Lesson 9: Diseases
9.1 - Epidemics
• Affect human populations most directly. Impact only on people, not on structures
• Most similar to droughts of any natural hazard.
• Relevant Key Terms:
o Outbreak: simultaneous, related occurrence of several cases
o Epidemic: uncontrolled outbreak of communicable (infectious or
o Pandemic: international or wide-travelling simultaneous epidemics of the
o Epidemiology: study of distribution and determinants of health-related
events in human population
o The Agent: the disaster
o The Environment: that which it affects
o The Host: affected people
• Communicable (contagious) diseases are the leading cause of mortality in
developing countries. Mostly due to socio-economic conditions, limited
prevention, and water contamination.
• Spread of disease will occur:
o if the population is not immune and includes carriers
o if susceptibility to disease increases through conditions such as
• Transmission rates increase because of:
o Water contamination
o Lack of routine prevention programs
o Overcrowding in refugee camps leading to increased contact with carriers
9.2 - Case Study: Bubonic Plague (Black Death)
• Disease spread by rodents – fleas to rats to humans. Swelling of lymph nodes,
infection, pneumonia leading to high fever, delirium, vomiting, bleeding and finally
• First pandemic – Justinian’s Plague in Asia, Africa and Europe – 100 000 victims.
• Second pandemic – Black Death – 50 000 000 deaths. Half in Asia and Africa,
other half in Europe.
• Third pandemic – Hong Kong – carried by rats aboard steamships. Spread
worldwide however preventative measures limited the deaths and outbreak.
• No noticeable groups had greater vulnerability. Gathering in groups spread more
easily. E.g. Religious gatherings.
• Use of historic documents to understand local populations and impact of
diseases. 9.3 – Cholera
• A water-borne disease that comes from sewage and contaminated water supply
• ‘Mapping’ used to find source of disease. Geographic information systems used
for locating the source and tracking spread of epidemics.
9.4 – Aids/HIV
• Transferred through exchange of infected body fluids including blood and semen
• Originally believed vulnerability was limited to homosexual activity, IV drug use
• Today, vulnerability linked to poverty. 95% of cases in poorer countries. No cure –
drugs to extend life – chronic disease now. Claimed 30 000 000 lives in two
decades. 40 000 000 infected estimated.
• Current Trend – Increasing at a decreasing rate
• Region Trend – Highest in Africa (specifically southern) with Asia next highest
• Age/Domestic Trend – Higher in Urban Areas. Higher in Women.
• Treatment levels are increasing in Africa.
9.5 – Bird Flu (Avian Influenza)
• Became evident in 1997 due to large poultry death
• Focus on the virus strain H5N1 because of its;
o Ability to transfer from birds to humans
o High mortality in humans
o Potential for a severe pandemic
• Caused by infection from avian influenza viruses – Occur naturally among birds.
Extremely contagious among birds but not human-to-human. Essentially eating
infected poultry, contact with fecal matter of poultry or other liquid secretions can
get you sick.
• Mortality rate is 70% in humans.
• Occur on average once every 10 to 50 years – typically spreading globally within
a year and highly contagious.
• Come with little warning, peak rapidly and then subside.
• Spread usually in waves with 2 and 3 waves stronger than the first.
• 1918-1919 – killed 40 million people. Spread by soldiers travelling through
Europe to N.A.
• Unique characteristics – mainly targeted the young adult age group.
• Ability to spread throughout the atmosphere.
Asian and Hong Kong Flu • Vulnerability greater in infants and elderly.
• Not as deadly due to the preventative measures taken to prevent outbreak.
Prediction and Warnings
• Disease is unpredictable in its severity, mortality, and pattern of spread
• Rapid exponential surge that overcomes a population's capacity to cope
• Disease occurs in waves with increasing severity and different targets
• Virological surveillance is critical in reducing the level of impact
• Many pandemics originate in Asia with close contact between humans, ducks
• While quarantine and restricted travel has little