1

Political Ecology of Infectious Disease

• Many changes that are relevant to understanding re-emergence of old and emergence of new infectious diseases are due to political and economic power at a variety of scales, ranging from:

– transnational– down to the household and – individual levels.

2

Political Ecology of Disease …

• Some or even much of this power is influenced by which groups control decisions over land use.

• This, in turn, influences the relationships of people and the environment.

• This is a basic principle of political ecology which has been used in understanding the consequences of human environment interactions.

3

Re-emerging Infectious Diseases

Antibiotic Resistant Bacteria

• The discovery of penicillin in 1928 and the introduction of other antibiotics e.g., such as streptomycin, in the 1940s raised hopes that cures could be found for all infectious diseases.

• Only one family of antibiotics (quinolones) have been developed since the 1960s.

4

Antibiotic Resistant Bacteria …

• Strains of Staphylococcus aureus developed immunity against penicillin in the 1960s. However, methicillin was still effective.

• Methicillin resistant Staphylococcus aureus were found by the 1980s. Vancomycin was used as a last resort.

• Now vancomycin resistant Staphylococcus aureus has been observed in hospitals around the world.

5

Antibiotic Resistant Bacteria …• Streptococcus A which caused scarlet fever more or less

vanished by the 1960s, but it re-emerged in a much more deadly form in the late 1980s.

• Streptoccous pyrogenes (dubbed the ‘flesh eating bug’) causes life threatening necrotizing fascitis unless stopped by amputation.

• Various strains of Pneumonoccus have resistance to whole classes of antibiotics.

• Hospitals are a major breeding ground for antibiotic resistant bacteria.

6

Re-emerging Infectious Diseases …

Some Examples

• Malaria• Yellow fever• Tuberculosis• Cholera• Bubonic plague

7

Malaria

• Malaria is a 3-factor disease: host, agent (plasmoduium) and vector (anopheles mosquito).

• The agent has a very complex life cycle.

• Part of its development takes place within the stomach of the mosquito, and part within the human host’s organs.

• Victims experience repeated attacks corresponding to the destruction of red blood cells.

8

Malaria …• Resistance to chloroquine was noticed in southern

Asia in the 1950s. • By the 1960s some strains of Plasmodium falciparum

had developed resistance to the 4 main anti-malarial drugs.

• A new drug, mefloquine, was adopted in the 1970s, but resistant strains of falciparum emerged by the 1980s.

• Strains of falciparum in Thailand have evolved an enzyme which expels all hostile chemicals, making it resistant to drugs that have not even been invented.

9

Tuberculosis

• Tuberculosis has been on the increase since the 1980s. It is one of the main cause of death worldwide.

• Many people carry the bacillus but do not develop symptoms unless their immune system is compromised.

• The resurgence in tuberculosis is associated with HIV infection.

• The problem is compounded by the emergence of drug resistant strains, partly due to HIV-infected drug users not completing antibiotic courses.

10

Cholera

• There were no new pandemics for most of the 20th century, but the 7th pandemic began in the 1960s (the El Tor strain). It spread to Latin America in the 1980s. Developed countries have so far escaped.

• An even more virulent strain (0139) has emerged in the Sea of Bengal. This may be the beginnings of 8th pandemic. There is no guarantee that developed countries will escape.

11

Re-emerging old infectious diseases …

• The re-emerging old infectious diseases have made relatively little impact upon the public imagination

• However, given the rapid development of drug-resistant strains, coupled with rapid air transportation, it may be only a matter of time before our ghosts from the past come back to haunt us.

12Desselberger, 2000

Emergence of New Infectious Diseases

13

Examples: Machupo

• Machupo (Bolivian Haemorrhagic Fever) originated in 1961 in the headwaters of the Amazon where the traditional cattle ranching/export economy was replaced by self-reliant peasant agriculture after a social revolution.

• Jungle was cleared to grow corn and vegetables, disrupting the habitat of Colomys callosis (a field mouse).

14

Machupo …

• The mouse population swelled given the availability of corn. They invaded the villages.

• A virus carried by the mice was passed by the mice in their urine.

• The virus in humans caused 50 people mortality.

• The disease was eventually contained by catching the mice.

15

Ebola

• Occurred almost simultaneously in two locations a few hundred miles apart in Zaire (Congo) and Sudan.

• Ebola is a horrific disease with 90 per cent mortality

• Transmission is by direct contact, but it is very contagious.

• The reservoir of the virus has never been discovered.

• Infected monkeys from the Phillipines almost caused an outbreak in Reston VA, near Washington in 1989.

