3.1

A glimpse at integrated rabies control

Rabies is a classic viral zoonotic disease, infecting all mammal species. It is generally transmitted through an invasive manner from saliva to a bite wound, leading to encephalitis with distinct, severe symptoms followed by death.

Since the earliest descriptions of this ancient disease, animals, and especially dogs, have been recognised as the source and cause of rabies in humans. To this day, rabies provides an exemplar of a One Health problem requiring an understanding of the linkages between human and animals and an integrated approach to disease control.

According to Rosset (1985), shortly before discovering the first rabies vaccine for humans aided by experiments on rabbits and dogs, Louis Pasteur wrote in 1882 in his third correspondence to the Academy of Science:

[…] l’homme ne contractant jamais la rage qu’à la suite d’une morsure par un animal enragé, il suffira de trouver une méthode propre à s’opposer à la rage du chien pour préserver l’humanité du terrible fléau. (People contract rabies only after a bite of a rabid animal; it would be enough to find a proper method to fight rabies in the dog to protect humanity from this terrible scourge.)

Although this statement by Pasteur simplifies the epidemiology of rabies by ignoring sylvatic rabies in wildlife reservoirs and lyssavirus transmission by bats, it describes the very essence of the prevention of rabies in humans.

Even today, the domestic dog is the main vector for transmission of rabies to people, being responsible for more than nine out of ten cases worldwide. An estimated seven million people per year come into contact with a rabid dog and should receive post-exposure prophylaxis (PEP). This treatment is the only measure available to prevent onset of the disease, but it is often inaccessible for various reasons, including lack of knowledge about where to seek help, lack of money to pay for it, or simply lack of the vaccine itself in local health facilities.

Despite exploration of different protocols, no consistently effective treatment exists against rabies encephalitis and the disease is almost always fatal. Although PEP is highly effective in terms of prevention, many hundreds of thousand people across Africa and Asia do not have access to prompt and appropriate PEP. As a result, it is estimated that at least 55’000 people die of rabies each year, which represents an under-reporting of human rabies cases by a factor of 20 (Asia) to 160 times (Africa).

Rabies can also be effectively prevented in both human and animal hosts through pre-exposure vaccination, with several highly immunogenic and effective vaccines available. The availability of effective vaccines raises the prospect for effective control and elimination of rabies, and several other features of rabies further meet the criteria for a disease that can be eliminated. The virus cannot persist in the environment, no carrier state has been identified, and the infectious period lasts only a few days until the host invariably dies.

Furthermore, the basic reproductive ratio ($R_0$) of canine rabies transmission is consistently below 2, regardless of dog density and demographic setting, which suggests that elimination should be epidemiologically feasible. This is supported by empirical evidence demonstrating the success of canine rabies elimination in Europe, North America and recently in Latin America, where human and dog rabies cases have declined considerably following dog mass vaccination campaigns.

The main burden from this disease is now found in Asia and Africa, where rabies continues to be neglected in many regions, and too often its public health impact is overshadowed by other priority diseases like HIV/AIDS, malaria and avian influenza. This situation typifies the inequities in health investments that are directed to the prevention of emerging zoonoses (perceived as a threat to high-income countries) in comparison to the prevention and control of neglected endemic zoonoses (predominantly affecting low-income communities).

Although the number of lives lost and the estimated costs may be viewed as less compelling than other public health priorities, several studies have demonstrated the cost-effectiveness of canine rabies control for preventing human rabies deaths. The threshold immunisation coverage of a reservoir species required to interrupt transmission has been estimated at 70%. For canine rabies, vaccination campaigns have successfully achieved this level, but challenges remain for reaching and maintaining sufficient coverage in some rural and urban low income settings, where dog populations are both dynamic and poorly supervised.

Awareness is also growing about the importance of ensuring completeness of vaccination campaigns among communities, in order to prevent gaps in coverage which can severely jeopardise control efforts. For human rabies prevention, poor access to pre- and post-exposure vaccines remains a problem for remote and marginalised communities. A major challenge also relates to surveillance systems for both human and animal rabies, which are very poor or non-existent in many parts of Africa and Asia.

In addition to all these points, information, education and communication activities must be included and disseminated widely and regularly within communities, in government agencies, hospitals, health centres, schools, parishes and private enterprise among all possible stakeholders and actors.