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TTrraannssmmiissssiioonn

VViirruuss TTrraannssmmiissssiioonn

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

species.

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

pathways.

There are a few different ways/modes of viral transmission:

11.. BBlloooodd 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

viraemia.

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).

22.. SSaalliivvaa 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.

33.. RReessppiirraattoorryy SSeeccrreettiioonnss 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.

44.. FFeeaacceess

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.

WWaayyss ooff VViirruuss EEnnttrryy

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.

1. SSkkiinn Viruses can enter through Abrasions and cuts.

Examples include:

o Papilloma virus

o Cow pox

o Molloscom contagiosum

o Rabies virus

o Injections Hepatitis B infections.

2. EEyyeess The conjunctiva helps in preventing microbes from entering the eye as well as

physical harm. So it is highly susceptible to infection.

3. UUrrooggeenniittaall TTrraacctt

Risky sexual behaviours increase the chances for viral entry/infection.

Example include:

o HIV

44.. RReessppiirraattoorryy TTrraacctt Airborne viruses are inhaled.

Examples include:

o Small pox

o Chicken pox

o Influenza virus

o Rhinovirus

55.. AAlliimmeennttaarryy TTrraacctt

Virus can enter through infected/contaminated food.

Examples include:

o Enterovirus

o Adenovirus

o Reovirus

o Hepatitis A, E

o Rota virus

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IInnhheerreenntt BBaarrrriieerrss

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.

1. SSkkiinn

The skin acts a formidable barrier to most viruses and only after this barrier is

breached will viruses be able to infect the host.

2. LLaacckk ooff MMeemmbbrraannee RReecceeppttoorrss

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

virus.

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.

3. MMuuccuuss

The mucus covering an epithelium acts as a barrier to prevent infection of host

cells.

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.

44.. CCiilliiaatteedd EEppiitthheelliiuumm

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.

55.. LLooww ppHH

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.