Can dog rabies be eliminated in Africa?
RationaleBrucellosis control by livestock mass vaccination and subsequent test-and-slaughter is effective and in this way brucellosis has been eliminated in several countries. Yet, its control is stagnating or even re-emerging in many parts of the world, especially in Africa and Asia. Depending on the context, the cross-sector nature of brucellosis involving wildlife, livestock and humans requires a systemic integrated approach when aiming towards elimination. However, the public health and animal health sectors work in too much separation from one another. While research on better vaccines is urgent and on-going, control and elimination of brucellosis is not merely an operational problem. Control and elimination of brucellosis is a science challenge because of complexity in the involved processes and the way in which these processes contribute to fundamental properties of the biology of brucellosis. From a matrix mathematical point of view, a brucellosis intervention aimed at elimination can be considered as a major perturbation leading towards a disease free equilibrium state. Here the different components of a science of brucellosis elimination involving all actors in public and animal health are outlined.
Components of a science of brucellosis elimination
- Pathogen biology in the social-ecological system
Prior to implementing brucellosis control and elimination activities, the main reservoirs and their population dynamics must be known. The population dynamics of reservoir hosts directly determines the effective reproductive number (Re) of brucellosis transmission and the persistence of transmission (Racloz et al. 2013). Because of the long incubation period, the role of density dependence and contact networks in brucellosis transmission are not well understood and require more research. In Mongolia, effective reproductive numbers were estimated at 1.2 in small ruminants and 1.7 in cattle and a vaccination coverage of 80% was recommended for the 2000-2010 mass vaccination campaign (Zinsstag et al. 2005a).
- Social determinants and public engagement
Effective interventions against brucellosis rely on important enabling public conditions. Both public and private veterinary services need to be sufficiently staffed and able to cover the area of intervention. Sufficient human and veterinary laboratory capacity is needed, along with the ability to characterize isolated bacterial strains. Implementing test-and-slaughter control schemes requires sufficient public funding to compensate farmers for culled stock and a relatively corruption-free environment. Above all, a societal consensus is needed, which is only achieved by including all actors in so called ‘transdisciplinary’ stakeholder processes (Hirsch Hadorn et al. 2008). Through this process, all involved stakeholders contribute to identify priority actions and this should create trust between them (Schelling et al. 2007).
- Systemic surveillance
Understanding the disease ecology allows for identification of interventions which have the highest effect. For this purpose, joint animal-human cross-sectional studies provide a snapshot of disease frequencies in the most important reservoir hosts and may indicate the main source of human infection. In a representative study in Kyrgyzstan human seroprevalence was significantly related to sheep seroprevalence but not to goats and cattle (Bonfoh et al. 2012).
- Mathematical model frameworks: transmission dynamics
Mathematical modelling of the transmission dynamics of brucellosis assists in following up the effectiveness of interventions (Zinsstag et al. 2005a). Such models are the backbone to intervention economic analysis (Roth et al. 2003) and can be used to assess animal-human interfaces. In this example, it can be shown that brucella melitensis seems to be more readily transmitted to humans than brucella abortus. In Mongolia, the small ruminant to human transmission constant was 13 times lower than that between small ruminants, ie one infected small ruminant infected 13 other small ruminants before one person was also infected. Assuming the cattle were mostly infected with brucella abortus, the cattle to human transmission constant was 165 times lower than that between cattle transmission. Such findings are still very rare and need to be further assessed (Zinsstag et al. 2015).
- Equity effectiveness
The effectiveness of an intervention is a multiplicative rather than additive process: for example, the product of the vaccine efficacy times the achieved coverage. The coverage, in other words, the proportion of animals effectively reached by a mass vaccination, is determined by the vaccine availability, accessibility, affordability, acceptability and adequacy. Further, it depends on the service provider compliance and the adherence to the mass vaccination by the animal holder (Obrist et al. 2007). An understanding of the determinants of the effectiveness of an intervention requires a close interdisciplinary collaboration between, among others, vaccine biology, health systems research, health economics, social and cultural sciences and animal health. Even if all intervention factors have a relatively high performance, they are all related to each other in a multiplicative way (Zinsstag et al. 2011a).
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- Intervention methods
The choice of intervention methods depends on the prevalence of the disease and the available funds. It is well established that mass vaccination of livestock is recommended in settings where brucellosis seroprevalence is above 1% (Zinsstag et al. 2012). Below this, a test-and-slaughter method is recommended, whereby seropositive animals would be culled after systematic sampling. However, one should bear in mind that most developing countries would not be able to compensate farmers for culled stock and the existing levels of corruption would probably not allow for successful implementation of such schemes. Intervention methods must be carefully analysed within a given political and socio-economic context.
