11: Infection basics Flashcards
What does a virus need to successfully infect a host?
- Enough viral load
- Accessible, susceptible and permissive cels
- Evasion/modulation of immune system
Define Pathogensis
The process of generating a disease
What is disease mediated by during viral infection?
- Effects of viral replication
- Effects of host immune response
What is the site of viral entry?
Respiratory tract
(upper or lower)
- Influence viruses reproduce in respiratory epithelial cells in humans. These particles are uncleaved form of HA and non infectious. Tryptase can clean HA which makes in infectious.
How do viruses shed and transmit?
Viruses are released by extra cellular fluids and taken up by lymphatics.
Lymphatic vessels drain into circulatory system (primary viremia), viruses reach and replicate in organs
Viruses move back into blood (secondary viremia) and relocate into organs to be transmitted.
What is Viremia?
-Passive Viremia
-Primary Viremia
-Secondary Viremia
It is the presence of virus particles in the blood
Passive Viremia:
when the host is a recipient of the virus from a mosquito
Primary Viremia: reproduction of the virus at the site of entry to release into the blood via lymphatics
Secondary Viremia:
Higher load of virus found in the blood and their reproduction in specific organs or tissues
How do viruses invade tissues?
Sinusoids:
line adrenal glands, liver, kidney and bone marrow (easy to invade)
Fenestrated endothelium:
villi of intestine, renal, pancreas and endocrine glands
(easy to invade)
Endothelium/Basement membrane:
CNS, skeletal and cardiac lungs/muscle
(hard to invade)
How to viruses travel from the blood tissue across the basement membrane of blood vessels?
- Reproduction ion endothelial cells
- Transcytosis
- Trafficking lymphocyte or monocyte
What is the neuronal spread of viruses?
- Anterograde Spread:
The virus invades the dendrites or cell bodies and then virus particles spread to the axon terminals and cross synaptic contacts to invade dendrites/cell bodies - Retrograde Spread:
The virus invades axon terminals and spreads to the body where reproduction occurs
What are the modes for CNS viral infection?
Neurotropic: Virus can infect neuronal cells
Neuroinvasive: Virus can enter the CNS after infection of the peripheral site (Rabies, MUMPS)
Neurovirulent: Virus can cause sever disease if it enters CNS (HSV, Rabies
Pathogenesis of mouse pox
There is a break in the skin, virus infects cells. Virus reproduces and disseminated via lymphatics.
Then there is primary or secondary viremia.
Virus sheds from the skin and reproduces causing a disease (rash)
What is a viral incubation period vs Prodromal?
Viral incubation: the time between the infection and the onset of symptoms (can/can’t be transmitted)
Prodromal: Period of non-specific symptoms before characteristics of the disease
Epidemiology
Incidence rate: # of infected people / # of population over a period of time
Morbidity rate: # of ill people / # of population over a period of time
Mortality rate: # of deaths / # of population over a period of time
(MOST ACCURATE) Case fatality rate: # of deaths / # of confirmed infected cases over a period of time
infection fatality rate: # of deaths / # of actual infections over a period of time
What are the patterns of transmission?
Horizontal: Between members of the same species
Vertical: Mother to child
Zoonosis: Animals to humans
Reverse Zoonosis: Humans to animals
Latrogenic: Activity of healthcare worker that leads to infection
Nosocomial: Individual is infected in hospital
Germ line transmission: Agent is transmitted as a part of the genome
