Unit 2 - Lecture 8 Mechanisms of Viral Entry & Spread of Infection in the Body Flashcards
What are the Preferred Routes of Entry?
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
Describe the Respiratory Tract Entry
- 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
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?
- 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
What is involved in the Gastrointestinal tract entry?
What organs does it involved?
Where do the viruses bind?
- 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
What is Gastroenteritis?
Name three viruses that are associated with it and the symptoms that are included.
- 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
How are many of the gastroinstestinal diseases transmitted?
Oral–Fecal Transmission
- Inadequate sewage disposal –> waters supply –> Ingestion
What are some of the characteristics of Genital Tract Entry?
How are the viruses transmitted and spread?
- 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
What are Viral Infections of the eye?
Where is it involved and what is the susceptibility to eye infections?
- 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
What is a rare route of entry?
Such as the Skin
Skin
- Skin is a natural barrier
- Viruses must enter breaks in the skin (cuts, bites, needles)
What are zoonotic viruses?
What type of vectors are involved?
Give Examples.
- 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
Describe the aspects of a rare Route of Entry…
Transplants
- 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
What is involved in the rare Iatrogenic Induction?
- 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*)
What are the Mechanisms of Viral Spread of Pathogenesis?
- Replication and infections within the host
—- Localized infections (site of entry)
—- Primary viremia (spread via lymph or blood)
—- Systemic infections—lymph vessels
What is an example of a localized infectino?
Papillomavirus
Warts!
What is a systemic Viral Infection?
- Viruses can use blood stream and PNS to spread throughout the host
- Lymphatic system
- Infection of neurons
Who is Fenner and what did he discover?
What are Lymphatics?
What is lymph?
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
What are some of the target Organs?
(Organs that viruses target)
Give examples viruses for each organ/
- Skin (e.g., Papillomaviruses)
- Lungs (respiratory tract viruses; e.g., influenza, SARS-CoV)
- Liver (hepatitis viruses)
- Brain (neurotropic viruses, e.g., varicella zoster)
What are neurotropic Viruses?
What do they infect?
Give Viral examples
- 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
How do viruses spread from blood to brain?
- Blood–brain barrier is semi-permeable
- Opening in capillary endothelium allow viruses to pass through
- “Trojan horse”; within infected immune cells
How do viral infections affect pregnancy?
What are three types of transmission?
- 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
- Transplacental
- Perinatal (during delivery)
- Postnatal (breast milk)
How do you describe the anatomy of the placenta with viruses?
- 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
What are the different patterns of diseases?
- 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*
What is Incubation period?
Incubation period: Time elapsed between exposure to a virus and when signs and symptoms of the disease first appear.
What is Latency?
Latency: dormant infection; episomal DNA
How do viruses exit?
eg. Shedding
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
What is involved in the Norovirus Spread?
- 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)
How are viruses that infect the brain exited?
What is the environmental survival of viruses?
- 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
What is the environmental Survival of Virus?
- Naked viruses more stable than enveloped viruses
- Enveloped are more sensitive to degradation
- Stability affected by environmental factors
- Humidity
- pH
- Temperature
- Whether viruses are present in organic matter (e.g., feces, mucus)
What is involved in the environmental survival of Influenza?
- 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
What are Human Viruses in a Water Environment?
- 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
