Recent Trends in Emerging Infectious Diseases

Syed Amin Tabish

Abstract


Infectious diseases are the worlds greatest killers that present one of the most significant health
and security challenges facing the global community. On April 15 and April 17, 2009, novel swineorigin
influenza A (H1N1) virus (S-OIV) was identified in specimens obtained from two
epidemiologically unlinked patients in the United States. The same strain of the virus was
identified in Mexico, Canada, and elsewhere. Enhanced surveillance was implemented in the
United States for human infection with influenza A viruses that could not be subtyped. Specimens
were sent to the Centre for Disease Control and Prevention for real-time reverse-transcriptase
polymerase-chain-reaction confirmatory testing for S-OIV. The S-OIV was determined to have a
unique genome composition that had not been identified previously. This virologic analysis
allowed for the development of a polymerase-chain-reaction (PCR) test to determine whether, in
any given person, illness with the protean manifestations of cough, fever, sore throat, diarrhea,
and nausea could be confirmed as a case. Armed with this critical tool, clinicians and
epidemiologists are able to make case assignments to define and track the outbreak and to
determine disease severity.
WHO declared the start of the Influenza A (H1N1) pandemic on June 11, 2009. The Director-
General of WHO raised the influenza pandemic alert to the highest level - Phase 6 - on the
guidance and advice from an Emergency Committee established for this purpose under the
International Health Regulations (IHR). As of 31 of July 2009, 168 countries and overseas
territories/communities have reported at least one laboratory confirmed case of pandemic (H1N1)
09. All continents are affected by the pandemic. Total cases reported were 162380 with 1154
deaths. The declaration of a pandemic essentially means wide geographic spread and does not
indicate any change in the severity of the illness. Currently the severity of the pandemic has been
assessed as "moderate" globally. In vast majority of cases the virus produces mild disease. In a
small proportion of people the illness can become severe and fatal.
There are important tools with which to fight this outbreak: a clear case definition, an aware
health care system, and an informed public.
Swine Influenza (swine flu) is a respiratory disease of pigs caused by type A influenza that
regularly cause outbreaks of influenza among pigs. Swine flu viruses do not normally infect
humans, however, human infections with swine flu do occur, and cases of human-to-human
spread of swine flu viruses has been documented. Laboratory testing has found the swine
influenza A (H1N1) virus susceptible to the prescription antiviral drugs oseltamivir and zanamivir.
In our daily life we are surrounded by a wealth of microorganisms, the majority of which are
nonharmful. Human existence would be impossible without these micro-organisms, which play
critical roles in processes as diverse as photosynthesis, nitrogen fixation, production of vitamins in
the human intestine and decomposition of organic matter. They are the sole, true recyclers of our
planet. Microorganisms are also the major driving force behind the evolution of life. Throughout
evolution, human being, like all mammalian species, has maintained an intimate relationship with
the microbial world. We have survived thanks to the efficient defense mechanisms we have
developed against potentially dangerous microorganisms. Pathogenic microorganisms are still
here because they have found ways of avoiding elimination by their host or by the microbial
competition. Successful pathogens have developed strategies to enter the body and reach and
choose their favourite niche, while defying the powerful human immune systems.
Humans have lived with emerging and re-emerging pathogens since before the dawn of
civilization. Is the situation worse now than in past decades or centuries? The answer is probably
yes because there are billions more of us and some of our activities allow such infections to
appear and flourish. Moreover, our mobility within and between countries is conducive to the rapid
spread of microorganisms. Similar observations hold true for animals and plants, with frequent
consequences for human health.
International Journal of Health Sciences, Qassim University, Vol. 3, No.2, (Jualy 2009/VI Jamada II 1430H)
Infectious diseases are among the worlds leading causes of death, and scientists from every
nation perform research, share information, build laboratory capacity in poorer nations and create
global surveillance networks to help prevent and control their spread.
When the incidence of such a disease in people increases over 20 years or threatens to
increase, it is called an emerging disease, and a growing number have made watch lists and
headlines in nearly every country -- highly pathogenic H5N1 avian influenza, severe acute
respiratory syndrome (SARS), Ebola virus, food- and waterborne illnesses, and a range of antimicrobial-
resistant bacterial diseases like multidrug-resistant and extensively drug-resistant
tuberculosis (TB).
Emerging infectious diseases are diseases that have not occurred in humans before; have
occurred previously but affected only small numbers of people in isolated places (AIDS and Ebola
hemorrhagic fever are examples); or have occurred throughout human history but have only
recently been recognized as distinct diseases due to an infectious agent (Lyme disease and
gastric ulcers are examples). Re-emerging infectious diseases are diseases that once were major
health problems globally or in a particular country, and then declined dramatically, but are again
becoming health problems for a significant proportion of the population (malaria and tuberculosis
are examples).
Emerging diseases can be new infections that arise from changes in existing organisms or
known infections that spread to new geographic areas or populations. They can be previously
unrecognized infections that appear when, for example, tropical forests are cleared to make way
for new roads, displacing disease-carrying animals and insects. And old infections can re-emerge
because of anti-microbial resistance or breakdowns in public health measures.
