This document discusses emerging and re-emerging infectious diseases. It provides examples of diseases that have emerged in recent decades like Ebola, SARS, and HIV/AIDS. It also gives examples of diseases that were once under control but are re-emerging like tuberculosis, malaria, and cholera. The document explores factors that contribute to disease emergence such as ecological disruption, globalization, and breakdowns in public health infrastructure. It emphasizes that infectious diseases remain a major global health challenge.

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EMERGING AND RE-EMERGING INFECTIOUS DISEASES
Introduction
1. The threat to public health posed by infectious diseases is
a matter of grave concern. These diseases are the leading cause
of death worldwide, claiming at least 17 million lives every
year. In the South-East Asia region, 7 million people die from
diseases annually.
2. Despite remarkable advances in medical science and
treatment during 20th century, infectious diseases remain the
leading cause of death worldwide for mainly three reasons:
emergence of new infectious diseases, re-emergence of old
infectious diseases and persistence of intractable infectious
diseases.
3. During the last 20 years, at least 30 new diseases have
emerged to threaten the health of hundreds of millions of
people. For many of these diseases there is no treatment, cure
or appropriate vaccine and the possibility of preventing or
controlling then is limited.
Aim
4. To introduce major concepts related to emerging and re-
emerging infectious diseases and to convey the relationship
between basic biomedical research and the improvement of
personal and public health.

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Scope
5. The topic will be unfolded on the following sequences
a. Emerging and Re-emerging infectious diseases
b. Factors contributing to emerge
c. Basic concept of the infectious diseases
d. Challenges to prevent the emergence
e. Conclusion
Emerging And Re-emerging Diseases
5. Infectious diseases have for centuries ranked with wars
and famine as major challenges to human progress and
survival. They remain among the leading causes of death and
disability worldwide. Against a constant background of
established infections, epidemics of new and old infectious
diseases periodically emerge, greatly magnifying the global
burden of infections. Studies of these emerging infections
reveal the evolutionary properties of pathogenic
microorganisms and the dynamic relationships between
microorganisms, their hosts and the environment.
Emerging Disease
6. Emerging infectious diseases are diseases that
a. Have not occurred in humans before and one that
has appeared in a population for the first time (this type
of all numbers of emergence is difficult to establish and is
probably rare)
b. Have occurred previously but affected only
somesmall numbers of people in isolated places (AIDS

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and Ebola hemorrhagic fever are examples)
c. Have occurred throughout human history but have
only recently been recognized as distinct diseases due to
an infectious agent and is rapidly increasing in incidence
or geographic range (Lyme disease and gastric ulcers are
examples).
Examples of Emerging Diseases
Year Recognized Disease Infectious Agent
New viral strains
emerge periodically
PandemicInfluenza Influenzavirus
1937 West Nile infection West Nile virus
1967
Marburghemorrhagic
fever
Marburgvirus
1969 Lassa fever Lassa virus
Before1976
Salmonellosis
(Salmonella poisoning)
Salmonella enteritidis
(Bacterium)
1976 Ebola hemorrhagic feverEbola virus
1977 Legionnaire’s disease
Legionella
pneumophila(Bacterium)
1977 Cyclospora
Cyclosporacayetanensis(Unicel
lular parasite)
1978 (linked to the
disease)
CDAD (Clostridium
difficile associated
disease)
C. difficile
(Bacterium)
1981 MRSA infection
methicillin-resistant
Staphylococcus

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aureus(Bacterium)
1982
Hemolytic uremic
syndrome
Escherichia coli
0157:H7 (Bacterium)
1982 Lymedisease
Borreliaburgdorferi
(Bacterium)
1983 AIDS
Human Immunodeficiency
Virus
1983 Gastric ulcers
Helicobacter pylori
(Bacterium)
mid-1980s VRE infection
Vancomycin-resistant
enterococci (Bacteria)
1989 Hepatitis C Hepatitis C virus(HCV)
early 1990s
Salmonellosis (salmonella
poisoning)
Salmonella serotype
Typhimurium DT104
(Bacteria)
1993
Hantaviruspulmonary
syndrome
Hantavirus
disease first described
in 1996
New variant Creutzfeldt-
Jakob disease
Prions (Misfoldedproteins)
1996 VISA infection
Vancomycin intermediate-
resistant S. aureus(Bacterium)
1998 Nipah encephalitis Nipah virus
2002 VRSA infection
Vancomycin-resistantS.
aureus(Bacterium)
2003 SARS (severe acute SARS-associated coronavirus

