Question

A. Explain and describe the key differences between these two sets of experiments (see below):

B. Also explain the the significance of having two experiments as opposed to one experiment.

C. Identify the independent and dependent variable for these experiments.

Sets of Experiments I: HCV Status Experiments

In the first set of experiments, examine the blood samples of individuals with known HCV status. There are three groups of individuals in this experimental set: (1) individuals with chronic hepatitis C (this includes patients known to have chronic hepatitis C or blood donors who are known to have passed HCV onto recipients); (2) individuals with acute hepatitis C infections or blood donors who may have passed HCV onto recipients; (3) a control group of individuals, including normal blood donors (long time blood donors with no history of passing HCV onto recipients) or patients with hepatitis caused by alcohol or primary biliary cirrhosis. Repeat the assay four times per sample to assure consistency.

Sets of Experiments II: Blood Transfusion Recipients Experiments

In the second set of experiments, examine the blood of transfusion recipients known to have received blood from HCV positive donors. Assay the positive donors to determine the levels of HCV antibodies in their blood. Assay the recipients' blood every three months for twelve months in order to determine if HCV antibody levels increase or remain stable. As a control, assay recipients of blood transfusion from blood donors who were negative according to the HCV antibody assay. Assay the recipients of these negative donors every three months for twelve months.

Answer 1

A) HCV testing involves the detection of HCV antibodies in sera of suspected individuals. Presence of HCV antibodies indicates HCV infection. In the first set of experiment, the assay tests for the levels of hepatitis C virus (HCV) antibodies in the sera samples mentioned: patients with chronic or acute hepatitis and control people without hepatitis or patients with hepatitis infection not caused by HCV. This experiment test the levels of HCV antibodies when there is chronic or acute hepatitis.In the second experiment set, the levels of HCV antibodies are tested in individuals that receive HCV positive blood. It will indicate whether HCV can be transmitted by blood transfusion. HCV transmission is studied by development of HCV antibodies in these patients. A time course is studies between 3-12 months as HCV antibodies detection may vary.

B) The first experiment detects the HCV status of the individuals. It detects presence of HCV antibodies only. It does not detect the time dependent formation of HCV antibodies as it is not known when the patients were first infected. This experiment is performed to ensure that these patients were infected with HCV. Acute hepatitis lasts for 6 months and transmission is possible to other individuals in this time. It is possible that the individuals may already have been cured of HCV, as detected by disappearance of HCV antibody in blood. Chronic infection will result in virus persisting for more than 6 months. The immune system is not able to rid of the infection. Viral titer should be low.  In the second set, the detection of HCV antibody is tested after blood transfusion. This experiment will test how soon HCV infection develops in transfused patient, whether it results in chronic or acute infection. Both experiments have to be sequential. Otherwise it cannot be understood whether HCV is transmitted by blood. The control patients without HCV infections are used in order to study whether other hepatitis infections can eb transmitted by blood as well.  If only one is conducted, blood transmission of HCV cannot be studied.

C) Experiment A:

Independent Variable: This variable can be altered by the investigator. Here, the type of patient selected-control/acute/chronic are the independent variable.

Dependent Variable: This variable is dependent on independent variable. The HCV antibody titer is the dependent variable.

Experiment B: Independent variable is the type of blood that is transfused to non-HCV people- control/HCV positive (acute/Chronic). Dependent variable is the levels of titer of HCV antibodies that are detected in transfused recipients post transfusion.