“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 HIV HBV + HCV Measles RSV, Rota virus Influenza Dengue 6 5 Tobacco Infant/child ARI & diarrhoeal dis Malaria Road accidents Non-HIV tuberculosis Viruses H Papilloma v 4 Hospital infection Suicide

10,000-fold difference in impact

West Nile virus SARS Ebola Polio Hanta virus 3 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 infection are not known.

Yonhap 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 10/97 02/98 11/98 1-2/99 02/99 03/99 04/99 05/99 02/00 Farm worker hospitalized with viral encephalitis (VE) .

First death (pig-farm worker) from VE.

3 farm workers develop VE. Health Minister declares it ‘Japanese Encephalitis’  control and vaccine program. But outbreak spreads.

mosquito Pig farmers begin ‘fire sales’ of pigs. Outbreak recedes a little.

Laboratories receive first samples of infected human tissue. “New” virus? Mass pig culling begins. Villagers flee. Virus isolated and identified with reagents used to characterize Hendra virus (a recently-identified horse virus, from Queensland).

‘Nipah virus’ discovery announced. Culling continues.

WHO declares outbreak over (265 cases, 40% fatal). 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 Cambodia Vietnam

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 abundance (log scale) 1.2

No. of survey sites = 2433

.9

.6

.3

0 1 2 3 Village

(deforested)

Farm

(deforested)

Secondary growth 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 cycle of tick

Expanding mouse populations

Less diversity

of vertebrate predators and viral hosts Many competent reservoir species  less dilution by incompetent reservoir species Poor inter-species regulation

Forest fragmentation, hunting (wolves, passenger pigeons)

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 Broome

.

.

Port Headland Darwin

.

.

Katherine

Current risk region for dengue .

.

Cairns Townsville

.

.

Mackay Rockhampton

.

Brisbane

.

.

Broome

.

Port Headland Carnarvon Darwin

.

.

Katherine

.

.

Cairns Townsville

Risk region under medium emissions scenario, 2050 .

.

Mackay Rockhampton

.

.

Broome Carnarvon

.

Port Headland Darwin

.

.

Katherine

.

.

Cairns Townsville

.

.

Mackay Rockhampton

Risk region under high emissions scenario, 2050

NCEPH/CSIRO/BoM/UnivOtago, 2003

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 Cervical cancer Chronic hepatitis, liver cancer Lyme disease (arthritis) Whipple’s disease Bladder cancer Stomach cancer Peptic ulcer disease Atherosclerosis (CHD) Diabetes mellitus, type 1 Multiple sclerosis Inflammatory bowel disease Cause Human papilloma virus Hepatitis B and C viruses

Borrelia burgdorferi Tropheryma whippelii Schistosoma haematobium Helicobacter pylori Helicobacter pylori 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 Backwards trajectory analysis of JE 27 Dec 1997: Tropical Cyclone Sid