Causes of Non-infectious Disease — Genetic, Environmental, Nutritional, Cancer

Activity 1 — Classify Each Disease

1. Cystic fibrosis: Non-infectious. Genetic disease — a mutation in both copies of the CFTR gene produces a dysfunctional chloride ion channel protein; the channel cannot transport Cl⁻ normally, leading to thick dehydrated mucus in airways and the digestive system. The disease is inherited in an autosomal recessive pattern — it requires mutations in both alleles.

2. Mesothelioma: Non-infectious. Both environmental and cancer — the primary trigger is environmental (inhaled asbestos fibres lodge in the pleural lining of the lung, causing chronic inflammation and DNA damage to mesothelial cells over decades); the outcome is uncontrolled cell division (cancer). It is best classified as cancer with a primary environmental cause. It is non-infectious — you cannot 'catch' mesothelioma from a patient, even though the trigger (asbestos) was an environmental exposure.

3. Scurvy: Non-infectious. Nutritional disease — caused by insufficient dietary vitamin C (ascorbic acid). Vitamin C is a required cofactor for prolyl hydroxylase, the enzyme needed to produce stable collagen. Without adequate vitamin C, collagen fibres are structurally defective → blood vessel walls weaken → bleeding gums, petechiae, poor wound healing. This is a direct nutritional deficiency disease with a clear molecular mechanism.

4. Type 2 diabetes: Non-infectious. Primarily nutritional but multifactorial — excess dietary refined sugar and saturated fat, combined with physical inactivity, leads to obesity and insulin resistance in target cells. However, genetic predisposition (some ethnic groups — Aboriginal and Torres Strait Islander Australians, South Asian populations — have 3–4× higher baseline risk due to genetic variants in insulin signalling pathways) and environmental factors (sedentary work, food access) are also significant. The 'primary' category is nutritional because dietary excess is the most modifiable trigger, but this disease sits at the intersection of all four categories.

5. Cervical cancer: Non-infectious (the cancer itself). Category: cancer. HPV (human papillomavirus) is an infectious organism, but cervical cancer is not. The HPV virus is a risk factor — a trigger that causes mutations in the CDKN2A gene (encoding p16, a tumour suppressor) and disrupts cell cycle control in cervical epithelial cells. The resulting cancer cannot be transmitted from person to person; only the HPV virus is transmissible. This is a key example of an infectious trigger for a non-infectious disease.

Activity 2 — Risk Factors and Multifactorial Disease

1. Same household, different outcomes: Risk factors are probabilistic — they increase the likelihood of disease but do not determine outcome. Even with identical household environments (same diet, same physical environment, similar activity levels), the two siblings have different genomes. Individual genetic variation in lipid metabolism (e.g. APOE allele variants), blood pressure regulation, inflammatory response, and cholesterol processing means different baseline cardiovascular risk. Additionally, subtle differences in behaviour (stress levels, exact dietary composition, sleep quality, alcohol intake), epigenetic variation, and random biological variation (e.g. spontaneous mutations in arterial wall cells) all contribute. This illustrates the core principle of multifactorial disease: identical environmental/nutritional exposures do not produce identical outcomes because genetic and individual biological variation modifies risk. A risk factor is a population-level statistical predictor, not an individual determinant.

2. Epidemiological transition: Coronary heart disease is now Australia's leading cause of death for several interconnected reasons. First, the epidemiological transition: effective vaccination programs (e.g. BCG for tuberculosis, childhood immunisation schedules), the development of antibiotics in the 1940s, improved sanitation (clean water, sewage systems), and better nutrition dramatically reduced mortality from infectious diseases throughout the 20th century. People who previously would have died from pneumonia, tuberculosis, or childhood infections at younger ages now survive into their 60s, 70s, and 80s. Second, non-infectious diseases like coronary heart disease take decades to develop — atherosclerosis typically begins in young adulthood and manifests clinically in middle to old age. As the Australian population has aged (median age has risen from ~25 in 1900 to ~38 today), more people live long enough to develop these conditions. Third, lifestyle factors associated with industrialised prosperity — sedentary occupations, energy-dense processed food, smoking — became widespread in the 20th century, increasing population-level NID risk. This demonstrates that patterns of disease are shaped by the interaction of social progress, medical technology, environmental change, and demographic shifts — not simply by biology alone.

Multiple Choice

1. C — The defining distinction is transmissibility via pathogen. Infectious diseases are caused by pathogens that spread; non-infectious are not. Option A is wrong — many non-infectious diseases are fatal and many infectious diseases are survivable. Option B is wrong — non-infectious diseases frequently involve the immune system (autoimmune disease). Option D is wrong — infectious diseases include viruses and parasites, not just bacteria; genetic mutations are a cause of some but not all non-infectious diseases.

2. B — Mesothelioma is both environmental (asbestos is the primary environmental trigger) and cancer (the outcome is uncontrolled mesothelial cell division). It is non-infectious — the cancer cannot be transmitted between individuals. Option A is technically partially true (cancer involves DNA mutations) but fails to identify the primary environmental cause. Option C is factually incorrect. Option D is wrong — asbestos fibres cause disease through physical/chemical damage, not as a living pathogen that transmits between people.

