Question

Lab Activity: Discovering the Virus Responsible for Hepatitis C.

Go to McGraw Hill Virtual Labs and select Part IX: Viruses and Simple Organisms.

You are required to perform only lab 9-1 and 9-1B.

-State the hypothesis and explain how you came up with it based on the initial observations.

-You are asked to set up two sets of experiments to determine the specificity and sensitivity of the assay.

-Briefly, explain the difference between these two experiments and the significance of having two as opposed to one experiment.

-Identify the independent and dependent variable for these experiments.

-As you gather data, you will see results represented by blue and red bars on the graph. What does each of these colors represent?

-What accounts for the radioactivity measured in the assay from the blood collected from chronic hepatitis C individuals?

-Why is there no radioactivity measured using the blood samples from acute infections?

-What conclusions are supported by your data? Explain.

-Do these results support your hypothesis? Explain.

Answer 1

The non-A, non-B hepatitis virus was identified in 1989 by scientists at a California biotechnology company called Chiron who were collaborating with investigators at the Centers for Disease Control and Prevention (CDC). The research confirmed that this was a new virus—now officially called the hepatitis C virus, or HCV. This was a landmark advance in medicine that allowed for development of tests to detect HCV, which were rapidly applied to screen blood donations. Over the next few years, as the testing improved, HCV was effectively eliminated from the blood transfusion supply. The identification of HCV also led to further studies, undertaken by NIAID- and NIDDK-funded researchers and others, to determine its molecular structure. This was crucial for the design of drugs that would specifically interact with components of the virus and inhibit its replication. The identification of the virus also allowed for a more accurate diagnosis and a better sense of its prevalence; in fact, it was eventually determined that HCV was the most common cause of chronic hepatitis, cirrhosis, and liver cancer in the Western world.

To test the hypothesis that person-to-person variability in blood levels of hepatitis C virus (HCV) RNA can be explained, the quantity of HCV RNA was assessed in 969 persons who acquired HCV infection in the context of injection drug use. Serum HCV RNA levels ranged from 200,000 to >120 million equivalents/mL (the linear range of the assay). The median log₁₀ HCV RNA level was 0.46 higher in 468 human immunodeficiency virus (HIV)-positive persons than in 501 HIV-negative persons (P < .001). In addition, among HIV-negative persons, lower HCV RNA levels were independently associated with younger age (P < .001), ongoing hepatitis B infection (P = .005), and the absence of needle sharing (P = .02). However, >90% of the person-to-person HCV RNA level variability was not explained by these sociodemographic, environmental, and virologic factors. Additional research is necessary to ascertain what determines the level of HCV RNA in blood.

In this heavily transfused population receiving a mean of 20 units per patient of predominantly paid-donor blood, 30 of 66 (45%) developed biochemical evidence of hepatitis; of these, 20 (67%) were infected with hepatitis C virus (HCV) alone, four (13%) with hepatitis B virus (HBV) alone, and six (20%) with both viruses. Among the 36 patients who did not develop hepatitis, four (11%) were newly infected with HCV alone, nine (25%) with HBV alone, and one (3%) with both viruses. Overall, 100% of patients with hepatitis and 39% of those without hepatitis were infected with HBV and/or HCV; one patient was also infected with hepatitis E virus. The donor carrier rate for HBV and/or HCV was estimated to be more than 6%; contemporaneously prepared pooled normal human plasma was also contaminated with multiple hepatitis viruses.