Vaccination of dogs in an African city interrupts rabies transmission and reduces human exposure

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Science Translational Medicine  20 Dec 2017:
Vol. 9, Issue 421, eaaf6984
DOI: 10.1126/scitranslmed.aaf6984

Stemming the spread of rabies

Rabies is still a problem in some developing countries. The authors examine the impact of two previously conducted vaccination campaigns that vaccinated about 70% of dogs against rabies in N’Djaména, the capital city of Chad. Transmission modeling and phylodynamic analysis supported the idea that the sequential vaccination campaigns reduced dog-to-dog and dog-to-human rabies transmission. A phylogenetic analysis suggested that post-campaign reintroduction of rabies to N’Djaména may have occurred due to unvaccinated dogs in regions surrounding the city, rather than ongoing transmission within immunized areas in the city. Thus, mass vaccination efforts may be effective tools to stem rabies incidence in regions still afflicted by this fatal disease.


Despite the existence of effective rabies vaccines for dogs, dog-transmitted human rabies persists and has reemerged in Africa. Two consecutive dog vaccination campaigns took place in Chad in 2012 and 2013 (coverage of 71% in both years) in the capital city of N’Djaména, as previously published. We developed a deterministic model of dog-human rabies transmission fitted to weekly incidence data of rabid dogs and exposed human cases in N’Djaména. Our analysis showed that the effective reproductive number, that is, the number of new dogs infected by a rabid dog, fell to below one through November 2014. The modeled incidence of human rabies exposure fell to less than one person per million people per year. A phylodynamic estimation of the effective reproductive number from 29 canine rabies virus genetic sequences of the viral N-protein confirmed the results of the deterministic transmission model, implying that rabies transmission between dogs was interrupted for 9 months. However, new dog rabies cases appeared earlier than the transmission and phylodynamic models predicted. This may have been due to the continuous movement of rabies-exposed dogs into N’Djaména from outside the city. Our results show that canine rabies transmission to humans can be interrupted in an African city with currently available dog rabies vaccines, provided that the vaccination area includes larger adjacent regions, and local communities are informed and engaged.

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