Is lower biodiversity linked to increased disease transmission?

17 December 2010

A recent paper in Nature provides some compelling arguments that loss of habitat and biodiversity might increase the risk of emergence and spread of infectious disease from wildlife to domestic animals and humans.

The US study, lead by Associate Professor Felicia Keesing, from the Department of Biology at Bard College, New York, argues that dominance of the landscape by a few species - an indicator of low biodiversity - can increase disease transmission, based on the premise that different species have different levels of susceptibility to various diseases; if fewer species exist in the landscape, more transmission events will be successful.

An even more compelling argument is that species that thrive in and dominate areas of low biodiversity ("weed species") might also be species that are more competent for disease transmission. The interaction is likely complex, and factors such as encroachment on wildlife areas and intensive agriculture increase the likelihood of disease emergence and spread.

Some of these themes were explored at GEOVET 2010 - a conference and three short courses hosted by the Faculty of Veterinary Science between 28 November and 5 December 2010.

GEOVET brought together more than 100 international scientists and policy advisors to showcase the latest techniques for examining and understanding how disease spreads across the landscape. The scientific program included six keynote and 11 senior presentations by scientists from Australia, the United Kingdom, the United States, Germany, Argentina, Chile, New Zealand, Denmark, China and Russia.

The conference was opened by Dr Andy Carroll, Australia's Chief Veterinary Officer, who highlighted the need to understand how diseases emerge and spread, in order to protect Australia's livestock health status and to protect humans from diseases that might be transmitted from animal populations, such as Hendra virus and bird flu.

Veterinary Science Faculty from the University of Sydney made nine presentations at GEOVET 2010 on subjects ranging from disease surveillance in dogs and cats, to diseases affecting our native fish stocks, to the recent equine influenza outbreak and diseases with international biosecurity implications - West Nile virus, bird flu, rabies, classical swine fever and foot-and-mouth disease.

One study presented highlights the issue of disease emergence, 'What role does wildlife play in emergency disease? The case of the feral pig'. This project aims to provide a better understanding of how endemic diseases are transmitted within populations of feral pigs. Based on such understanding, the potential spread of exotic diseases in feral pigs and cattle can be inferred, allowing effective surveillance and mitigation strategies to be developed.

Another study examined the risk of West Nile virus entering Australia via infected mosquitoes introduced at Sydney International Airport. The spread of West Nile around Australia was modeled based on experience from the United States during 1999 to 2005. The potential number of human and equine deaths and sickness were then calculated. Future work will look at the economics of surveillance strategies - how much should be spent to prevent an incursion of West Nile virus.

The field of spatial methods for examining and understanding how disease spreads across the landscape is developing quickly, with new analytical and visualisation techniques becoming available. A challenge is to communicate findings to decision- and policy-makers so that the impact of emerging diseases on animal and human health can be minimised. We are looking forward to a future GEOVET, likely to be held at the University of California at Davis.

Professor Michael Ward is Chair of Veterinary Public Health & Food Safety, Faculty of Veterinary Science.

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