Survey of animal bite injuries and their management for an estimate of human rabies deaths in N'Djaména, Chad.

OBJECTIVE: To estimate the annual human rabies incidence as a baseline prior to mass dog vaccination campaigns in N'Djaména, Chad. METHODS: Survey of animal bites, involving 50% of all healthcare providers in N'Djaména, from September 2008 to April 2009. Of 86 people exposed to a suspected rabid animal, 50% received post-exposure vaccination and a further 8% had their wound cleaned. We estimated annual incidence of bites from suspected rabid animals of 12.9/100,000 and an incidence of 0.7 human rabies deaths/100,000, resulting in 7 estimated deaths (95% confidence interval 4-10 deaths) per year in N'Djaména. 14% of bite victims sought help from veterinarians. CONCLUSIONS: Closer cooperation between physicians and veterinarians warrants more effective rabies control. The high proportion (42%) of potentially exposed people without post-exposure vaccination or wound treatment necessitates urgent attention.

[Transmission dynamics and cost-effectiveness of rabies control in dogs and humans in an African city]. / Dynamique de transmission et coût de la lutte contre la rage chez les chiens et les hommes dans une ville Africaine.

Control of human rabies in developing countries depends on prevention in dogs. The purpose of this study was to evaluate the cost-saving potential for the public health sector of intervention to control rabies in animal-host reservoirs. An existing deterministic model was adapted to allow study of dog-to-human rabies transmission. Model parameters were fitted to data from routine weekly reports on the number of rabid dogs and human rabies exposures in N'Djamena, Chad. At the onset of study, the estimated effective reproductive ratio (Re) was 1.01 indicating stable low-level endemic rabies transmission. Simulations were performed to determine what effects mass vaccination and culling of dogs would have on the incidence of human rabies. Findings showed that a mass campaign allowing single parenteral vaccination of at least 70% of the canine population would be sufficient to interrupt transmission of rabies to humans for at least 6 years. The cost-effectiveness of mass dog vaccination was compared to that of "postexposure prophylaxis" (PEP) which would not reduce future human exposure. Results showed that a sustained 5-year PEP program together with a dog-vaccination campaign would be as cost-effective as PEP alone. Beyond a time-frame of 7 years, combining parenteral dog vaccination campaigns with human PEP appeared to be more cost-effective than human PEP alone.

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

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'Djaména, the capital of Chad. The estimated transmission rates between dogs (beta(d)) were 0.0807 km2/(dogs x week) and between dogs and humans (beta(dh)) 0.0002 km2/(dogs x week). 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 dog-vaccination campaigns with human PEP compared to human PEP alone.

Effectiveness of dog rabies vaccination programmes: comparison of owner-charged and free vaccination campaigns.

We investigated the percentage of dogs that could be vaccinated against rabies by conducting a pilot campaign in N'Djaména, Chad. Owners were charged US$4.13 per dog vaccinated, and 24% of all dogs in the three city districts covered by the campaign were vaccinated. Total campaign costs were US$7623, resulting in an average of US$19.40 per vaccinated dog. This is five times more expensive than the cost per animal vaccinated during a previous free vaccination campaign for dog-owners, conducted in the same districts. The free campaign, which vaccinated 2605 more dogs than this campaign, cost an additional US$1.45 per extra dog vaccinated. Campaigns in which owners are charged for vaccinations result in lower vaccination rates than in free campaigns. Public health officials can use these results when evaluating the costs and benefits of subsidizing dog rabies vaccination programmes.

Cost-description of a pilot parenteral vaccination campaign against rabies in dogs in N'Djaména, Chad.

In the discussion about policies and strategies for rabies prevention in developing countries, intervention costs arise as a major issue. In a pilot mass vaccination campaign against rabies in N'Djaména, Chad, 3000 dogs were vaccinated. We assessed vaccination coverage and cost, showing the cost per dog vaccinated for the public sector and for society. An extrapolation to city level calculated the approximate cost of vaccinating all 23 600 dogs in N'Djaména. In the pilot mass campaign with 3000 dogs the average cost per dog was 1.69 euro. to the public and the full societal cost was 2.45 euro. If all 23 600 dogs in N'Djaména were vaccinated, the average cost would fall to 1.16 euro to the public and 1.93 euro to society. Private sector costs account for 31% of the cost to vaccinate 3000 dogs, and 40% of the cost to vaccinate 23 600 dogs. Mass dog vaccination could be a comparatively cheap and ethical way to both control the disease in animals and prevent human cases and exposure, especially in developing countries. The cost-effectiveness of dog vaccination compared with treating victims of dog bites for prevention of human rabies should be further assessed and documented.