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respiratory syndrome)
Re-emerging Diseases
7. 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. Diseases thought to be
adequately controlled making a “comeback” are “re-emerging”
Examples of Re-emerging Diseases
Disease Infectious Agent
Chikungunya Chikungunyavirus
Cholera Vibrio cholerae0139(Bacterium)
Cryptosporidiosis
Cryptosporidium
parvum(Protozoan)
Denguefever Denguevirus
Diphtheria
Corynebacteriumdiptheriae(Bacteri
um)
H5N1 influenza InfluenzaH5N1 virus
Malaria Plasmodium species (protozoan)
Meningitis, necrotizing fasciitis
(flesh-eating disease), toxic-
shock syndrome, and other
Group A Streptococcus (bacterium)

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diseases
Pertussis(whooping cough)
Bordetella pertussis
(Bacterium)
Polio (infantparalysis) Poliovirus
Rabies Rabies virus
Rift Valley fever (RVF) RVF virus
Rubeola(measles) Measles virus
Schistosomiasis
Schistosoma species
(Helminth)
Trypanosomiasis
Trypanosomabrucei
(Protozoan)
Tuberculosis
Mycobacteriumtuberculosis
(Bacterium)
West Nile encephalitis West Nile virus
Yellow fever Yellow fever virus
New Diseases Emerge
8. Emerging diseases new infections that arise from changes
in existing organisms Or known infections that spread to new
geographic areas or populations. Incidence of such a disease in
people increases over 20 years or threatens to increase.
Old Diseases Re-Emerge

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9. The re-emergence of some diseases can be explained by
a. Evolution of the infectious agent
1) Mutations in bacterial genes that confer
resistance to antibiotics – 20%
2) Multidrug-resistant & extremely drug-resistant
TB Multi drug resistant P.falciparum
b. Reduced human immunity
1) Immunization failure (breakdowns in public
health measures). A greater proportion of
susceptible individuals in a population and an
increased reservoir of the infectious agent.
2) Increased number of immunocompromised
hosts - due to the stress of famine, war,
overcrowding or diseases.
Factors Predisposing To Emergence
10. Ecological disruption and human intrusion into new
ecological system are often cited as major factor in the
emergence of new infectious diseases. Such exposure usually
increases the exposure of human to new infectious agents
rather than unearthing new or previously known disease
(Morse 1991). Ecological changes take many forms:
deforestation/deforestation, construction of dams and
irrigation system, extension of agricultural process or climate
change. Both deforestation and reforestation enhance border
contact between human and disease agent and increase the
possibility of exposure to disease. Deforestation for crop
farming and ranching can create supportive habitats for both
parasites and their host vectors. The primary malaria vector in
the Peruvian rainforest of the United State prefers to bread in
grass and crop land and bite rates are much higher in

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deforested agricultural areas than in the forest. Contstruction
of dams to control seasonal flooding and irrigation system to
support agricultural may also have unintended effects on
diseases emergence.
11. Another link to agriculture is through farming practices
such as intensification and expansion which can encourage the
geographic spread of the diseases. For example, the
intensification and expansion of irrigated rice into the semi-
arid regions of South-East Asia since 1980s has had an
important effect on the disease burden caused by Japanese
Encephalitis. The flooding of the rice fields at the start of each
cropping cycle leads to an explosion in the mosquito
population. This may cause virus, which usually circulate
among birds and pig hosts, to jump to the human population.
12. Climate change is another potential driver that shifts the
ecological niche or range of the diseases. While we may not
know the long-term impact of global warming, there are some
major climatic events caused disease outbreaks in the areas
that have not experienced the disease before.
13. Ecological changes are not limited to natural
environment. Changes in the structural and built environment
related to urbanization and industrialization impact the
prevalence and scope of both infectious and chronic diseases.
The prevalence of Tuberculosis decreased dramatically with
better housing quality and water born diseases such as Cholera
and Typhoid are problematic in areas with poor sanitation and
water supply infrastructure.
14. The spread of HIV is affected by social norms and the
larger social environment both of which directly influence
human behavior. Social norms that may influence whether or

