A lecture in 4 parts, for source see Haggett, 2000, The Geographical Structure of Epidemics, Oxford: Clarendon Press (or numerous other publications by Haggett - see reading list too).

1. Epidemics as Diffusion Waves
2. Epidemics on Small Islands
3. Global Origins and Dispersals
4. Containing Epidemic Spread

• Globally kills 16.4 million people a year (heart disease kills 9.7 million).
• Diarrhoea kills 3 million children a year (1.8 billion episodes). Measles 2 million people a year
• The rhinovirus causes the largest number of infections in the USA a year (125 million) but with the lowest ‘kill ratio’.

Used to study epidemics as it is the simplest infectious disease as:

1: virologically: Virus identified in 1954 - no intermediate host/vector required, virus does not mutate.

2: epidemiologically: distinctive waves.

3: clinically: readily identified by spots in the mouth (99% of cases identified).

4: statistically: high rate of incidence leads to large number of cases.

5: geographically: disease is spread worldwide - but behaves differently in isolated communities compared to large cities.

6: mathematically - first studied in 1888 by D’Enko on rates in a St. Peterburg boarding school.

• Hammer Soper model developed in 1906 - contains susceptibles, infectives, recovered, births, infection rate, etc...
• Critical community size for measles to survive constantly is 250,000 to 300,000
• Effected by population density and vaccination levels.
• Reintroduction is via disease reservoirs, but the rate depends on geography too.

Iceland as key laboratory

• Perfect size and population distribution
• No circular road until 1945 - and island of islands, in the mid-Atlantic Ocean.
• birth and disease records since 1751 allow 200 years of study - best data set.
• Fine scale of data - monthly by 50 areas. And a great deal of demographic change.

• 93,000 cases 1840 to 1990, 99% of these in 19 distinct epidemic waves.
• The wave of 1904 was begun by Whaler ship crew and ignited in a church service.
• It involved an ‘index case’, quarantine an analysis of the epidemic.
• Different wave patterns depended on population size, travel and behaviour.

• Waves in Iceland changed from being local to regional to national - with air transport and the growth of Reykjavik.
• They peak in May (thaw) and June (haymaking) rather than winter (Europe)
• The modeling has not been hugely successful and has been largely of the past (my reading, not Haggett’s).

• 14 waves from 1875 to 1982 - from widely spaced to smaller and frequent.
• Reservoir cities and regions around the Pacific (of 250,000+) rose from 4 in 1850 to 12 in 1900 to 40 by 1950.
• The 1875 first ever outbreak is infamous - brought by the returning royal family having just become a British colony.

• From Fiji and other cases the rate is thought to be 1 in 5 of the population.
• 100,000 people were infected in Fiji - normal life breaks down. Deaths from other causes rise (dysentery/starvation).
• Rates of 25% recorded in Alaska in 1900 and of isolated American Indians 1952+
• Later in Fiji steamships reduced cases on board needed from 5/6 generations to 2.

• 8000 mummified Egyptian bodies are largely all we have before the historical record (e.g. around 1500BC a picture of a priest with a leg shriveled by polio).
• However, DNA studies can spot genes in West African’s that protect people from Malaria.

• Diseases that require threshold populations of 300,000 can only be 2000 years old (i.e. Measles).
• Domestication of animals may be key also as many diseases cross-over.
• The topics have a greater diversity of viruses just as they have of all species.
• Old and new world diseases, like plants and animals were distinct (Andes 1585).

• Improved transport is critical - it collapses geographical barriers.
• Demographic growth also vital
• land use change may also be key
• global warming may be a fourth reason why we are seeing more diseases now.

Geography of Demography

• World population growth from 2.5 billion in 1950 to 5 billion in 1988 is a rate unprecedented - many more susceptible.
• Relocation of growth is towards the tropics - highest microbiological diversity.
• The growth is increasingly concentrated in cities (25 have over 11 million people).

• Agricultural expansion and abandonment both linked to new diseases + dam building helps spread some diseases.
• Global warming increases the area many diseases can reach (i.e. malaria) - but could also reduce winter indoor crowding and greater susceptibility.
• Shanty town / refugee camp growth provide long and short term areas of very high susceptibility to disease outbreak.

• Within your grandparents lifetime travel has changed out of all recognition.
• 20% of travelers get diarrhoea; 0.001% polio - malaria has occurred in Geneva.
• Doubling aircraft size quadruples infection risk amongst passengers.
• No part of the globes population is more than a few hours travel time away.

• isolate to safe areas
• quarantine areas of outbreak
• create cordon sanitaire (i.e. foot & mouth)

• immunization

Local Elimination

• Vaccinate so that fewer susceptibles than basic population needed to sustain (50% makes it 1 million, 90% makes it 25m.).
• Defensive Isolation - quarantino = 40 days. Offensive - culling foxes for rabies.
• Ring control strategy - Tinline’s (PhD) suggested vaccinate from 20km inwards for cattle in event of foot and mouth.

 Global eradication

• Smallpox last case outside labs - October 1977 - only global WHO success.
• Mass vaccination then selective vaccination- last case in Somalia.
• However smallpox was severe enough to ‘bother’, had no animal reservoir, was easily identified, spread by face to face contact, no prolonged carriers, only one serotype and a stable vaccine available.

• Measles - vaccine only 80% effective.
• Polio - only 15% reported and too little money in countries where it remains and short-sighted policies from rich countries - since 1977 the United States saved its total contribution to eradicating smallpox every 26 days. It will not pay for polio.

• Spatial barriers are now less effective.
• rapid reporting is now critical (weekly).
• Growing disease lists make reporting hard. Legal problems with vaccination, identification and quarantine growing.
• Models grow in use to spot aberration.
• Socioeconomic factors will also come to the fore - WHO ICD10 cause Z 59.5 now biggest global killer: "extreme poverty".