Zoonoses are diseases that can be passed between vertebrate animals and humans. They are caused by all types of pathogenic agents, including bacteria, parasites, fungi, and viruses. Approximately 75% of recently emerging infectious diseases affecting humans are diseases of animal origin; approximately 60% of all human pathogens are zoonotic (Center for Disease Control 2013).
The last two decades have seen a surge in incidence of viral diseases in animals that pose a real threat to human health. SARS, avian and swine flu and other diseases have spread globally. For example, the incidence of highly pathogenic strains of avian influenza has increased dramatically (Nguyen et al. 2005). This spread of animal disease has been linked to the global growth in industrial factory farming (Bueckert 2004 in Greger 2006, Webster 2004) and in some cases to the global trade routes for transporting live animals and animal products (Benun 2006).
In factory farms many thousands of chickens are kept crowded together in each shed. The chickens are likely to be of a uniform breed, selected to grow at an unnaturally fast rate. This causes stress and can make them more vulnerable to infection (Rauw et al. 1998). Once an influenza virus invades a commercial poultry farm, it has an optimum number of susceptible poultry for rapid viral evolution (Webster and Hulse 2004).
The H5N1 avian flu virus spread across Asia, the Middle East, Europe and Africa. By August 2011, 564 people were confirmed to have been infected, of whom 330 died – a fatality rate of almost 59 per cent (World Health Organisation 2011).
Although avian flu does not spread easily to humans as yet, further mutations of the virus could make it easily spreadable and a global pandemic could result (Appenzeller 2005). However, public health experts have estimated that such a flu pandemic could kill as many as 62 million people, mostly in developing countries (C. J. L. Murray et al. 2006).
During the SARS outbreak in 2002-3, there were 8,098 reported cases of SARS in humans and 774 deaths (National Health Service 2013). A similar disease to SARS, known as MERS (Middle East Respiratory Syndrome), is now circulating in that region and is believed to be possibly of pig or bat origin.
Most of these outbreaks of disease have been dealt with by mass culling, not just of infected animals, but of healthy animals too. Often the culling has been undertaken in a manner which totally ignores the welfare of the animals. This is in spite of detailed requirements on humane culling issued by the World Animal Health Organisation, known as the OIE (World Animal Health Organisation 2013) (http://www.oie.int/index.php?id=169&L=0&htmfile=chapitre_1.7.6.htm ). Nearly all countries in the world belong to the OIE and have a duty to follow its recommendations.
Other options for dealing with outbreaks include early detection, confinement and separation of infected animals and vaccination strategies.
Some viral diseases, such as foot-and-mouth disease (FMD) have very limited risk to humans, yet animals are still subject to mass culling for economic and trade reasons. During the 1997 FMD outbreak in Taiwan, 3.8 million pigs were destroyed and in the 2001 UK outbreak over 6 million cattle, sheep, pigs and goats were slaughtered to stop the spread of the disease (Extension Disaster Education Network 2013). This raises the ethical issue of killing perfectly healthy animals for trade advantages.
This paper will discuss how can we deal with these diseases in an ethical and compassionate manner that protects both public health and the welfare of animals. It will also look at the relationship between these diseases and farming methods.
Center for Disease Control website as at Nov. 2013 http://www.cdc.gov/ncezid/
Nguyen D.C., Uyeki T.M., Jadhao S. et al. 2005. Isolation and characterization of Avian Influenza Viruses, Including Highly Pathogenic H5N1, from Poultry in Live Bird Markets in Hanoi, Vietnam, in 2001. Journal of Virology 79(7): 4201-4212.
Bueckert 2004 in: Greger, M. 2006. Avian Influenza: Unjustly Blaming Outdoor Flocks. Available at:
The Lancet. 2006. Global avian Influenza controls must be scaled up now. The Lancet 367: 184.
Webster, R.G. 2004 Wet markets – a continuing source of severe acute respiratory syndrome and influenza? The Lancet 363: 234-36.
Bennun L. 2006. Reality takes wings over bird flu. BBC News (online). 17 February. Available at: http://news.bbc.co.uk/1/hi/sci/tech/4721598.stm
Rauw W. M., Kanis E., Noordhizen-Stassen E.N., Grommers F.J. 1998. Undesirable side effects of selection for high production efficiency in farm animals; a review. Livestock Production Science 56: 15-33.
Webster R.G. and Hulse D.J. 2004. Microbial adaptation and change: avian influenza. Revue Scientifique et Technique 23(2): 453-465.
World Health Organisation: Cumulative Number of Confirmed Human Cases of Avian Influenza A/(H5N1) Reported to WHO, 9 August 2011.
Appenzeller T. 2005. Tracking the next killer. National Geographic, October: 2-31.
Banks J., Speidel E.S., Moore E. et al. 2001. Changes in the haemaggluttinin and the neuraminidase genes prior to the emergence of highly pathogenic H7N1 avian influenza viruses in Italy. Archives of Virology 146: 963-973.
C. J. L. Murray et al., ‘Estimation of potential global pandemic influenza mortality on the basis of vital registry data from the 1918–20 pandemic: a quantitative analysis’, Lancet 368 (2006), pp. 2211–18.
National Health Service UK website as at Nov 2013:
World Animal Health Organisation (OIE) website as at Nov 2013:
Extension Disaster Education Network website as at Nov 2013: