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Questions and Answers
The process of how viruses cause disease within a host is known as ______ pathogenesis.
viral
For a virus to initiate a successful infection, sufficient numbers of ______ must enter the host.
virions
The host cells must be ______ to the virus, and those cells must be susceptible to infection.
accessible
The affinity for susceptible tissues is known as ______.
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The respiratory tract is the most common ______ of virus entry.
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Alveolar ______ are a kind of immune system cell that is specialized in phagocytosis.
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Viruses are able to gain entry into the body through a variety of different ______, including the respiratory tract, gastrointestinal tract, or genital tract.
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Successful viruses must also be resistant to the low pH of ______ acid and the detergent qualities of bile in the gastrointestinal tract.
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The ______ of the conjunctiva is caused by accidental infection with vaccinia.
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Congenital infections occur when a mother infects a ______ before its birth.
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The effects of congenital infections can be severe, including ______, low birth weight, and intellectual deficiencies.
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Vertical transmission occurs when the virus is spread from one ______ to the next generation.
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HIV can be transmitted through ______ during the birthing process.
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Several viruses can be transmitted through ______ transfusion, including hepatitis and HIV.
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Localized infections occur when viruses infect and replicate only within cells at the site of ______.
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Rhinovirus infects the epithelial cells of the ______ respiratory tract and replicates there.
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Papillomavirus strains that infect the skin replicate locally in the ______.
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Virions spread to other organs through one of two ways: ______ spread and neurotropic spread.
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In ______ spread, viruses spread to target organs using the bloodstream.
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The shedding of virus refers to the release of infectious ______ from the host.
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Viruses that infect the skin are spread through ______-to-skin contact.
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Gastrointestinal viruses are shed within aerosolized ______ or diarrhea, potentially contaminating food or water.
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Viruses such as HIV and herpesviruses can replicate within genital compartments and be shed in ______ or vaginal secretions.
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The presence of virus within the urine is known as ______.
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Some acute infections are inapparent or subclinical, meaning that they produce no ______ of disease
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Occur when the host immune system is unable to effectively clear the virus, but the virus does not replicate to levels that kill the ______.
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Persistent infections can also result from viral ______ or slow infections.
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An example of a virus that establishes ______ is varicella zoster virus that causes chickenpox.
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HIV establishes a ______ infection: it takes around 8–10 years for an individual to progress to a stage of disease where symptoms are apparent.
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Due to ______, HIV establishes a slow infection.
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Rhinovirus has an average incubation period of ∼______ hours.
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The period of communicability of Influenza A virus begins ______ hours before symptoms begin.
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Variola virus is infectious as long as blood or secretions contain the ______.
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Measles virus is communicable from ______ days before to four days after onset of rash.
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HIV is communicable early during infection and continues ______.
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The replication and persistence of a virus within a host generally follow one of two different patterns of ______ disease.
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Acute infection is typically cleared by the immune system within ______–10 days.
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Epidemics are most often caused by viruses that cause ______ infection.
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Study Notes
Virus Transmission and Pathogenesis
- Viral pathogenesis: how viruses cause disease within a host
- For a virus to initiate a successful infection, sufficient numbers of virions must enter the host, and the host cells must be accessible to the virus and susceptible to infection
- Tropism: the affinity for susceptible tissues
Portals of Virus Entry
- Respiratory Tract: most common portal of entry
- Viruses contained in larger droplets are deposited in the upper respiratory tract
- Smaller aerosolized particles or liquids travel into the lower respiratory tract
- Mucus in the upper and lower respiratory tract traps many viral particles
- Gastrointestinal Tract: small intestine contains M cells, goblet cells, and glands that secrete mucus, which lines the epithelium
- Under the epithelium, lymph node–like masses called Peyer’s patches contain millions of antibody-secreting lymphocytes, macrophages, and other immune system cells
- Genital Tract: viruses can gain entry through the genital tract
- Skin: viruses can gain entry through the skin
- Placenta: congenital infections occur when a mother infects a fetus before its birth
- Examples: cytomegalovirus, herpesvirus, variola (small-pox), rubella, and measles
- Transplants: viruses can be transmitted through blood transfusion, organ transplants, and other medical procedures
- Examples: hepatitis A virus, hepatitis B virus, HIV, and dengue virus
Dissemination within a Host
- Localized infections: viruses that infect and replicate only within cells at the site of infection
- Examples: rhinovirus, papillomavirus strains
- Systemic infections: viruses that initiate infection through one organ but then spread to other sites within the body
- Examples: hematogenous spread, neurotropic spread
- Viremia: the presence of virus within the bloodstream
Portals of Virus Exit
- Respiratory viruses are shed within respiratory secretions, passed along through a cough or sneeze
- Gastrointestinal viruses are shed within aerosolized vomit or diarrhea, potentially contaminating food or water
- Viruses that replicate in the lungs, nasal cavity, or salivary glands can be shed in saliva
- Viruses that replicate in the genital compartments can be shed in semen or vaginal secretions
- Viruses can be transmitted through blood
Patterns of Disease
- Acute infection: the virus replicates rapidly within the host and is spread to other individuals, but the immune system clears the virus within 7-10 days
- Epidemics are often caused by viruses that cause acute infection
- Persistent infections: the host immune system is unable to effectively clear the virus, but the virus does not replicate to levels that kill the host
- Examples: HIV, herpesviruses
- Viral latency: a state in which the virus becomes dormant within host cells
- Example: all herpesviruses establish latency
- Slow infections: viruses that can take years to reach a symptomatic phase
- Example: HIV
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Description
Learn how viruses enter, spread, and exit hosts, and understand viral pathogenesis and the conditions necessary for a successful infection. Explore the role of virions, host cells, and susceptibility to infection.
