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SHORT COMMUNICATION
Horizon Scanning for Emergence of New Viruses: FromConstructing Complex Scenarios to Online GamesP. Gale and A. C. Breed
Animal Health and Veterinary Laboratories Agency, Weybridge, New Haw, Addlestone, Surrey, UK
The aim of this study is to draw attention to the devel-
opment of novel proactive approaches for horizon scan-
ning for emerging viruses in the medium to long term.
By definition, viruses yet to emerge are not in the scien-
tific literature as shown, for example, by the recent emer-
gence of Schmallenberg virus in northern Europe, while
others that are known may re-emerge in unexpected ways,
for example, the transmission of Nipah virus from fruit
bats (Pteropus giganteus) to persons through drinking
fresh date palm sap (Luby et al., 2006). Horizon scanning
techniques can be developed to identify novel routes and
sources, some of which will not yet have been considered.
A major challenge for horizon scanning is that it is
against a background of change. The world is changing
and viruses emerge through adapting to new niches aris-
ing from novel combinations of events.
Central to horizon scanning is prediction of the com-
plex scenarios through which viruses could emerge before
they occur. For example, it seems logical when told after-
wards that there could be a link between the use of a
drug (diclofenac) in cattle and an increased incidence of
rabies in humans (Markandya et al., 2008). The use of
diclofenac decimated vulture populations in India result-
ing in a build-up of cattle carcases that served as a food
source for feral dogs, which increased in abundance
resulting in increased incidence of dog bites in humans.
Talking to scientists in different and diverse fields is one
approach to investigating new combinations of events.
For example, the retreat of glaciers because of climate
change on the island of South Georgia in the South
Atlantic is allowing the spread of rats, previously intro-
duced by whalers, to rat-free parts of the island (Prof.
Alan Rodger, British Antarctic Survey, personal commu-
nication). Rats can be vectors of disease and also may
indirectly affect disease transmission by changing the eco-
systems and affecting population dynamics of other spe-
cies. However, being alerted to new complex
combinations of events is a rare luxury, and for horizon
scanning, we need to develop new tools and approaches
to generate complex scenarios for consideration.
One potential approach involves ‘spidergrams’. This
was explored recently at a workshop funded by the Euro-
pean Science Foundation (ESF; Gale and Jansen, 2010).
The idea is based on ‘cut-up’ techniques where multiple
texts are cut up into smaller portions at random and
rearranged to create new and innovative phrases. The
generation of complex scenarios requires a database of
factors including those known to be linked to the emer-
Keywords:
horizon scanning; emerging viruses; online
games
Correspondence:
P. Gale. Animal Health and Veterinary
Laboratories Agency, Weybridge, New Haw,
Addlestone, Surrey, KT15 3NB, UK.
Tel.: +44 (0)1932 357575;
Fax: +44 (0)1932 359429;
E-mail: [email protected]
Received for publication June 1, 2012
doi:10.1111/j.1865-1682.2012.01356.x
Summary
Horizon scanning techniques can be developed to identify novel routes and
sources for the emergence of viruses in the medium to long term. Central to
horizon scanning is prediction of the complex scenarios through which viruses
could emerge before they occur. One approach involves ‘spidergrams’ in which
complex scenarios are generated by combining factors randomly selected from
different categories of events. Spidergrams provide a framework for how differ-
ent factors could interact, irrespective of the virus, and also enable testing of
combinations not previously considered but which would be ‘tested’ in nature
by a virus. The emergence of viruses through new routes is often related to
changes, for example, in environmental and social factors, and the Internet will
undoubtedly be used to identify long-term trends for consideration. In addi-
tion, online games may provide horizon scanners with suggestions for new
routes and strategies that could be used by emerging viruses.
Transboundary and Emerging Diseases
ª 2012 Crown copyright • Transboundary and Emerging Diseases. 1
gence of viruses. Categories for these factors include: zoo-
logical, farming practice, sustainability, environment and
climate, land use, ecological, socio-economic, human
behaviour, political, technology and medicine. By ran-
domly taking factors from each category and combining
them, many complex scenarios can be generated. Most
will probably be implausible, but somewhere in there,
amongst others of potential interest, is the dichlofenac/
rabies scenario described previously. The approach can be
taken further to include branches and extensions. For
example, a build-up of cattle carcasses may not only
increase the abundance of feral dogs (which could lead to
an increase in ectoparasites that may in turn be vectors
for microbial pathogens), but could also result in more
rubbish building up (because of pressure on municipal
services) and increases in rodent populations. Similarly,
combinations can be built-in. Thus, flooding and higher
temperatures at the same time could increase rodent pop-
ulations and arthropod and snail vectors, for example.