[Impact of canine demography on rabies transmission in N'djamena, Chad]. / La démographie canine et son importance pour la transmission de la rage humaine à N'djaména.

A transversal study using the clustering technique was carried out in 600 households to estimate dog-population density in the city of N'Djamena and evaluate the knowledge of the inhabitants concerning the risk of rabies. Dog-population density as estimated by negative binomial modelling was 0.03 dogs per person. The dog population estimated taking into account the extrapolated human population for 2001 was at 23 575 dogs (95% confidence interval, 14579-37921 dogs). Three-fourths of inhabitants reported that they had heard of rabies. Most respondents knew some rabies symptoms such as frothing at the mouth, restlessness, and aggressivity. In case of dog-bite injury many respondents said that they would seek care in medical facilities, e.g., health-care centers, hospitals and veterinary clinics, but some said they would also use traditional remedies, witch-doctor services, and self-medication. More than half of the respondents believed that symptomatic rabies could be cured. Because of confinement and feeding needs stray dogs are common. The canine vaccination rate is low (19%) for various reasons including limited financial resources, absence of transportation, unavailability of vaccination facilities, ignorance and negligence. Since access to health care after exposure can be difficult, mass vaccination of dogs is the recommended strategy to control rabies in cities like N'Djamena. Cooperation of all those involved in rabies control is necessary to promote the education and awareness action necessary to promote canine vaccination and reporting of exposure cases to competent authorities.

Incidence of canine rabies in N'Djaména, Chad.

This work describes for the first time the incidence risk of passively reported canine rabies, and quantifies reported human exposure in N'Djaména (the capital of Chad). To diagnose rabies, we used a direct immunofluorescent-antibody test (IFAT). From January 2001 to March 2002, we were brought 34 rabies cases in dogs and three cases in cats. Canine cases were geographically clustered. The annual incidence risk of canine rabies was 1.4 (95% CI: 1.2, 1.7) per 1000 unvaccinated dogs. Most of the rabid dogs were owned-although free-roaming and not vaccinated against rabies. Most showed increased aggressiveness and attacked people without being provoked. Eighty-one persons were exposed to rabid dogs and four persons to rabid cats (mostly children<15 years old). Most of the exposed persons were neighbours or family members of the animal owner. Most exposures were transdermal bites, but nearly half of all exposed persons did not apply any first wound care or only applied a traditional treatment. In N'Djaména, humans are often exposed to canine rabies but do not use the full-course post-exposure treatment and wound care is insufficient. Most rabid dogs would be accessible to parenteral vaccination. Pilot vaccination campaigns are needed to determine the success of dog mass vaccination in N'Djaména as a way to prevent animal and human rabies.

Coverage of pilot parenteral vaccination campaign against canine rabies in N'Djaména, Chad.

Canine rabies, and thus human exposure to rabies, can be controlled through mass vaccination of the animal reservoir if dog owners are willing to cooperate. Inaccessible, ownerless dogs, however, reduce the vaccination coverage achieved in parenteral campaigns. This study aimed to estimate the vaccination coverage in dogs in three study zones of N'Djaména, Chad, after a pilot free parenteral mass vaccination campaign against rabies. We used a capture-mark-recapture approach for population estimates, with a Bayesian, Markov chain, Monte Carlo method to estimate the total number of owned dogs, and the ratio of ownerless to owned dogs to calculate vaccination coverage. When we took into account ownerless dogs, the vaccination coverage in the dog populations was 87% (95% confidence interval (CI), 84-89%) in study zone I, 71% (95% CI, 64-76%) in zone II, and 64% (95% CI, 58-71%) in zone III. The proportions of ownerless dogs to owned dogs were 1.1% (95% CI, 0-3.1%), 7.6% (95% CI, 0.7-16.5%), and 10.6% (95% CI, 1.6-19.1%) in the three study zones, respectively. Vaccination coverage in the three populations of owned dogs was 88% (95% CI, 84-92%) in zone I, 76% (95% CI, 71-81%) in zone II, and 70% (95% CI, 66-76%) in zone III. Participation of dog owners in the free campaign was high, and the number of inaccessible ownerless dogs was low. High levels of vaccination coverage could be achieved with parenteral mass vaccination. Regular parenteral vaccination campaigns to cover all of N'Djaména should be considered as an ethical way of preventing human rabies when post-exposure treatment is of limited availability and high in cost.