Friday, 1 February 2013

Rabies epidemic spread by pet dogs in China - but it isn't crossing borders

Rabies is being transmitted across China from the south by relocation of domestic pet dogs
by Michael Woodhead
China's increasing affluence is behind an upsurge in rabies, which is being spread from southwestern provinces by wider ownership of pet dogs and longer distance travel, new research shows.
However the "massive resurgence" in rabies seen in China over the last 15 years is not spilling over into neighbouring countries, according to an in-depth  genetic analysis of rabies cases carried out by researchers at the  Chinese Center for Disease Control and Prevention, Beijing and Wuhan Institute of Virology.
The researchers analysed 3275 samples of dog brain tissue collected from dog meat markets across seven provinces of China. They found two main strains of rabies in 84 samples, and the strain appeared to have evolved form those seen in previous smaller Chinese outbreaks from the 1980s and 1990s.
However, apart from a few isolated cases of strains being picked up in neighboring countries such as Vietnam, the major strain responsible for the current Chinese epidemic has not been exported.
"Our observation of a dominant variant strain that is unique to China is significant in that it suggests that neighboring countries have not been seriously impacted by the epidemic. In spite of the increasing trade between China and other countries in South East Asia, it further suggests that current border controls remain effective at restricting the passage of infected animals … national geographical boundaries and border controls are effective at halting the spread of rabies from China into adjacent regions," they conclude.
Their genetic analysis found that the current rabies epidemic is dominated by variant strains of 'type B' rabies lyssavirus that originated in southwestern provinces such as Sichuan, and which were being translocated to provinces in eastern and northern China.
"It is the rapid economical expansion in China over the last twenty years that has probably had the most significant impact on the spread of rabies," they say.
"Prior to the plan for economic reform plan instigated by Deng XiaoPing, travel was more restricted and more commonly at the local level. Long distance travel was generally by train or bus and large scale transportation of goods only began to increase as the industrial infrastructure expanded. As the economy grew and relocation was more straightforward the population became more mobile. This likely facilitated the spread of [rabies virus] as people moved from villages to towns and cities, or between cities, transporting their dogs as part of the relocation process.
They say their theory is also supported by recent reports of rabies cases in Beijing where infected dogs were brought to the capital by migrant workers.
The researchers say dog meat markets are unlikely to be a major factor in the long distance spread of rabies as dogs are confined in living quarters and when transported to market and are not allowed to roam freely,as is the case with domestic pet dogs.
They say that domestic dogs are the main reservoir for rabies in China, and a government goal of eradicating rabies by 2020 will have to rely on widespread vaccination of domestic dogs if it is to be successful. There has already been some success seen with local dog vaccination programs against rabies in rural areas, and such programs should be extended beyond high prevalence areas and implemented nationally, they suggest.
Source: PLOS Neglected Tropical Diseases

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