Title: Emerging and Reemerging Infectious Diseases and Pathogens
1Emerging and Reemerging Infectious Diseases and
Pathogens
- Lecture Week 13
- Medical Microbiology SBM 2044
2FIGURE 1. Leading causes of death worldwide.
About 15 million (gt25) of 57 million annual
deaths worldwide are the direct result of
infectious disease.
3Emerging 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)
4- After great advances in medical research and
antimicrobial drug discovery, technology
development, improvement in sanitation.. - WHY are microbes still posing such a problem?
5Factors involved in the emergence of infectious
diseases
- Unprecedented worldwide population growth,
urbanization - Increased international travel
- Increased worldwide transport, migration, and
relocation of animals and food products - Changes in food processing, handling, and
agricultural practices - Changes in human behaviour, technology and
industry - Human encroachment on wilderness habitats that
are reservoirs for insects and animals that
harbour infectious agents
6Factors involved in the emergence of infectious
diseases
- Microbial evolution and the development of
resistance to antibiotics and other antimicrobial
drugs - Changes in ecology and climate
- Modern medicine (e.g. immunosuppression)
- Inadequacy of public infrastructure and
vaccination programs - Social unrest and civil wars
- Bioterrorism
- Virulence-enhancing mechanism of pathogens (the
mobile bacteriophages, plasmids, transposons)
7- 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
8FIGURE 2. Global examples of emerging and
re-emerging infectious diseases.
9Classification 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
10- Newly emerging infections
- Have not previously been recognised in man
11AIDS model
- AIDS have affected gt 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
post-colonial sub-Saharan Africa - urban poverty, a weakening of family structure
all promoted promiscuous sexual practices, and
increased travel.
12Dead-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
13Other 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
- Burkitts lymphoma Epstein-Barr virus
- Gastric ulcers and gastric cancer
14- Re-emerging and Resurging Infections
- Existed in the past but are now rapidly
increasing either in incidence or in geographical
or human host range
15Geographical 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
16FIGURE 3. Probable cases of severe acute
respiratory syndrome (SARS) with onset of illness
from 1 November 2002 to 31 July 2003.
17FIGURE 4 The severe acute respiratory syndrome
(SARS) pandemic and important findings.
18FIGURE 5 Schematic representation of the severe
acute respiratory syndrome coronavirus (SARS-CoV)
particle.
19Infectious 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
20Re-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
21Influenza 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
22FIGURE 6. Documented human infections with avian
influenza viruses, 19972004.
23Infectious 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 O157H7 - 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
24FIGURE 7 Generic model of the organization of a
rapid research response to an emerging infectious
disease.
25Reference
- 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/repor
ts/0601fauci/0601fauci.html