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not a person is infected include the acceptability of specific
high risked sexual practices, multiple sexual prtners, choice of
contraceptives and the use of substances that lower the sexual
inhibitions or directly transmit the diseases. But the larger
social environment like Africa and Asia also influence the
sexual and drug using behavior. The presence of commercial
sex workers or brothels, the crack houses and bathhouses
create physical environments where transmission is more
likely to occur.
15. Political conflict and breakdown of public health
infrastructure has role in emergence of diseases. Strong
surveillance and public health system are important in
identifying diseases outbreaks and minimizing the exposure to
and dissemination of diseases within a population. Even the
incidence of a disease declined dramatically due to effective
prevention programs, the pathogen that caused the disease
remain in the environment. A strong public health system
providing funding for clinics and public health professionals,
disease control measures, such as vaccination and vector
control and makes these accessible to the population. The re-
emergence of a disease often results from lapse in public health
measures which allow the pathogens to enter into and
disseminated through the population once again.
16. Increased mobility and globalization shows history is full
of examples of how international travel, commerce and war
have helped to disseminate disease to new geographical areas
(e.g. small pox in new world).
17. International trade of goods and services can also
facilitate the spread of disease. Vehicles transporting goods
through international border can inadvertently transport
pathogens to new geographical areas. Even regional trade of

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goods and services can facilitate the spread of infectious
diseases. Travelers are exposed to a variety of pathogen while
on vacation or business trips, many of which have never
encountered and no immunity to many diseases.
The Annual Cause-Specific Mortality Estimates From The
World Health Organization (WHO)
Respiratory infections: 4.3 million deaths
Diarrheal diseases 2.5 million deaths
HIV/AIDS 1.8 million deaths
Tuberculosis 1.3 million deaths
Malaria 0.8 million deaths
Meningitis 0.8 million deaths
Pertussis 0.8 million deaths
Measles 0.8 million deaths
Hepatitis B 0.8 million deaths
Other infectious diseases 0.8 million deaths
Examples Of Recent Emerging And Re-emerging Diseases
Worldwide

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Hepatitis
18. Hepatitis C First identified in 1989 in mid 1990s
estimated global prevalence 3%. Hepatitis B- Identified
several decades earlier.Upward trend in all
countries.Prevalence >90% in high-risk population.
Creutzfeldt-Jakob Disease (CJD)
19. Creutzfeldt-Jakob disease is a progressive neurologic
disorder, one of the sub-acute spongiform encephalopathies
caused by prions. Clinical features of CJD include a progressive
cerebellar syndrome, including ataxia, abnormalities of gait
and speech, and dementia. In most patients, these symptoms
are followed by involuntary movements (myoclonus) and the
appearance of a typical electroencephalogram pattern (burst
suppression, consisting of intermittent sharp and slow wave
complexes on a flat background). Changes in the CSF are

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absent or nonspecific. Mild cortical atrophy and ventricular
dilation may be grossly evident. On microscopic examination
the distinctive finding is spongiform encephalopathy in gray
matter throughout the brain and spinal cord. Severe neuronal
loss and gliosis are also present and mild demyelination may
occur. Ultrastructural changes include formation of
intracytoplasmic vacuoles, which account for the spongy
appearance.
20. CJD occurs worldwide at a rate of about 1 or 2 cases per
million population per year. Most cases are sporadic, but 10 to
12% are inherited. The peak incidence is between 55 and 65
years of age, and the disease is rare before age 30. The average
survival time is less than one year after onset of symptoms.
Dengue Fever
21. Dengue fever, also known as breakbonefever, is a
mosquito-borne infection that causes a severe flu-like illness.
There are four different viruses that can cause dengue fever, all
of which spread by a certain type of mosquito.Dengue fever can
vary from mild to severe; the more severe forms include
dengue shock syndrome and dengue hemorrhagic fever (DHF).
22. A study published in Nature (April 2013 issue) showed
that there are approximately 390 million people worldwide
infected with the dengue virus each year, over three times as
many as the World Health Organization's estimate of up to 100
million.
AIDS

