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Rabies exposure incidence

In this video, Jakob Zinsstag explains how to measure the incidence of rabies exposure.
Dog rabies is obviously transmitted by dogs biting humans. Here you see a classical scenario of schoolchildren walking in the street next to dogs playing around, in N’Djamena, the capital city of Chad. Today, Chad reports officially no human rabies case. Why? Because rabies is almost never etiologically diagnosed on human cases. Most often, a person dead from rabies is buried without a brain biopsy. Human health facilities are not equipped with the standard immunofluorescence rabies diagnosis for humans. An alternative way of assessing the burden of rabies is by measuring the incidence of rabies-suspected dog bites. From a probability tree, and knowing the incidence of dog rabies, one can infer on the incidence of human rabies.
This has been developed by Sarah Cleaveland and her team. However, not all humans who are bitten by dogs go to health centres, and we don’t empirically know the true incidence of rabid bites. Here you see a One Health method that is currently tested on how a representative estimate of the true incidence of dog rabies exposure can be measured. We start with a representative, cross-sectional household survey proportional to size. In every sampled household or compound, we record the number of people living together with dogs. Of course, we record also households without dogs. The definition of a ’household’ is the unit of humans living with their dogs.
We ask the people to recall the number of dog bites in the last six months. Among the dog bites, a fraction went to seek help in a health centre. For the assessments of dog bites in the health centres, we will record all the health centres and hospitals dispensing animal-bite care in the study area of the household survey. In the health centres, we record the number of rabies-suspected bites and the proportion of suspected bites for which the biting animal was actually tested for rabies. The number of biting animals being tested depends actually very much on the level of communication and interaction between the health centre and the veterinary diagnostic centre. This is a clear case for One Health.
The better this communication is, and the better trained the doctors and veterinarians are for their mutual communication, the more biting animals are tested and the more precise is the incidence estimate of human dog rabies exposure. In the veterinary diagnostic laboratory, the number of actually rabid animals among the suspected indicates the number of truly rabid animal exposures. We can use a backward extrapolation from the proven rabid biting animals to the number of suspected dog bites in the health centres and to the number of people actually exposed to rabies in the household. In this way, we can estimate the true incidence of dog-rabies exposure in a given area. In many countries, rabies-diagnostic laboratories exist only in the capital cities.
This is because standard rabies diagnosis by immunofluorescence requires a fluorescence microscope. So what can we do in rural areas or provincial cities who have no fluorescence microscopes? One alternative is the so-called direct immunohistochemical test– DRIT of the CDC– which can be read by a light microscope. There is also a new lateral flow test which is currently tested and which does not require a microscope. If this test could be successfully validated, it would allow establishing rabies diagnosis in many remote areas. The example of estimating the burden of dog rabies exposure shows the importance of a good and well-established communication between human and animal health for an accurate assessment.

In this video Jakob Zinsstag uses the example of dog rabies to explain why a communication between a human health centre and a veterinary diagnostic centre is a clear case of One Health.

In order to find out if a person died of rabies it is necessary to do a brain biopsy. Since this is often not possible, veterinarians have to find different ways to measure the incidence of the illness. A possible solution is a closer cooperation between the human health centres and the veterinary diagnostic centres to enable calculation of how many persons are infected.

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One Health: Connecting Humans, Animals and the Environment

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