Magai Kaare

Transmission Dynamics and Prospects for the Elimination of Canine Rabies

Rabies has been eliminated from domestic dog populations in Western Europe and North America, but continues to kill many thousands of people throughout Africa and Asia every year. A quantitative understanding of transmission dynamics in domestic dog populations provides critical information to assess whether global elimination of canine rabies is possible. We report extensive observations of individual rabid animals in Tanzania and generate a uniquely detailed analysis of transmission biology, which explains important epidemiological features, including the level of variation in epidemic trajectories. We found that the basic reproductive number for rabies, R0, is very low in our study area in rural Africa (∼1.2) and throughout its historic global range (<2). This finding provides strong support for the feasibility of controlling endemic canine rabies by vaccination, even near wildlife areas with large wild carnivore populations. However, we show that rapid turnover of domestic dog populations has been a major obstacle to successful control in developing countries, thus regular pulse vaccinations will be required to maintain population-level immunity between campaigns. Nonetheless our analyses suggest that with sustained, international commitment, global elimination of rabies from domestic dog populations, the most dangerous vector to humans, is a realistic goal.

Estimating human rabies mortality in the United Republic of Tanzania from dog bite injuries

OBJECTIVE To make quantitative predictions about the magnitude of underreporting of human rabies deaths in the United Republic of Tanzania. METHODS Human rabies deaths were estimated by using a series of probability steps to calculate the likelihood of rabies developing after the bite of a suspected rabid dog, incorporating field data on the incidence of animal bite injuries, the accuracy of rabies recognition, the distribution of bite wounds, and post-exposure treatment. FINDINGS Predicted human rabies mortality was estimated to be (a) 1499 deaths per year (95% confidence interval 891-2238), equivalent to an annual incidence of 4.9 (2.9-7.2) deaths/100,000, when active surveillance data on bite incidence were used, and (b) 193 deaths per year (32-409), corresponding to an annual incidence of 0.62 (0.1-1.32) deaths/100,000, when national bite statistics were used. The annual mean number of rabies deaths officially recorded for the same period was 10.8 (7.7-14.0). CONCLUSION In the United Republic of Tanzania, cases of rabies in humans have been greatly underreported. Dog bite injuries are an accessible source of epidemiological data that may be used to estimate the public health burden of rabies and to monitor epidemiological trends in developing countries.

The Feasibility of Canine Rabies Elimination in Africa: Dispelling Doubts with Data

Background Canine rabies causes many thousands of human deaths every year in Africa, and continues to increase throughout much of the continent. Methodology/Principal Findings This paper identifies four common reasons given for the lack of effective canine rabies control in Africa: (a) a low priority given for disease control as a result of lack of awareness of the rabies burden; (b) epidemiological constraints such as uncertainties about the required levels of vaccination coverage and the possibility of sustained cycles of infection in wildlife; (c) operational constraints including accessibility of dogs for vaccination and insufficient knowledge of dog population sizes for planning of vaccination campaigns; and (d) limited resources for implementation of rabies surveillance and control. We address each of these issues in turn, presenting data from field studies and modelling approaches used in Tanzania, including burden of disease evaluations, detailed epidemiological studies, operational data from vaccination campaigns in different demographic and ecological settings, and economic analyses of the cost-effectiveness of dog vaccination for human rabies prevention. Conclusions/Significance We conclude that there are no insurmountable problems to canine rabies control in most of Africa; that elimination of canine rabies is epidemiologically and practically feasible through mass vaccination of domestic dogs; and that domestic dog vaccination provides a cost-effective approach to the prevention and elimination of human rabies deaths.

A dog rabies vaccination campaign in rural Africa: impact on the incidence of dog rabies and human dog-bite injuries

Despite the availability of safe and effective rabies vaccines, the incidence of dog rabies has been increasing throughout much of sub-Saharan Africa. Here we describe a vaccination strategy that has resulted in successful control of rabies in a rural dog population of Northwestern Tanzania. From October 1996 to February 2001, four central-point dog vaccination campaigns were conducted in villages within Serengeti District with a mean interval between campaigns of 338, 319 and 456 days. Vaccination coverage of the dog population was estimated from household questionnaires as 64.5, 61.1, 70.6 and 73.7% following each of the four campaigns, respectively. The incidence of dog rabies declined significantly in Serengeti District falling by 70% after the first campaign and by 97% after the second campaign. Over the same period, the incidence of dog rabies did not differ significantly in unvaccinated control villages of Musoma District. The incidence of human bite injuries from suspected rabid dogs declined significantly in Serengeti District after dog vaccination but not in adjacent unvaccinated districts. Vaccination of 60-70% of dogs has been sufficient to control dog rabies in this area and to significantly reduce demand for human post-exposure rabies treatment. Dog-bite injuries can provide a valuable and accessible source of data for surveillance in countries where case incidence data are difficult to obtain.