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23. AIDS (Acquired immune deficiency syndrome or acquired
immunodeficiency syndrome) is a syndrome caused by a virus
called HIV (Human Immunodeficiency Virus). The illness alters
the immune system, making people much more vulnerable to
infections and diseases. This susceptibility worsens as the
syndrome progresses.
24. HIV is found in the body fluids of an infected person
(semen and vaginal fluids, blood and breast milk). The virus is
passed from one person to another through blood-to-blood
and sexual contact. In addition, infected pregnant women can
pass HIV to their babies during pregnancy, delivering the baby
during childbirth, and through breast feeding.
25. HIV can be transmitted in many ways, such as vaginal,
oral sex, anal sex, blood transfusion, and contaminated
hypodermic needles.
The red ribbon is the worldwide symbol of support and awareness for people living
with HIV.
26. Both the virus and the syndrome are often referred to
together as HIV/AIDS. People with HIV have what is called HIV
infection. As a result, some will then develop AIDS. The
development of numerous opportunistic infections in an AIDS
patient can ultimately lead to death.

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27. According to research, the origins of HIV date back to the
late nineteenth or early twentieth century in west-central
Africa. AIDS and its cause, HIV, were first identified and
recognized in the early 1980s.
Tuberculosis
28. Tuberculosis has a long, rich history, dating back as far as
Ancient Egypt, with evidence of its presence found in the
preserved spines of Egyptian mummies.
29. In the 18th and 19th centuries, a tuberculosis epidemic
rampaged throughout Europe and North America,2 before the
German microbiologist Robert Koch discovered the microbial
causes of tuberculosis in 1882.
30. Following Koch's discovery, the development of vaccines
and effective drug treatment led to the belief that the disease
was almost defeated. Indeed, at one point the United Nations,
predicted that tuberculosis (TB) would be eliminated
worldwide by 2025.
31. However, in the mid-80s, TB cases began to rise once
more in the US and worldwide, so much so that in 1993 the
World Health Organization (WHO) declared that TB was a
global emergency; the first time that a disease had been
labelled as such.
32. Fortunately, with proper treatment almost all cases of
tuberculosis are curable. Cases of TB have decreased in the
US since 1993, but the disease remains a concern. Without
proper treatment up to two-thirds of people ill with
tuberculosis will die.

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Highly Pathogenic Avian Influenza (H5N1)
33. After a period of quiescence in Southeast Asia, outbreaks
of highly pathogenic avian influenza (A/H5N1) are again
being reported in chickens and ducks in China, Indonesia,
Thailand and Viet Nam. In Thailand, outbreaks have been
reported in 21 of 76 provinces; and in Viet Nam outbreaks
were reported in the northern, central and southern parts of
the country. These outbreaks, many without apparent
epidemiological links to each other, suggest A/H5N1 is now
widely prevalent and is very likely to have become endemic.
The outbreaks in birds pose a significant threat to human
health.
34. As WHO has stated since the first A/H5N1 outbreaks
were reported, this virus has the potential to ignite a global
influenzapandemic in humans. In a number of these outbreaks
since the beginning of 2004, the virus has jumped from
infected chickens or ducks directly to humans. These direct
human infections have produced severe and sometimes fatal
outcomes. WHO's continuing concern is that this virus may
reassort its genes with those from a human influenza virus,
thereby acquiring the ability to move easily from human to
human and thus triggering a pandemic.
Swine Flu
35. Since December 2014, swine flu has claimed the lives of
over 1,300 people in India, making it the worst outbreak of the
virus in the country since 2009. But according to a new study
by researchers from the Massachusetts Institute of Technology,
the virus that has caused the current epidemic is not the same
as the one responsible for the 2009 outbreak; it has acquired
mutations that make it more virulent.

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Ebola Hemorrhagic Fever
36. The 2014 Ebola outbreak is the largest in history,
primarily affecting Guinea, northern Liberia, and Sierra Leone.
The Centers for Disease Control and Prevention (CDC)
estimates that the epidemic has caused more than 11,000
deaths, with almost all those deaths occurring in countries in
West Africa. In the US, reports indicate that there have been
two imported cases, including one death, and two locally
acquired cases in healthcare workers. A small number of cases
were reported in Nigeria, Mali and Senegal, with health
authorities able to contain these cases and prevent further
spread.

