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Drivers of emerging and re-emerging diseases
Drivers of Emerging and Re-emerging
Diseases
Author: Prof Gavin Thomson
Licensed under a Creative Commons Attribution license.
RECENT PANDEMICS AND EPIDEMICS CAUSED BY ERIs
Recent examples of emerging and re-immerging zoonoses that have resulted in human pandemics or
epidemics include severe acute respiratory syndrome-associated coronavirus (SARS-CoV) infection in
China and elsewhere in 2002/3; West Nile virus (WNV) infection which spread across continental north
America between 1999 and 2004; Rift Valley fever (RVF) that spread from the Horn of Africa to the Arabian
Peninsula in 2000, highly pathogenic avian influenza (HPAI – H5N1) that arose in northern China and from
2003 spread to other parts of Asia, the Middle East, Europe and Africa and the occurrence of
Schmallenberg virus infection across Europe from 2011 onwards. It is also apparent in retrospect that the
historically most dramatic pandemic in modern times, the H1N1 (so-called ‘Spanish flu’) pandemic of 1918 ‒
which killed in the vicinity of 50 million people ‒ was probably caused by a virus derived from wild birds
(Taubenberger, J.K. & Morens, D.M., 2006).
Many other more localised epidemics attributable to emerging zoonoses, mostly in tropical and sub-tropical
regions of the world, have occurred in the recent past caused by a variety of infectious agents (e.g. anthrax,
Ebola-, Marburg-, Hendra-, Nipah-, bat lyssa- and Chikungunya viruses (Morens et al., 2004).
Remarkable recent events related to emerging animal infections have been the appearance of multiple
serotypes of blue tongue (BT) virus in northern Europe from 2006 ‒ possibly as a result of climate variation
as mentioned above, a highly pathogenic form (about 25% mortality rate) of porcine reproductive and
respiratory syndrome (PRRS) that affected about 2 million pigs in China, Vietnam and Myanmar in 2006/7
(http://www.cdc.gov/eid/content/14/11/1774.htm), expansion of the distribution of peste des petites
ruminants (PPR) in both Africa and Asia, and the spread in 2007 of African swine fever (ASF) from eastern
Africa to Georgia, Armenia and the Russian Federation (Costard, 2009).
Prior to the turn of the 21st century a number of widely recognised TADs ‒ at that time generally referred to
as OIE ‘List A’ diseases ‒ were recognised as being important, especially in the context of potential
geographic spread through trade in animals and animal products. These included FMD, rinderpest (no
longer extant outside laboratories), PPR, contagious bovine pleuropneumonia (CBPP), sheep and goat pox
(SGP), classical swine fever (CSF) and Newcastle disease (NCD). Well known indirectly (vector)
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Drivers of emerging and re-emerging diseases
transmitted TADs included vesicular stomatitis, Venezuelan equine encephalomyelitis (VEE), RVF, BT and
African horse sickness (AHS).
In more recent times the OIE has adopted a new approach with only one list of terrestrial animal diseases
being recognised (see Chapter 1.2 of the Terrestrial Animal Health Code, 2013 – www.oie.int). The reason
for this is that it is now appreciated that many animal disease not previously included in List A can have
major impact in particular circumstances and it is difficult to differentiate clearly between important and less
important animal disease across the gamut of global agro-ecological situations. So a disease can have
limited impact in a particular set of circumstances but in other circumstances its effects become severe.
FMD provides a good example of this phenomenon: In extensive livestock systems, especially in tropical
and sub-tropical climates, the impact of FMD may be minor but, conversely, where these viruses infect
intensively farmed livestock in temperate climates the effects of the disease may be so severe as to render
commercial livestock production unsustainable.
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