Saturday, July 9, 2011

Animals harbor a deadly time bomb

Deborah Smith in the Brisbane Times (Australia): ...It is estimated that 75 per cent of emerging infectious diseases in people - many of them fatal - originate in animals. The current Hendra outbreak in Queensland and NSW is a prime example. The virus was unknown 20 years ago, but now there are regular outbreaks and it has killed four of the seven people who have become infected since 1994.

Bats carry the virus without any ill effects, but when horses contract it, possibly after exposure to the faeces, urine or birth fluids of the bats, they develop a serious respiratory illness. Humans in contact with the sick horses can then also become infected, with deadly consequences. Many other viruses follow a similar pattern, moving from wildlife to domestic animals and then on to people. The virus that causes Severe Acute Respiratory Syndrome, or SARS, emerged from bats and affected civet cats before infecting more than 8400 people in 2003, killing about 750.

The deadly H5N1 bird flu has also been passed from wild birds to domestic birds to people. This pattern of transmission demonstrates why a ''One Health'' approach - that recognises the interdependence of human, animal and environmental health, and seeks to improve all three - is needed to successfully tackle emerging diseases, says Dr Martyn Jeggo, director of the CSIRO's high-security Australian Animal Health Laboratory in Geelong. ''To manage the risks effectively we need to get wildlife ecologists and those who study the environment working with those who deal with animal health, working closely with the medical fraternity, to look at things from a more holistic point of view,'' he says.

The threat of emerging diseases is increasing for a variety of reasons, says Jeggo, who chaired the organising committee for the 1st International One Health Congress held in Melbourne earlier this year. ''We encroach far more on our environment than we ever did before - into habitats where wildlife traditionally existed.'' This not only brings people, but also their domesticated animals, into greater potential contact with infectious agents carried by wild animals.

Intensification of livestock industries has also contributed to the problem. In a large poultry enclosure, for example, a virus has more opportunity to mutate as it passes between the birds, possibly becoming more infectious to people. ''We've increased that risk,'' says Jeggo. Global travel adds to the woes, with people moving rapidly around the world, taking viruses from places where people might have immunity to those where most people are vulnerable, he says.

''One can't but be amazed at the speed with which SARS moved around the world, from China through to Hong Kong and right across to Canada in such a short time.'' Climate change can also influence the spread of disease, in particular by shifting the regions where insects like mosquitoes, which harbour viruses, can exist....

An X-ray image of someone infected with SARS, from the Centers for Disease Control

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