Causes and Effects of Non-infectious Disease

In short: Non-infectious diseases cannot be passed from person to person, and are caused by genetics, nutrition, the environment, lifestyle or the body attacking itself. Cancer is uncontrolled cell division caused by mutations, and epidemiology studies how diseases spread through populations.

Starting point: what you already know

Infectious diseases are caused by pathogens. Non-infectious diseases are not (see Pathogens and the Spread of Disease).
Mutations can be caused by radiation and chemicals (see Mutations).
Homeostasis keeps the body stable, and disease follows when it fails (see Homeostasis).

Types of non-infectious disease

Cause	What happens	Examples
Genetic	Inherited faulty alleles or chromosome changes	Cystic fibrosis, haemophilia, Down syndrome, Huntington's disease
Nutritional	Too little or too much of a nutrient	Scurvy (vitamin C), iron-deficiency anaemia, obesity
Environmental	Exposure to harmful things	Skin cancer from UV, asbestosis and mesothelioma from asbestos, lung disease from smoke
Lifestyle	Habits that build up risk over years	Type 2 diabetes, heart disease, many cancers
Autoimmune	The immune system attacks the body's own cells	Type 1 diabetes, coeliac disease, rheumatoid arthritis
Degenerative	Body parts wear out or break down with age	Osteoarthritis, macular degeneration, Alzheimer's disease

Many diseases have several causes working together. Heart disease depends on genes, diet, smoking, exercise and age.

Case studies

Cystic fibrosis (genetic). A recessive allele of the CFTR gene makes a faulty chloride channel. Thick mucus clogs the lungs and pancreas, so patients get frequent lung infections and poor digestion. About 1 in 25 Australians is a carrier.

Melanoma (environmental). UV light causes mutations in skin cells that control cell division. Australia and New Zealand have the highest melanoma rates in the world. Early detection by skin checks greatly improves survival.

Type 2 diabetes (lifestyle and genetic). Cells stop responding properly to insulin, so blood glucose stays high. Risk rises with obesity, inactivity and family history. It can damage eyes, kidneys, nerves and blood vessels. It is often managed with diet, exercise and medicine.

Cancer

Cancer is uncontrolled cell division. Normally, genes tightly control when a cell divides. Mutations in two types of genes can cause cancer:

Proto-oncogenes tell cells to divide. A mutation can jam them "on", turning them into oncogenes.
Tumour suppressor genes (like p53) stop division or repair DNA. A mutation can switch them "off".

Usually several mutations are needed. A mass of dividing cells is a tumour. Benign tumours stay in one place. Malignant tumours invade nearby tissue and can spread through the blood or lymph to other parts of the body (metastasis).

Epidemiology

Epidemiology is the study of the patterns, causes and effects of disease in populations.

Type of study	What it does	Example
Descriptive	Describes who gets a disease, where and when	Mapping melanoma rates in each state
Analytical (cohort or case-control)	Compares groups to find causes	The British doctors study comparing smokers and non-smokers
Intervention (clinical trial)	Tests a treatment or prevention by giving it to one group and not another	Testing a new vaccine or drug

Non-infectious disease

Causes

Genetic: cystic fibrosis
Nutritional: scurvy
Environmental: UV, asbestos
Lifestyle: type 2 diabetes
Autoimmune: type 1 diabetes

Cancer

Uncontrolled division
Oncogenes on
Tumour suppressors off
Benign or malignant
Metastasis

Epidemiology

Descriptive
Analytical
Intervention trials
Incidence, prevalence, mortality

Year 11Designing and judging a clinical trial

A good intervention study (randomised controlled trial):

has a large sample of people,
assigns people randomly to a treatment group and a control group,
gives the control group a placebo (a fake treatment that looks the same),
is double blind: neither the patients nor the researchers know who gets the real treatment, which avoids bias, and
is approved by an ethics committee, with informed consent from everyone.

Epidemiology can show a strong link (correlation) between a factor and a disease. To argue cause, scientists look for a dose-response pattern (more smoking, more risk), a link that appears in many studies, and a biological reason (chemicals in smoke damage DNA).

Cohort or case-control? A cohort study follows a group forward in time and records who gets the disease (like the British doctors). A case-control study starts with people who already have the disease and compares their past with similar people who do not.

More reliable results come from a larger sample, and from repeating the study in other groups.

Correlation is not cause. Finding that people who eat more processed meat get more bowel cancer shows a link, but other factors (like smoking or exercise) might explain it.

Year 12Prevention programs in Australia

Epidemiology guides health programs. HSC questions often ask you to evaluate one.

Cancer screening: the National Bowel Cancer Screening Program mails free test kits to people aged 45 to 74. BreastScreen and the cervical screening program (testing for HPV) catch disease early.
HPV vaccination: Australian scientists Ian Frazer and Jian Zhou developed the technology behind it. Australia is on track to eliminate cervical cancer as a public health problem by about 2035.
SunSmart: "Slip, slop, slap" since 1981, with UV alerts and shade in schools. Melanoma rates in younger Australians have started to fall.
Newborn screening: a heel-prick blood test checks every baby for conditions like cystic fibrosis.

A good evaluation looks at cost, reach, participation rates, evidence of reduced incidence or mortality, and equity for groups such as rural and Aboriginal and Torres Strait Islander communities.

More rates. Prevalence: 1200 people with diabetes in a town of 40 000 is $\frac{1200}{40 000} \times 100 = 3%$ . Mortality: 150 deaths in 2 500 000 people is $\frac{150}{2 500 000} \times 100000 = 6$ per 100 000. Using "per 100 000" lets places of different sizes be compared fairly.

Relative risk $= \frac{rate in exposed group}{rate in unexposed group}$ . Smokers 140 and non-smokers 10 per 100 000 gives a relative risk of 14: smokers are 14 times as likely to die of lung cancer.

Long delays. Cancers take decades to develop after exposure, so mesothelioma cases kept rising long after asbestos was banned, and lung cancer deaths fell about 20 years after smoking rates fell.

Mother's age and Down syndrome. Eggs are formed before birth and wait for decades. Older eggs are more likely to have non-disjunction in meiosis.

Tricky categories. Skin cancer is non-infectious because it cannot pass between people, even though the environment causes it. Cervical cancer is usually started by HPV, an infectious virus, but the cancer itself cannot spread to another person; vaccination against HPV prevents it.

Quick summary

Non-infectious diseases can be genetic, nutritional, environmental, lifestyle-related, autoimmune or degenerative. Many have several causes.
Cancer is uncontrolled cell division caused by mutations in oncogenes and tumour suppressor genes.
Malignant tumours can spread by metastasis.
Epidemiology studies disease in populations: descriptive, analytical and intervention studies.
Incidence counts new cases. Prevalence counts all current cases.

Quiz

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Which is a genetic disease?
1. A Cystic fibrosis
2. B Scurvy
3. C Influenza
4. D Mesothelioma
Show answer
A: Cystic fibrosis
It is caused by an inherited faulty allele.
Scurvy is caused by a lack of
1. A iron
2. B vitamin D
3. C vitamin C
4. D protein
Show answer
C: vitamin C
It is a nutritional disease.
Which is an environmental cause of disease?
1. A Inheriting a faulty allele
2. B Exposure to asbestos
3. C An extra chromosome
4. D Getting older
Show answer
B: Exposure to asbestos
Asbestos causes lung disease and cancer.

Causes and Effects of Non-infectious Disease

Starting point: what you already know

Types of non-infectious disease

Case studies

Cancer

Epidemiology

Quick summary

Quiz

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