Thirty Four Flashcards
What kind of virus is rubella? What does it cause? What is its genome like? Where does it replicate?
Togaviruses: Rubella
- Causes “German measles”
- Enveloped + strand RNA virus: genome is
template for protein translation and is
incorporated into infectious daughter virions
- non-segmented genome
- replicates in cytoplasm
What are rubella infections like in adults? What symptoms occur in children? Describe them. What symptoms might occur in infected young adults? Describe them. How is a diagnosis confirmed?
- 50% of infections are inapparent (esp. in healthy adults)
- Infected children develop fever followed by rash
- Rash characteristically begins on face and then
spreads down body (unevenly)
• Lymph nodes at back of head (over occiput) may
be swollen
• Infected young adults may get URI symptoms
before the rash develops. Infections are
associated with joint pain (arthralgia) or arthritis
(joint inflammation). Occasionally arthritis can
last for weeks.
• Check rubella serum
antibody titers to
confirm diagnosis
How is rubella transmitted? Where and how does the virus spread once it is in the body?
• Person to person via respiratory secretions
(coughing, sneezing)
• As with many infections, people are infectious
before they develop symptoms, thus disease is
easily transmitted.
Rubella virus is inhaled, replicates in respiratory
epithelium then disseminates to blood
Of the adults that do become symptomatic, what occurs? What are the results of most adults being asymptomatic?
• Some adults (<50%) have fever, rash and
arthralgia/arthritis, but most are asymptomatic
• Most healthy adults have few/no symptoms-
therefore people become infected and are
infectious without knowing it.
– Facilitates viral transmission
– Pregnant women can be infected without
aware of it
Describe how congenital rubella occurs. What are the results in the fetus?
Maternal
• Pregnant women w/out protective antibodies
(unvaccinated/never infected)
• Inapparent maternal disease
• First trimester infections can cause miscarriage and
deformities
• Defects rare if infection after 20 weeks
Infant infected in 1st trimester
- Fetal growth retardation
- Deafness
- Cataracts/blindness
- Mental retardation/small brain
- Heart defects (PDA)
- Up to 85% of infants infected in first trimester will have a
defect
What is the rubella vaccine like? How are non-vaccinated pregnant women advised?
- Developed in 1960s
- live attenuated virus
- Given with measles and mumps vaccines
(MMR) or with MMRV (varicella zoster vaccine
added)
• Not licensed for pregnant women/immunocompromised because it’s a live vaccine
• However some women have been accidentally
vaccinated (before they knew they were
pregnant) and no adverse events occurred in the fetus.
• Pregnant women are tested for antibodies to
make sure they are immune
• If not immune, advised not to travel to rubella-
endemic areas and avoid children with rash until 20 weeks
What is the genome of the coronaviruses like? What illnesses do they usually cause? What lends them their great infectivity? How does MERS and SARS differ from most coronaviruses?
- Enveloped, + sense RNA unsegmented genome
- Cause upper respiratory infections/the ”common
cold”(along with rhinoviruses, etc)
- Virus retains infectivity in environment for hours
- Coronaviruses that cause the “common cold”:
replication limited to upper respiratory tract.
• Coronaviruses that cause MERS or SARS are
able to invade the lower respiratory tract (lungs)
and disseminate through blood to other tissues.
What is SARS? Describe its history/epi? Mortality rate? What are the symptoms associated with it? Where does it replicate in the body?
- Severe Acute Respiratory Syndrome
- 1st reported in asia in 2003
- 8000 cases worldwide, ~775 deaths (~ 10% mortality)
- Flu-like illness with progressive respiratory
failure
• Virus replicates in upper and lower
respiratory tract, leading to severe
pneumonia and respiratory failure.
Diarrhea also a common symptom.
Describe the transmission of SARS. How was it treated/eradicated?
- Transmitted by resp. secretions
- Also transmitted by objects with
respiratory secretions as virus is stable
and infectious in environment for hours.
Therefore objects such as doorknobs,
elevator buttons, etc. that harbored live
virus were able to infect people who
touched them and then touched their
mouth or nose.
SARS spread globally within weeks (via
infected people travelling from
Guangdong)
• No specific treatment available: cases
quarantined and contacts traced and
evaluated
• Virus identified within weeks of outbreak
using PCR
• Quarantine led to containment and finally
eradication; only cases since 2003 in lab
workers
Describe the history of MERS. What is its mortality rate? What are the symptoms? How is it transmitted? How does it compare to SARS?
