-rabies post-exposure treatment (PET) (755 per 100,000 in 2003). Dogs are the main reservoir and transmitters of rabies in Sri Lanka. Present study evaluates the effectiveness of dog rabies control strategies on reducing incidence of human rabies deaths. Analysis is based on data from last three decades and showed strong correlations between the interventions and human rabies incidence. GIS maps provided a method for illustrating the district distribution of human rabies deaths and dog population density and for recognizing districts at risk. Interrupting the natural transmission cycle of rabies in dogs would be a logical approach in eliminating dog rabies in Sri Lanka. However, interventions implemented so far, such as dog vaccination, elimination of stray dogs (abandoned in 2005), and animal birth control have been inadequate to do so. Better understanding of the ecology of stray and owned dogs (e.g. population density, population structure, confinement status) in the context of the human environment and culture, are needed to strategize the control activities, requiring coordination among regional Public Health and Veterinary services.

Transmission dynamics and economics of rabies control in dogs and humans in an African city

Human rabies in developing countries can be prevented through interventions directed at dogs. Potential cost-savings for the public health sector of interventions aimed at animal-host reservoirs should be assessed. Available deterministic models of rabies transmission between dogs were extended to include dog-to-human rabies transmission. Model parameters were fitted to routine weekly rabid-dog and exposed-human cases reported in N'Djaména, the capital of Chad. The estimated transmission rates between dogs (beta(d)) were 0.0807 km2/(dogs x week) and between dogs and humans (beta(dh)) 0.0002 km2/(dogs x week). The effective reproductive ratio (R(e)) at the onset of our observations was estimated at 1.01, indicating low-level endemic stability of rabies transmission. Human rabies incidence depended critically on dog-related transmission parameters. We simulated the effects of mass dog vaccination and the culling of a percentage of the dog population on human rabies incidence. A single parenteral dog rabies-mass vaccination campaign achieving a coverage of least 70% appears to be sufficient to interrupt transmission of rabies to humans for at least 6 years. The cost-effectiveness of mass dog vaccination was compared to postexposure prophylaxis (PEP), which is the current practice in Chad. PEP does not reduce future human exposure. Its cost-effectiveness is estimated at US $46 per disability adjusted life-years averted. Cost-effectiveness for PEP, together with a dog-vaccination campaign, breaks even with cost-effectiveness of PEP alone after almost 5 years. Beyond a time-frame of 7 years, it appears to be more cost-effective to combine parenteral dog-vaccination campaigns with human PEP compared to human PEP alone.