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Viral pathogenesis refers to how viruses cause _______________ within a host.
Viral pathogenesis refers to how viruses cause _______________ within a host.
disease
For a virus to initiate a successful infection, sufficient numbers of _______________ must enter the host.
For a virus to initiate a successful infection, sufficient numbers of _______________ must enter the host.
virions
The affinity for susceptible tissues is known as _______________.
The affinity for susceptible tissues is known as _______________.
tropism
The most common portal of entry for viruses is the _______________ tract.
The most common portal of entry for viruses is the _______________ tract.
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Alveolar _______________ are immune system cells that are specialized in phagocytosis.
Alveolar _______________ are immune system cells that are specialized in phagocytosis.
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Ciliated epithelial cells of the respiratory tract display receptors for respiratory viruses, such as _______________ or rhinovirus.
Ciliated epithelial cells of the respiratory tract display receptors for respiratory viruses, such as _______________ or rhinovirus.
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The small intestine contains M (microfold) cells, goblet cells, and glands that secrete _______________.
The small intestine contains M (microfold) cells, goblet cells, and glands that secrete _______________.
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Peyer’s patches contain millions of antibody-secreting _______________ (of the IgA antibody variety).
Peyer’s patches contain millions of antibody-secreting _______________ (of the IgA antibody variety).
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The membrane envelopes of most enveloped viruses are disintegrated by ______.
The membrane envelopes of most enveloped viruses are disintegrated by ______.
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Acid-labile viruses are unable to withstand the low pH of the ______.
Acid-labile viruses are unable to withstand the low pH of the ______.
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Viruses can be transmitted from mother to child in ______ milk.
Viruses can be transmitted from mother to child in ______ milk.
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The flow of fluid over the skin makes viral attachment difficult due to the presence of ______.
The flow of fluid over the skin makes viral attachment difficult due to the presence of ______.
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HPV can gain access through small cuts or ______ in the skin.
HPV can gain access through small cuts or ______ in the skin.
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Tears function by washing away any potential ______.
Tears function by washing away any potential ______.
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Infection of the cornea can occur with ______ simplex virus (HSV).
Infection of the cornea can occur with ______ simplex virus (HSV).
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Viral conjunctivitis, also known as “pink eye,” is usually caused by ______.
Viral conjunctivitis, also known as “pink eye,” is usually caused by ______.
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Viruses that infect and replicate only within cells at the site of infection cause ______ infections.
Viruses that infect and replicate only within cells at the site of infection cause ______ infections.
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Congenital infections occur when a mother infects a ______ before its birth.
Congenital infections occur when a mother infects a ______ before its birth.
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Rhinovirus infects the epithelial cells of the upper ______ tract and replicates there.
Rhinovirus infects the epithelial cells of the upper ______ tract and replicates there.
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Horizontal transmission, meaning that direct ______-to-host transmission occurs.
Horizontal transmission, meaning that direct ______-to-host transmission occurs.
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Vertical transmission of HIV most often occurs by ______ transmission, although breastfeeding can also transmit the virus via the gastrointestinal tract.
Vertical transmission of HIV most often occurs by ______ transmission, although breastfeeding can also transmit the virus via the gastrointestinal tract.
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Several viruses can be transmitted through ______, including hepatitis A virus, hepatitis B virus, and hepatitis C virus.
Several viruses can be transmitted through ______, including hepatitis A virus, hepatitis B virus, and hepatitis C virus.
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Herpesviruses, which remain in tissues or cells in a dormant state after infecting a healthy host, are common viral pathogens in ______.
Herpesviruses, which remain in tissues or cells in a dormant state after infecting a healthy host, are common viral pathogens in ______.
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Shows ______, the inflammation of the conjunctiva, caused by accidental infection with vaccinia.
Shows ______, the inflammation of the conjunctiva, caused by accidental infection with vaccinia.
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A host typically goes through four stages of disease development when it is infected with a ______.
A host typically goes through four stages of disease development when it is infected with a ______.
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The time between when the ______ initially infects the host and when symptoms appear is called the incubation period.
The time between when the ______ initially infects the host and when symptoms appear is called the incubation period.
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The rhinovirus, a cause of the common cold, has an incubation period of about ______ days.
The rhinovirus, a cause of the common cold, has an incubation period of about ______ days.
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During the prodromal period, nonspecific, mild symptoms such as ______, muscle aches, or a low-grade fever may occur.