Most emerging infectious diseases (60.3 percent) are zoonoses, or animal diseases that can
be transmitted to people.
Emerging infectious diseases (EIDs) are a significant burden on global economies and public
health. Their emergence is thought to be driven largely by socio-economic, environmental and
ecological factors, but no comparative study has explicitly analysed these linkages to understand
global temporal and spatial patterns of EIDs. Here we analyse a database of 335 EID 'events'
(origins of EIDs) between 1940 and 2004, and demonstrate non-random global patterns. EID
events have risen significantly over time after controlling for reporting bias, with their peak
incidence (in the 1980s) concomitant with the HIV pandemic. EID events are dominated by
zoonoses (60.3% of EIDs): the majority of these (71.8%) originate in wildlife (for example, severe
acute respiratory virus, Ebola virus), and are increasing significantly over time. We find that 54.3%
of EID events are caused by bacteria or rickettsia, reflecting a large number of drug-resistant
microbes in our database. Our results confirm that EID origins are significantly correlated with
socio-economic, environmental and ecological factors, and provide a basis for identifying regions
where new EIDs are most likely to originate (emerging disease 'hotspots'). They also reveal a
substantial risk of wildlife zoonotic and vector-borne EIDs originating at lower latitudes where
reporting effort is low. We conclude that global resources to counter disease emergence are
poorly allocated, with the majority of the scientific and surveillance effort focused on countries
from where the next important EID is least likely to originate.
Emergent infection is recognized as a global threat. At least 17 million die annually from
infectious diseases. Of these, the South-east Asia Region accounts for almost 41 per cent, or 7
million deaths.
Factors responsible for EIDs as identified by Board on Global Health (BGH) and the
Institute of Medicine (IOM), include: Microbial adaptation and change, Human Demographics and
Behavior, International Travel and Commerce, Economic Development and Land Use, Technology
and Industry, Breakdown of public health measures, Human susceptibility to infection, Climate
and weather, Changing ecosystems , Poverty and social inequality, War and famine, Lack of
political will, Intent to harm, A global political commitment is rather vague, Who will be the parties
in a global social contract?, How is their will determined?, How can the liberties of individual
coutnries be balanced against collective responsibility?, Is there collective responsibility? Must
have commitment from four groups: donors, health care professionals, country authorities, and
patients, and Developing world diseases dont matter to politicians here.
International Journal of Health Sciences, Qassim University, Vol. 3, No.2, (Jualy 2009/Jamada II 1430H) VII
EIDs include Avian Flu, Swine Flu and the threat of Pandemic Influenza, E. coli
O157:H7/Salmonella, Norovirus Not just the cruise ship virus anymore, MDR, XDR
tuberculosis, Novel pathogens: Bocavirus, Chikungunya virus, Community-acquired MRSA/
Epidemic C. difficile, Mumps, Measles, Rubella, Pertussis (Whooping Cough), Monkeypox,
SARS, West Nile Virus, Anthrax, ricin and other bioterrorism agents.
Every year there are around 600 million travelers. Some will already be carrying pathogens;
others will be traveling to areas in which they will suffer unintended exposure to, for them, new
pathogens that, potentially, they can introduce to their communities upon their return home.
Modern civilization dates from approximately 10,000 BC. It took until 1830 for the world
population to reach 1 billion persons; however, from there the world population doubled in the
next 100 years and reached 6 billion 70 years after that. By the end of 21st century the world
population could be between 14 and 18 billion.
In the global human population, the emergence of 335 infectious diseases between 1940 and
2004 has been reported. The emergence of these pathogens and their subsequent spread has
caused an extremely significant impact on global health and economies13. Previous efforts to
understand patterns of EID emergence have highlighted viral pathogens (especially RNA viruses)
as a major threat, owing to their often high rates of nucleotide substitution, poor mutation errorcorrection
ability and therefore higher capacity to adapt to new hosts, including humans.
The majority of pathogens involved in EID events are bacterial or rickettsial (54.3%). This group is
typically represented by the emergence of drug-resistant bacterial strains. Viral or prion pathogens
constitute only 25.4% of EID events. This follows our classification of each individual drug-resistant
microbial strain as a separate pathogen in our database, and reflects more accurately the true
significance of antimicrobial drug resistance for global health, in which different pathogen strains can
cause separate significant outbreaks. In broad concurrence with previous studies on the characteristics
of emerging human pathogens, we find the percentages of EID events caused by other pathogen types
to be 10.7% for protozoa, 6.3% for fungi and 3.3% for helminths.
The incidence of EID events has increased since 1940, reaching a maximum in the 1980s.
Increased susceptibility to infection caused the highest proportion of events during 198090
(25.5%), and we therefore suggest that the spike in EID events in the 1980s is due largely to the
emergence of new diseases associated with the HIV/AIDS pandemic.
