Mechanism of Viral Infection and Pathogenesis Flashcards
Why do most viruses we come across not infect us?
Most of these don’t “infect” us:
- They are adapted to non-human hosts
- They are excluded by surface barriers
- Innate Immunity prevents them establishing
- Adaptive immune response has seen something similar
What are the different sites of microbe entry?
- Conjunctiva
- Respiratory tract
- Arthropod bite
- Capillary
- Scratch injury
- Skin
- Anus
- Urogenital tract
- Alimentary tract
Name common viruses causing disease in humans
> Smallpox and (almost) Poliomyelitis are eradicated through vaccination
- Influenza
- Common cold
- Measles
- Mumps
- Chicken pox/Shingles
- Glandular fever
- Hepatitis
- Papillomas (Warts)
- AIDS
- Kaposi’s sarcoma
- COVID-19?
What are the 3 general patterns of viral infection?
- Acute infection
- Latent, reactivating infection
- Persistent infection
What is the virus load?
Virus load: viral replication - virus detected in us
What happens during acute infection?
The virus load gets cleared by the immune response or else we die
Disease symptoms occupy when virus load is at its highest but generally recover and develop long-lasting immunity
Name common acute viral infections
- common cold
- measles
- ebola lesion
- smallpox
Outline the pattern of infection of common cold
The virus remains in upper respiratory tract and nose and sore throat - easily resolved
How does measles present?
There are typical spots and ulceration of tongue - difficulty eating, as well as CNS problems
Describe the effects of an ebola lesion
A complete destruction of endothelium, massive haemorrhage - bleed to death; poorly resolved
Describe the pathogenicity of influenza
different strains produce a huge range of outcomes
e.g. 1918 vs 2005
Describe the 2005 influenza strain
2005 strain: circulating seasonal strain didn’t compromise people’s health greatly - similar to common cold
Describe the 1918 influenza strain
1918 strain: highly pathogenic strain with high fatality rate (great pandemic)
What causes chronic viral infections?
Virus persists throughout life, immune system responsible for keeping it under control
What is a latent reactivating infection?
Burst of viral replication and disease controlled by immune system to become disease free
However episodic reactivations of virus occur dut reservoir in host still present - mediated by immune system
What causes reactivation of a viral infection?
If immune system breaks down by the smallest degree the virus can be reactivated causing disease symptoms
Outline the various human herpes viruses
- Herpes simplex virus type 1
- Herpes simplex virus type 2
- Varicella Zoster virus
- Epstein-Barr virus
- Cytomegalovirus
- Human Herpes virus 6
- Human Herpes virus 7
- Human Herpes virus 8
Describe the structures of all 8 herpes viruses
All related viruses containing large dsDNA genomes - highly specific
What is the consequence of herpes virus infection?
lifelong infection, controlled by immunity
What are the effects of Herpes simplex virus HHV1?
Primary gingivostomatitis & cold sores
Primary facial rash (spotty) and causes temperature for ~1 day and then symptoms resolve
But the virus remains and at various points in life when under immune stress, produces cold sores
Which herpes viruses are responsible are similar to chicken pox HHV3?
Varicella Zoster Virus (VZV)
Shingles
What is the effect of HHV3?
Disseminated rash and pock marks, symptoms worsen the later in life you acquire the infection
Why is HHV3 reactivation worse than other herpes viruses?
Many years later after immune system wanes, it can reactivate same virus to cause highly septic, painful, blistering infections
Describe the mechanism of primary infections in herpes virus
During primary infection, these viruses give very specific fevers e,g.
- Disseminated rash in Herpes Simplex
- Delocalised rash in Chickenpox