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Virology Exam #2 Review > Unit 2 - Lecture 8 Mechanisms of Viral Entry & Spread of Infection in the Body > Flashcards

Unit 2 - Lecture 8 Mechanisms of Viral Entry & Spread of Infection in the Body Flashcards

1
Q

What are the Preferred Routes of Entry?

A

Viruses gain entry into the host and then target specific cell types.

  • Respiratory tract
  • Gastrointestinal tract
  • Genital tract
  • Conjunctiva (eyes)
  • Crossing the placenta—may cause teratogenic effects
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2
Q

Describe the Respiratory Tract Entry

A
  • Approx. ½ liter of air inhaled per breath
  • Avg. 12 breaths per minute
  • Sneezes contain 40,000 droplets
  • Viruses contained in both large and small droplets
  • Thousands of viral particles per droplet
  • Single sneeze can infect an entire room
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3
Q

The biological parts of the Respiratory Tract.

What area’s do they include?

What type of cells are infected?

What happens to the infectious particles?

A
  • Upper: nasal cavity and throat
  • Lower: trachea, bronchi, and lungs
  • Covered in ciliated epithelial cells
  • Particles trapped in mucus
  • 10-100 mL of mucus produced daily in nasal cavity and lungs

Ciliary action

  • Immune cells protect terminal alveolar sacs
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4
Q

What is involved in the Gastrointestinal tract entry?
What organs does it involved?
Where do the viruses bind?

A
  • Large intestine: 5 ft. long (H2O absorption)
  • Small intestine: 22 ft. long (food digestion & absorption)
  • Mucosa layer comes in direct contact with food
  • Viruses bind intestinal epithelial cells
  • Microvilli
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5
Q

What is Gastroenteritis?
Name three viruses that are associated with it and the symptoms that are included.

A
  • Inflammation of the GI tract due to infection (viral, bacteria)
  • Rotavirus, Norovirus, Adenovirus
  • Diarrhea, vomiting, and abdominal cramps
  • Mild to severe dehydration
  • Acute viral gastroenteritis is a leading cause of infant mortality throughout the world
  • Half a million children die of rotavirus gastroenteritis annually (1 child/minute worldwide)
  • 90% of deaths occur in Asia and Africa
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6
Q

How are many of the gastroinstestinal diseases transmitted?

A

Oral–Fecal Transmission

  • Inadequate sewage disposal –> waters supply –> Ingestion
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7
Q

What are some of the characteristics of Genital Tract Entry?

How are the viruses transmitted and spread?

A
  • Viruses can be transmitted through sexual contact
  • Infection occur at skin or mucous membranes
  • Viral STDs cannot be cured, only treated
  • Infection can be spread even if no signs of disease are present
  • Adolescents and young adults at greatest risk

—–Rate of disease has doubled among middle-aged adults and the elderly over past 10 yrs

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8
Q

What are Viral Infections of the eye?

Where is it involved and what is the susceptibility to eye infections?

A
  • Conjunctiva: thin, transparent tissue covering the eye
  • Rare route of entry due to tear secretions
  • Minor abrasions/injuries increase susceptibility to infection
  • Inflammation of the cornea and conjunctiva
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9
Q

What is a rare route of entry?

Such as the Skin

A

Skin

  • Skin is a natural barrier
  • Viruses must enter breaks in the skin (cuts, bites, needles)
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10
Q

What are zoonotic viruses?

What type of vectors are involved?

Give Examples.

A
  • Infectious disease transmitted from animals (wild and domestic) to humans or from humans to animals
  • Usually involves arthropod vectors
  • – also via animal bite, contact with infected animals, or fomites
    e. g., West Nile virus, Dengue, Rabies
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11
Q

Describe the aspects of a rare Route of Entry…

Transplants

A
  • Majority of individuals are asymptomatic seronegative carriers of viruses
  • –Epstein-Barr virus (EBV)
  • –Cytomegalovirus (CMV)
  • Viruses present in solid organ transplants became “reactivated” when placed in an immunosuppressed recipient

—-Health complications and morbidity

  • Blood screened for known viral pathogens as well as emerging pathogens
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12
Q

What is involved in the rare Iatrogenic Induction?

A
  • Infections generated by a physician
  • – 80,000 deaths in U.S. due to nosocomial infections
  • — Minor medical procedures, surgeries, and dental care

e.g., surgical procedures using contaminated equipment/tools; poor hand hygiene

    • Hepatitis viruses
    • CJD and vCJD (prion diseases*)
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13
Q

What are the Mechanisms of Viral Spread of Pathogenesis?

A
  • Replication and infections within the host

—- Localized infections (site of entry)

—- Primary viremia (spread via lymph or blood)

—- Systemic infections—lymph vessels

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14
Q

What is an example of a localized infectino?

A

Papillomavirus

Warts!

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15
Q

What is a systemic Viral Infection?

