The document discusses various portals of entry for viruses into the human body. It describes how the respiratory tract is the most common entry point, with viruses being inhaled through aerosolized droplets. It also discusses how the gastrointestinal tract and skin can allow viral entry. The eyes and placenta are mentioned as additional entry sites, with herpes viruses often infecting the cornea and cytomegalovirus able to transmit vertically from mother to fetus. In summary, the document outlines the major routes viruses use to infect humans, focusing on the respiratory tract, gastrointestinal tract, skin, eyes, and placenta as key portals of entry.

1. INTRODUCTION TO VIROLOGY
BIOT-4210
Lecture [14] : PORTALS OF VIRUS ENTRY, EXIT AND INFECTION PATTERNS (1)
Dr. IMRAN ALI
Assistant Professor
Date:

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INTRODUCTION TO VIROLOGY
IMPORTANT DEFINITIONS
A Succeptible cell has a functional receptor for a given
virus - the cell may or may not be able to support viral
replication
A resistant cell has no receptor - it may or may not
be competent to support viral replication
A permissive cell has the capacity to replicate virus - it
may or may not be susceptible. A susceptible and
permissive is the only cell that can take up a virus and
replicate it

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INTRODUCTION TO VIROLOGY
Cont……
Tropism is the affinity for susceptible cells
and can be defined at 3 levels: cells, tissues,
species (host range)
Pathogenesis is the process of producing a
disease.

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INTRODUCTION TO VIROLOGY
PORTALS OF VIRUS ENTRY

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INTRODUCTION TO VIROLOGY
Cont……
Most viruses interact with the cells of
the host epithelium.
The epithelium acts as the main barrier
between the outer world and the
internal environment of the body.

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INTRODUCTION TO VIROLOGY
RESPIRATORY TRACT
Respiratory tract is the most common portal of entry for viruses
into the human body.
A resting human inhales around 2 gallons of air/min, and within
each breath are aerosolized droplets and particles that could
contain viruses, such as from cough or sneeze of and infected
individual.
Viruses contained in larger droplets are deposited in the upper
respiratory tract, while smaller aerosolized particles or liquids are
able to travel into the lower respiratory tract.
The upper respiratory tract epithelium contains abundant goblet
cells that produce mucus, majority upper respiratory epithelium is
lined with cilia.

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INTRODUCTION TO VIROLOGY
GASTROINTESTINAL (GI) TRACT
doi.org/10.1155/2018/2819154
Small intestine also contains
goblet cells. Upper the
epithelium of the small
intestine, lymph node-like
masses called Peyer’s patches
contain millions of Ab secreting
lymphocytes, macrophages, and
other immune system cells.
Interspersed, M cells constantly
survey the contents of the small
intestine lumen.

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INTRODUCTION TO VIROLOGY
SKIN
Skin is composed of two layers of tissue: the outermost
epidermis and the underlying dermis.
Subcutaneous tissue is found beneath the skin and contains
primarily fat and loose connective tissues.
Bites of insect vectors (mosquitoes, ticks, mites) can introduce
viruses into the dermis, and the subcutaneous tissue can be
accessed by viruses through animal bites, needle punctures
or improperly sterilized tattooing or piercing equipment.
Some viruses, like human papillomavirus, are able to
replicate within the living part of the epidermis, but other
viruses must gain entry to the dermis or underlying
subcutaneous tissue in order to replicate or disseminate.

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INTRODUCTION TO VIROLOGY
EYES
White covering of the eye is the sclera,
which becomes colorless and transparent
cornea in the front and center area of the
eye that covers the pupil, lens, and iris.
The conjunctiva is a thin layer of
epithelium that covers the sclera and part
of the eyelid.
Infection of the cornea with herpesvirus
exposure and herpes simplex virus
infection of the cornea is the most
common.
Conjunctivitis also known as “pink eye”
is usually caused by adenoviruses.

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INTRODUCTION TO VIROLOGY
PLACENTA
Congenital infections occur
when a mother infects a fetus
before its birth. Congenital
infections occur via vertical
transmission. Most viral
infections exhibit horizontal
transmission.
Cytomegalovirus, a herpes virus,
is the most common cause of
congenital infections, occurring in
about 2.5% of live births.

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INTRODUCTION TO VIROLOGY
Common Portals of Entry and the Viruses That Use Them

12. THANKS