Rabies Exposures, Post-Exposure Prophylaxis and Deaths in a Region of Endemic Canine Rabies

Background Thousands of human deaths from rabies occur annually despite the availability of effective vaccines following exposure, and for disease control in the animal reservoir. Our aim was to assess risk factors associated with exposure and to determine why human deaths from endemic canine rabies still occur. Methods and Findings Contact tracing was used to gather data on rabies exposures, post-exposure prophylaxis (PEP) delivered and deaths in two rural districts in northwestern Tanzania from 2002 to 2006. Data on risk factors and the propensity to seek and complete courses of PEP was collected using questionnaires. Exposures varied from 6–141/100,000 per year. Risk of exposure to rabies was greater in an area with agropastoralist communities (and larger domestic dog populations) than an area with pastoralist communities. Children were at greater risk than adults of being exposed to rabies and of developing clinical signs. PEP dramatically reduced the risk of developing rabies (odds ratio [OR] 17.33, 95% confidence interval [CI] 6.39–60.83) and when PEP was not delivered the risks were higher in the pastoralist than the agro-pastoralist area (OR 6.12, 95% CI 2.60–14.58). Low socioeconomic class and distance to medical facilities lengthened delays before PEP delivery. Over 20% of rabies-exposed individuals did not seek medical treatment and were not documented in official records and <65% received PEP. Animal bite injury records were an accurate indicator of rabies exposure incidence. Conclusions Insufficient knowledge about rabies dangers and prevention, particularly prompt PEP, but also wound management, was the main cause of rabies deaths. Education, particularly in poor and marginalized communities, but also for medical and veterinary workers, would prevent future deaths.

Rabies control in rural Africa: Evaluating strategies for effective domestic dog vaccination

Effective vaccination campaigns need to reach a sufficient percentage of the population to eliminate disease and prevent future outbreaks, which for rabies is predicted to be 70%, at a cost that is economically and logistically sustainable. Domestic dog rabies has been increasing across most of sub-Saharan Africa indicating that dog vaccination programmes to date have been inadequate. We compare the effectiveness of a variety of dog vaccination strategies in terms of their cost and coverage in different community settings in rural Tanzania. Central-point (CP) vaccination was extremely effective in agro-pastoralist communities achieving a high coverage (>80%) at a low cost (US

Dynamics of a morbillivirus at the domestic–wildlife interface: Canine distemper virus in domestic dogs and lions

5/dog) and inadequate (<20% coverage); combined approaches using CP and either house-to-house vaccination or trained community-based animal health workers were most effective with coverage exceeding 70%, although costs were still high (>US

Dynamics of a morbillivirus at the domestic -wildlife interface

6 and >US

Metapopulation dynamics of rabies and the efficacy of vaccination

4/dog, respectively). No single vaccination strategy is likely to be effective in all populations and therefore alternative approaches must be deployed under different settings. CP vaccination is cost-effective and efficient for the majority of dog populations in rural Tanzania and potentially elsewhere in sub-Saharan Africa, whereas a combination strategy is necessary in remote pastoralist communities. These results suggest that rabies control is logistically feasible across most of the developing world and that the annual costs of effective vaccination campaigns in Tanzania are likely to be affordable.

A rabies serosurvey of domestic dogs in rural Tanzania: results of a rapid fluorescent focus inhibition test (RFFIT) and a liquid-phase blocking ELISA used in parallel.

Significance Morbilliviruses are a growing concern because of their ability to infect multiple species. The spill-over of canine distemper virus (CDV) from domestic dogs has been associated with severe declines in wild carnivores worldwide, and therefore mass dog vaccination has been suggested as a potential control strategy. Focusing on three decades of CDV exposure data in dogs and lions of the Serengeti, we show that cyclic infection dynamics in lions initially driven by dogs became more frequent and asynchronous, suggesting that the wider dog population and other wildlife species drive CDV dynamics. Hence, although widespread dog vaccination reduced the infection in dogs, transmission to lion populations still occurred, warranting further investigation into effective management options of CDV in this species-rich ecosystem. Morbilliviruses cause many diseases of medical and veterinary importance, and although some (e.g., measles and rinderpest) have been controlled successfully, others, such as canine distemper virus (CDV), are a growing concern. A propensity for host-switching has resulted in CDV emergence in new species, including endangered wildlife, posing challenges for controlling disease in multispecies communities. CDV is typically associated with domestic dogs, but little is known about its maintenance and transmission in species-rich areas or about the potential role of domestic dog vaccination as a means of reducing disease threats to wildlife. We address these questions by analyzing a long-term serological dataset of CDV in lions and domestic dogs from Tanzania’s Serengeti ecosystem. Using a Bayesian state–space model, we show that dynamics of CDV have changed considerably over the past three decades. Initially, peaks of CDV infection in dogs preceded those in lions, suggesting that spill-over from dogs was the main driver of infection in wildlife. However, despite dog-to-lion transmission dominating cross-species transmission models, infection peaks in lions became more frequent and asynchronous from those in dogs, suggesting that other wildlife species may play a role in a potentially complex maintenance community. Widespread mass vaccination of domestic dogs reduced the probability of infection in dogs and the size of outbreaks but did not prevent transmission to or peaks of infection in lions. This study demonstrates the complexity of CDV dynamics in natural ecosystems and the value of long-term, large-scale datasets for investigating transmission patterns and evaluating disease control strategies.