From Epidemic to Elimination: Density-Vague Transmission and the Design of Mass Dog Vaccination Programs
Daniel T Haydon, Sunny Townsend, Sarah Cleaveland, Katie Hampson
Institute of Biodiversity, Animal Health and Comparative Medicine, College of Medical, Veterinary and Life Sciences, University of Glasgow
Objectives: Rabies is one of the most important zoonotic diseases in the world, causing an estimated 55,000 human deaths each year, primarily in Asia and Africa. Momentum is building towards development of a strategy for the global elimination of canine rabies, which has recently been identified as a priority by WHO, OIE and FAO as well as other international human and animal health agencies. This presentation will address several critical issues relating to the design of mass dog vaccination campaigns for the cost-effective control and elimination of canine rabies.
Methods: Our findings are based on the analysis of data generated from a high-profile and well-studied outbreak in Bali, Indonesia, and the on the results of a closely parameterized spatially explicit computer simulation of the dynamics of rabies outbreaks.
Results: We present three main findings. The first is that although dog densities on Bali are at least an order of magnitude higher than other populations in which rabies has been studied, our estimate for the basic reproduction number (R0) of ~ 1.2 is similar to other populations with much lower dog densities, which suggests that, counter to expectations, R0 for rabies is essentially density independent.
The second result follows directly from these consistent values of R0: across a wide range of settings, and even in very high-density dog populations, control and elimination of canine rabies by dog vaccination is an entirely feasible control option. Additional measures to reduce dog population density are not likely to be necessary.
Our third result is that the effectiveness of vaccination depends primarily upon reaching a sufficient vaccination coverage (70%) across the population in successive campaigns, and does not improve with more complex, reactive or synchronized campaigns. However, even small ‘gaps' in vaccination coverage can significantly impede prospects of elimination, and therefore regional coordination and participation in such campaigns is critical.
Conclusions: This study has enabled us to evaluate the impact of different vaccination strategies on human deaths averted and the time it will take for rabies to be eliminated from Bali under a range of plausible scenarios. Modeling can be used to develop simple, pragmatic and operational guidelines for regional rabies vaccination campaign that will be of immediate practical relevance for developing strategies for the global elimination of canine rabies.