Unit 4 Flashcards
What is the name of the virus that causes mononucleosis?
EBV - Epstein-Barr Virus
Epstein-Barr Virus is part of what virus family?
The herpesvirus family
What 4 layers make up the EBV virus?
- nucleoprotein core 2. polyhedral capsis 3. tegument
4. envelope
What is the nucleoprotein core of EBV made up of?
DNA genome and proteins to fold it.
What is tegument?
It is the space between the capsid and envelope in EBV which contains 10-20 regulatory proteins
What are some examples of regulatory proteins?
Transcription factors and enzymes
What is unique about the envelope of the EBV virus?
in is roughly 150nm in diameter and contains up to 10 different spaces
What characteristics make up the genome of the EBV virus?
- linear dsDNA - up to 150 different proteins
2. not dependent on host cells for any DNA replication and has many proteins which regulate host cell activities
What is the reservoir for mononucleosis (EBV)?
- humans during infection: incubation through convalescence
- carriers who recover from mono produce virus periodically for life.
What are the 2 routes of transmission for mono?
- direct contact - saliva
2. fomites - saliva
What are the 2 primary types of cells infected by EBV?
- epithelial cells of nasopharynx and salivary glands
2. B lymphocytes
What are the three possible outcomes for EBV once it enters a host cell’s nucleus?
- can remain linear
- can become an episome (circular)
- can splice into chromosome
What are the 4 possible results of EBV infection?
- latent
- virus replication = lytic
- host cell replication with expression of some viral genes = mono
- host cell replication w/o expressing viral antigens = cancer
Where is the name “mononucleosis” derived from?
It is because mononuclear (lymphocytes) are proliferating
What are the outcomes of a lytic infection of EBV?
new viruses are being made and all viral genes are being expressed -> infectious. The symptoms here are roughly equivalent to that of a cold.
What happens to the nucleus of a host cell infected with EBV?
It becomes dimpled
What is occuring in an EBV infection resulting in mono?
no new viruses are being made, and only a few of the viral proteins are being expressed. The virus triggers infected B lymphocyte proliferation and random IgM antibodies are secreted by these infected B lymphocytes. Both B cells and CTL’s can attack infected B cells
How is it that EBV causes cancer?
Because the virus in this circumstance causes proliferation of the infected cells however no viral proteins are being expressed, so there is nothing to stop the proliferation
What are the two types of cancer that can occur as a result of EBV?
- B - cell lymphoma
2. nasopharyngeal carcinoma
What would put a person at risk for lymphoma?
A weakened immune system
Why are EBV infections in young children usually asymptomatic?
Because of the speed and intensity of their immune system
Why are 15-25 year old people most at risk for developing mononucleosis?
Because of their lifestyle which produces both weakened immune system and close proximities which promote transmission
What is the incubation period for mono?
4-7 weeks
Why is it that a person who has recovered from mono is likely a carrier for life?
Because if they have a latent form of the virus in their cells it can periodically become lytic with very little symptoms for the rest of their life.
What are the 3 most noteable symptoms of mononucleosis?
- a high and fluctuating fever
- sever pharyngitis
- lymphadenopathy
What is pharyngitis?
inflammation of the pharynx and nearby tonsils - possibly obstructing breathing
What is lymphadenopathy?
noticeable swelling of lymphocyte reservoirs (spleen and lymph nodes) due to lymphocyte proliferation
How long do the symptoms for mono generally last?
2-3 weeks
How long is the convalescence period for mononucleosis?
12-18 months
What are the 4 main complications that can arise from mononucleosis?
- ruptured spleen => internal bleeding
- Infection of other cell types => meningitis, encephalitis, carditis, nephritis, hepatitis or pneumonia
- B cell lymphoma (Burkitt’s lymphoma)
- Nasopharyngeal carcinoma
Why is it that the EBV is capable of infecting so many different types of cells in the body?
Because it has 10 spike proteins, so a receptor can be found almost anywhere
Why is it difficult to set a morbidity/mortality rate for mono?
Because it depends on where the person was infected
What is the morbidity rate of mononucleosis in developing countries?
<0.1%
What is the morbidity rate of mononucleosis in developed countries?
<10%
What is the incidence of mono in the U.S.?
1.5 million cases per year
What is the mortality rate of mono?
10/1.5 million, it is very rare
What is the mortality rate of B cell lymphoma?
10-70% dependent upon when it was detected and treatments available
What is the mortality rate of nasopharyngeal carcinoma?
50%
What are the 5 ways to diagnose mononucleosis?
- High mononuclear cell count
- lobed nucleus in lymphocytes - can be seen in blood smear
- prolonged prodromal symptoms
- look for heterophile antibodies
- antibodies being made by healthy B cells to EBV will be produced
What is the most general treatment of mono?
Simply rest
What medication is given for sever cases of mono?
acyclovir - base analog
What are the 2 behavioral preventions for mono?
- avoid the routes of transmission 2. expose kids when they are young
What can be done to prevent mono chemically?
acyclovir could be taken prophylactically, but normally wouldn’t be
What are the 2 current vaccine candidates against EBV?
- gp350 => spike protein
2. LMP2 => spike protein (naked DNA)
EBV is considered what type of carcinogen?
A class I carcinogen (the first human tumor virus)
What is the prevalence of EBV in adult populations worldwide?
> 90%
EBV is found in roughly 10% of all ________ cancers
stomach
Aside from EBV what other two herpesviruses have been linked to causing cancer?
- Human herpesvirus 8 (HHV8) also known as KSHV (kaposi sarcoma associated herpes virus)
- Human Papillomaviruses (HPVs)
What other viruses or infectious agents have begun to be associated with human cancer etiology?
- hepatocellular carcinoma viruses (hepatitis C and B)
- T cell leukemia virus (human T-lymphotropic virus I and II)
- Merkel cell carcinoma virus
It is estimated that overall ____ of all cancers are a result of infectious agents
1/5
In addition to being the first human cancer virus to be discovered, EBV was also….?
The first large herpesvirus genome to be completely sequenced
What do studies show may explain the variation in cancer risk from EBV?
polymorphisms
How many open reading frames does the EBV genome contain?
close to 100
What are the two proteins expressed consistently in human cancers that were found in EBV?
- EBV nuclear antigen (EBNA 1)
2. latent membrane protein (LMP 1)
How many microRNAs does the EBV genome code for?
over 20
Why are the expression of microRNA and other non-coding RNA’s in EBV significant?
Because they are expressed at high amount and have tumorigenic properties (including the potential to be transmitted via exosomes to noninfected neighboring cells
EBV latent infection is also capable of providing a mechanism for viral oncogenesis, why is this?
Because is epigenetically suppresses host tumor suppressor genes
What exactly does the gp350 vaccine target? Why is it not effective at reducing cancer associated with EBV?
It targets the glycoprotein of EBV, because it does not prevent the occurence of latent infection
How have B cell lymphomas arising from EBV been successfully treated?
Using adoptive immunotherapy
What types of selective treatments against EBV are currently being developed?
Biological and pharmacological inhibitors of viral proteins and oncongenes
What other diseases have been linked to EBV?
multiple sclerosis and lupus erythematosis