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“Moving targets” – humans and
microbes in a globalising world
Tony McMichael
National Centre for Epidemiology & Population Health
The Australian National University
Email: [email protected]
Examples of Emerging and Re-Emerging
Infectious Disease: past 10 years A Fauci,
NIAID/NIH, 2005
Major and minor killers: global impact viewed
on a ‘Richter’ (logarithmic) scale
7
Tobacco
Infant/child ARI & diarrhoeal dis
Malaria
Road accidents
Non-HIV tuberculosis
HIV
Viruses
HBV + HCV
6
Measles
RSV, Rota virus
Influenza
Dengue
5
H Papilloma v
Hospital infection
Suicide
4
10,000-fold
difference in
impact
West Nile virus
3
SARS
Ebola
Polio
Hanta virus
2
vCJD
1
Log
10
Weiss & McMichael, 2004
Outline of Talk
• Microbes, infectious diseases: recent trends
• Infectious diseases as result of major changes in
human ecology and environmental – historical
transitions; current conditions
• Examples of infectious disease risks
–
–
–
–
Travel, trade
Land use, agriculture
Intensive animal husbandry
Climate variability, climate change
• Needed: a more ecological perspective
Receding – then Resurging?
1950s-60s: Infectious diseases apparently
receding in developed countries
• Antibiotics and vaccines
• Pesticides to control mosquitoes
• Improved surveillance and control measures –
internationally coordinated
Early 1970s: Authorities proclaimed end of
infectious disease era. Premature!
• >30 new or newly-discovered human IDs over past 30 yrs
• We overlooked the ecological/evolutionary dimensions
Avian ’flu, H5N1
Mad Cow Disease (BSE)  vCJD
Nipah viral encephalitis, Malaysia (1997-99)
Choi Young-Soo/Associated Press Yonhap
South Korean health workers disinfecting a chicken farm north of Seoul last week. Though 140 million birds have died or been killed as a preventive measure in Asia, the risks of wide human
infection are not known.
Previous ’flu epidemics (1918-19, ’57, ’68)
South Korean health workers disinfecting a chicken farm in April, 2005.
Though several hundred million birds have died or been killed as a
preventive measure in Asia, the human epidemic risk remains unknown.
Human-Microbe Transitions
over the Millennia
Pre-historic: hunter-gatherers disperse into
distant new environments
1. Local agrarianism/herding: 5-10,000 yrs ago
2. Trans-continental: 1,000-3,000 yrs ago
3. Inter-continental: From c. 1500 AD
4. Today, global: Fourth historical transition
Factors in Emerging/Re-emerging
Infectious Diseases
• Microbial adaptation and change
• Human susceptibility to infection
ageing, HIV, IV drugs, transplantation, transfusion
• Population growth and density
• Urbanization, crowding – social and sexual relations
• Globalization of travel and trade
• Live animal markets
• Intensified livestock production
• Misuse of antibiotics (humans & domestic animals)
• Changes to ecosystems (deforestation, biodiversity loss)
• Global climate change
Zoonotic Sources: Land-use,
Livestock, Wild-life
Clearing forests for agriculture
Viral haemorrhagic fevers in South America: peasant-farmers
Guanarito, Sabia, Kunjin, etc.
Eating infected animals
New variant Creutzfeldt Jacob disease (from BSE)
Cultivation of infected animals
Nipah viral encephalitis (pig farms in Malaysia)
West Nile virus (goose “fois gras” farms in Ramala, Israel)
Collection and trade of wild game
HIV (bush meat: primates)
Ebola (bush meat?)
SARS (civet cat?)
Incidence of BSE in UK, 1987-99 (c.180K cases)
1988/9 bans: Sale of nervous tissue and offal for human consumption
Eating cattle >30 months old
Mammalian products in ruminant feed
BUT: no ban on feed for swine or poultry
Human vCJD (end 2003) -- 125 cases: UK-117, France-6, Ireland-1, Italy-1
Nipah Viral Encephalitis, in Malaysia
01/97
Farm worker hospitalized with viral encephalitis (VE).
10/97
First death (pig-farm worker) from VE.
02/98
3 farm workers develop VE.
11/98
Health Minister declares it ‘Japanese Encephalitis’  mosquito
control and vaccine program. But outbreak spreads.
1-2/99 Pig farmers begin ‘fire sales’ of pigs. Outbreak recedes a little.
02/99
Laboratories receive first samples of infected human
tissue. “New” virus? Mass pig culling begins. Villagers flee.
03/99
Virus isolated and identified with reagents used to characterize
Hendra virus (a recently-identified horse virus, from Queensland).
04/99
‘Nipah virus’ discovery announced. Culling continues.
05/99
WHO declares outbreak over (265 cases, 40% fatal).
02/00
Last death. Fruit bats (flying foxes) deemed the likely reservoir.
