The importance of dog population contact network structures in rabies transmission

Abstract

Canine rabies transmission was interrupted in N’Djaména, Chad, following two mass vaccination campaigns. However, after nine months cases resurged with re-establishment of endemic rabies transmission to pre-intervention levels. Previous analyses investigated district level spatial heterogeneity of vaccination coverage, and dog density; and importation, identifying the latter as the primary factor for rabies resurgence. Here we assess the impact of individual level heterogeneity on outbreak probability, effectiveness of vaccination campaigns and likely time to resurgence after a campaign. Geo-located contact sensors recorded the location and contacts of 237 domestic dogs in N’Djaména over a period of 3.5 days. The contact network data showed that urban dogs are socially related to larger communities and constrained by the urban architecture. We developed a network generation algorithm that extrapolates this empirical contact network to networks of large dog populations and applied it to simulate rabies transmission in N’Djaména. The model predictions aligned well with the rabies incidence data. Using the model we demonstrated, that major outbreaks are prevented when at least 70% of dogs are vaccinated. The probability of a minor outbreak also decreased with increasing vaccination coverage, but reached zero only when coverage was near total. Our results suggest that endemic rabies in N’Djaména may be explained by a series of importations with subsequent minor outbreaks. We show that highly connected dogs hold a critical role in transmission and that targeted vaccination of such dogs would lead to more efficient vaccination campaigns.

Evaluating the contact rate between companion dogs during dog walking and the practices towards potential cases of rabies among dog owners in Japan

“…In Japan, the companion dog population is estimated to be 8.9 million and about 13% of the households own at least one dog; the most popular dog breeds are small‐breed dogs such as miniature dachshund, Chihuahua, toy poodle and shiba‐inu (JPFA, ). Various studies both in Japan and overseas have examined the epidemiology of dog walking and its associated health benefits, while recent studies have focussed on the interaction and contact rate between domestic dogs with particular reference to rabies (Christian et al, ; Hidano, Hayama, & Tsutsui, ; Laager et al, ; Oka & Shibata, ).…”

Rabies-induced behavioural changes are key to rabies persistence in dog populations: investigation using a network-based model

“…Global sensitivity analysis indicated that population size (a parameter of reasonable certainty) and degree of connectivity had the greatest influence on duration, size and initial spread; this makes intuitive sense, and as expected, the largest and longest outbreaks were predicted in the Warraber network which had the highest median degree. Degree distribution might vary between populations of free-roaming dogs; however, a study in N’Djaména, Chad, found that the average degree was 9 and 15 (maximum 20 and 64, respectively) in two populations of size 272 and 237 dogs, respectively (19), which is not dissimilar to the Torres Strait dog populations. Reassuringly, input parameters about which there was more uncertainty – for example, bite probabilities – were less influential on variation in outputs.…”

“…Without behavioural change, we could not demonstrate rabies propagation in the social networks in the current study; disruption of social contacts appears to be key for rabies maintenance in small populations of dogs. Social network studies have shown that dogs form contact-dense clusters (12, 19). Increased bite probability and spatio-temporal association between contacts (edge-weight in the model) were most influential in our model, but it is possible that ‘re-wiring’ of dogs is also influential in larger populations in which there is a greater probability that a dog would ‘re-wire’ to completely new set of dogs in another cluster, thus increasing total contacts and enhancing spread (degree was also found to be highly influential on rabies spread).…”

“…The World Health Organization recommends repeated mass parenteral vaccination of 70% of dog populations to achieve herd immunity (28). Whilst the origin of this recommendation is unclear, it has been accepted for decades – for example, legislation allowed free-roaming of dogs in designated areas if at least 70% of the dog population was vaccinated in New York State in the 1940s (29) – previous modelling studies of pre-emptive vaccination support this threshold (19, 30-32). We found that vaccination with 70% coverage is expected to provide protection to the majority of dogs and that outbreaks were self-limiting.…”

“…The effect of contact heterogeneity on disease spread is well-researched and models can provide useful insights about disease control strategies in heterogeneously mixing populations (16-18). Most recently in the context of rabies, Laager et al (19) developed a network-based model of rabies spread using GPS telemetry data from dogs in urban N’Djamena, Chad. Other models of rabies-spread in which parameters that describe contact heterogeneity were derived from telemetry data include canine (20) and raccoon models (21, 22).…”