During the prodromal period, nonspecific, mild symptoms such as ______, muscle aches, or a low-grade fever may occur.
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The ______ period occurs when specific symptoms of the disease occur.
The ______ period occurs when specific symptoms of the disease occur.
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The symptoms of the disease subside as the host begins feeling better, having entered into the ______ period.
The symptoms of the disease subside as the host begins feeling better, having entered into the ______ period.
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Rhinovirus has an incubation period of approximately _______________ hours.
Rhinovirus has an incubation period of approximately _______________ hours.
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Influenza A virus has a period of communicability from _______________ hours before to 5-10 days after symptoms begin.
Influenza A virus has a period of communicability from _______________ hours before to 5-10 days after symptoms begin.
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Variola virus, also known as _______________, has a period of communicability from 24 hours before fever begins until disappearance of all scabs.
Variola virus, also known as _______________, has a period of communicability from 24 hours before fever begins until disappearance of all scabs.
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Ebola virus has an incubation period of approximately _______________ days.
Ebola virus has an incubation period of approximately _______________ days.
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Measles virus has a period of communicability from _______________ days before to four days after onset of rash.
Measles virus has a period of communicability from _______________ days before to four days after onset of rash.
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HIV has a period of communicability that begins _______________ during infection and continues indefinitely.
HIV has a period of communicability that begins _______________ during infection and continues indefinitely.
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Hepatitis A virus has a period of communicability that begins in the _______________ half of the incubation period and continues for a week into jaundice.
Hepatitis A virus has a period of communicability that begins in the _______________ half of the incubation period and continues for a week into jaundice.
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Acute infection is typically cleared by the immune system within _______________ days.
Acute infection is typically cleared by the immune system within _______________ days.
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Study Notes
Virus Transmission
- Viruses enter the host through various portals, including the respiratory tract, gastrointestinal tract, genital tract, skin, and eyes.
Portals of Virus Entry
- Respiratory Tract:
- Most common portal of entry
- Viruses are trapped by mucus in the upper and lower respiratory tract
- Antibodies (IgA isotype) bind to virus particles
- Alveolar macrophages and ciliated epithelial cells play a role in virus entry
- Gastrointestinal Tract:
- Viruses must be resistant to low pH of stomach acid and detergent qualities of bile
- Acid-labile viruses are unable to withstand low pH of stomach
- Acid-resistant viruses contain capsid proteins that are not denatured by low pH
- Genital Tract:
- Viruses are sexually transmitted diseases
- Human papillomavirus (HPV) has tropism for the epithelium of the cervix or penis
- Skin:
- Viruses gain access through small cuts or abrasions in the skin
- Bites of insect vectors (mosquitoes, ticks, mites) can introduce viruses into the dermis
- Eyes:
- Tears wash away potential pathogens
- Traumatic events (puncture wounds) provide entry of virus into the eye
- Placenta:
- Congenital infections occur when a mother infects a fetus before its birth
- Vertical transmission leads to long-term persistence of the virus within the child
Dissemination Within a Host
- Localized infections:
- Viruses infect and replicate only within cells at the site of infection
- Example: Rhinovirus infects the epithelial cells of the upper respiratory tract
- Systemic infections:
- Viruses spread throughout the body
Patterns of Infection
- Incubation period:
- Time between viral infection and symptom appearance
- Example: Rhinovirus (1-3 days)
- Prodromal period:
- Nonspecific, mild symptoms appear
- Virus replicates quickly within the host
- Illness period:
- Specific symptoms of the disease occur
- Virus is multiplying to high levels, and immune system is activated
- Convalescent period:
- Symptoms subside as the host begins feeling better
Incubation Period and Period of Communicability for Selected Human Viruses
- Table 1 lists the incubation period and period of communicability for various viruses, including Rhinovirus, Influenza A virus, Variola virus (smallpox), Ebola virus, Measles virus, Rubella virus, HIV, Mumps virus, Hepatitis A virus, Hepatitis C virus, and Hepatitis B virus
Replication and Persistence of a Virus Within a Host
- Acute infection:
- Virus replicates rapidly within the host and is spread to other individuals
- Immune system clears the virus within 7-10 days
- Persistent infections:
- Virus persists in the host for an extended period
- Examples: HIV, Hepatitis B virus, and Hepatitis C virus
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Description
Learn about the process of viral transmission, how viruses enter and spread within a host, and the factors that contribute to a successful infection.