• 1st reported in saudi arabia in 2012; all
cases identified to date were in people in
or traveling from the Middle East
• 2nd known coronavirus capable of
invading and replicating in human lungs
• Symptoms: fever and cough progressing
to severe pneumonia.
- ~30% mortality rate
- Transmission via resp. secretions during close contact (within 6 feet for several hours).
- Limited transmission outside the Middle East suggest virus has less infectious potential than SARS
What are paramyxoviruses like? Where do they replicated in the cell? What proteins do they contain ? What are the 3 genera? What are 5 pathogens?
- Enveloped virus
- Neg. strand
nonsegmented RNA
genome
• Replicates in
cytoplasm
• Hemagglutinin (+/- Neuraminidase) mediates cell
attachment
• Fusion protein mediates membrane fusion
Paramyxovirus
Rubulavirus
Morbillivirus
- Parainfluenza virus (paramyxovirus)
- Measles (note: not German measles/rubella) (morbillivirus)
- Mumps (rubula)
- Respiratory Syncytial Virus (RSV)
- Human metapneumovirus
What is the transmission of the paramyxovirus species? What is their mech. of replication/spread in body? What is an example?
- Respiratory secretions.
- Virus remains infectious in air and on
surfaces for over an hour- people can
acquire infection from doorknobs, elevator
buttons, etc. Infectious virus is picked up
on hands and carried to mouth, eyes, nose
- Attaches via H/N proteins
- Fuses to host cell membrane via F protein
- Viruses released by cell lysis (kill host cells)
- Virus remains confined to resp. tract and does not spread thru body
Parainfluenza virus
What symptoms does the parainfluenza virus cause? Describe croup. What is the cause? Symptoms?
• Commonly causes flu-like illness in young
children. Also common cause of ear infections
(otitis media), bronchitis, rare cause of
pneumonia
• One of many viruses causing “common cold”
• Croup: acute inflammation of larynx/trachea,
often due to paramyxovirus. Can lead to airway
obstruction b/c of accumulated respiratory secretions.
• Croup is fairly common on young children;
progressive barking cough as airway gets
compromised
How is mumps transmitted? What are the symptoms/disease progression? What is its dissemination like? Prevention?
- transmission by respiratory secretions
- flu-like illness followed rapidly by development of
swollen parotid glands - unlike parainfluenza (but like rubella), virus
spreads into bloodstream and can infect brain
(meningitis/encephalitis), pancreas (pancreatitis),
gonads (orchitis, oophoritis) - MMR or MMRV vaccination prevents disease
What proteins are found on measles? What significance does this have? What proteins do they bind and which cells contain these proteins?
• Lacks Neurominidase activity (no N protein)
• F protein causes cells to form syncytia (lose
cell membranes)
• Binds CD46, complement receptor, found on leukocytes, epithelial cells, fibroblasts- wide
range of host cells
Describe the transmission of measles. Where does its start replicating? Describe its dissemination from there. What symptoms does it cause?
• Transmission by respiratory secretions
• Virus is extremely infectious (low inoculum required to
establish infection and people are infectious prior to
symptoms)
• Virus replicates in respiratory epithelium (mouth: causes
Koplick spots) then spreads to blood
• Use of CD46 receptor allows rapid dissemination from
respiratory epithelia to lymphoid and other tissues
- fever, cough, runny nose (coryza and cough)
- conjunctivitis followed by rash
- rash begins in mouth (koplick spots), spread to face and travels down body. Changes color as disease progresses.
What are some complications of measles? How are they caused? How could they be prevented?
• Complications: virus disseminates throughout
body on lymph tissue/leukocytes
- pneumonia- (1/20 cases: still a leading killer of
children in developing world (164,000
deaths/year, ~0.2% mortality)
- encephalitis
- corneal scarring and blindness
Prevention: vaccination (MMR or MMRV) (live
attenuated vaccine against measles, mumps,
rubella)
How is the diagnosis of measles made?
• 3 C’s: coryza
(inflammation of
upper respiratory
tract), cough,
conjunctivitis
• Presumptive
diagnosis requires
fever for 3 days, rash,
and one of 3 C’s
• Definite diagnosis
requires detection of
antibodies or viremia
