Zoonotic Disease Risks of Live Export of Cattle and Sheep, with a Focus on Australian Shipments to Asia and the Middle East

SIMPLE SUMMARY: Most human disease emanates from animals, and there is a significant risk of zoonotic diseases being transmitted from livestock that travel long distances between countries as part of the live export trade. Both cattle and sheep are subject to many stressors when transported long distances by ship, including starvation, ship motion, ammonia, heat stress, high stocking density, an unhygienic environment and mixing of animals. These are believed to deplete immune system responses, fostering disease transmission between livestock. Several zoonotic diseases commonly occur in livestock exported from Australia, and this sometimes triggers rejection by importing countries. Trade restrictions have been imposed in the past by both importing and exporting countries as a means of controlling disease spread. It is concluded that the live export trade in cattle and sheep poses a significant risk of spreading zoonotic diseases. ABSTRACT: The growing human and livestock populations in the world today and increased international transport of livestock is increasing the risk of both emerging and endemic zoonotic diseases. This review focuses on the potential for the live export trade to transmit zoonotic diseases. Both cattle and sheep are exposed to major stresses during the transport process, which are described, together with the impact of these stresses on the immune function of transported animals. Heat stress, overcrowding, inanition, ship and vehicle motion and accumulation of noxious gases are analysed for their ability to potentiate infectious diseases. The major zoonoses are described: pustular dermatitis, pneumonia, salmonellosis, as well as some common conditions, such as conjunctivitis, with specific reference to stressors associated with each disorder. Historical precedents exist for restriction of the trade based on disease risks. Finally, the economic and regulatory frameworks are considered to evaluate ways in which the spread of zoonotic diseases can be controlled.