Introduction to Clinical Virology - how viruses are spread Flashcards
What are the 7 entry routes of viruses?
- Oral-faecal
- Droplet
- Skin
- Inoculation
- Sexual
- Transplacental
- Genomic
Give example of each:
1. Oral-faecal
2. Droplet
3. Skin
4. Inoculation
5. Sexual
6. Transplacental
7. Genomic
- Enteroviruses
- Influenza
- Papillomaviruses
- Rabies
- HIV
- Rubella
- Endogenous retrovirus
What are the Obligatory steps of a viral infection?
- Entry
- Dissemination of viruses
- Multiplication of the viruses
- Antiviral defense of the body
- Viral evasion of the immune system
- Secretion
What are the important steps of a virus infection?
- Attachment
- Penetration
- Uncoating
- Transcription and replication
- Assembly
- Release
Difference between lytic and lysogenic cycles?
In lytic cycle, the host cell is killed and the viral particles are released but in lysogenic cycle, the host is not killed instead the viral genome is incorporated into the genome of the host and is passed onto the next generation.
What are localized viral infections? Characteristics? Two types of localized infection and their examples?
A type of viral infection in which viral replication and tissue destruction takes places at or near the entry site.
Short incubation period and localized disease occurence
Surface infection - Influenza virus
Deep tissue infection - Herpes simplex virus
Characteristics of generalized infection?
- Many sites of viral multiplication
- Viremia - spread of viruses through blood
- Long incubation period
- Immune system has time to react
What are the two types of immune responses? Explain their types as well.
- Innate immunty - first line of defense:
a. Interferon response
b. Natural killer cells (NKCs)
c. Intrinsic cellular responses - Adaptive immunity - memory is very important
a. Humoral immunity - B cells that secrete abs
b. Cellular immunity: Cytotoxic t cells and T helper cells
What is FC? What are the five types of antibody classes?
- Constant region of an ab
- IgG, igM, igA, igE, igD
Immune attack may
contribute to disease
symptoms. How?
Cytotoxic T cells (Tc cells) destroy virus infected cells and thus lead to tissue destruction causing disease symptoms.
Give an example of immune attack causing disease symptoms.
Hepatitis B virus and hepatocytes.
HBV does not kill hepatocytes, instead it incorporates its DNA into the genome of hepatocytes. So these viral particles are recognized by the Tc cells which in turn kills them, causing tissue damage.
What are privileged sites? Give examples of viruses and their privileged sites.
Privileged sites are sites that are protected against immune response or face only limited immune response. Example:
Papillomavirus also replicates at the epidermis where the humoral response is limited.
“Synthesis of viral proteins that act as Fc-receptors” Meaning and consequence of this.
The viruses cause the infected cells to produce a protein that is expressed on their surfaces and it causes the antibodies to bind to it via the fc region. As a result, the abs get inactivated.
“Stronger the immune response, ____ will be the course of viral infection”
What is a multiplication threshold of disease.
- weaker
- An amount of viral particles that have to be reached in order for it to cause diseases.
If immune response is quick, then it will not be reached however if immune response is weak or delayed, then disease will be caused.
Name an important microbial strategy to cause diseases and escape the immune response. Give examples for this. What is the consequence.
- Antigenic variation (viruses have particular antigens that are recognised by the immune system. However, during an infection, these viruses keep changing these antigens thereby escaping an attack by the memory of the immune system.
- HIV, HCV
- Persistent infection and the virus is not removed.
