Patterns of viral infection Flashcards
What are the forms of viral transmission?
Iatrogenic: due to medical care Nosocomial: hospital acquired Vertical: patient to offspring Horizontal: everything else Germline: part of host genome
What are the ways of viral dissemination?
- Local infection
- Primary viremia
- Amplification
- Secondary viremia
- Target organ
Local infection:
apical release
Dissemination:
basal release
Systemic:
hematogenous/neural spread
How are viral rashes caused?
- if have systemic infection blood can enter skin and cause rash
- May also happen when virus leaves blood and enters skin
What is the replication cycle of HIV
- Fusion of the HIV cell to the host cell surface.
- HIV RNA, reverse transcriptase, integrase, and other viral proteins enter the host cell.
- Viral DNA is formed by reverse transcription.
- Viral DNA is transported across the nucleus and integrates into the host DNA.
- New viral RNA is used as genomic RNA and to make viral proteins.
- New viral RNA and proteins move to cell surface and a new, immature, HIV virus forms.
- The virus matures by protease releasing individual HIV proteins.
Tropism:
predilection of virus to infect certain tissues but not others (where virus replicates)
What is tropism dependent on?
- Susceptibility: receptor interactions
- Accessibility: ability to reach tissue
- Permissivity: ability to use host cell to complete replication
- essential intracellular host cell components.
- host cell receptor
- extracellular factors
What is the HIV tropism?
determined by cell surface receptor and viral attachment proteins
- 2 chemokine receptors CCR5 (macrophages) and CXCR4 (T cells)
What is the measles tropism?
CD155/SLAM or Nectin 4
- SLAM causes immunosuppression (because immune cell express SLAM) - Exit via airway epithelial Nectin 4
What is the influenza tropism?
- HA binds ubiquitous sialic acid receptors
- Fact that only influences resp. can’t be explained by receptors
- Influenza’s tropism determined by availability of host proteases protease found in respiratory tract secretion
What are the patterns of viral infection:
- Acute: followed by viral clearance
- Long: incubations
- Persistent: latent, slow, transforming
- Oncogenesis: affect the way cells control themselves
Chronic:
low level of replication in tissue which regenerate
Latent:
viral genome maintained but no virus seen until episodes of reactivation when immunocompromised
How do viruses cause cancer?
- May encode oncogene
- Interferes with cell cycle and enhance own replication
- By making host into cancer cell virus can replicate more and keep moving into new cells
What affects the severity of the infection?
- Viral load
- Viral sequence - strain of virus may affect virulence
- Host immune response
- Host co-morbidities
- Co infections
- Genetics
What are some predisposing co morbidities?
- Asthma and resp. viruses
- Obesity
- Immunosuppression
- Elderly
- Diabetes mellitus
- Pregnancy
How can viruses enter the body?
- Through the epithelial layers; respiratory tract, GI tract, genital tract
- Directly into the blood through a bite or needle
- Through the skin, often following abrasion
respiratory, faecal-oral, contact (saliva, fomites, lesions), zoonoses (insects, animals), blood, sexual contact, maternal-neonatal and germ-line (retroviruses) - 7% of germline = viral
What enzymes does HIV use?
Preintegration complex (PIC) – It is composed of viral RNA and proteins, as well as some host proteins. It functions to reverse transcribe genomic RNA into double stranded DNA prior to integration into the host genomic DNA.
Reverse transcriptase – creates double stranded DNA using viral RNA as a template and host tRNA as primers.
Integrase – permits the viral DNA to be integrated into the DNA of the infected cell.
Protease