Travel and Trade: examples
Aedes albopictus mosquito eggs in
shipments of used tyres  dengue fever
Long-distance travel; wild animal trade
– HIV/AIDS
– West Nile Virus (New York City, 1999)
– SARS, 2003
SARS
Severe
Acute
Respiratory
Syndrome
A genetic model for the Coronavirus family.
(Photo: J Oxford, Retroscreen Virology Ltd)
Key wildlife trade routes in SE Asia and China
China
Lao PDR
Vietnam
Cambodia
Environmental Changes
•
•
•
•
Land use, forest clearance
Biodiversity losses, extinctions
Dams, irrigation
Climate change
Density of An. darlingi (malaria
vector) in Peruvian Amazon
Log-transformed A. darlingi abun
An. 1.5
Darlingi abundance
(log scale)
No. of survey
sites = 2433
1.2
.9
.6
.3
0
1
2
3
Secondary
(deforested) (deforested) growth
Village
Farm
4
Forest
Patz et al, 2003
Lyme Disease: Influences of Habitat
Fragmentation & Biodiversity Loss
High Lyme
Disease risk
Woodland suburban
housing (NE USA)
High tick density
and high tick infection
prevalence  infected deer
Complex life- Expanding mouse
populations
cycle of tick
Less diversity of vertebrate
predators and viral hosts
Forest fragmentation,
hunting (wolves,
passenger pigeons)
Many competent
reservoir species 
less dilution by
incompetent reservoir
species
Poor inter-species
regulation
Adapted from: R. Ostfeld
Climate Change and Infectious Disease
Some recent changes in ID patterns may reflect the
influence of climate change (debate continues)
– Tick-borne encephalitis (north spread in Sweden)
– Cholera in Bangladesh (strengthening relationship with El
Niño events)
– Malaria ascent in east African highlands
– Time-trends in incidence of (reported) food poisoning,
esp. Salmonellosis
Dengue Fever: Estimated geographic region
suitable for maintenance of Ae. aegypti, under
alternative climate scenarios for 2050
.
.
Darwin
Katherine
.
Darwin
.
.
Katherine
.
Broome
.
Port Headland
.
..
Townsville
Port Headland
.
Current risk region for
dengue
.
Risk region under medium
emissions scenario, 2050
.
Rockhampton
.
.
.
Darwin
Brisbane
Katherine
.
Broome
.
Port Headland
.
Carnarvon
NCEPH/CSIRO/BoM/UnivOtago, 2003
.
Rockhampton
Carnarvon
Mackay
.
Mackay
Cairns
Townsville
.
.
Cairns
Broome
.
.
Cairns
Townsville
.
Mackay
.
Rockhampton
Risk region under high
emissions scenario, 2050
MALARIA IN ZIMBABWE, UNDER CLIMATE CHANGE
Baseline 2000 2025 2050 2075 2100
Source: Kris Ebi
Baseline 2000 2025 2050 2075 2100
Source: Kris Ebi
Baseline 2000 2025 2050 2075 2100
Source: Kris Ebi
Summary
Humans, domestic animals and wildlife are inextricably
linked by epidemiology of infectious diseases (IDs).
IDs will continue to emerge, re-emerge and spread.
Human-induced environmental changes, inter-species
contacts, altered social conditions, demography and
medical technology affect microbes’ opportunities.
Also:
New research, technology and collaborative networks
will also elucidate role of infection in diverse, mostly
chronic, diseases of unknown cause . . . .
INFECTIOUS CAUSES OF
CHRONIC DISEASE: Examples
Disease
Cause
Cervical cancer
Chronic hepatitis, liver cancer
Lyme disease (arthritis)
Whipple’s disease
Bladder cancer
Stomach cancer
Peptic ulcer disease
Human papilloma virus
Hepatitis B and C viruses
Borrelia burgdorferi
Tropheryma whippelii
Schistosoma haematobium
Helicobacter pylori
Helicobacter pylori
Atherosclerosis (CHD)
Diabetes mellitus, type 1
Multiple sclerosis
Inflammatory bowel disease
Chlamydiae pneumoniae
Enteroviruses (esp. Coxsackie)
Epstein-Barr v, herpes vv?
Mycobacterium avium sub-spp.
Paratuberculosis, Yersinia
Conclusion I: Understanding what
promotes human-microbe contacts
(i) Intensified modification/exploitation of
natural environments and food
production.
(ii) Disturbance of natural ecosystems and
their various internal biotic controls.
(iii) Poverty, crowding, social disorder,
mobility and political instability.
Conclusion II:
Microbes as Co-Habitants
Microbes’ interest is in survival and
reproduction. They have no malign
intent; morally neutral!
Their evolution-based drive to survive is
as strong as ours (and draws on much
longer experience).
That’s all,
folks
Cyclone Sid: Precursor to 1998
Japanese Encephalitis incursion?
Air trajectories @ 100 m altitude
27 Dec 1997: Tropical Cyclone Sid
Backwards trajectory analysis of JE