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Reducing Pandemic Risk, Promoting Global Health
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PHOTO BY RICHARD GIDDINGS
INTRODUCTION
E
merging infectious diseases (EIDs) pose substantial threats to the health of
animals and people and economies globally. Over the past several decades,
the emergence and spread of viruses such as severe acute respiratory syndrome
(SARS) coronavirus, Ebola virus, and H5N1 and H1N1 pandemic influenza A viruses,
have had profound global health and economic impacts, illustrating our vulnerability
to the emergence and re-emergence of zoonotic diseases.
Zoonotic diseases result in millions of deaths annually, and the economic losses from a single
outbreak can amount to tens of billions of dollars (e.g. SARS; Lee and McKibbin 2004;
Keusch et al. 2009; World Bank 2012). Prevention and early control of outbreaks is key to
reducing their impact, but there remains a critical need to improve the capacity of developing
countries to effectively implement prevention and control activities as demonstrated by the
2014 Ebola virus disease outbreak in West Africa.
Zoonotic pathogens shared with wildlife or livestock account for the majority of emerging
infectious diseases of people, and viruses comprise 25-44% of these emerging and re-emerging
pathogens (Jones et al. 2008; Taylor et al. 2001). Because of their diversity and rapid evolution,
viruses, in particular RNA viruses, are perceived to pose the greatest global pandemic threat
(Morse 1995; Cleaveland et al. 2001; Pulliam 2008). For instance, two of the most devastating
pandemics in human history, the 1918 influenza pandemic (50 million deaths) and the HIV/
AIDS pandemic (35 million deaths as of 2012; Morens et al. 2008; Fauci and Folkers 2012),
were caused by zoonotic RNA viruses.
Despite greater recognition of EIDs on a global scale,
there is limited understanding of the underlying causes
for emergence and spread of zoonotic pathogens in
people (Murray and Daszak 2013). Factors associated
with emergence, re-emergence, and spread of pathogens
have been categorized into four broad domains worthy
of investigation: 1) genetic and biological factors of
pathogens and hosts, such as microbial adaptation
and human susceptibility to infection; 2) physical
environmental factors (e.g. climate variability and
weather); 3) ecological factors (e.g. land-use change);
and 4) social, political, and economic factors, including
poverty and animal and public health infrastructure
(Bogich et al. 2012; Daszak et al. 2001; Smolinski et
al. 2003). For example, factors such as rapid human
population growth, land use change, intensification of
livestock production, natural resource extraction, and
Indochinese
silvered langur
(Trachypithecus
germaini) kept as
a pet alongside
domestic dogs in
Cambodia.
PHOTO BY WILDLIFE CONSERVATION SOCIETY
REDUCING PANDEMIC RISK, PROMOTING GLOBAL HEALTH
17
Figure 1: Emergence of pandemic zoonotic disease. From Morse et al. 2012.
Stage 1 is a pre-emergence state, in which microbes are transmitted between animal
reservoirs. Ecological disturbances (e.g. due to land use change) modify the dynamics of
microbial transmission, which can lead to a heightened risk of pathogen spillover to wildlife
or livestock hosts.
Stage 2 is localized emergence, either through self-limiting spillover events (green peaks
and troughs, representing increases and decreases in the numbers of infected people with
time) or large-scale spillover (red peaks, representing spikes in the number of infected
people with time), that leads to person-to-person transmission for a few pathogen
generations.
In stage 3, some spillover events might lead to sustained person-to-person outbreaks,
international or global spread, and the emergence of a pandemic. The size, spread, and
potential effect of events increase from stage 1 to stage 3, but the frequency falls so
that full stage 3 pandemics are quite rare. By dissecting this process and analyzing the
interactions of the underlying drivers with the risk of spillover and spread, development
of a more structured approach to pandemic prevention is possible. The ultimate goal of
successful pandemic prevention is to target control at stage 1.
