viral genome silent and hidden from the host immune system. The latency

can be retracted if the host cell is introduced to stress signals. Example:

Herpesvirus, retrovirus (HIV)

2.4.4

KEY ELEMENTS OF A VIRAL INFECTION

Also, there are a few key elements to consider along with the type of infection to

establish the outcome of an infection:

1. Virus strain: The virus strain determines the host cellular receptors for

attachment and release of the newly formed particles from the host cell

surface.

2. Inoculum size: The virus load, that is the inoculum size, is a key factor in

determining the virus spread kinetics and outcome of the infection. A

lower dose of the inoculum might get cleared out from the host system

whereas, a higher viral load could lead to severe immunopathology and

eventually could cause mortality.

3. Route of exposure: The first occurrence of virus-host interaction is the

exposure of the susceptible host to the virus. The infection could be via

respiratory droplets or aerosols, contaminated food, and water, or through

body fluids and tissue. Sometimes the exposure could be directly through

contaminated needles or even through the bite of an animal vector. In some

cases, the virus could be transmitted from an infected mother to the infant.

4. Susceptibility of the host: Susceptibility to a virus is greatly affected by

the age and sex of the host. For some viruses, younger hosts could show a

higher mortality rate and for some older animals could have a higher

susceptibility. The sex of the animal could also contribute to the outcome

of an infection, depending on their genetics, respectively.

5. Immune status of the host: The host uses its wide range of immune defense

mechanisms to either avoid infection or to reduce the degree of tissue da-

mage done by the virus. But in the case of an immunocompromised host, the

host has a lower ability to respond to the virus due to its weak immune

system, ultimately leading to a higher mortality rate compared to a healthy

host. This could be caused by several conditions such as cardiovascular or

lung disease, HIV infection, diabetes, or even obesity.

2.4.5

DISEASE OCCURRENCE

Different terms have been used to describe the occurrence of a specific disease at a

given time. This also depends on the disease-causing agent, its background, and risk

factors. In the case of viruses, they are mostly termed infectious diseases that could

be emerging (newly identified) or re-emerging (reoccurrence). Some commonly

used terms are:

1. Sporadic: Diseases that are irregular and non-frequent within a given

population and time.

Introduction to basic virology

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