Study offers hope for rabies eradication in central and western Africa
Most cases of rabies found in dogs in western and central Africa can be traced back to a common ancestor that arrived in Africa, probably with European colonists, around 200 years ago, according to new EU-funded research. The study, published in the Journal of General Virology, also reveals that there is little movement of the virus between different areas; this means that if neighbouring countries work together, it should be possible to eliminate the devastating disease from sub-Saharan Africa. EU support for the work came from the RABMEDCONTROL ('Identifying ecological and epidemiological key factors for rabies dynamics and control in North Africa and implications for rabies status in South West Europe') project, which is funded under the International Cooperation budget line of the Sixth Framework Programme (FP6). Rabies kills some 24,000 people a year in Africa; most of the victims of the disease are children and people living in poor, rural areas. The majority of cases are caused by dogs, so controlling the disease in dogs is pivotal to eliminating the disease. Unfortunately, preventing and treating rabies is expensive and the necessary resources are often simply not available. Although the rabies virus has been widely studied in wildlife populations in Europe and North America, little is known about the diversity, distribution and origins of the dog-rabies virus in western and central Africa. In this latest study, scientists from Europe, Africa and the US analysed 182 samples of the dog rabies virus taken from 27 African countries over a period of 29 years. Their investigations revealed that there are two main types of the dog rabies virus circulating in Africa. The first, dubbed 'Africa 1', is largely prevalent in northern, central, eastern and southern Africa. In contrast, the second virus type, Africa 2, is found in western and central Africa. There is little overlap between the two virus types. The results suggest that the Africa 2 strain of the virus was first introduced into western and central Africa, probably in Chad, in around 1845. Over the next 100 years, it spread westward and south to cover the entire region. The researchers note that the pattern of spread follows the pattern of French colonial expansion in Africa. 'Overall, our study illustrates how the establishment and intensification of travel and trade routes between African countries following colonisation and during the first half of the 20th century have been accompanied by the spread of rabies in dogs among a large part of west/central Africa,' they write. Today, eight distinct subgroups of the Africa 2 strain of the virus can be identified in different countries. Furthermore, there appears to be little movement of the virus between countries. 'Some scientists have suggested that rabies outbreaks in Africa might be caused by 'super-spreader' dogs transmitting the disease over large distances,' commented Dr Hervé Bourhy of the Pasteur Institute in Paris, France. 'Our findings show that this is extremely unlikely as there is strong geographical clustering of the dog-rabies subspecies and the time scale for diffusion of the virus is measured in decades. 'Similarly, people transporting dogs, some of them eventually becoming infectious or in incubation, over this vast region does not seem to have had much, if any, impact on the spread of the disease.' The researchers emphasise that more research is needed to improve our understanding of how rabies circulates in Africa. Nevertheless, the discovery that there is little movement of the virus between northern Africa and sub-Saharan Africa, and among the countries of western and central Africa, suggests that a successful, progressive strategy to eliminate rabies from western and central Africa is possible. 'Rabies kills a patient, most often a child, every 20 minutes in Africa,' said Chiraz Talbi, also of the Pasteur Institute. 'By identifying the species of the virus that is the most prevalent and demonstrating how it spreads through the region, we have shown that, with collaboration, it should be possible for African countries to eliminate rabies by controlling dog rabies.'