16

Rift Valley Fever

• Originally confined to sheep and cattle in Africa, it jumped species and affected 200,000 people in Egypt in 1977.

• The virus is transmitted by a mosquito.

• The 1977 outbreak is believed to have been triggered by the construction of the Aswan dam which created favourable conditions for the mosquitoes to breed.

• There was a similar outbreak in Mauritania after the Senegal river was dammed.

17

Lyme Disease

• Unknown before 1962, but now the most common vector disease in the USA.

• Caused by a bacteria transmitted by bites from a tick that lives on deer.

• Lyme disease has increased due to former farm land reverting back to scrub which favours the growth of the deer population.

• Especially common in the suburbs where people come in contact with the deer population.

18

Examples – Other

• Dengue Haemorrhagic Fever. Originally confined to South East Asia, but now a growing threat in other areas including the southern USA due to the diffusion of the vectors (Aedes aegypti or Aedes albopictus).

• Latin American Haemorrhagic Fevers (Sabia, Guaranito, Junin). Similar causes to Junin – i.e. expansion of agriculture into new areas.

• The main risk to developed countries is the possibility of a new air-borne disease. Hence the concerns about SARS (2003) and Asian bird flu (2004), both of which originated in Asia.

19

Factors Leading to the Emergence of New Infectious Diseases

1. Cross-species transfer of pathogens

2. Spatial diffusion of microbes

3. Microbial mutation through recombination

4. The new description of a pathogen that had been present in humans for years, but which is “newly recognized''.

5. Changes in the human-environment relationship.

20

Cross-species transfer of pathogens

• Cross-species transfer of pathogens is the first reason for emergence, reflecting the de novo introduction of a pathogen into the human population.

• This is usually due to alterations in the stability of human–environment relations, usually by human encroachment of previously isolated environments that are habitats for zoonotic infectious diseases.

21

Cross-species transfer of pathogens …

• Frequently, this is the result of deforestation, public works projects in previously stable ecosystems, or other intended or unintended changes in human–environment relations

• Thus, human movement into these areas allows species jumps of zoonotic microbes into the human population.

22

The spatial diffusion of microbes

• The diffusion of microbes from isolated endemic areas to new foci of endemicity, with the concomitant identification of what is thought to be a new agent.

23

Microbial mutation through recombination

• The third explanation for the emergence of new diseases is a result of microbial mutation through recombination, either increasing the pathogenicity of microbes, or the transformation of microbes into pathogens.

• This frequently allows the development of resistance to the immune response or to effective antimicrobial treatment.

• The latter happens periodically with the genetic drift and shift of influenza viruses, resulting in epidemics and pandemics

24

Recognition of a previously unidentified pathogen

• Another cause for emergence of new disease is the new recognition or specification of a previously unidentified pathogen.

25

Changes in Human-Environment Relatioship

• The increased demand for food has resulted in new areas being brought under cultivation, disrupting existing ecosystems

• Monocultivation has reduced biodiversity, forcing viruses to seek new hosts

• Rapid urbanisation results in high population densities and insanitary conditions

• Global warming is extending the habitats of mosquitoes and other vectors

• Competition for resources contributes to wars which disrupt public health systems and trigger mass population movements.

26

Climate change and emerging infectious diseases

• The ranges of infectious diseases and vectors are changing in altitude, along with shifts in plant communities and the retreat of alpine glaciers.

• Additionally, extreme weather events create conditions conducive to ’clusters’ of insect-, rodent- and water-borne diseases.

• Accelerating climate change carries profound threats for public health and society.

27

Infectious Disease Emergence and Human Action

• Most of the factors are social and geographical

• Two key factors:

– human ecology

– behaviour

28

Emergence and Human Action

• There is great urgency in improving the surveillance for newly or recently emerging diseases, and resurgent diseases.

• The containment and control of emerging infectious diseases are of paramount importance.

29

Emergence and Human Action

• Many of these diseases are potentially preventable, through vaccination and adequate medical treatment, but because much of the mortality from infectious diseases occurs in developing countries, the cost of vaccination and treatment is high—prohibitively so—in many cases.

30

Main priorities in emerging and reemerging diseases research

• Supporting the application of recent discoveries and new biomedical technologies to the identification, management and control of emerging diseases

• Providing information for developing prevention and treatment strategies by expanding research on host susceptibility to emerging or reemerging pathogens

31

HIV/AIDS

• The major lesson to be learned from the HIV/AIDS pandemic is that the assumption that infectious diseases are a phenomenon of the past, largely restricted as major health threats to developing countries, and that “international health” consists of the study of problem of developing countries, are all erroneous.