Topic 9.2 Notes – Technological Advances and Limitations After 1900: Disease

How Disease Patterns Changed After 1900

Disease did not disappear once modern medicine improved. What changed was the pattern of disease. Many people died less often from infections, lived longer, and then faced chronic illnesses that become more common with age.

A few terms have to stay clear in your head:

• Infectious disease means a disease caused by a transmissible pathogen.
• Chronic disease means a long-lasting disease, usually not spread person to person.
• Endemic means constantly present in a region.
• Epidemic means an outbreak above normal levels.
• Pandemic means an epidemic spread across many countries or continents.
• Incidence means new cases. Mortality means deaths.

The environment here means both nature and human-built conditions:

• Climate, standing water, and insect vectors like mosquitoes shape exposure.
• Crowding, weak ventilation, bad housing, and poor nutrition make people more vulnerable.
• Clean water, sewage systems, hospitals, transportation, and medicine access lower death rates.

Medical advances changed survival:

• Vaccines prevented many infections.
• Antibiotics treated bacterial disease.
• Sanitation and water treatment cut waterborne illness.
• Diagnostic testing and surveillance helped detect outbreaks faster.
• Insect control, oral rehydration therapy, and antiviral drugs saved lives too.

The catch is the main AP point. Technology existed, but poverty, war, weak states, unequal access, and pathogen resistance limited what it could do.

This broad shift is the epidemiological transition. Many societies moved from high infectious-disease mortality to longer life expectancy and more chronic disease, but richer regions usually made that transition earlier than poorer ones.

Diseases Associated with Poverty

These diseases lasted because prevention and treatment were unevenly available, not because people did not know what caused them.

Malaria

Malaria is caused by a parasite spread by infected Anopheles mosquitoes. It hit tropical sub-Saharan Africa especially hard, and also parts of South Asia.

Global malaria mortality map

• Warm climates and standing water help mosquitoes breed.
• The map makes the pattern clear. The highest mortality is concentrated in tropical Africa, with smaller hotspots in South and Southeast Asia.
• Human choices matter too. Drainage, screened housing, bed nets, and mosquito control can reduce cases.
• Prevention and treatment included insecticide-treated nets, preventive drugs, antimalarial medicines, and later vaccines.
• It persisted because of cost, weak administration, and resistance in both parasites and mosquitoes.

Tuberculosis

Tuberculosis is a bacterial disease, usually in the lungs, spread through the air.

• It thrives in crowded, poorly ventilated places.
• Malnutrition and weak immune systems make infection worse.
• Antibiotics can cure TB, but treatment takes months and uses multiple drugs.
• Incomplete treatment helped create drug-resistant TB.
• It remained common in parts of Africa and Asia and was often linked with HIV.

Cholera

Cholera is a bacterial disease spread through contaminated water or food.

• It causes severe diarrhea and dehydration and can kill fast.
• It appears where sewage and drinking water mix, especially in refugee camps, disasters, or state breakdown.
• Treatment includes oral rehydration solution, IV fluids, some antibiotics, and vaccines.
• Cholera is the clearest proof that infrastructure matters.

Emergent Epidemic Diseases

Older diseases persisted, and new epidemic threats spread under modern conditions like war, travel, urbanization, and shifting social behavior.

The 1918 influenza pandemic

The 1918 flu spread globally at the end of World War I.

• Troop movement, ships, camps, crowded cities, and wartime malnutrition sped transmission.
• It was called Spanish flu because Spain reported openly during wartime censorship.
• It killed tens of millions, often estimated around 50 million.
• There was no vaccine, no antivirals, and no antibiotics for secondary infections.
• Responses included quarantine, masks, school closures, and bans on gatherings.

Its significance is huge. Global war and transportation could turn outbreak into pandemic very quickly.

HIV/AIDS

HIV attacks the immune system. Untreated HIV can develop into AIDS.

• It spreads through sexual contact, blood, shared needles, and mother-to-child transmission.
• Recognized in the early 1980s, it devastated sub-Saharan Africa especially.
• It lowered life expectancy, created orphan crises, reduced labor forces, and overwhelmed hospitals.
• Stigma and discrimination, especially against gay men and other groups, made the crisis worse.
• Responses included blood screening, testing, safer-sex education, sterile needles, and antiretroviral therapy.
• AIDS activism pushed governments and drug companies to speed research and expand access.

Ebola

Ebola spread by direct contact with bodily fluids, not through the air like influenza.

• First identified in 1976.
• The biggest outbreak came in 2014-2016 in Guinea, Liberia, and Sierra Leone.
• It exposed weak health systems, poor lab capacity, lack of PPE, and weak contact tracing.
• Control depended on isolation, safe burials, protective gear, contact tracing, and community trust.
• It helped speed vaccine and diagnostic development.

Diseases Associated with Increased Longevity

When more people survive childhood and infection, more people live long enough to develop age-related disease.

Heart disease

Heart disease became a leading cause of death in many wealthy societies, and later in many middle-income ones.

• Risk rises with age.
• Smoking, high blood pressure, diet, obesity, diabetes, and inactivity also matter.
• Survival improved with blood-pressure drugs, cholesterol drugs, surgery, and emergency care.

Alzheimer’s disease

Alzheimer’s disease causes progressive memory and reasoning loss and is strongly tied to old age.

• Rising cases reflect longer life expectancy more than simple medical failure.
• It created major needs for elder care, long-term caregiving, and family support.
• There is no cure comparable to antibiotics for bacterial disease.

Why This Topic Matters

This topic ties continuity and change together. Malaria, TB, and cholera persisted because inequality and weak infrastructure persisted. New epidemics spread faster in an interconnected world. Longer life expectancy then increased chronic and age-related disease.