HSCBiology

Inquiry Question 3: Why are epidemiological studies used?

Content Descriptor: Analyse patterns of non-infectious diseases in populations, including their incidence and prevalence, including not limited to:

Nutritional diseases: (8.3.1)

Prevalence of diabetes within the USA:

Analysis of Prevalence

Diabetes a partially nutritional disease which results in the body being unable to correctly regulate blood sugar levels (8.1.2).

While most of the west and central united states is sporadic and random in the prevalence, there is a definite trend of increase prevalence in the south east, namely the states of Mississippi and Alabama, which have almost entirely the highest rate of >11.66%. Generally, diabetes is inversely related to income and education, with major risk factors including heart disease, poor diet and high sugar and fat intake. In general, these states tend to have lower levels of education (49^th and 45^th out of 56 territories). These lower education levels can also be correlated with lower income which can contribute to the poor diet risk factor. Although somewhat anecdotal, there is a cultural trend of southern states to regularly eat fried and deep-fried foods, which tend to be high in fats. This may explain the poor diet of some of these states but does not account for the differences between states which have similar diets (Louisiana vs Mississippi).

Disease caused by environmental exposure: (8.3.2)

Incidence of melanoma worldwide:

Analysis of Incidence:

Melanoma is a skin cancer which is mostly attributed to exposure to UV radiation. When considering the rotation of the Earth and the corresponding seasonal oscillations, the areas around the equator tend to receive far more sunlight and thus UV radiation than those further towards to poles. Thus, it would be expected that those towards the equator would have higher incidence of Melanoma. However, this is not reflected in the data, with the highest incidence occurring in nations far away from the equator (USA, Canada, New Zealand, Australia, Norway), all of which have the highest incidence (4.1+/100,000), compared to nations along or next to the equator (Somalia, Ethiopia) which have extremely low incidence (<0.89/100,000). This may be accounted for by the physical adaptations of many of the inhabitants of these regions, which tend to have high amount of melanin in the skin which helps protect against UV radiation. For example, Nigeria, which has an incidence of 0.48- 0.89/100,000 has less than 1% of the population Caucasian. This biological advantage for those in these areas outweighs the increased exposure to the sun.

Content Descriptor: Investigate the treatment/management, and possible future directions for further research, of a non-infectious disease using an example from one of the non-infectious disease categories listed above: (8.3.3)

Cystic fibrosis treatment: (6.2.2)

Cystic fibrosis (CF) is caused by a frameshift mutation, causing cells to not produce an enzyme which mediates the conditions in normal humans. Thus, it is a genetic condition.

A large area of research is currently dedicated to using biotechnology to reverse the mutation of the CFTR gene. To achieve this reversal, correct pieces of DNA need to be delivered to individual cells. From there, either the cell incorporated the correct version of the CFTR gene (integrating gene therapy), or it temporarily uses an attached copy (non- integrating gene therapy). While trials in mice have been promising, the appropriate method of delivery of the genes still requires further research.

One method currently under investigation is through attachment to a hybrid virus, which delivers the DNA.

The benefit of genetic treatments for CF is that it will likely be effective for any mutation of the CFTR gene and therefore useable by all CF patients.

Other areas of research include non-genetic treatments, such as the development of anti-inflammatory micro-molecules which block multiple of the enzymes involved in inflammation.

Content Descriptor: Evaluate the method used in an example of an epidemiological study: (8.3.4)

Epidemiological studies:

For the scope of the HSC, epidemiological studies can be divided into two primary areas:

1. Case control – Composed of two groups, one with the condition (case) and one withoutcondition (control). A large amount of data is collected about these two groups, and trends are searched for which the case group have in common which the control group does 
2. Cohort – Two groups of people are assembled, those who have a set exposure to a potentialrisk factor and those who do have the exposure. These two groups are closely monitored over a large amount of time to track the development of the disease. If there is a strong correlation between the case group and the development of the disease, there may be a link between the exposure and the condition.

Qualities of a good epidemiological study:

1. Largesample group
2. Identificationof confounding factors (external unaccounted for variables)
3. Diversesample group (ages, ethnicity, sex)
4. Accountsfor participation bias (for example those who have had food poisoning may perceive the food they ate differently after being diagnosed. There may also be social pressure to respond in a certain way to questions, for example regarding smoking, alcohol or sexual 
5. Uses medical examination where possible rather than simply a survey. This may includeblood tests or microbial 
6. Ensuringthat the participation group is reflective of the demography of the entire population
7. Clearlystating exclusion factors and exclusion qualifications
8. Largequantities of data
9. Followup investigation or medical check-ups
10. Peerreviewed

Content Descriptor: Evaluate, using examples, the benefits of engaging in an epidemiological study: (8.3.5)

Benefits:

The primary benefit which arises from epidemiological studies is to discover or provide substantial evidence for significant risk factors associated with a non-infectious disease. The most famous example of this was from the studies performed lining smoking cigarettes to lung cancer. Through a length number of studies, there was significant evidence that linked smoking to lung cancer. This pressured governments, such as the Australian government to implement laws to disincentivise smoking and protect the population from harm. Thus, engagement in an epidemiological study helped understanding of disease which has caused reduction in death as a result.

Knowledge of the causative agents of disease aids in targeting methods to prevent, control and treat non-infectious diseases.

Inquiry Question Review: Why are epidemiological studies used? (8.3.6)

You should be able to:

• Analysethe patterns and provide reasons for the distribution of non-infectious disease
• Describean area of further research for a non-infectious disease
• Describe the components of a good epidemiological study and use this knowledge to evaluatemethods of an epidemiological study