MCB Lecture 53 Transmission and Pathogenesis of viruses Flashcards
How is polio transmitted?
Faecal-oral route, face ally contaminated food is ingested
How is influenza transmitted?
It is airborne
How is Papillomavirus transmitted?
Sexual intercourse
How is HIV transmitted?
Needles, Rectal route, congenital
How is Hep B transmitted?
Needles, congenital
How is yellow fever transmitted?
Vertebrate reservoir and an insect vector
How is Ross river fever transmitted?
Vector transmission
Give an overview of the different routes of entry that viruses exploit
Conjunctiva Respiratory tract Alimentary tract Urogenital tract Across abrasions or cuts of the skin Parental inoculation
How do adenoviruses get into the body?
Conjunctiva
How does papilloma virus get into the body?
Urogenital tract and cuts or abrasions on the mouth
How does influenza get into the body?
Respiratory tract
How does poliovirus get into the body?
Faecally contaminated food is ingested
How does herpes simplex get into the body?
Urogenital tract
Direct contact with bodily fluids of a infected person
Describe how viruses can get across the skin
There must be a cut or abrasion. Normally, viruses can’t get across the skin because the skin cells filled with keratin is hostile for the viruses
What are the protective mechanisms of the respiratory tract?
Mucus, ciliates cells to elevate the mucus, alveolar macropages
Once a virus has been breathed in, where can it go? (2)
Give example of types of viruses that do both of these
- Remain localised
Rhinovirus, Influenza, bronchitis causing viruses - Move further within the body
Measles, mumps, rubella, Varicella-Zoster
How does Varicella-Zoster get into the body?
Respiratory tract
How does measles get into the body?
Respiratory tract
Describe the Pathogenesis of Mumps, and what it can lead to in some cases
- Enters respiratory tract
- Primary infection and replication in the upper respiratory tract
- Spreads further within the body, to many organs, via sialic acid receptors
10% of sufferers get meningitis, very few will also get encephalitis
4. Salivary gland is often affected
What are the two ways that viruses may be introduced into the mouth or oropharynx?
List some bacteria in each category
Sharing of saliva
Herpes
Faecal-oral
Picornaviridae (polio)
What are the protective mechanisms of the alimentary tract?
Bile salt secretion
Acid secretion
Mucus lessens attachment
How do picornaviridae get into the body?
Faecal-oral transmission
Describe the Pathogenesis that leads to Poliomyelitis
- Faecally contaminated food is ingested
- Virus infects tonsils and Peyer’s patch cell
- Replication within the cells, and lysis of cells to escape
- Invasion of subepithelial tissues
- Viremia
- Other organs can be infected if they have the correct receptors
motor neurons destroyed, polio
What are enteroviruses?
These are viruses that enter the body through the alimentary tract, such as picornaviridae
What determines which tissues are infected by the different enteroviruses after viremia?
The affinity of the glycoproteins on the virus for receptors of the organs in the body
Describe the stages of spread of viruses within the body
- Local infection
- Spread to subepithelial tissues
- Viremia
What is dissemination?
This is when the virus spreads beyond the site of primary infection
What is a systemic infection?
This is when a virus spreads to many areas within the body
What are tissue tropisms?
This is when viruses infect certain tissues
What are the factors that determine tissue tropisms?
The receptors on the cells of the tissue and the proteins on the virus
What is special about rotaviruses in terms of tissue tropisms?
They have multilayered capsids, so they are very hardy and can survive in the acidic environment of the stomach
Other viruses would get killed at this point
What is special about rhinoviruses in terms of tissue tropisms?
They can only survive and replicate in the nasal cavity, because it is cooler here than the rest of the body.
Compare 33-34 degrees with 37 of the rest of the body
Polarised spread is when a virus bursts out at either the apical or basal surface. Which has a higher chance of sub epithelial invasion?
When the viruses burst out from the basal end
Why are macrophages and lymphocytes important for tissue tropisms?
If a virus can survive in these cells, they get a free ride around the body and thus will infect more tissues
What are the two ways that viruses can be present in the blood? Give an example of each
- Free in the blood
Eg. HBV - Associated with a host cell
Eg. HIV in CD4+, Measles in monocytes
Which virus causes Varicella-zoster?
Herpesviridae
Describe the Pathogenesis of varicella-zoster
- Infection via conjunctiva or respiratory tract
- infection and replication in the regional lymph nodes
- Primary Viremia
- Infection and replication in the liver and spleen
- Secondary viremia
- Infection of skin and formation of vesicles
- Infection of neurons up to the dorsal root ganglion
What are the vesicles in Varicella-zoster?
Fluid and virus filled
What is viral shedding?
Viral shedding is the exit of viruses from the host cell after they have invaded, infected the cell and undergone replication
What are the three modes of shedding?
Exocytosis
Budding
Apoptosis
Into which areas / fluids do viruses shed?
Faeces Milk Genital secretions Blood Urine Skin
What are the outcomes of viral infection. Give example of each
1. Fatal Eg. Ebola 2. Full recovery Eg. Influenza 3. Recovery, but permanent damage Eg. Polio 4. Persistent infection Eg. HIV, - latent: herpesviridae - chronic infection: Hep C virus
What do we feel sick when we have a viral infection?
- Damage to tissue
- Related to immune response
- immuno pathology eg. Measles rash
- immune supression eg. HIV
How is the virus for Epstein Barr disease get transmitted?
- Babies sucking objects
2. Adolescents kissing –> glandular fever
If a virus is free in the blood, what extra pressures does it face?
Must avoid macrophages
Thus, must be present in huge amounts so that it is not completely cleared
Differentiate between primary and secondary viremia
Primary: few viruses in the blood
Secondary: many viruses in the blood after replication of the virus in the liver and the spleen
What are the mechanisms by which viruses cause recurring disease?
a. Continually mutating –> influenza
b. Multiple stereotypes –> rhinovirus
c. Remain in epithelium –> ineffective immunity
By which mechanisms do viral genomes constantly change?
- Point mutation
- Recombination
- Reassortment (two viruses with different segmented genomes infect a cell at the same time and genes reassort)
What are latent infections? Give an example of how these can cause recurring disease
These are infections that are never cleared and flare up when the individual is stressed or the immune system is weakened.
Herpes viridae, Varicella-zoster
- After the primary infection, the virus infects neurons and moves up them to the dorsal root ganglion where it becomes latent (non-replicating)
- Many years later (often in old age) the virus is given the chance to become active again because the immune system is weakened
- Virus comes back down every neuron in the dorsal root ganglion
- Skin infection of the entire dermatone
What factors affect host resistance and immunity?
- Genetic factors
- Age; young and old do not have fully functional immune systems
- Malnutrition
- Hormones, pregnancy
- Dual infection
How do enteroviruses cause disease?
They enter via the alimentary canal, and then move into the circulation
What is the function of mucus in the alimentary tract ?
It lessens adhesion of viruses to host cells.
This reduced invasion
