Transcript Emerging and Reemerging Infectious Diseases and Pathogens

Emerging and Reemerging
Infectious Diseases and
Pathogens
Lecture Week 13
Medical Microbiology SBM 2044
FIGURE 1. Leading causes of death worldwide.
About 15 million (>25%) of 57 million
annual deaths worldwide are the direct
result of infectious disease.
Emerging infectious diseases
• CDC: new, reemerging or drug-resistant
infections whose incidence in humans has
increased within the past three decades or
whose incidence threatens to increase in
the near future
• Infections that have newly appeared in a
population or have existed previously but
are rapidly increasing in incidence or
geographic range (Morse 1995)
After great advances in medical research
and antimicrobial drug discovery,
technology development, improvement in
sanitation..
WHY are microbes still posing such a
problem?
Factors involved in the emergence
of infectious diseases
1. Unprecedented worldwide population growth,
urbanization
2. Increased international travel
3. Increased worldwide transport, migration, and
relocation of animals and food products
4. Changes in food processing, handling, and
agricultural practices
5. Changes in human behaviour, technology and
industry
6. Human encroachment on wilderness habitats
that are reservoirs for insects and animals that
harbour infectious agents
Factors involved in the emergence
of infectious diseases
7. Microbial evolution and the development of
resistance to antibiotics and other antimicrobial
drugs
8. Changes in ecology and climate
9. Modern medicine (e.g. immunosuppression)
10. Inadequacy of public infrastructure and
vaccination programs
11. Social unrest and civil wars
12. Bioterrorism
13. Virulence-enhancing mechanism of pathogens
(the mobile bacteriophages, plasmids,
transposons)
Emergence of infectious disease are the
results from dynamic interactions
between rapidly evolving infectious
agents and changes in the environment
and in host behaviour that provide such
agents with favourable new ecological
niches
FIGURE 2. Global examples of emerging and reemerging infectious diseases.
Classification of Emerging
Infectious Diseases
• Newly emerging
– Have not previously been recognised in man
• Reemerging/resurging
– Existed in the past but are now rapidly
increasing either in incidence or in
geographical or human host range
• Deliberately emerging
– Microbes are those that have been developed
by man, usually for nefarious use
Newly emerging infections
Have not previously been recognised in man
AIDS model
• AIDS have affected > 60 million people
worldwide
• jumping to humans species, may be a
consequence of the consumption of ‘bush meat’
from non-human primates
• this allow HIV-1 and HIV-2 to evolve in host
• emergence is amplified by disruptions in the
economic and social infrastructure in postcolonial sub-Saharan Africa
• urban poverty, a weakening of family structure
all promoted promiscuous sexual practices, and
increased travel.
Dead-end transmission of zoonotic and
vector-borne diseases
• Arenavirus haemorrhagic fevers (inc Lassa
fever) and hantavirus pulmonary syndrome
(HPS)
– viruses in these groups have co-evolved with specific
rodent species
– increased human-rodent contact as a result of
modern environmental factors: farming, keeping
domestic pets, hunting and camping, deforestation
• Malaysian Nipah virus epidemic 1998-1999
– pigs crammed together in pens located in or near
orchards, attracted fruit bats which are the natural
hosts of the Nipah and Hendra viruses
– virus aerosolisation caused infection of pigs
– Overcrowding results in viral transmission to pig
handlers
Other newly emerging agents
• Environmentally persistent organisms
– Legionnaires caused by Legionella pneumophila due
to the use of air-con
– Campylobacter jejuni, Shiga-toxin-producing E. coli
infect agricultural animals
• enter through food, milk, water or direct contact
• Microbial agents and chronic diseases
– Chronic liver damage, hepatocellular carcinoma Hep B and C
– Cervical cancer – papillomaviruses
– Burkitt’s lymphoma – Epstein-Barr virus
– Gastric ulcers and gastric cancer –
Re-emerging and Resurging
Infections
Existed in the past but are now rapidly
increasing either in incidence or in
geographical or human host range
Geographical spread of infections
• Depend on the rate and degree to which they
spread across geographical areas
– the movement of human hosts/vectors/ reservoirs of
infections
• 1933 – commercial air travel
• 1981 – pandemic spread of acute haemorrhagic
conjunctivitis
• Epidemics of meningococcal meningitis during
the Hajj
• Epidemic SARS (a newly emerging disease)
from China to elsewhere worldwide
FIGURE 3. Probable cases of severe acute respiratory syndrome
(SARS) with onset of illness from 1 November 2002 to 31 July
2003.
FIGURE 4 | The
severe acute
respiratory
syndrome
(SARS)
pandemic and
important
findings.
FIGURE 5 | Schematic representation of the severe acute
respiratory syndrome coronavirus (SARS-CoV) particle.
Infectious agents
• Malaria
– Plasmodium falciparum was thought to be eradicated
because of the effective use of DDT insecticide
– But mosquito gain resistance
• Tuberculosis
– Isoniazid was initially effective to cure TB
– By 1980s, the era of HIV/AIDS, increased immune
deficiencies of people, increases the risk of latent M.
tuberculosis
– Also the fact that TB is a disease of poverty –
crowding, inadequate hygiene
• Staphylococcus aureus
– Drug-resistant organism
– Sulpha drugs 1940s  penicillin 1950s  methicillin
1980s  vancomycin 2002
Re-emerging vector-borne
diseases
• Flavivirus which caused dengue
– vector Aedes aegypti mosquitoes
– 2001-2002 epidemic in Hawaii
– dengue has recently been transmitted by
Aedes albopictus, which spreads into areas
where A. aegypti are not found and persisting
for longer seasonal periods
Influenza A
• Was known as endemic gastrointestinal
viruses of wild waterfowl, now has jump
species into domestic fowl, farm animals
and humans
• Antigenic changes in haemagglutinin and
neurominidase glycoproteins – ‘shifts’
(major antigenic changes in HA or NA)
• Deadly pandemics has occurred in 1888,
1918, 1957 and 1968
FIGURE 6. Documented human infections with avian influenza
viruses, 1997–2004.
Infectious diseases on the rise
• Global spread of AIDS
• Resurgence of tuberculosis
• Appearance of new enemies (hantavirus,
pulmonary syndrome, hepatitis C and E, Ebola
virus, Lyme disease, cryptosporidiosis and E.
coli O157:H7
• Bird flu which attacks the Southeast Asia
• Prion disease of Creutzfeldt-Jakob disease
• Antibiotic resistance Staphylococcus bacteria
• Several major multistate foodborne outbreaks
• A new strain of drug resistance tuberculosis
FIGURE 7 | Generic model of the organization of a rapid research
response to an emerging infectious disease.
Reference
• Morens DM, Folkers GK and Fauci AS (2004)
The challenge of emerging and re-emerging
infectious diseases. Nature 430: 242-249.
• Prescott. Chapter
• Brooks Chapter 29 pages 390-391 only.
• Emerging and Re-emerging Infectious Diseases:
the Perpetual Challenge
http://www.milbank.org/reports/0601fauci/0601fa
uci.html