The way forwardBrucellosis elimination is also achievable in developing countries. Above all, it requires a societal consensus addressing issues like compensation or intervention types which should not be decided over the heads of livestock owners. Successful examples of disease elimination shows that all actors need to be involved from the start, as all of them play important roles. Specifically, the public health and animal health sectors should work as closely together as possible (Zinsstag et al. 2015, Zinsstag et al. 2005b).Regional approaches, for example involving Mongolia, China and Russia, will also be needed to address issues of cross border transmission, and, in this way, brucellosis control would probably make a significant practical contribution to the create trust and peace building. The proposed science of brucellosis elimination does not stand alone, it should learn from other initiatives, like the science of malaria eradication or the science of rabies elimination (Zinsstag 2013).Further orientations could aim at combining, for example brucellosis and echinococcosis mass vaccination. One could also think about a locally adapted extended farm package including dog rabies, echinococcosis, brucellosis, anthrax, and FMD. Brucellosis can be eliminated, but we need to all work together in an evidence based systemic way.
ReferencesBonfoh, B. et al. (2012). Representative Seroprevalences of Brucellosis in Humans and Livestock in Kyrgyzstan, in: Ecohealth 9(2), 132-138.Durr, S. et al. (2013). Bayesian estimation of the seroprevalence of brucellosis in humans and livestock in Kyrgyzstan, in: Revue Scientifique Et Technique, 32(3), 801-15.Hirsch Hadorn, G. et al. (2008). Handbook of Transdisciplinary Research, London, Springer.Kasymbekov, J. et al. (2013). Molecular epidemiology and antibiotic susceptibility of livestock Brucella melitensis isolates from Naryn Oblast, Kyrgyzstan, in: PLoS Neglected Tropical Diseases, 7(2), e2047.Obrist, B. et al. (2007). Access to Health Care in Contexts of Livelihood Insecurity: a Framework for Analysis and Action, in: PLoS medicine 2007, 1584-1588.Racloz, V. et al. (2013). Persistence of brucellosis in pastoral systems, in: Revue Scientifique Et Technique, 32(1), 61-70.Roth, F. et al. (2003). Human health benefits from livestock vaccination for brucellosis: case study, in: Bulletin of the World Health Organization, 81(12), 867-876.Schelling, E. et al. (2008). Toward Integrated and Adapted Health Services for Nomadic Pastoralists and their Animals: A North-South Partnership, in: Hirsch Hadorn, G. et al. (2008). Handbook of Transdisciplinary Research, London, Springer, 277-291.Shabb, D. et al. (2013). A mathematical model of the dynamics of Mongolian livestock populations, in: Livestock Science, 157, 280-288.Tsend, S. et al. (2014). Representative survey on human brucellosis among rural people in Mongolia, in: Western Pacific Surveillance and Response Journal, (in press).Zinsstag, J. (2013). Towards a Science of Rabies Elimination, in: Infectious diseases of poverty 2(1), 22 pp.Zinsstag, J. et al. (2012). It’s time to control brucellosis in Central Asia, in: Bonfoh, M. A. a. B., (ed.) Evidence for policy series, regional edition Central Asia,Bishkek, Kyrgyzstan and Abidjan, Côte d’Ivoire, 1-4.Zinsstag, J. et al. (2005a). A Model of Animal-Human Brucellosis Transmission in Mongolia, in: Preventive veterinary medicine 69(1-2), 77-95.Zinsstag, J. et al. (2005b). Potential of cooperation between human and animal health to strengthen health systems, in: Lancet, 2142-2145.Zinsstag, J. et al. (2007). Human Benefits of Animal Interventions for Zoonosis Control, in: Emerging infectious diseases 13(4), 527-531.Zinsstag, J. et al. (2011a). From ‘One Medicine’ to ‘One Health’ and Systemic Approaches to Health and Well-being, in: Preventive veterinary medicine 101, 148-156.Zinsstag, J. et al. (2011b). Towards Equity Effectiveness in Health Interventions, in: Perspectives of the Swiss National Centre of Competence in Research (NCCR) North-South, Bern, Geographica Bernensia, 623-639.Zinsstag, J. et al. (2015). One Health. The Theory and Practice of Integrated Health approaches, Wallingford, CABI.
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