Biology • Year 12 • Module 8 • Lesson 6
Causes of Non-infectious Disease — Overview
Apply the four-category framework and risk-factor reasoning to Australian mortality data, cause-and-effect chains, and a real case study involving disease classification.
1. Interpret Australian mortality data — AIHW 2022
The bar chart below shows the five leading causes of death in Australia in 2022, expressed as a percentage of all deaths. Data are adapted from the Australian Institute of Health and Welfare (AIHW) Burden of Disease Study 2022. 8 marks
Adapted from AIHW (2022) Burden of Disease Study. COPD = Chronic obstructive pulmonary disease.
1.1 Using the lesson’s four-category framework, classify each of the five diseases shown in the chart into its primary non-infectious disease category (genetic, environmental, nutritional, or cancer). Justify each classification with a one-sentence mechanism. 5 marks
1.2 What does the fact that all five leading causes of death are non-infectious diseases tell you about the success of Australia’s public health measures against infectious disease? Use the term ‘epidemiological transition’ in your answer. 3 marks
2. Trace the cause-and-effect chain
The chain below starts with a known risk factor and ends at the disease. Fill in each missing effect box using precise biological language. 5 marks
Disease pathway: Iron-deficiency anaemia in a 16-year-old female distance runner.
Chronic low dietary iron intake (below 18 mg/day recommended for adolescent females)
Overall outcome (so…): Iron-deficiency anaemia is classified as a disease because .
3. Compare and contrast
Complete the table by filling in the empty cells. Draw on information from all four lesson cards. 6 marks (1 per row, or as indicated)
| Feature | Infectious disease | Non-infectious disease |
|---|---|---|
| Causative agent | Pathogen (bacterium, virus, fungus, or parasite) | |
| Transmissible between individuals? | No | |
| Typical timeline to clinical presentation | Often acute — rapid onset | |
| Primary prevention strategy | Lifestyle modification, genetic screening, avoiding harmful exposures | |
| Australian top-five cause of death? | Yes — coronary heart disease, dementia, cerebrovascular disease, lung cancer, COPD | |
| Named Australian example | Tuberculosis (historically a leading killer in 1900) |
4. Apply to a new scenario — mesothelioma in former asbestos workers
Between 1945 and 1980, the town of Wittenoom in Western Australia was the site of Australia’s largest asbestos mine. Workers and their families were exposed to high concentrations of blue asbestos (crocidolite) fibres. By the 1990s, epidemiologists reported that former Wittenoom workers had a mesothelioma rate approximately 8.5 times the national average. Mesothelioma is a cancer of the pleural lining of the lungs, typically appearing 20–40 years after asbestos exposure. 8 marks
4.1 Classify mesothelioma using the lesson’s four-category framework. Is it infectious or non-infectious? State the primary non-infectious category and explain the mechanism by which asbestos causes this cancer at the cellular level. 3 marks
4.2 Asbestos exposure is identified as a risk factor rather than a direct guaranteed cause of mesothelioma. Explain what this means using population-level data: not all workers exposed at Wittenoom developed mesothelioma, yet the rate was 8.5 times the national average. 3 marks
4.3 The 20–40 year latency period between exposure and disease onset is a defining feature of many non-infectious diseases. Explain one reason why this long latency makes non-infectious diseases harder to control than acute infectious diseases. 2 marks
Q1.1 — Classification of AIHW top-five diseases
Coronary heart disease: Multifactorial — classified primarily as environmental/nutritional because the key modifiable triggers are dietary (saturated fat, refined carbohydrate) and lifestyle (smoking, physical inactivity) factors that cause atherosclerosis of coronary arteries, with genetic predisposition as a contributing (non-modifiable) risk factor.
Dementia (including Alzheimer’s): Multifactorial, primarily genetic + environmental. The progressive loss of neurons results from a combination of genetic variants (e.g. APOE-ε4 allele significantly raises risk) and environmental/lifestyle factors (physical inactivity, cardiovascular risk factors, social isolation). Accept: genetic disease with environmental contributors.
Cerebrovascular disease (stroke): Multifactorial, primarily environmental/nutritional. Risk factors include hypertension (dietary salt, obesity), smoking, physical inactivity, and genetic predisposition. Ischaemic or haemorrhagic stroke results from disrupted blood supply to brain tissue.
Lung cancer: Cancer with primary environmental cause. Tobacco smoke carcinogens (including polycyclic aromatic hydrocarbons and nitrosamines) cause DNA mutations in bronchial epithelial cells, disrupting tumour suppressor genes (e.g. TP53) and promoting uncontrolled cell division.
