“Moving targets” – humans and microbes in a globalising world

  

Tony McMichaelNational Centre for Epidemiology & Population Health

The Australian National University

Email: tony.mcmichael@anu.edu.au

Examples of Emerging and Re-Emerging Infectious Disease: past 10 years A Fauci,

NIAID/NIH, 2005

2

HIV

Dengue

H Papilloma v

Ebola

Hanta virus

West Nile virus

Tobacco

Malaria

Non-HIV tuberculosis Road accidents

3

5

6

Influenza

Polio

SARS

vCJD

Measles HBV + HCV

4

Log 10

RSV, Rota virus

7

Hospital infection

Suicide

Major and minor killers: global impact viewed on a ‘Richter’ (logarithmic) scale

Weiss & McMichael, 20041

Viruses

Infant/child ARI & diarrhoeal dis

10,000-fold difference in impact

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

                                                                         

              

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.

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.

Avian ’flu, H5N1

Mad Cow Disease (BSE) vCJD

Nipah viral encephalitis, Malaysia (1997-99)

Previous ’flu epidemics (1918-19, ’57, ’68)

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

Successive increases in SCALE

• 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

Factors in Emerging/Re-emerging Infectious Diseases

Clearing forests for agricultureViral haemorrhagic fevers in South America: peasant-farmers

Guanarito, Sabia, Kunjin, etc.

Eating infected animalsNew variant Creutzfeldt Jacob disease (from BSE)

Cultivation of infected animalsNipah viral encephalitis (pig farms in Malaysia)West Nile virus (goose “fois gras” farms in Ramala, Israel)

Collection and trade of wild gameHIV (bush meat: primates)Ebola (bush meat?)SARS (civet cat?)

Zoonotic Sources: Land-use, Livestock, Wild-life

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

Incidence of BSE in UK, 1987-99 (c.180K cases)

Human vCJD (end 2003) -- 125 cases: UK-117, France-6, Ireland-1, Italy-1

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.

Nipah Viral Encephalitis, in Malaysia

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)

Vietnam

Cambodia

Lao PDR

China

Key wildlife trade routes in SE Asia and China

Environmental Changes

• Land use, forest clearance

• Biodiversity losses, extinctions

• Dams, irrigation

• Climate change

Density of An. darlingi (malaria vector) in Peruvian Amazon

Village(deforested)

Farm(deforested)

Secondarygrowth

Forest

Patz et al, 2003

0

.3

.6

.9

1.2

1.5

Log-transformed A. darlingi abun

1 2 3 4

No. of survey sites = 2433

An. Darlingi abundance (log scale)

Forest fragmentation, hunting (wolves,

passenger pigeons)

Less diversity of vertebratepredators and viral hosts

High Lyme Disease risk

Expanding mousepopulations

Poor inter-species regulation

High tick densityand high tick infection

prevalence infected deer

Many competent reservoir species less dilution by incompetent reservoir species

Lyme Disease: Influences of Habitat Fragmentation & Biodiversity Loss

Adapted from: R. Ostfeld

Complex life-cycle of tick

Woodland suburban housing (NE USA)

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

NCEPH/CSIRO/BoM/UnivOtago, 2003

Dengue Fever: Estimated geographic region suitable for maintenance of Ae. aegypti, under alternative

climate scenarios for 2050

Risk region under mediumemissions scenario, 2050

Darwin

Katherine

Cairns

Mackay

Rockhampton

Townsville

Port Headland

Broome..

....

..Carnarvon.

Darwin

Katherine

Cairns

Mackay

Rockhampton

Townsville

Port Headland

Broome..

..

....

Brisbane.Current risk region for dengue

Darwin

Katherine

Cairns

Mackay

Rockhampton

Townsville

Port Headland

Broome..

..

..

..

Carnarvon. Risk region under high emissions scenario, 2050

Baseline 2000 2025 2050 2075 2100Source: Kris Ebi

MALARIA IN ZIMBABWE, UNDER CLIMATE CHANGE

Baseline 2000 2025 2050 2075 2100Source: Kris Ebi

Baseline 2000 2025 2050 2075 2100Source: Kris Ebi

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 . . . .

Summary

INFECTIOUS CAUSES OF CHRONIC DISEASE: Examples

DiseaseCervical cancerChronic hepatitis, liver cancerLyme disease (arthritis)Whipple’s diseaseBladder cancerStomach cancerPeptic ulcer disease

Atherosclerosis (CHD)Diabetes mellitus, type 1Multiple sclerosisInflammatory bowel disease

CauseHuman papilloma virusHepatitis B and C virusesBorrelia burgdorferiTropheryma whippeliiSchistosoma haematobiumHelicobacter pyloriHelicobacter pylori

Chlamydiae pneumoniaeEnteroviruses (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?

27 Dec 1997: Tropical Cyclone Sid

Air trajectories @ 100 m altitude Backwards trajectory analysis of JE