Progress towards rabies elimination from Pemba Island, Southern Tanzania

Abstract

ObjectiveUsing active surveillance approaches to investigate the transmissiondynamics of rabies on Pemba Island and across Southern Tanzania,whilst a large-scale dog vaccination program was underway1, to gaina greater understanding of the dynamics of infection as the disease isdriven towards elimination.IntroductionRabies is endemic in Tanzania and has circulated on Pemba Islandsince the late 1990s. In 2010, an elimination programme was initiatedin Southern Tanzania to demonstrate that human rabies deathscan be eliminated through mass dog vaccinations. We used activesurveillance approaches2to investigate the dynamics of rabies acrossthe area where this programme was implemented.MethodsGovernment census data and post-vaccination transects were usedto estimate the dog population and coverages achieved by vaccinationcampaigns. Routine surveillance of animal bite injuries using a mobilephone-based surveillance system3and active contact tracing wereused to identify animal rabies cases and human exposures. Epidemictrees were constructed using spatiotemporal distances between casesand used to estimate the effective reproduction number (Re). Weexamined factors affecting rabies incidence and transmission usinggeneralized linear mixed models.ResultsWe estimated a small dog population of 4095 and low dog:humanratio on Pemba (1:105). Overall island-wide vaccination coverageincreased from 16.8% in 2011 to 68.2% in 2014. We found a further48 human exposures (343%), who either were not reported or did notobtain post exposure prophylaxes (PEP). Routine surveillance wasfound to detect less than 10% (~8.75%). There was a rapid declinein cases detected on Pemba, from 42 before mass dog vaccinationswere implemented in 2011, to 2 cases in 2014 (Figures 1). Since May2014, no rabies cases have been detected. Similarly, Redeclined from1.02 to 0 and a significant relationship was found with rabies casesdecreasing with increasing vaccination coverage (p= 0.013, Figure 2).Across seven other districts on the Tanzanian mainland we alsoobserved major declines in rabies cases with very few cases of rabiesin dogs detected in 2016 (Figure 3).ConclusionsWe conclude that rabies has been eliminated from domestic dogpopulations on Pemba over the five years since vaccination campaignshave been implemented. Continued surveillance and investigationsof any bite incidents are therefore needed to ensure any subsequentincursions are controlled and freedom from rabies is maintained.On the Tanzanian mainland, it has taken longer to control rabies,however trajectories look promising with several districts close toeliminating the disease. However, detection of some wildlife casesin the last 12 months in these districts indicates the need to furtherinvestigate remaining foci and the role of wildlife in maintenance.