Multiscale transmission dynamics of rabies in Africa: The urban-rural interface
Project Abstract
Background and rationale: Dog mediated rabies, although entirely preventable, kills every year over 25’000 people in Africa. In the foregoing SNF project 310030_160067 we demonstrated that two consecutive dog mass vaccination campaigns were sufficient to interrupt rabies transmission for more than two years in N’Djaména the capital of Chad. We confirmed the mathematical assessment by a phylodynamic analysis of rabies virus (RABV) sequences. The re-introduction of rabies from the outside of the city was captured by a meta-population model which indicated that importation of latently infective dogs is the most likely cause, rather than the heterogeneity of transmission or underreporting. Research in Bangui, Central Africa suggests that chains of transmission in the city are too short to sustain the transmission and that regular import of latently infective dogs is needed to sustain transmission. The research questions arising are thus: 1) Can rabies transmission in an African city be interrupted or reduced by avoiding the (human-mediated) import of latently infective dogs? 2) Can rabies reservoirs be identified that sustain transmission (Re>1) and what are their characteristics? 3) What is the effect of dog movement restriction on the transmission of dog rabies in a free roaming context?
Overall objectives and specific aims: 1) We aim to understand the role of (human-mediated) dog importation on the transmission dynamics of rabies by creating a ring of permanently staffed vaccination posts around N’Djaména. 2) We attempt to identify rabies transmission reservoirs in urban areas with high dog densities. 3) We assess the effect of dog movement restriction on occurrence of rabies outbreaks in a rural context.
Approach and methods: 1) The Institut de Recherches en Elevage pour le Developpement (IRED) in N’Djaména estimates weekly passive dog rabies incidence since twenty years which serves as baseline for the effect of the vaccination. A ring of 13 permanently staffed vaccination posts will be maintained during 12 months at all road entries to the N’Djaména district. In collaboration with the security sector, all cars entering N’Djaména will be checked for transported dogs. After informed consent of the owner, dogs will be vaccinated against rabies and distemper, unless the owner presents a valid vaccination certificate. A lateral photograph will be taken from each dog for their identification by machine learning algorithms. Weekly changes of dog rabies incidence will be assessed by IRED before, during and 24 month after the ring vaccination intervention. 2) To identify rabies reservoirs that sustain transmission, the origin of each dog entering N’Djaména will be recorded. In the most important places of origin (>80% of imports), active surveillance of rabies will be initiated to collect as many rabies strains as possible for a phylodynamic analysis. This will include the city of Sarh, one of the cities known for dog exports, who has a high dog-to-human ratio. 3) Participatory transdisciplinary stakeholder processes will be used to identify locally adapted dog leashing practices in Sarh, Southern Chad. An incentive-based dog leashing scheme (with daily walks), embedded in the ongoing Program for Guinea Worm Eradication (PGWE), will be implemented in 20% of the dog population for its effect on reducing the transmission of rabies. Rabies transmission will be followed as above before, during and 24 months after the leashing intervention.
Expected results: We expect 1) a strong reduction or even interruption of transmission of rabies in N’Djaména by the vaccination of imported dogs, 2) to identify and characterise source areas of dog export that sustain rabies transmission as reservoirs, 3) the unequivocal identification of dogs by smart phone based machine learning algorithms, and finally 4) a reduction of rabies incidence by dog leashing.Impact: While it is known that dog mass vaccination is the most cost-effective way to eliminate rabies, African national governments are currently still reluctant to invest in dog mass vaccination campaigns. Any alternative intervention as tested here plays thus an important role to progressively reduce human rabies exposure to reach the zero-human rabies goal by 2030.