3. D — The shift reflects successful control of infectious disease mortality through vaccines, antibiotics, and sanitation (freeing people to live long enough to develop NID), combined with population ageing and lifestyle changes. Option A is wrong — NID did not become 'more dangerous'; Option B is wrong — infectious diseases were not eliminated. Option C contains a partially true element (lifestyle changes) but misrepresents the full picture and implies NID did not exist previously.

4. A — Risk factors increase probability but do not guarantee or exclude disease. Random somatic mutations can cause cancer in anyone; no set of risk factors is either necessary or sufficient for most non-infectious diseases. Options B, C, and D are factually incorrect.

5. C — The claim overstates personal choice. Purely genetic non-infectious diseases (CF, Huntington's, Type 1 diabetes) involve no lifestyle component at all. Even multifactorial diseases with strong lifestyle components have genetic predispositions and are shaped by socioeconomic determinants of health. Option A and B overstate lifestyle. Option D understates it entirely.

Short Answer Model Answers

Q6 (4 marks): Disease 1 — Cystic fibrosis. Category: genetic disease. Primary cause: autosomal recessive mutation in both copies of the CFTR gene. Cellular mechanism: the CFTR protein functions as a chloride ion channel in epithelial cell membranes. The mutation (most commonly F508del — deletion of phenylalanine at position 508) causes the CFTR protein to misfold and be degraded before reaching the membrane. Without functional Cl⁻ channels, chloride and water cannot be secreted into airways → thick, dehydrated mucus accumulates → chronic infection, lung damage, malabsorption [2 marks]. Disease 2 — Melanoma. Category: cancer with primary environmental cause. Primary cause: UV radiation from sunlight (or tanning beds) causes thymine dimers in skin cell DNA, disrupting tumour suppressor genes (e.g. CDKN2A encoding p16) and proto-oncogenes (e.g. BRAF). Cellular mechanism: accumulated mutations in melanocytes disrupt the cell cycle checkpoints → cells divide uncontrollably → malignant melanoma [2 marks — 4 marks total].

Q7 (5 marks): AIHW data: coronary heart disease is the leading cause of death in Australia (~10% of all deaths annually), followed by dementia, cerebrovascular disease, lung cancer, and COPD — all non-infectious diseases. Infectious diseases do not appear in the top five causes of Australian mortality [1 mark]. Epidemiological transition: this is the shift from infectious to non-infectious disease as the dominant cause of mortality, which occurred across the 20th century as infectious disease mortality was dramatically reduced by medical and public health advances [1 mark]. Factor 1 — Infectious disease control: the introduction of antibiotics in the 1940s, widespread vaccination programs, improved sanitation (clean water, sewage systems), and better nutrition dramatically reduced mortality from tuberculosis, pneumonia, childhood diarrhoeal diseases, and other infections that killed many Australians before age 50 in 1900. People now survive long enough to develop non-infectious diseases [1½ marks]. Factor 2 — Ageing populations: as average life expectancy rose from ~55 years in 1900 to ~83 years today, a larger proportion of Australians now live into the age range where non-infectious diseases typically manifest. Coronary heart disease, dementia, and cancer predominantly affect people over 60 — a group that is now a much larger share of the population than in 1900 [1½ marks — 5 marks total].

Q8 (5 marks): Genetic factors: type 2 diabetes has a strong genetic component — first-degree relatives of people with Type 2 diabetes have 2–3× increased risk; certain ethnic groups (Indigenous Australians, South Asian, Pacific Islander populations) have significantly higher genetic susceptibility, likely involving variants in genes controlling insulin secretion and sensitivity. Genetic predisposition sets a baseline risk that cannot be changed through lifestyle [1 mark]. Environmental factors: physical inactivity, sedentary work, and lack of access to safe spaces for exercise contribute. These are environmental but are strongly shaped by socioeconomic conditions — people in lower-income areas often have less access to healthy food and physical activity infrastructure [1 mark]. Nutritional factors: chronic excess of refined carbohydrates and saturated fats leads to sustained hyperinsulinaemia, eventual beta cell exhaustion, and cellular insulin resistance. Obesity, particularly central adiposity, produces chronic low-grade inflammation that impairs insulin receptor signalling [1 mark]. Socioeconomic factors: the distribution of Type 2 diabetes in Australia shows it is more prevalent in lower-income, regional, and Indigenous populations — populations with less access to fresh produce, more reliance on energy-dense processed food, higher rates of financial stress (which contributes to cortisol-mediated insulin resistance), and reduced access to preventive healthcare [1 mark]. Evaluation of 'lifestyle disease' label: the label is partially accurate — lifestyle factors (diet, exercise) are important modifiable risk factors, and lifestyle modification is the primary treatment strategy. However, the label is also misleading because it implies the disease is purely a result of personal choices, ignoring genetic predisposition beyond individual control, socioeconomic determinants that limit 'choices,' and the complex multifactorial nature of the disease. The label can contribute to stigma and victim-blaming while diverting attention from systemic public health solutions. It is most accurate to describe Type 2 diabetes as a multifactorial non-infectious disease in which lifestyle factors are important but not solely determinative [1 mark — 5 marks total].