The majority (60.3%) of EID events are caused by zoonotic pathogens (those which have a
non-human animal source), which is consistent with previous analyses of human EIDs.
Furthermore, 71.8% of these zoonotic EID events were caused by pathogens with a wildlife
originfor example, the emergence of Nipah virus in Perak, Malaysia and SARS in Guangdong
Province, China. The number of EID events caused by pathogens originating in wildlife has
increased significantly with time, controlling for reporting effort, and they constituted 52.0% of EID
events in the most recent decade (19902000). This supports the suggestion that zoonotic EIDs
represent an increasing and very significant threat to global health. Vector-borne diseases are
responsible for 22.8% of EID events in our database, and 28.8% in the last decade. Our analysis
reveals a significant rise in the number of EID events they have caused over time. This rise
corresponds to climate anomalies occurring during the 1990s, adding support to hypotheses that
climate change may drive the emergence of diseases that have vectors sensitive to changes in
environmental conditions such as rainfall, temperature and severe weather events. EID events
caused by drug-resistant microbes (which represent 20.9% of the EID events in our database)
have significantly increased with time, controlling for reporting effort. This is probably related to a
corresponding rise in antimicrobial drug use, particularly in high-latitude developed countries.
Perhaps no human activity is as conducive to emergence of infectious diseases as warfare, a
human behaviour that, measured by the number of people involved, becomes more extensive
every century. The 20th century has been the bloodiest in history. There have been 150 wars in
the second half of the century, resulting in more than 20 million deaths, two-thirds of them
civilians. The prospects for less warfare are not good. Ethnic, religious, racial and tribal strife will
be exacerbated by population growth, overcrowding and rivalries over increasingly depleted
natural resources.
International Journal of Health Sciences, Qassim University, Vol. 3, No.2, (Jualy 2009/VIII Jamada II 1430H)
The economic impact of new, emerging and re-emerging infectious diseases can be
enormous. The 1991 cholera epidemic in Peru cost that country an estimated $770 million. The
plague epidemic in India cost that country $1.8 billion. BSE in the United Kingdom cost more than
$6 billion. By the year 2000, the overall costs to Thailand and India on account of AIDS have been
estimated at US$ 9 billion and 11 billion, respectively. The global cost of SARS has crossed $30
billion. Infectious diseases like malaria and AIDS act as a massive societal brake, slowing both
economic and human development.
Recent outbreaks, such as SARS in China & 32 other countries, the plague episode in India,
Ebola hemorrhagic fever in Zaire, and leptospirosis in Nicaragua, depict the limited global
capacity to rapidly diagnose and respond to emerging disease threats.
The goal of an optimal harmony between groups of people in society and their environment
can be achieved by methods to improve host resistance of populations to environmental hazards;
by effective plans to improve the safety of the environment, and by improving healthcare systems
designed to increase the likelihood, efficiency and effectiveness of the first two goals (systems
approach). One might view communicable diseases as an imbalance in the relationship of people
and their environment which favours microbial dominance in populations. The social, economic,
legal and administrative forces important for health must operate in the interest of the public.
Responding to the global threats of EID requires a coordinated global response with development of
expertise in epidemiology, laboratory science, behavioural science, increased surveillance, adequate
public health infrastructure, primary prevention and adequate communication.
Efforts to prevent and control problems must begin with a search for better understanding of
the societal roots of disease, disability and premature death.
Extrapolation of current trends is a poor way to think about the future, particularly at times of
great change. The best method seems to be to bring together a diverse group of people
knowledgeable about the subject of interest, provide them with good data, and ask them to
imagine a series of possible scenarios.
Further Reading:
1. Daszak, P.,Cunningham, A. A.&Hyatt, A. D.Emerging infectious diseases of wildlife threats to
biodiversity and human health. Science 287, 443449 (2000).
2. Kate E. Jones, Nikkita G. Patel, Marc A. Levy, Adam Storeygard, Deborah Balk, John L.
Gittleman & Peter Daszak. Global trends in emerging infectious diseases. NATURE Vol 451:
21 February 2008
3. Ferguson, N. M. et al. Strategies for containing an emerging influenza pandemic in Southeast
Asia. Nature 437, 209214 (2005).
4. Morens, D. M., Folkers, G. K. & Fauci, A. S. The challenge of emerging and reemerging
infectious diseases. Nature 430, 242249 (2004).
5. King, D. A., Peckham, C., Waage, J. K., Brownlie, J.&Woolhouse, M. E. J. Infectious
diseases: Preparing for the future. Science 313, 13921393 (2006).
6. Weiss, R. A. & McMichael, A. J. Social and environmental risk factors in the emergence of
infectious diseases. Nature Med. 10, S70S76 (2004).
7. Wolfe, N. D., Dunavan, C. P. & Diamond, J. Origins of major human infectious diseases.
Nature 447, 279283 (2007).
8. Woolhouse, M. E. J. & Gowtage-Sequeria, S. Host range and emerging and reemerging
pathogens. Emerging Infect. Dis. 11, 18421847 (2005).

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