A
  • Viruses can use blood stream and PNS to spread throughout the host
    • Lymphatic system
    • Infection of neurons
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16
Q

Who is Fenner and what did he discover?

What are Lymphatics?

What is lymph?

A

Fenner (1948)

  • Sequential spread of mousepox
  • Epidermis of footpad
  • Lymphatics
  • Bloodstream
  • Organs

Lymphatics: fine vessel network beneath the skin that returns fluids to the body’s tissues

Lymph: watery fluid; contains lymphocytes

17
Q

What are some of the target Organs?

(Organs that viruses target)

Give examples viruses for each organ/

A
  • Skin (e.g., Papillomaviruses)
  • Lungs (respiratory tract viruses; e.g., influenza, SARS-CoV)
  • Liver (hepatitis viruses)
  • Brain (neurotropic viruses, e.g., varicella zoster)
18
Q

What are neurotropic Viruses?

What do they infect?

Give Viral examples

A
  • Viruses infect nervous system
  • Most infect other cell types
  • Infect neurons of PNS
  • Spread to CNS
  • via PNS, olfactory nerves, bloodstream

e.g., Rabies, Varicella zoster virus

19
Q

How do viruses spread from blood to brain?

A
  • Blood–brain barrier is semi-permeable
  • Opening in capillary endothelium allow viruses to pass through
  • “Trojan horse”; within infected immune cells
20
Q

How do viral infections affect pregnancy?

What are three types of transmission?

A
  • The placenta is a protective interface between the mother and developing fetus
    • Exchange of nutrients, gas, waste products
  • –Share blood supply

3 types of transmission

  1. Transplacental
  2. Perinatal (during delivery)
  3. Postnatal (breast milk)
21
Q

How do you describe the anatomy of the placenta with viruses?

A
  • Often infections during pregnancy are unnoticed
  • Few viruses infect the developing embryo and fetus causing severe damage

— Spontaneous abortion, stillbirth, neonatal death

  • Some viruses can cause congenital (teratogenic) effects
  • – Cytomegaloviruses
  • – Rubella
  • Maternal immunity
22
Q

What are the different patterns of diseases?

A
  • Acute, non-persistent infections

—– Self-limiting and short duration

  • Acute infections followed by a persistent infection

—- DNA viruses (EBV)

  • Chronic infections—latency
    • Hepatitis
  • -Chronic inflammation leads to organ failure or cancer
  • Slow infections
  • -Slow, progressive disease
  • -Prion diseases*
23
Q

What is Incubation period?

A

Incubation period: Time elapsed between exposure to a virus and when signs and symptoms of the disease first appear.

24
Q

What is Latency?

A

Latency: dormant infection; episomal DNA

25
Q

How do viruses exit?

eg. Shedding

A

Viruses usually shed through routes of entry:

  • Mucus
  • Saliva
  • Semen
  • Feces
  • Skin abrasions
  • Breast milk
  • Cervical secretions
  • Urine
  • Viremia—blood

Viruses can be shed asymptomactically

26
Q

What is involved in the Norovirus Spread?

A
  • Infection with norovirus causes gastroenteritis
  • Food and drinks can easily become contaminated with norovirus (100 particles cause disease)

— Contact with contaminated hands or surfaces

  • Cruise ships
  • – 25 outbreaks in 2002 (~2,648 ill passengers)
  • – 500 cases on Princess Cruise Line ships (Feb 2012)
  • Resorts

– Outbreak at Six Flags Great Escape Lodge, NY (2008)

27
Q

How are viruses that infect the brain exited?

What is the environmental survival of viruses?

A
  • Most brain viruses affect other target organs and are perpetuated and shed that way.
  • Environmental survival of viruses
  • –Non-enveloped vs. enveloped viruses
  • –Human viruses in water
  • Intestinal viruses
28
Q

What is the environmental Survival of Virus?

A
  • Naked viruses more stable than enveloped viruses
  • Enveloped are more sensitive to degradation
  • Stability affected by environmental factors
  1. Humidity
  2. pH
  3. Temperature
  4. Whether viruses are present in organic matter (e.g., feces, mucus)
29
Q

What is involved in the environmental survival of Influenza?

A
  • Purified influenza virus alone survived 3 days on bank notes, 17 days when in the presence of respiratory mucus1
  • Cold temperatures and low relative humidity are favorable to the spread of influenza virus2
  • Highly pathogenic H5N1 avian influenza virus remained stable in wet feces in the environment for >40 days at 4°C3
30
Q

What are Human Viruses in a Water Environment?

A
  • Environmental (water) virology is a separate scientific discipline.
  • It began in the 1950s when efforts were needed to detect poliovirus in water.
  • In general, viruses are more stable in water than bacteria.
  • 2.5 x 108 viral particles per mL of water (most bacteriophages)
  • One gram of stool can contain 105-1011 viral particles

Virology Exam #2 Review (4 decks)

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