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37. Ebola virus disease (EVD), previous known as Ebola
hemorrhagic fever (Ebola HF), is a serious, often fatal condition
in humans and nonhuman primates such as monkeys, gorillas
and chimpanzees. Ebola is one of several viral hemorrhagic
fevers (VHF), caused by infection with a virus of the Filoviridae
family, genus Ebolavirus.
38. Ebola has a case fatality rate of up to 90% and is currently
one of the world's most infectious diseases. The infection is
transmitted by direct contact with the blood, body fluids and

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tissues of infected animals or people. Severely ill patients
require intensive supportive care.
Zika Virus
39. Zika virus is a mosquito-borne illness that is spread by
the Aedes species of mosquito, the mosquito also responsible
for the transmission of dengue and chikungunya viruses.
40. The two known species responsible for Zika transmission
are the Aedesalbopictus, known as the Asian Tiger mosquito,
and the Aedesaegypti species.The Zika virus was first identified
in monkeys in Uganda in 1947. The first human case, however,
was detected in Nigeria in 1954, and following that there have
been further outbreaks in Africa, South East Asia and the
Pacific Islands.
Marburg

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41. Varying pathogenicity (mortality ranging from 21-80%)
.Responsible for 1967 outbreak in Europe.Outbreaks in 2000 in
Democratic Republic of the Congo and 2005 in Angola.
Emerging Infectious Disease (EID) in SEA Region
42. EID is a leading cause of death globally. 17 millions
people die annually from EID. SEA accounts for 41% or 7
millions deaths.EID cause suffering & impose financial burden
on society. Plague outbreak in 1994 cost India over 1.5 B USD
due to loss in trade, employment & tourism. In Thailand cost of
one AIDS patient more than 5000 USD. Overall costs for India
on account of AIDS estimated at 11 billions USD. Increasing or
persistent poverty & poor living conditions continue to expose
millions of people to the hazards of infectious diseases.The low
priority & support given to public health services is most
important factor.
Management Of Emerging Of Diseases
43. A proactive and planned approach to ensure the
appropriate prevention and control of the spread of disease.
Strategic planning should include:
Phase I (non-alert) is a routine, preparatory state;
Phase II (alert) is the detection, confirmation and declaration
of changes identified during non-alert conditions;
Phase III (response) includes the ongoing assessment of
information and the planning and implementation of an
appropriate response, which includes the coordination and
mobilization of resources to support intervention activities

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Phase IV (follow-up) activities include re-evaluation,
restructuring, reporting and continuing education, and
redefining strategic parameters.
Recommendation
44.
a. Strengthening epidemiological surveillance
b. Strengthening laboratory capabilities and services
c. Establishment of a rapid response team
d. Monitoring antimicrobial resistance
e. Establishment of international disease surveillance
networking and advocacy
f. Mobilization of the international support.
g. Networks of laboratories that link countries and
regions need to be established.
h. Strengthened national and regional public health
systems.
Conclusion
45. Throughout human history, diseases have emerged and
re-emerged and swept through the population becoming
serious health problems. Many emerging and re-emerging
infections originate from pathogens already present in the
environment but changes to the environment and the
populations living in those environments cause the disease to
enter into and disseminate through the population once again.
46. In this discussion, we introduced the concept of infectious
diseases that emerge due to changes in human demographics,
behaviors and upstream changes in the structural
environment. Thus emergence and re-emergence of disease
linked to the changing geographies where disease occurs.

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Avian influenza emerging through genetic changes that occur
in particular human-environment ecosystem. Global travel and
trade facilitate international spread of the disease. Cholera is
re-emerging because of both natural environmental patterns
and poor socio-economic conditions in the world’s poorest
nations.
47. It is crucial that we understand how shifting demographic,
behavior, economic and political forces interact with
alternations to the environment to produce new pattern of
disease. It is only through examining such complex interactions
that we can gain an understanding of spatio-temporal changes
in diseases distribution. Detailed studies of ecologies and
strong surveillance system are the key to understanding why
diseases emerge, predicting when and where they may emerge
and how we can effectively prevent them.
References
 A Companion To Health And Medical Geography- Tim
Brown, Sara McLaffarty, Graham Moon.
 National Institutes of Health, Department of Health and
Human Services.
 Medical News Today
 AIDS.org
 International Society For Infectious Disease (ISID)
 Journal Of Global Infectious Diseases (JGID)

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 WHO