COPD: Environmental disease. Chronic exposure to cigarette smoke and air pollutants causes progressive destruction of alveolar walls (emphysema) and airway inflammation (chronic bronchitis), with irreversible loss of lung function. Genetic predisposition (α-1 antitrypsin deficiency) contributes in a subset of cases.
Marking: 1 mark per disease for a correct primary category + a mechanistic justification (not just naming the category). Maximum 5 marks.
Q1.2 — Epidemiological transition interpretation (3 marks)
The fact that all five leading causes of death are non-infectious diseases reflects the epidemiological transition: the historical shift in population-level mortality from infectious disease to non-infectious disease [1]. This transition occurred in Australia because public health advances — widespread vaccination, use of antibiotics from the 1940s, improved sanitation and clean water, and better nutrition — dramatically reduced premature death from infectious diseases like tuberculosis, pneumonia, and childhood diarrhoeal diseases [1]. As people now survive into older age (average life expectancy ~83 years), non-infectious diseases that take decades to develop have become the dominant cause of death. This represents a success for public health, not evidence that Australians are becoming less healthy overall [1].
Q2 — Cause-and-effect chain (iron-deficiency anaemia)
Effect 1: Insufficient iron reduces haemoglobin synthesis in red blood cells (iron is a cofactor in haem production). Effect 2: Reduced haemoglobin concentration lowers the oxygen-carrying capacity of the blood. Effect 3: Tissues receive less oxygen per unit volume of blood (reduced O&sub2; delivery). Effect 4: Fatigue, breathlessness during exercise, impaired athletic performance, and possible cognitive impairment. Overall outcome: Iron-deficiency anaemia is classified as a nutritional disease because it is caused by deficiency of an essential dietary nutrient (iron) that disrupts normal physiological processes (haemoglobin synthesis and oxygen transport).
Q3 — Compare and contrast table
Non-infectious causative agent: Genetic mutation, environmental exposure, nutritional deficiency/excess, or disruption of cell cycle regulation (cancer) — no pathogen involved.
Infectious transmissible? Yes — can spread between individuals via direct contact, airborne droplets, vectors, or contaminated water/food.
Non-infectious typical timeline: Often chronic — develops over months to decades; symptoms may appear late in the disease course.
Infectious primary prevention: Vaccines, antimicrobials (antibiotics/antivirals), hygiene and sanitation, vector control.
Infectious Australian top-five cause? No — infectious diseases do not appear in the top five causes of death in contemporary Australia.
Non-infectious named Australian example: Accept any from the lesson — coronary heart disease, mesothelioma (Wittenoom), melanoma, cystic fibrosis, Type 2 diabetes, bowel cancer, etc.
Q4.1 — Classification of mesothelioma (3 marks)
Mesothelioma is non-infectious — it cannot be transmitted from patient to patient via a pathogen [1]. It is classified as cancer (primary category) with an environmental cause (primary trigger) [1]. Mechanism: inhaled crocidolite asbestos fibres lodge in the pleural lining and are not effectively cleared; the fibres cause chronic inflammation and directly damage the DNA of mesothelial cells over years to decades. Accumulated mutations in tumour suppressor genes (e.g. BAP1, CDKN2A) disrupt cell cycle checkpoints, leading to uncontrolled proliferation of mesothelial cells (mesothelioma) [1].
Q4.2 — Risk factor vs guaranteed cause (3 marks)
A risk factor is a population-level statistical association, not an individual guarantee [1]. Even though the mesothelioma rate at Wittenoom was 8.5 times the national average, not every worker developed the disease — this shows that asbestos exposure alone is not sufficient or necessary to guarantee mesothelioma in every exposed individual [1]. The elevated rate reflects that exposure dramatically increased the probability of disease across the exposed group; individual outcomes also depend on the dose of exposure (duration and concentration), genetic susceptibility to DNA damage, the body’s ability to clear fibres, and random variation in which cells sustain critical mutations. This is a defining feature of a risk factor: it predicts population-level probability without determining individual destiny [1].
Q4.3 — Why long latency makes NID harder to control (2 marks)
Long latency means the causal exposure and the clinical disease are widely separated in time, making the link between cause and disease difficult to establish and easy to overlook [1]. For example, a worker exposed at Wittenoom in 1955 who develops mesothelioma in 1985 may no longer associate the disease with the past exposure. This makes it harder to identify causes early, target prevention measures, and alert at-risk individuals in time to intervene before disease onset. By contrast, acute infectious diseases show symptoms within days of exposure, making the causal chain obvious and public health responses rapid [1].