Lecture 26

Question 1

Parvovirus

Answer 1

smallest DNA virus
only human pathogen is B19
Also canine, feline, goose, porcine parvoviruses

Question 2

Parvovirus structure

Answer 2

non-enveloped
single-stranded DNA
Three structural proteins and two non-structured proteins

Question 3

Parvovirus

Answer 3

B19 is widespread
Infections occur throughout the year in all age groups
Common outbreaks in schools and in childhood
Mode of transission - person to person, direct, respiratory droplets, indirect fomites
Viruses are stable in environment so contaminated surfaces involve transmission
Sibling transfer is important

Question 4

Parvovirus replication

Answer 4

The virus is trophic for erythroid cells (bone marrow or fetal liver also prefers mitotically active cells)
Attachs to RBC blood group P antigen to enter cell
Uncoding takes place in the nucleus
Host cell polymerase produces a complimentary negative strand of DNA

Question 5

Parvovirus replication

Answer 5

mRNA is translated in cytoplasm on ribosomes

Virus is released by lysis

Question 6

Parvo patho

Answer 6

Virus first replicated in the upper respiratory tract, next virus enters blood - viremia, next virus is spread to bone marrow and other erythroid precursor cells
B19 disease is determined by direct killing of these cells and the immune response is rash and arthralgia

Question 7

Parvo clinical disease

Answer 7

Erythema infectiosum AKA fifth disease
Rash (slapped cheek appearance)
Incubation period virus shed into blood
Pt is infectious
Prodromal period 
- once virus enters blood, rash on face in children
- Flu-like symptoms
- pt infectious for up to fourteen days

Symptomatic stage - get IgM Ab (immune complexes)

• rash appears on face spreads to extremities in children
• adults: rash may or may not occur but has polyarthritis of hands, wrists, knees and ankles

Question 8

Parvo clinical disease

Answer 8

Aplastic crisis
- RBC and platelet levels drop
- in pt's with sickle cell
Hydrops fetalis
- aplastic crisis of pregnant females
- B19 infection of seronegative mother increases risk of fetus

Question 9

Paramyxovirus

Answer 9

measles (morbillivirus)
mumps and parainfluenza (paramyxovirus)
respiratory syncytial (pneumovirus)
All have similar structures and cause formation of syncytia (cell to cell fusion resulting in multi-nucleated giant cells

Question 10

paramyxovirus structure

Answer 10

single stranded RNA
negative sense
helical capside
enveloped 
-two glycoproteins F-fusion factor
-H, HN, or G - viral attachment proteins
----H-measles
----HN-mumps and parainfluenza
----G-respiratory synctial virus

Question 11

Measles patho

Answer 11

acquired by inhalation of infectious droplets
highly contagious
replication followed by spread to local lymph nodes and then to lymphatics and blood
about 6 days after infection, virus spreads systemically resulting in infection of all epithelial surfaces (conjunctiva, skin, respiratory tract, bladder)

Question 12

Measles patho 2

Answer 12

Mucosal lesions in mouth may be observed these lesions are pathognomonic of measles and are called kopliks spots
symptoms become worse until rash appears at day 10-14
rash is caused by T lymphocytes targeting infected endothelial cells lining the small blood vessels
starts on forehead and moves down
lifelong immunity after recovery

Question 13

Measles patho 3

Answer 13

complications - otitus media, diarrhea and pneumonia

Vaccination MMR

Question 14

Rubella

Answer 14

Actually a togavirus
virus: rubivirus
prodrome
-mild catarrhal 
-tender lymph nodes

Exanthem
-starts on face spreads down - 
Day 1 - 1-4mm macules 
Day 2 - pinpoint papules
Day 3 - Clears

Question 15

Rubella

Answer 15

fetuses of non-immune women infected with Rubella have many complications

• hearing loss
• heart defects
• neurological
• opthalmic

First trimester - 65-85% of neonates have sequelae
Prevention - MMR

Question 16

Mumps Patho

Answer 16

Paramyxovirus with one antigenic type
Respiratory transmission
Replication in nasopharynx and lymph nodes
Viremia 12-25 days after exposure
Multiple tissues infected

Question 17

Mumps clinical disease

Answer 17

incubation 14-18 days
Parotitis in 30-40%
up to 20% asymptomatic
Acute onset of limited swelling of the carotid or other salivary gland lasting more than 2 days without a apparent cause

Question 18

mumps complications

Answer 18

1. CNS involvement 15%
2. Orchitis 20-50% post-puberty males
3. Pancreatitis 2-5%
4. deafness 1 in 20,000
5. death - one per year

Question 19

mumps transmission

Answer 19

reservoir - human
transmission - respiratory drop
seasonal pattern - peak in late winter and spring
communicability - 3 days to 4 days after onset of active disease
prevention - MMR

Question 20

Respiratory Syncytial

Answer 20

Pneumovirus of paramyxoviruses
widespread - 75% of infants seropositive by 1 year old
annually in US 50,000-80,000 hospitalizations, 100 infant deaths, 17000 elderly deaths
post range limited to humans, single serotype
respiratory transmission is highly contagious
localized to respiratory tract, no viremia or systemic infection

Question 21

respiratory synctytial disease

Answer 21

children less than one year old = bronchiolitis
pneumonia
common cold in older children and adults
poor immunity infections reoccur throughout life
maternal antibody does not prevent infection

Question 22

respiratory synctyial virus treatment

Answer 22

ribavirin - reduces severity of symptoms in weak pt’s
no vaccine
passive vaccine for high risk infants
-palivizumab (synagis) - anti-F monoclonal antibody

Question 23

parainfluenza virus

Answer 23

four serotypes limited to humans
respiratory transmission - non-systemic
causes cold like symptoms, bronchitis and croup (serotypes 1 & 2) common in children
immunity following infection is short-lived subject to reinfection
vaccines in clinical trials