Download Global Health

Global Health
Tom D. Y. Chin, MD, MPH
This lecture was given to the
first year medical students
at the University of Kansas
School of Medicine
in 2005
Objectives
 This
presentation will give an overview of
infectious diseases in relation to global
health.
 The objective is to identify some of the
diseases of global importance, enumerate
their disease burden and consider
measures for coping with them.
 To discuss briefly the concept of emerging
and reemerging infections and its impact
on the practice of medicine and public
health.
West Nile Virus





First isolated from the blood of a patient in
Uganda in 1937.
The virus spread to Egypt, Middle East, Northern
Mediterranean, Western Asia.
It was introduced in New York City in 1999,
probably from Israel.
Since then, it has spread extensively throughout
the United States.
It is spread by primarily mosquito bites
WNV Activity 9/04 T=1386 Deaths 35
Life
Lifecycle
cycleofofWNV
WNV
Transmission of WNV





Mosquitoes: the principal vector
Blood transfusion
Organ transplant
Transplacental
Breast milk
This knowledge has a direct impact on the practice of
medicine and public health
Infectious Diseases Worldwide
Size of the Problem
 Biggest
killers of children and young
adults: >13 million deaths per year.
 Particularly important in developing
countries: average of 1 in 2 die of
infectious disease.
 In developing countries, the leading cause
of deaths.
 Developed countries, 3rd leading cause of
deaths.
ACUTE
RESPIRATORY
INFECTIONS
MALARIA
HIV/AIDS
MEASLES
DIARRHEAL DISEASES
TUBERCULOSIS
Disability-adjusted
life years or years of
health life lost
AIDS Pandemic
 AIDS
undoubtedly was one of the most
devastating diseases emerged during the
20th century.
 From 1981 to the end of 2004, 24.9 million
people world-wide have succumbed to HIV
infections.
 The pandemic is expected to progress well
into the 21th century.
HIV/AIDS
 AIDS
is caused by a virus--human
immunodeficiency virus.
 Virus destroys the immune system. Thus
termed acquired immunodeficiency
syndrome or AIDS
 AIDS represents complications of HIV
infection when the immune system is
sufficiently lowered.
Prevalence of HIV Infections
End of 2004
 Estimated
39.4 million people world-wide
are living with HIV/AIDS.
 2/3 of infected persons reside in Africa
where the epidemic originated.
 1/5 of those with HIV/AIDS are among
people in Southeast Asia where the
epidemic has been progressing rapidly.
This area with the population of >2 billion
may well be the future epicenter.
Global HIV/AIDS Epidemic
 During
the year 2004
4.9 million people became
infected with HIV (incidence)
3.1 million people died of AIDS
HIV/AIDS in U.S.
 At
the end of 2003, a total of 902, 223
cases of AIDS have been reported to the
CDC, 505,801 (56%) have died.
 About 1 million of U.S. residents are living
with HIV/AIDS
Primary Modes of Transmission

Globally, unprotected sexual intercourse
between men and women is the predominant
mode of transmission. Ratio M:F 1:1.1
 In Sub-Saharan Africa, the primary mode of
transmission is by contact with sex workers.
Ratio F:M 13:1
 In China, Myanmar (Burma), parts of Europe, IV
drug use is the principal mode.
 Thus, prevention rests on determination of mode
of transmission.
Prevalence of HIV
 In
some countries in Africa, such as
Botswana, HIV prevalence among adults
is as high as 25 to 35 percent, with a
drastic decrease in life expectancy.
 Even in the United States, HIV prevalence
averages 25% among men having sex
with men (MSM), with the rate as high as
48% in some ethnic groups
 Thus, sexual transmission is most
common.
Major Problems

