Fact Check 3: Livestock and Zoonotic Disease

Facts that highlight the incidence of zoonotic diseases are commonly used to encourage control and maintenance of livestock health. But where do such facts come from?

Figures that highlight the incidence of zoonotic diseases (transmittable between animals and humans) and associated risks to human health, are commonly used to encourage improved control and maintenance of livestock health^1-3.

Where do these facts originate?

The suggested proportions of both human emerging infectious disease (EID) epidemics that are of animal origin, and the human pathogens of zoonotic nature (75% and 60% respectively), were calculated by Taylor and co-authors in 2001⁴. They recognised that previous human EID studies had largely been descriptive and lacking of quantitative assessment. Using a literature review of 39 previous texts concerning human pathogens (dating from 1975 to 2000), 1415 species of infectious agents reported to cause human disease were identified; 868 (61%) of these were understood to be zoonotic. In addition, animal populations were the main disease reservoir of 97% of the zoonotic pathogens identified; and 132 out of the 175 pathogens associated with EIDs were zoonotic (75%)⁴.

Is the fact up-to-date and relevant?

These figures are now 17 years old and based on information potentially 43 years old. Further literature review by Woolhouse and GowgateSequeria5 , in 2005, updated the database used in 2001, and reported similar figures. Of human pathogenic species 58% were zoonotic; 177 pathogens associated with EIDs were identified, of which 73% were zoonotic^4,5. Of emerged human disease epidemics, have 75% been of animal origin? And overall, are 60% of human pathogens zoonotic? Livestock and Zoonotic Disease FACT CHECK Photo courtesy of Supporting Evidence-Based Interventions (SEBI) Both of the previous literature reviews considered species of infectious pathogen rather than specific diseases or outbreaks. Conversely, in 2008 Jones and co-authors investigated EID events within literature from 1940 to 2004 (including 747 references to 335 EID events)⁶ . Zoonoses were found to cause 60% of human EIDs; however, 72% of the zoonotic EID events were found to be of wildlife origin. This suggested a diminished role played by livestock in zoonotic disease transmission⁶. The study by Jones and co-authors⁶ was further developed to predict the likely conditions for future emergence of zoonotic disease. Low to Middle Income Country tropical forests, with high mammalian biodiversity, were identified as being high risk⁷.

The future of this fact

The initial literature review⁴ highlighted the significant risks to human health from zoonotic diseases, with updates and further research strengthening this position⁵. From the information reviewed, no global trends in zoonotic disease can be stated. However, the growing ‘One Health’ paradigm (promoting collaboration between human and veterinary healthcare, whilst recognising environmental issues) is likely to increase the respect and investigation of this human-animal link^8,9. In particular, the role livestock play, as opposed to wildlife populations, in zoonotic disease transmission needs to be understood^3,10. This would assist allocation of responsibilities and resources for future improvements to animal health control, and the realisation of associated benefits to human populations.

1. Gebreyes, W. A. Dupouy-Camet, J., Newport, M. J., Oliveira, C. J. B., Schlesinger, L. S., Saif, Y. M., Kariuki, S., Saif, L. J., Saville, W., Wittum, T., Hoet, A., Quessy, S., Kaswala, R., Tekola, B., Shryock, T., Bisesi, M., Patchanee, P., Boon mar, S. & King, L. J. 2014. The Global One Health Paradigm: Challenges and Opportunities for Tackling Infectious Diseases at the Human, Animal, and Environment Interface in Low Resource Settings. PLOS Neglected Tropical Diseases, 8, e3257.
2. Karesh, W. B. Dobson, A., Looyd-Smith, J. O., Lubroth, J., Dixon, M. A., Bennet, M., Aldrich, S., Harrington, T., Formenty, P., Loh, E. H., Machlaba, C. C., Thomas, M. J., & Heymann, D. L. 2012. Ecology of zoonoses: natural and unnatural histories. The Lancet, 380, 1936-1945.
3. Cunningham A. A., Daszak P., & Wood J. L N. 2017. One Health, emerging infectious diseases and wildlife: two decades of progress?, Philos Trans R Soc Lond B Biol Sci, 372.
4. Taylor, L. H., Latham S. M. & Woolhouse, M. E. J. 2001. Risk factors for human disease emergence. Philos Trans R Soc Lond B Biol Sci, 356. 983-989.
5. Woolhouse, M. E. J. & Gowtage-Sequeria, S. 2005. Host Range and Emerging and Reemerging Pathogens. Emerging Infection Diseases, 11, 1842-1847.
6. Jones, K. E., Patel, N. G., Levy, M. A., Storeygard, A., Balk, D., Gittleman J. L., & Daszak P. 2008. Global trends in emerging infectious diseases. Nature, 451, 990-3.
7. Allen, T., Murray, K. A., Zambrana-Torrelio, C., Morse, S. S., Rondinini, C., Di Marco, M., Breit, N., Olival K. J., & Daszak P. 2017. Global hotspots and correlates of emerging zoonotic diseases. Nature Communications, 8, 1124.
8. One Health Initiative. 2018.
9. FAO. 2011. One Health: Food and Agriculture of the United Nations Strategic Action Plan. Rome.
10. Daszak P., Cunningham, A. A. & Hyatt, A. D. 2000. Emerging Infectious Diseases of Wildlife - Threats to Biodiversity and Human Health. Science, 287.

Header photo: Vance, C. (SEBI)