process. In the cytoplasm, the viral structural proteins interact with cellular

factors such as enolase (ENO1) or heat shock proteins (HSP90/70).

2. Nucleus: In the nucleus, the virus interacts with many of the elongation

factors (eEF1G, eEF1B) and mRNA decay factors (SMG9, DDX5) to

control the host DNA and protein metabolism, therefore promoting its

replication.

3. Plasma membrane: Interaction with the host cell plasma membrane is the first

(entry of the virus) and the last step (exit of virions) in an infection cycle. To

achieve this, the virus interacts with the components of the host cell lipid

bilayer such as phospholipids, sphingolipids, and annexin (ANXA2).

4. Cytoskeleton: Structural changes in the host cell plasma membrane are

required during cell entry, viral assembly, and extracellular release of the

virus. The host cell cytoskeleton, namely, actin filaments (globular and

filamentous actin), microtubules (tubulin chains), and small GTPases (Rac,

Rho, Cdc42) are the major players in these events.

2.4.3

TYPES OF INFECTION

There are different degrees of a viral infection, depending on the outcome and

transmission of an infection:

1. Abortive infection: The virus would enter the host cell but cannot com-

plete the replication successfully. This could be a result of non-permissive

host cell or formation of defective virions. Example: MP strain of herpes

simplex virus with canine kidney cells

2. Asymptomatic infection: In this type, the host is considered the carrier of

the virus without experiencing any symptoms of the infection. This type

of infection can also be called an inapparent or subclinical infection.

Asymptomatic infections do not prompt the infected host to take proper

precautions and care, leading to higher chances of transmitting the infec-

tion. Example: Most cases of Human papillomavirus infections

3. Symptomatic (Active) infection: In this, the virus successfully completes

its genome expression in the host cell, producing infectious virions.

Symptomatic infections are clinical and apparent, showing more than one

symptom related to the specific infection. Examples: Fever in most cases,

cough in case of respiratory infections such as SARS, influenza A virus

4. Self-limiting infection: These kinds of viral infections run their course

(generally seven days) and get cleared out from the host system without

severe medications. Examples: Common cold, chickenpox

5. Latent infection: This kind of infection remains hidden or inactive or

dormant. They remain static, persistent, and can exist for a very longer

duration inside the host cell before becoming active. This is achieved

through either escaping the cell-mediated immune response or by infecting

the cells of immune-privileged sites such as the brain and eyes. The viral

genome can remain as an episome or integrated into the host genome. The

virus maintains its latency by expressing very few viral genes that keep the

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Bioprocessing of Viral Vaccines