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Saturday, January 30, 2010

Portal of Entry and Portal of Exit


Virus can enter into our body at many different sites and these are called portals of entry.

Skin

Skin when intact is usually a barrier to most pathogen as it has a tough outer layer of cornified cells. However, our skin is frequently breached by trauma or by inoculation (e.g. Cuts and insect bites). Virus inoculation by injection or transfusion is now common as a result both of medical procedures and of social practices such as sharing needles by intravenous drug users. Usually hepatitis B and hepatitis C viruses are usually transmitted in this way. They may also be transferred by minor “surgical” procedures like tattooing, dentistry and ear piercing. Furthermore, some pathogens can enter our body via our hair follicles, sweat glands, cuts and bruises.


Respiratory

Respiratory is one of the most common route of viral infection. As the average human adult breathes in about 600 L of air every hour; small suspended particles ( <>



Alimentary Tract

Although the surface of the alimentary tract is potentially exposed to a great number and variety of viruses, the harsh conditions in the stomach and duodenum protect it from many viruses. For instance, viruses that have a lipid-containing envelope are usually inactivated by the acid, bile salts and enzymes that occur in the stomach and duodenum. Infection via the gut, therefore, is due to viruses that resist these chemicals. These viruses multiply in the cells of the small intestine and are excreted in the feces (Table48-3). Such viruses usually resist environmental conditions and may cause water- and food-borne epidemics.



Placenta

Placenta transfer of virus from parent to offspring, and may occur via the ovum, across the placenta, during birth, or via the mother's milk. Viruses that cross the placenta include rubella virus and cytomegaloviruses, which may cause congenital defects or severe neonatal disease, and HIV. It can also result in spontaneous abortion, birth defect and premature birth.

In the end viruses escape from the body via the same surfaces, often but not necessarily by the route used as a portal of entry. Usually they leave our bodies via secretion ( tears, saliva, vaginal, semen etc. ) or excretion ( faeces, urine )


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