HSC Biology Syllabus Notes
Module 8 / Inquiry Question 3
Week 15 Inquiry Question – Why are epidemiological studies used?
Learning Objective #1 – Analyse patterns of non-infectious diseases in populations, including their incidence and
prevalence, including but not limited to:
Nutritional diseases
Diseases caused by environmental exposure
Learning Objective #2 – 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 diseases categories listed above
Learning Objective #3 – Evaluate the method used in an example of an epidemiological study
Learning Objective #4 – Evaluate, using examples, the benefits of engaging in an epidemiological study
Learning Objective #1 - Analyse patterns of non-infectious diseases in populations, including their incidence and prevalence, including but not limited to:
- Nutritional diseases
- Diseases caused by environmental exposure
This has already been covered in last week’s notes.
Please see the practical problems in this week’s homework set to get comfortable with spotting and interpreting patterns in data that is tabulated and/or graphed.
Learning Objective #2 - 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 diseases categories listed above
We have already explored the cases of Iron and Vitamin C deficiency & how to treat them in last week’s notes.
However, there is not a lot to examine here and we will be exploring gene therapy in the following week’s notes so we will introduce it here by exploring the case of skin cancer as a non-infectious disease.
Currently to treat skin cancer, techniques such as surgery, immunotherapy, chemotherapy as well as target drug therapy are used.
Target drug therapy can be reduced to manage skin cancer by reducing or stopping the development and spread of cancerous melanoma cells. For skin cancer, Tafinlar can be used which is a substance that can prevent the function of the mutated BRAF protein responsible for the growth of melanoma cells.
Tafinlar is able to block the signals of the mutated BRAF protein to manage skin cancer by minimising or stop the growth and spread of cancerous melanoma cells.
Chemotherapy involves drugs that eliminate cancer cells to be injected or orally consumed by the patient. This form of treatment is not particularly effect for treating melanoma, however, it can serve to reduce symptoms and lifetime of affected individual.
Other techniques such as target drug therapy and immunotherapy are more effective.
Immunotherapy stimulates the immune system such as by injecting cytokines so that it can fight off antigens present on cancerous melanoma cells.
Specific immunotherapy involves the use of cancer vaccines could involve extracting an affected individual’s T Helper cell and activate it in the presence of an antigen that is specific to melanoma cells. This activated T Helper cell can be re-inserted back into the affected individual’s body whereby it initiates the appropriate immune response that is specific to the melanoma cancerous cells present in the patients body.
So, if you recall from Module 7, this would lead to activation of B cells with specific surface receptor proteins, production of antibodies that are specific to the melanoma cancerous cells, etc.
Surgery: When the melanoma (or skin cancer) is in the early stage, surgery can be performed whereby the localised melanoma cancer cells can be cut out. However, in later stages of melanoma, where it has spread to many different parts of the body and to large numbers, surgery will not be a viable option.
The FUTURE of curing skin cancer could lie in the field of gene therapy
This gene therapy can exist many forms however one form involves extracting the affected individual’s T-cells. These cells are then genetically modified such that it contains a gene specifying for a receptor that is unique to the antigens that are present in the skin cancer cells that cause melanoma.
The purpose of the receptor is target and bind to antigens on cancerous melanoma cells. This will activate the Helper T cells which secrete cytokines (and all the other mechanisms that discussed in Module 7). The result is the elimination of the cancerous melanoma cells.
As a result of this, cancer tumours can be removed. There has been clinical trials where such techniques has been performed to kill melanoma cells. However, it resulted in the affected individual having other genes mutated resulting in the development other forms of cancer such as lung and breast cancer.
The ultimate objective here is to deactivate the expression of oncogenes by introducing suicide genes into the cells using gene therapy.
However, more research is required to be conducted to resolve the complex matters surrounding unexpected results such as causing mutation of other genes which result in the development of other forms of cancer rather than curing the skin cancer itself.
Besides this, there are also many ethical issues pertaining to advancing research in the field of gene therapy. For example, whether or not it will can be used to elevate intelligence and only be available to rich people in the future.
There is already significant progress made into vector technology used to deliver the gene such as using the Adeno-Associated Virus (AAV) that is used as a viral vector to deliver the gene as they only initiate a weak immune response and does not appear to cause disease in humans.
We use viral vectors it has been observed that the insertion of gene directly into a cell will render the cell to stop functioning. As a result, we inject the virus carrying the gene into a tissue whereby the genetic information can then enter cells via virus’s invasion mechanism as we have explored in Module 7.
Also, there has been progress with identifying and researching animals that are excellent laboratory test species for specific diseases.
NOTE: Other forms of gene therapy involves the delivery of a gene that encodes for a protein that is lacking in the individual rather than coding for the receptor that binds to antigens. Here, genes that specifies for receptors that bind to antigens to destroy cancerous cells.
We will examine other cases of the two different types of gene therapy in Week 16’s Notes.
Learning Objective #3 - Evaluate the method used in an example of an epidemiological study
Epidemiology is the study of the cause (potential cause), distribution and frequency of a disease in specific populations in order to establish measures to prevent and control the disease.
NOTE: Nowdays, epidemiology can be used for both infectious and non-infectious diseases.
From the definition of epidemiology that we used above, we can be classify epidemiology into three types. These are being descriptive epidemiology, analytic epidemiology and intervention epidemiology.
In the order of being named:
The first involves gathering data to determine the distribution of a disease within a population.
The second involves testing and verifying a hypothesis pertaining to the potential cause of the disease.
The third involves determining the effectiveness of preventive and control measures that has been implemented to prevent and control the disease respectively.
NOTE: The third category is probably ‘outside’ the scope of HSC Biology as no epidemiological questions have been asked about that category in the past.
For such reasons, we will only be exploring descriptive and analytic epidemiology in detail.
