One World, One Disease - effects of climate change on animal and human health

Three quarters of emerging human diseases are transmitted from animals. Professor Malcolm Bennett, from the National Centre for Zoonoses Research at the University of Liverpool, reminded delegates of this statistic at the ‘One World, One Disease,’ seminar at the Royal Society of Medicine (RSM), on 24 June 2008.

It was one of the facts that made the event - which explored the impact of climate change on plant, human and animal health - such an important one.

The event was jointly organised by the RSM and the Royal College of Veterinary Surgeons (RCVS), and in her welcome address, RSM President Professor Baroness Ilora Finlay of Llandaff suggested that the organisation should really be considered “the Royal Society of Dentists, Medics and Veterinary Surgeons”, as all shared common interests and must work closely together.

In the first presentation of the day, Chief Scientific Advisor to DEFRA, Professor Bob Watson, stated that the fact of man-made global warming was unequivocal: “The observable changes cannot be explained by natural phenomena alone,” he said.

The health implications of climate change include increases in vector- and water-borne diseases, heat stress and ecological erosion, and decreases in productive land and biodiversity. Action must be taken now, he said: “We cannot wait for perfect knowledge.”

This call to action set the scene for a series of challenging presentations that addressed issues such as food security, biosecurity, food distribution and disease preparedness.

That diseases affecting humans are often zoonotic is not a new phenomenon. This was underlined by Dr Colin Fink, Directory of Micropathology Ltd, who offered a history of infection patterns to show how pathogens come from animals and evolve to affect humans.

However, climate change and new patterns of travel have exacerbated the problem.

A specific example of the impact of climate change on infection patterns was given by Professor Martin Shirley, Director of the Institute of Animal Health, who explained how warmer temperatures have favoured the midges that act as vectors for bluetongue, allowing them and the virus to move rapidly northwards so that the disease now affects cattle and sheep in the UK.

Other vector-borne diseases that climate change has enabled to spread into new areas include African Horse Sickness, which has a greater than 90% mortality rate in horses and could have a serious effect on the £3.4billion UK equine industry if it reaches our shores.

Professor Quintin McKellar, Principal of the Royal Veterinary College, and Dr Caroline Lucas MEP both tackled the issue of food security.

Professor McKellar considered the world’s ability to feed its rapidly expanding population. Despite the fact that it takes ten calories of wheat to produce one calorie of meat, and the advent of an increasing number of potentially devastating diseases, he was optimistic about the sustainability of food supply.

He believed that genetic improvements could have a rapid and lasting impact on livestock production efficiency, although this might bring its own problems in terms of the vulnerability of homogeneous or naïve animal populations to disease.

Professor McKellar felt that, in some cases, livestock trade and movement was a greater contributory factor to the spread of disease than climatic factors, using the 2001 Foot and Mouth epidemic as an example. This issue was echoed by Green Party MEP Dr Caroline Lucas, who focused on food miles. “Fifty percent of vegetables and 95% of fruit in the UK is imported,” she said.

She suggested that the concept of protectionism was now perceived purely negatively, whereas to protect food production and marketing at a local level, in the face of increasing supermarket monopoly, could be seen as positive protectionism and should be encouraged.

That the trade in illegal animals is second only to the drugs trade was an issue mentioned by both Dr Lucas and Professor Malcolm Bennett.

The latter suggested that human-animal interaction was key to an understanding of emerging infectious diseases and that the introduction of exotic animals, often as pets, to new human populations was a key factor in the spread of infectious disease.

However, this risk was not limited to exotic animals: “I could take you into any park in London and introduce you to an animal that is carrying a disease that could kill you!” he said, stressing that the vast majority of people would not interact with such animals in a way that would put them at risk.

Continuing the theme of risk, Lt Col Tim Brooks, Head of Novel and Dangerous Pathogens at the Centre for Emergency Preparedness and Response within the Health Protection Agency, spoke about the impact of the media on perceptions of risk.

On the one hand, it was important to take account of public perceptions, often shaped by the media, as funding frequently followed such perceptions.

On the other, Lt Col Brooks had some concern when the only two diseases for which the UK had detailed preparedness plans were smallpox, which has been eradicated, and avian influenza, which at present was only a disease of birds in the UK, but about which the media had played a part in creating an atmosphere of fear.

Perhaps the focus should be elsewhere, he suggested: “For example, there is no similar plan to deal with norovirus, where winter outbreaks can paralyse up to a third of hospital beds.”

He also gave some sobering facts about what might happen in the event of a major pandemic. For example, although we are an island nation, a ‘lock-down’ to prevent incoming infection would not be practical: we only have enough food to last three days in such a situation.

Meanwhile, vaccination development can cost up to £500 million, even before replication and marketing, and building a vaccine plant from scratch can take up to five years.

Lt Col Brooks suggested that one option suitable for influenza vaccine would be to build a library of strains in advance, suitable for use in vaccine production in the event of an epidemic with a related strain. This way, any vaccine manufacturers could hit the ground running.

He highlighted that the FLUSECURE programme is developing a library of strains along these lines.

Although the messages were not always cheering, that the ‘One World, One Disease’ event took place was in itself very positive as it demonstrated an acknowledgment of the key role that veterinary surgeons and doctors must play in tackling disease threats.

The day should be seen as the start of a process, not a one-off, according to Professor Sheila Crispin, RCVS Senior Vice-President, who was one of the key organisers of the day, and delivered the final paper which drew the contributions together.

“I hope it marks a new determination for pure scientists and applied scientists - both medical and veterinary scientists - to work together,” she said.