Although drugs are available, and effective, for
the treatment of AIDS, there are major
deficiencies. Among them are inadequate
distribution to developing countries (high cost),
requiring prolonged treatment (not curative),
adverse drug reactions, development of drug
resistance.
 Primary prevention such as use of condoms and
needle exchange have been advocated, but with
varying results
 Vaccine for primary prevention not yet available.
Therapeutic vaccine for treatment is being
explored.
Emergence of Infections
 New
infectious disease agents continue to
emerge in populations throughout the
world.
 More than 30 agents have emerged during
the past two decades.
 Infectious diseases may also reemerge
after a period of quiescence, e.g. tbc
 May appear in a new locality, WN
encephalitis, monkey pox
 An agent may undergo genetic changes
(e.g. influenza).
Emergence of Influenza
 An
agent of great concern globally is
influenza virus.
 Influenza virus is known to cause
epidemics as early as the 1500’s, and
pandemics have been described as early
as 1889.
 The most extensive pandemic ever known
is the pandemic of influenza of 1918-1919,
which killed more 20 million people.
Ref Business Week, April 14, 2003
Discovery of Influenza Virus
First isolated
from a pig in
1931 (swine
flu)
Isolated from
human in
1933
Characteristics of Influenza
Virus
 Types
A, B, C
 Diameter 80 - 120 nm
 Pleomorphic, spherical, filamentous
particles
 Single-stranded RNA
 Segmented genome, 8 segments in A
and B
 Hemagglutinin and Neuraminidase on
surface of virion
Pandemic Influenza Viruses
Pandemic
1889
1899
1918
1957
1968
1977
Subtype
H2N?
H3N8
H1N1
H2N2
H3N2
H1N1
Mechanisms of Transmission
of Influenza Viruses
Aquatic
birds
Pigs
Humans
Reservoir Mechanism (a)
 Aquatic birds,
particularly wild
ducks, are primary
reservoirs of
influenza virus. The
virus multiplies in
the gastrointestinal
tract and usually
causes no illness. It
is excreted in the
feces.
Reservoir Mechanisms (b)
 Pigs are considered
intermediate hosts
for influenza viruses.
 Pigs possess
receptors for avian
influenza viruses.
Thus, they can be
readily infected by
come in contact with
viruses from aquatic
birds.
Avian (Bird) Influenza
 1997, an outbreak of avian influenza, H5N1
occurred in Hong Kong. 6 of 18 infected
persons died. It was spread from domestic
poultry. Illness and mortality also occurred
in chickens. Many chickens were
slaughtered to control the spread.
Fortunately influenza did not spread widely
in the human population.
Avian Influenza --Continued
 H5N1 avian influenza became widespread
in late 2003 and 2004. This is a highly
pathogenic strain, involving largely
countries in southeast Asia, Vietnam,
Thailand, South Korea, China, Japan.
 Avian influenza spread to humans in
Vietnam and Thailand, killing at least 24
persons.
Coping with Emerging Infections
 During
the past several years, the public
as well as health professionals are keenly
aware of the potential of global spread of
emerging infectious diseases, particularly
SARS, avian influenza.
 Agencies such as WHO, CDC, NIH as well
as Global Health Council, World Bank,
Global Forum for Health Research are
taking up the challenges of global health.
Millions of dollars have been appropriated
to meet these challenges.
Preparing for the next pandemic
Are we ready for the next
influenza pandemic?
Many epidemiologists and
virologists feel another
pandemic of influenza is
inevitable; the question is when.
Bioterrorism
Similarly, use of biological agents
to attack against civilian
population is a likely possibility,
the question is which agent;
anthrax, smallpox, pneumonic
plague?
Infectious Causes of Chronic
Diseases
 Helicobacter
pylori: peptic ulcer
 Hepatitis B & C: Hepatocellular ca
 Human herpesvirus 8: Kaposi’s ca
 Human papilllomavirus: cervical ca
 Epstein-Barr virus: nasopharyngeal ca,
Burkett’s lymphoma
 Mycoplasma pneumoniae: coronary artery
disease ?
suggested Reading
 Anthony
S. Fauci. Infectious diseases:
Considerations for the 21st Century.
Clinical Infectious Diseases. 2001:32:675685