Descriptive Epidemiology
In descriptive epidemiology, we examine person, place and time (PPT) as the main characteristics of disease. Due to this, we can generate a hypothesis regarding the “4W” of the disease, i.e. who has the disease, where is the disease found, in what groups is the disease found and when (e.g., age, developmental stage) is the disease found?
We can also answer how many people the disease affects via descriptive epidemiology.
This type of study does not require comparison groups (i.e. control groups).
Rather, we can obtain information and answer the “4W” of the disease using surveys, case reports, ecological and cross-sectional studies which are examples of descriptive epidemiology.
In terms of Person, we will be examining the following factors to see if there are any pattern(s) related to the disease.
Age, gender, ethnic group
Genetic predisposition
Concurrent disease
Diet, physical activity, lifestyle
Risk taking behaviour
SES, education, occupation
In terms of Place, we will examining things like:
Presence of agents or vectors
Climate
Geology
Population density
Economic developments
Nutritional practices
Medical practices
Lastly, for Time, epidemiologists will have a look at:
Calendar time
Time since an event
Physiologic cycles
Age (time since birth)
Seasonality
Temporal trends
Analytic Epidemiology
Epidemiologists can use analytic epidemiology if they are concerned with investigating the questions “how is the disease caused or transmitted and why?”
Therefore, sometimes, analytic epidemiology is said to test the hypothesis formulated in descriptive epidemiology.
This type of study can serve to answer the trends and patterns that are identified in descriptive epidemiology. In order to do this, we need a control group so that affected and unaffected people are measured.
Examples of analytic epidemiology include cohort studies and case control studies.
For epidemiologist that are using analytic epidemiology, they will be examining the host, environment and agent (e.g. pathogen, vectors, chemicals, etc) as potential factors that may be responsible for causing the disease.
For the host (i.e. individual affected with the disease), the following factors will be looked at, such as:
Host’s traits
Host’s Behaviour
Host’s genetic predisposition
Host’s immunologic factors
Comparatively, for the environment, epidemiologists will be examining:
Any changes in the environment that results in change in the transmission of the agent or development of the agent.
Lastly, the study will involve looking into following characteristics which the agent may possess that cause, influence or increase the severity of the disease:
Biological features
Physical features
Chemical features
EXAMPLE: EPIDEMIOLOGY CASE STUDY
Centers for Disease Control & Prevention have a database of real-life epidemiology case studies.
The one that I reviewed that is pretty decent is the epidemiology study on the typhoid outbreak in Tajikistan.
Students Version (without Answers): https://www.cdc.gov/epicasestudies/downloads/typhoid_stu.pdf
Instructor Version (with Answers): https://www.cdc.gov/epicasestudies/downloads/typhoid_inst.pdf
Other epidemiology case studies that you may wish to consider:
https://www.cdc.gov/epicasestudies/index.html
Your objective here for HSC Biology Syllabus purposes is to summarise the epidemiology case study (e.g. typhoid in Tajikistan) by including as much the methods used to collect data to form AND test hypothesis.
You are also required to assess the effectiveness of the epidemiological method. There are questions shown in the both the student & instructor versions that help you evaluate the effectiveness of the data collection methods. The answers to these questions are found in the instructor version.
You should also refer to the features of descriptive and analytic epidemiology that we mentioned in the previous section to see if the case study addressed all the relevant factors that may contribute to the potential cause, distribution and frequency of the disease.
Learning Objective #4 - Evaluate, using examples, the benefits of engaging in an epidemiology study
Benefits of using descriptive epidemiology studies:
We will be answer questions pertaining to “who has the disease, where is the disease found, in what groups is the disease found and when (e.g., age, developmental stage) is the disease found?”
We can also answer how many people the disease affects via descriptive epidemiology.
Benefits of using analytic epidemiology:
It will be possible to identify the risk factors and potential causes of the disease. This is because the study allows us to establish correlation or association between risk factors and the incidence of the disease.
This allows us to analyse the potential cause and effects of the disease – that is, why (cause) and how (effect) of the disease.
Benefits of using intervention epidemiology:
Determine the effectiveness of preventive and control measures that has been implemented to prevent and control the disease respectively.
Case Study Examples of the benefit of epidemiology:
Refer to the link in the above question. Write out the successful outcomes of the epidemiology and use them in your HSC Biology exam response.
I recommend looking through 3 cases in the link provided in the previous section and write down 3 successful outcomes or benefits of each epidemiology study.
NOTE: You cannot prove that a specific factor (e.g. a vector) is responsible for a disease. The study can show the correlation between the specific risk factor and the incidence of the disease.
So, for instance, you found that the greater the exposure to the risk factor, the higher the incidence of the disease. This would mean that there is a high positive correlation between the risk factor and the disease. However, you cannot prove the risk factor actually caused the disease.
There can be due to the confounding in which another factor or variable that is associated with both the risk factor being studied as well as the disease being studied.
There was an epidemiological study performed to determine whether children had a higher chance of suffering from leukemia if they lived in areas with large electric power lines than others that did not. However, it was also known at the high traffic density and the pollutants produced by traffic (e.g. car engines) could be responsible for the potential cause of leukemia. This possibility is apparently where areas that have larger electric power lines had higher traffic densities.
To determine the potential cause of the disease, two studies where performed. One of the studies involved children that lived near traffic density. In this group, there was a relationship between the size of power lines and the disease.
However, when comparing children who lived near large electric power lines, the relationship between traffic density and leukemia was not evident.
So, one conclusion could be that traffic density is the confounder and the possible risk factor of the disease is the size of the power line.
However, more studies are required to be conducted to determine whether traffic density is a confounder or, perhaps, the power line size could be the confounder if a new risk factor showing higher correlation is discovered.