Transmission dynamics and economics of rabies control in dogs and humans in an African city

Abstract

Human rabies in developing countries can be prevented through interventions directed at dogs. Potential cost-savings for the public health sector of interventions aimed at animal-host reservoirs should be assessed. Available deterministic models of rabies transmission between dogs were extended to include dog-to-human rabies transmission. Model parameters were fitted to routine weekly rabid-dog and exposed-human cases reported in N Djamé na, the capital of Chad. The estimated transmission rates between dogs (␤ d) were 0.0807 km 2 /(dogs⅐week) and between dogs and humans (␤ dh ) 0.0002 km 2 /(dogs⅐week). The effective reproductive ratio (R e) at the onset of our observations was estimated at 1.01, indicating low-level endemic stability of rabies transmission. Human rabies incidence depended critically on dog-related transmission parameters. We simulated the effects of mass dog vaccination and the culling of a percentage of the dog population on human rabies incidence. A single parenteral dog rabies-mass vaccination campaign achieving a coverage of least 70% appears to be sufficient to interrupt transmission of rabies to humans for at least 6 years. The cost-effectiveness of mass dog vaccination was compared to postexposure prophylaxis (PEP), which is the current practice in Chad. PEP does not reduce future human exposure. Its cost-effectiveness is estimated at US $46 per disability adjusted life-years averted. Cost-effectiveness for PEP, together with a dog-vaccination campaign, breaks even with cost-effectiveness of PEP alone after almost 5 years. Beyond a time-frame of 7 years, it appears to be more cost-effective to combine parenteral dogvaccination campaigns with human PEP compared to human PEP alone.M ost human deaths from rabies occur in tropical resourcelimited countries (1). In Africa and Asia, an estimated 24,000 to 70,000 people die of rabies each year (2). The domestic dog is the main source of exposure and a primary vector for human rabies (3). Rabies in humans can be prevented by appropriate postexposure prophylaxis (PEP), a treatment not always available and affordable in resource-limited countries. Human rabies can also be prevented through vaccination of the animal vector. Recent work in Africa demonstrates that the intensity of rabies-control efforts seems to depend on the level of perceived prevalence. In the past decades, such efforts have not been able to interrupt cyclical epidemics showing significant synchrony between countries (4). However, evidence of successful and sustained vaccination programs to eliminate dog rabies from South America, Mexico, and the Caribbean provide hope for similar efforts in Africa (5). Unfortunately, human resources, diagnostic capacity, and financial resources of most sub-Saharan African countries are far away from those in South America. Bögel and Meslin show that in areas where the virus continually circulates in the dog population, over a period of 15 years, dog vaccination combined with PEP of dog-bite patients, is more cost-effective than PEP alone (6). In...

Anthropogenic and environmental risk factors for rabies occurrence in Bhutan

“…Since no wildlife rabies cases have been reported in Bhutan, it can be concluded that rabies in cattle or in other domestic animals is due to rabies in dogs. In developing countries, including Bhutan, the domestic dog is the main source of exposure and a primary vector for human rabies and other domestic livestock (Knobel et al, 2005;Zinsstag et al, 2009;Tenzin and Ward, 2012b). Therefore, rabies cases in cattle were used as proxy for the dog rabies problem in Bhutan since the reporting of rabies cases in cattle is more sensitive, reliable and timely than that of dog reported cases.…”

Optimal frequency of rabies vaccination campaigns in Sub-Saharan Africa

“…Based on both field data and previous modelling [2,3,16,17], we included three model parameters that together determine mortality rates of dogs and wildlife, respectively: a frequencydependent term, a density-dependent term, and rabies-related mortality. The frequency-dependent term, m, was included as a constant rate of removal from each compartment to represent adult canine mortality in Tanzania.…”

“…Previous analyses have been based on relatively closed systems [2,3,7], ignoring the possible impact of rabies reintroduction from unvaccinated regions. However, rabies virus transmission across national and sub-national borders has been documented in Sub-Saharan Africa [8].…”

“…Alternatively, less frequent campaigns might provide significant monetary savings with minimal adverse consequences in limited-resource settings. Furthermore, previous cost-effectiveness evaluations have focused on annual campaigns [2,10] or one-time campaigns [3], and have not considered the simultaneous optimization of both coverage and frequency, nor even optimization of frequency alone. However, from an implementation standpoint, it is more straightforward to decide how often to conduct vaccination campaigns than to control the coverage achieved.…”

“…As more than 99% of human rabies cases arise from exposure to rabid dogs [1], canine vaccination is a highly effective One Health intervention, with veterinary campaigns able to directly avert canine rabies and indirectly prevent rabies transmission to humans [2][3][4]. Canine rabies virus transmission has been successfully eliminated in all developed countries, with a subsequent dramatic impact upon the human disease burden [1].…”