Magor- Lecture 2: Viral lifestyles and pathogenesis Flashcards
What does a virus need to initiate an infection?(3)
- Sufficient virus at site of entry
- Host cells must be susceptible- susceptible cells have receptors required for viral entry.
host cells cells are permissive (factors needed for replication and dissemination) - Local antiviral defense must be breached
Sites of viral entry (5) into the host and examples of diseases
- Aerosol transmission
-Coronavirus
-Rhinovirus
-Influenza
-Measles - Oral-fecal transmission
-Poliovirus
-Norovirus - Arthropod vector
-West Nile virus
-Yellow fever - Sexually transmitted
-HIV
-Herpes - Contact with blood/secretions
-Hepatitis B virus
-Rabies
-Ebola
-Mpox
Acute infections
Rapid and self limiting
Example of acute infections
- rhinovirus
- rotavirus
- influenza virus
- coronavirus
- poliovirus
TRUE or FALSE
Virus can be present before symptoms
TRUE
Influenza
- an acute infection rapidly spread by aerosolized droplets
- the 1918 influenza pandemic killed 40 million people worldwide.
Most SARS-CoV2 transmission occurs through
Aerosols- aerosolized droplets that contains particles of virus.
Persistent infections
are on-going infections
ex: Hepatitis B
Hepatitis B has 2 different lifestyles:
- can either be an acute infection that gets cleared
- persistent infection that never gets cleared
TRUE or FALSE
Viruses can persist and overwhelm the immune system later
TRUE
Why is it an advantage for a virus to have a persistent lifestyle?
The virus can just hangout and then infect the person for their entire life.
Two types of Hepatitis B infection
- Acute HBV
- Chronic HBV
Acute HBV
- fever
- loss of appetite
- nausea
- vomiting
- abdominal pain
- yellow coloring of the eyes
- dark urine
- clay colored or light stools
Chronic HBV
symptomatic or not, approximately 5-10% of adults and 95% of perinatally infected infants are unable to clear the virus, thus becoming chronic carriers.
HBV is transmitted in _________________
infected blood
In many parts of Asia, there are already many chronic HBV carriers & most people get infected at birth through the exchange of blood between the mother & baby. If you get infected at birth, ____% will be chronic carriers.
95%
Case Study: A patient complains of fever, nausea and loss of appetite. On examination you notice yellow whites of eyes. You also notice a tattoo that seems recent enough to still have scabs/bleeding. You suspect a hepatitis B infection.
- What are the tools for diagnosis of this infection?
- How long until you can make a conclusive diagnosis?
- Can do blood test- PCR
- Quickly
Latent infections
an extreme persistent infection (sometimes hidden)
symptoms may not always be present while virus is infectious
viruses hide from the immune system in a latent infection
Example of a latent, reactivating infection
Herpes simplex virus
Difference between a latent and persistent virus
A latent virus is a persistent virus but it has times where it’s not actually replicating
Herpes simplex I virus
- can remain latent for years
- forever; we don’t get rid of Herpes
- 20% of the population have recurrent symptoms
- Herpes simplex hides in the trigeminal ganglia and can reactivate when you are stressed. Nerves are typically protected from immune responses
Slow viruses
- have a long latency period followed by acute infection
- persistent virus
- virus may be present at times during latency (HIV) or undetectable for years (measles SSPE)
Examples of slow virus infection
- Measles SSPE= measles subacute sclerosing panencephalitis
- HIV
Measles
- causes acute infection and a rare latent disease
- can be cleared
- human-only pathogen- It’s a pathogen for which we have a really good vaccine
- rash, hypersensitivity reaction, fever, cough, conjunctivitis
- only once in a lifetime
- Measles impairs B cell memory to other vaccines and pathogens
How HIV get transmitted?
Many people don’t know that they’re infected with HIV for years
What makes measles so contagious?
- Extremely contagious for unvaccinated. Up to 90% of the unvaccinated people who come into contact with a contagious individual will also become infected. The measles virus can remain in the air for up to two hours after an infected person leaves an area.
- Measles has long incubation period. In infected people, the time from exposure to fever is an average of about 10 days, and from exposure to rash onset is about 14 days -but could be up to 21 days. In addition, infected people are contagious from 4 days before rash starts through 4 days after. That’s a long period of time where they could unknowingly infect others.
Measles have an ________ effect where if a kid gets measles (say at 5 yrs old) it wipes out their B cell response.
immunosuppressant
The primary repertoire of B cells that they make is not complete after a measles infection. They lost the immunity to everything that they’ve previously been vaccinated to.
Andrew Wakefield
- connected MMR vaccine to Autism
- person who started the anti-vaccine movement
Pathogenesis: Injury caused by viruses (3)
- Cytopathic effects on cells directly
-cells may be lysed - Viruses can ne oncogenic (cause cancer)
-cells lose contact inhibition and their normal interactions (anchorage-independence) and become immortal
-can be transformed by virally encoded oncoproteins (v-oncogenes)
-viral disruption of host genes (c-oncogenes) - Immunopathology- damage as a result of local inflammation
Poliomyelitis
- damage caused by viruses
- paralysis in 1% of infected individuals
- children used to be exposed to polio from their mothers while they were still getting maternal antibodies in breastmilk.
- in early 1900s there was an increased incidence because of improved sanitation. This was because infants were not exposed to poliovirus while still protected by maternal antibodies.
Cytopathic effect in poliovirus
Cell rounding and lysis by poliovirus infection
Anchorage independence
cancer cells lose their attachments and become mobile
Peyton Rous
- In 1965, 55 years after his discovery of RSV, he was awarded a Nobel Prize in recognition of the key role that the virus has played in unlocking the secrets of cancer.
Retroviruses
- can take up cellular DNA. They integrate a provirus form into the genome
Rous sarcoma virus
- has taken up a src gene, called v-src to distinguish it from cellular scr.
Src
- a cell signalling molecule that phosphorylates proteins involved in signal transduction. Unregulated cell signalling from v-src causes cancer
