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This is important in the survival/propagation of the virus. The virus needs to be
spread so that it can continue reproducing and ensuring the survival of the virus
The effectiveness of viral transmission depends on the virus concentration and the
route of transmission.
The higher the viral concentration, the higher the chances of transmission.
Some modes of virus transmission include respiratory secretions and salivary
There are a few different ways/modes of viral transmission:
There are a few ways that the virus can infect the blood and one way is by
arthropods. They transmit arthropod-borne viruses (arbovirus) such as flaviviruses
and togoviruses upon biting and the virus enters the blood which may cause
Another way of blood infection would be via direct blood/bodily fluid contact or
exposure infected items or people. Some of such viruses include the Hepatitis
strain and well as the Human Immunodeficiency Virus (HIV).
The most common way for transmission is via kissing.
Sharing of utensil may also promote virus transmission as there is saliva involved.
Examples of such viruses are the herpes viruses and retroviruses.
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Air-borne viruses and viruses that can only infect the respiratory tract can also be
spread by sneezing, coughing, breathing and singing.
Although some viruses can be inactivated by drying, it activates again when it
enters the body as there is moisture.
Contaminated hands from covering a cough or sneeze may also pass on the virus.
Infection via this method not very common in developed countries where
sanitation is relatively good but rather common in areas or poor sanitation,
especially third-world countries.
Unlike viruses that spread by respiratory means, these viruses are highly resistant
to drying meaning they do not get inactivated so easily. This explains allows them
to easily infect.
Examples of such viruses are the enteric and hepatic viruses.
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After spreading, propagation or transmission of virus it can suffer variety of
barriers through which virus have to gain entry into the specific receptor cell.
There are a variety of ways that viruses can enter the host.
Viruses can enter through Abrasions and cuts.
o Papilloma virus
o Cow pox
o Molloscom contagiosum
o Rabies virus
o Injections Hepatitis B infections.
The conjunctiva helps in preventing microbes from entering the eye as well as
physical harm. So it is highly susceptible to infection.
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Risky sexual behaviours increase the chances for viral entry/infection.
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Airborne viruses are inhaled.
o Small pox
o Chicken pox
o Influenza virus
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Virus can enter through infected/contaminated food.
o Hepatitis A, E
o Rota virus
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The host has a number of barriers to infection that are inherent to the organism. These
represent the first line of defense which functions to prevent or limit infection.
The skin acts a formidable barrier to most viruses and only after this barrier is
breached will viruses be able to infect the host.
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Viruses gain entry into host cells by first binding to specific receptors on cells.
The host range of the virus will depend upon the presence these receptors. Thus, if
a host lacks the receptor for a virus or if the host cells lack some component
necessary for the replication of a virus, the host will inherently be resistant to that
For example, mice lack receptors for polio viruses and thus are resistant to polio
virus. Similarly, humans are inherently resistant to plant and many animal viruses.
The mucus covering an epithelium acts as a barrier to prevent infection of host
In some instances the mucus simply acts as a barrier but in other cases the mucus
can prevent infection by competing with virus receptors on cells.
For example, orthomyxo- and paramyxovirus families infect the host cells by
binding to sialic acid receptors.
Sialic acid-containing glycoproteins in mucus can thus compete with the cell
receptors and diminish or prevent binding of virus to the cells.
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The ciliated epithelium which drives the mucociliary elevator can help diminish
infectivity of certain viruses.
This system has been shown to be important in respiratory infections since, when
the activity of this system is inhibited by drugs or infection, there is an increased
infection rate with a given inoculum of virus.
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The low pH of gastric secretions inactivates most viruses.
However, enteroviruses are resistant to gastric secretions and thus can survive and
replicate in the gut.