Implications of Canine Population Dynamics on Rabies Control in Madagascan Rainforests

Abstract

Background: Domestic dogs (Canis lupus familiaris) have co-evolved with and maintained close relationships with humans over the past few millennia. However, such canine interactions can facilitate the spread of zoonotic diseases like rabies, a neglected tropical disease with a high case fatality rate. Rabies remains a public health concern in many developing countries, but some success in locally eliminating rabies has been found in rabies control programs. Implementation of these programs requires an understanding of canine population dynamics, which informs the distribution of limited rabies vaccines. Nonetheless, there are gaps in knowledge which contribute to persistent endemicity. This study aimed to characterize rural Madagascan rainforest canine populations in context of rabies control efforts.

Methods: Rainforest study sites included villages in and around Ranomafana National Park and Andasibe village, both of which are rural. Household survey data and demographic data were collected alongside mass rabies vaccination and sterilization campaigns during field seasons in 2014, 2016, and 2017. Descriptive analyses were used to better characterize and contextualize household characteristics, canine interactions, population size, and sex ratios. Population analyses involved generating stable age distributions and calculating population growth rates using observed, predicted, and bootstrap adjusted demographic data collected during the 2016 and 2017 field seasons in Ranomafana and Andasibe.

Results: Dogs were reported to spend most of their time with owners rather than roaming into the rainforest. Attitudes towards dog ownership were favorable but utilitarian; dogs served as household protectors first and companions second. The observed population size was 88 and 39 dogs, with moderate density in Ranomafana given that 46.2% of households owned dogs. The mean age of dogs was consistent, between 33 and 34 months. The sex ratio was male biased, with 2.52 and 2.5 males per female. Canine populations were predicted to be composed of 32.1% (95% CI: 31.8 – 32.6%) and 36.2% (95% CI: 31.8 – 43.5%) dogs younger than one year, in Ranomafana and Andasibe. Population growth using observed and adjusted data was estimated to be 26.7% and 40.0% in Ranomafana and 2.5% and 29.7% in Andasibe.

Conclusions: Rabies vaccines are the most effective means of interrupting transmission. Almost all dogs are owned, which indicates that dogs are accessible; the type of vaccine used should be parenteral rather than oral. After an initial mass rabies vaccination campaign, in which about 70% of all individuals are vaccinated to achieve herd immunity, subsequent campaigns should focus on vaccinating infant and juvenile dogs to boost immunity and account for waning vaccine efficacy. Sterilization in the form of spaying/neutering should be used as an adjunct to control population growth and reduce the number of susceptible unvaccinated puppies born into the population. This study also highlights the importance of vaccine availability and accessibility, especially in rural areas where canine interactions are frequent. Future studies should focus on refining and standardizing parameters for improved comparisons between regions, as well as environmental and body condition factors that might influence demographic parameters.