Problems

1 This part described the various patterns of viral infection that can be observed, among them acute, persistent, and latent. What common features may exist among these three types of infection? What are the distinguishing characteristics of each of these three types of infection?

2 The five hepatitis viruses have the same tissue tropism (the liver) and yet each is in a different virus family. One of them (hepatitis D or the delta agent) is actually a defective virus, sometimes called a subviral entity.

(a) In the table below, indicate the mode of transmission of each of these agents:

PART

Agent

Transmitted by

Hepatitis A virus

Hepatitis B virus

Hepatitis C virus

Hepatitis D (delta) agent

Hepatitis E virus

(b) What functions of the liver may allow all of these agents to have a common tissue tropism, despite their differing modes of transmission?

3 As part of a larger project, you have been given five unknown viruses to characterize. Your job is to determine, given the tools at your disposal, the host range and tissue tropism of these unknown viruses. You will be using two kinds of cells: human and mouse. In each case you have a cell line that grows continuously in culture and is therefore representative of the organism, but not of a particular tissue (human: HeLa cells; mouse: L cells). In addition, you have cells that are derived from and still representative of specific tissues: muscle or neurons. For each virus, you have an assay system that indicates if the virus attaches to ("+") or does not attach to ("—") a particular type of cell. Using the data in the table below, determine, if possible, the host range and tissue tropism of each unknown virus.

Human

Mouse

Vi rus

HeLa

Muscle

Neuron

L

Muscle

Neuron

#1

+

-

-

-

-

-

#2

+

+

-

+

+

-

#3

-

-

-

+

+

+

#4

-

-

-

-

-

-

#5

+

-

+

-

-

-

Here is the report form you will send back with your results. Indicate with a check mark (✓) what your conclusions are for each of the unknown viruses.

Virus

#1

#2

#3

#4

#5

Host range

Human

Mouse

Both

Neither

Tissue tropism

Muscle

Neuron

No tropism

Cannot be determined from data

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