Flooding may not only promote mixing of sheep and cat-
tle (which is a factor for malignant catarrhal fever and
fasciolosis) and increase livestock contacts in general, but
also causes power station failure as happened in the UK
in the summer of 2007. This can lead to failure of water
supplies such that people resort to storing water in open
containers that could serve as breeding sites for certain
urban mosquito species (with associated implications for
mosquito-borne viruses). Similarly, other mosquito spe-
cies, for example, Ochlerotatus caspius in England, could
use the floodplains as breeding sites. The main challenge
of the spidergram approach is eliminating those pairings
of factors that are irrational, rather than unlikely, and
identifying those that interact in some way. At the ESF
workshop (Gale and Jansen, 2010), a spidergram was
developed for the effect of environmental temperature on
the emergence of Nipah virus (Fig. 1). A 2 · 2 table was
used to assess the linkages of factors with respect to Ni-
pah virus (Table 1). The level of containment of the pigs
is an important factor in Nipah virus transmission and is
rationally linked to the other six factors displayed that are
linked to temperature. Spidergrams provide a framework
for how different factors could interact, irrespective of the
virus, and also enable the assessment of combinations not
previously considered but which would be tested in nat-
ure by a virus.
Spidergrams also generate novel discussion points and
new perspectives. An unexpected outcome of the ESF
workshop was the proposed use of spidergrams to
develop questionnaires for case–control studies. Some epi-
demiological observations have no obvious explanations,
for example, the increase in hantavirus incidence in Ger-
many in older persons (Faber et al., 2010). At the work-
shop, a spidergram was developed to identify potential
new reasons and routes of rodent exposure for older per-
sons. The focus was on socio-economic factors and
changes in behaviour. Dementia was also added, which
has caused surprise in some audiences as the increase in
hantavirus incidence was observed in people older than
30 years, which is too young for dementia. However, this
is the age group who may be caring for parents with
dementia in a home that has become rodent-infested. The
question in the case–control study could therefore be,
‘Do you care for an elderly relative with dementia?’ Thus,
links which at first seem inappropriate may prove relevant
on deeper consideration.
Web search data are being used as a proxy to monitor
dengue epidemics (Chan et al., 2011) in the short term.
For the purpose of horizon scanning in the medium to
long term, the Internet is an important resource for iden-
tifying changes and long-term trends that could affect the
emergence of viruses. For example, could the route of
highly pathogenic avian influenza virus, H5N1, through
frozen duck meat to backyard chickens in Germany in
2007 (Harder et al., 2009) have been anticipated through
looking at Internet chat rooms on feeding of meat and
kitchen scraps to backyard poultry? Perhaps of greater
potential application though is using the online commu-
nity to generate spidergrams and ‘design’ new viruses
through online games. The game would include a virus
toolbox and a pathway toolbox. The player would click
on certain icons in the toolbox to build features into the
virus design to allow it to adapt its strategy to the path-
way being designed. Points would be given for the num-
ber of nodes in the spidergram providing the player
could explain each paired linkage. More points would be
given for feedback loops and combinations of interacting
events. Tapping the resource of the online community
has previously been used through a game to determine
the structure of a viral protein (Good and Su, 2011). As
Migration
Level ofcontainment ofpigs/biocontrol
WarHostbehaviour
Poverty
Deforestation
Temperature
Fig. 1. Spidergram generated for potential effect of temperature on
emergence of Nipah virus (adapted from Gale and Jansen, 2010).
Horizon Scanning for Viruses P. Gale and A. C. Breed
2 ª 2012 Crown copyright • Transboundary and Emerging Diseases.
horizon scanners, we would welcome not only the help of
lateral thinkers from extremely diverse backgrounds but
also views on the feasibility of generating spidergrams
through online databases and more importantly spotting
the more meaningful pathways.
References
Chan, E. H., V. Sahai, C. Conrad, and J. S. Brownstein, 2011:
Using web search query data to monitor dengue epidemics:
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Faber, M. S., R. G. Ulrich, C. Frank, S. O. Brockmann, G. M.
Pfaff, J. Jacob, D. H. Kruger, and K. Stark, 2010: Steep rise
in notified hantavirus infections in Germany, April 2010.
Euro. Surveill. 15, 19574.
Gale, P., and V. Jansen, 2010: New approaches to horizon
scanning for emerging and infectious viruses in Europe.
Report of ESF exploratory workshop. Available at http://
www.esf.org (accessed June 26, 2012).
Good, B. M., and A. I. Su, 2011: Games with a scientific pur-
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Luby, S. P., M. Rahman, J. Hossain, L. S. Blum, M. M. Hus-
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har, E. Kenah, J. A. Comer, and T. G. Ksiazek, 2006:
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Table 1. Assessment of pairwise linkages of factors with respect to Nipah virus. For each pair, the factor listed in the left column is the primary
driver of the linkage, and the factor in the top row is the factor that may be affected (adapted from Gale and Jansen, 2010)
Affected factor
Migration Level of containment Temperature Conflict Host behaviour Poverty Deforestation
Primary Driver
Migration + NL +/? + ++ +
Level of containment NL NL NL + ? NL
Temperature ++ + + + + ++
Conflict + + NL + + +
Host behaviour NL + NL NL/+ + NL
Poverty + ++ NL + + +
Deforestation ++ + + + + +
NL, No apparent linkage; +, rational linkage.
P. Gale and A. C. Breed Horizon Scanning for Viruses
ª 2012 Crown copyright • Transboundary and Emerging Diseases. 3