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USAID PREDICT
the demands for global trade result in greater interactions between animals and people and
therefore more opportunities for cross species transmission and disease emergence (Daszak et
al. 2001; Smolinski et al. 2003). International travel has also contributed to the spread of many
infectious diseases regionally or globally with one of the most notable being the spread of SARS
coronavirus from Hong Kong to North America, Latin America, Europe, Asia, and Australia
resulting in 8,422 documented cases and 916 deaths worldwide (Heymann and Rodier 2004).
Wildlife play a major role in the emergence of infectious diseases in human populations. Analysis
of over 300 EID events occurring between 1940 and 2004 revealed that more than 70% of
emerging zoonotic pathogens originated in wildlife, and that the incidence of EID events caused
by wildlife pathogens has significantly increased over time (Jones et al. 2008). Certain wildlife
taxa are known to harbor a high proportion of zoonotic pathogens. Among assessed wildlife taxa,
zoonotic viruses have been most commonly detected in rodents, bats, primates, ungulates, and
birds (Woolhouse and Gowtage-Sequeria 2005; Calisher et al. 2006; Luis et al. 2013; Smith and
Wang 2013). Therefore, focusing surveillance efforts on these wildlife hosts is likely to enhance
the identification of viruses with pathogenic and disease emergence potential prior to spillover to
people (Parrish et al. 2008; Morse et al. 2012). Efforts in this realm must also be cognizant of the
need for clear messaging to not vilify wildlife, as the mechanisms for disease spillover tend to be
primarily human-induced, not animal-driven, and biodiversity and conservation goals must also
be maintained for a healthy world.
Rodents being sold
for consumption in
an African market.
The seriousness of these threats has led to the recognition
that a shift from a conventional, reactive approach toward
a proactive, predictive approach is necessary for EID
prevention and timely control (Figure 1; Karesh et al.
2012; Morse et al. 2012). Infrastructure improvements
and technological advances have dramatically and rapidly
improved our ability to identify high-risk interfaces for
disease transmission and to detect novel pathogens before
widespread spillover occurs. These advances include
improvements in information technology, molecular
diagnostics, and risk modeling. The challenge lies in
developing a strategic framework to identify zoonotic
pathogens of pandemic potential that have not yet emerged
in human populations.
To this end, USAID initiated the Emerging Pandemic
Threats (EPT) program in 2009. The initial goal of the
EPT program was to strengthen capacities in developing
countries to prevent, detect, and control infectious
diseases. Efforts were focused on early detection and
response to potentially high-consequence animal viruses
before they became significant public health threats in
regional “hotspots” for emerging diseases, such as central
Africa, South and Southeast Asia, and Latin America
(USAID 2013).
PHOTO BY PIOTR NASKRECKI
REDUCING PANDEMIC RISK, PROMOTING GLOBAL HEALTH
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PREDICT, a surveillance and virus discovery component of the EPT program, focused on
building capacity to identify potential zoonotic disease threats at high-risk wildlife-human disease
transmission interfaces where diseases are most likely to emerge. PREDICT was implemented
in more than 20 countries, including Bangladesh, Bolivia, Brazil, Cambodia, Cameroon,
China, Democratic Republic of Congo, Gabon, Indonesia, Laos, Malaysia, Mexico, Nepal,
Peru, Republic of Congo, Rwanda, Tanzania, Thailand, Uganda, and Vietnam. The program
aimed to improve early detection and response to disease threats through five main objectives: 1)
strengthening disease surveillance systems; 2) improving viral discovery by developing laboratory
and disease outbreak response capacity; 3) characterizing drivers of pathogen spillover and spread
from animals to people; 4) optimizing predictive models for disease emergence and spread, and
5) deploying cutting-edge information management and communication tools to advance a more
integrated, global approach to emerging zoonotic diseases.
Through EPT, PREDICT worked to enhance in-country capacity for response and prevention
of pathogen spillovers by strengthening laboratory and diagnostic systems and increasing
connectivity among government sectors (wildlife, livestock, and human health) to operationalize
a One Health platform and promote early detection. In addition, PREDICT conducted
surveillance and monitoring for viruses in wildlife at high-risk animal-human interfaces to detect
potential zoonotic threats and prevent their emergence in human or livestock populations.
20
USAID PREDICT
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