Transcript Systemic virus infections

“MMR”
Measles, Mumps, Rubella
Leslie Lobel
Dept. of Virology
Pathology Building Room 255
E-mail: [email protected]
Office: 08-6282851
Mobile: 052-6488000
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“Childhood” diseases:
Measles, mumps, and rubella
What do they have in common?
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Infection via respiratory tract
Systemic illness, which begins only after
two cycles of viremia
No natural hosts other than man known
Infection provides (more or less) life-long
immunity
(Early childhood infection is often milder
than adolescent or adult infection)
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Measles and Mumps are
Paramyxoviridae (RNA-)
HN
F
rNP
M
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Structure of Paramyxoviruses
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RESPIRATORY SYNCTIAL VIRUS
F&G
Serotypes A & B
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Respiratory syncytial virus in cell culture
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Comparison of Ortho- and Para
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Similarities
General structure, lipid
membrane
ssRNA (-)
Two proteins extending
from the membrane
For now, it seems that
all viruses in these
families that infect
humans do so in the
respiratory tract
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Differences
Segmented genome
vs. continuous
Paramyxoviridae are
somewhat larger
Genetic stability
Mode of entry into the
host cell
Location of genome
replication
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Paramyxoviruses
Parainfluenza
1. bronchitis and croup
2. usually relatively milder disease, but…
3. bronchitis and pneumonia
4. mainly upper respiratory infection (URI)
Respiratory Syncytial Virus (RSV)
• milder illness
• bronchiolitis
• Pneumonia
Metapneumovirus
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Individual viruses and their illnesses:
(1) Measles
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Relatively short incubation period about
1.5-2 weeks, 10-14 days
There is practically NO subclinical infection
Even simple infection (without
complications) is incapacitating for a week
to 10 days
About 95% of exposed susceptible
persons will become infected
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High fever starts
about 2-3 days
before appearance
of maculopapular
rash (centrifugal
spread), and
continues,
gradually abating
Cough,
coryza,
conjunctivitis,
photophobia
Malaise,
anorexia
Recovery after
simple infection,
one week to 10
days
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Diagnosis
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Koplik’s spots, tiny white dots on an inflamed
buccal mucosa: appear 2-3 days after start of
fever, disappearing after first day or two of rash.
The general rash is not pathognomonic—a
heavy rubella rash may be difficult to distinguish
from a light measles rash.
Serologic diagnosis may be made from shortly
after appearance of the rash: IgM at first, then
rising titer of IgG. Usually carried out by ELISA.
At one time HI was the most common assay
method.
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Koplik’s spots in measles
Note: Koplik’s spots may
appear as tiny dots or as
ulcerations
“Enanthem”
Exanthem
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Measles exanthem
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Measles: desquamation and
conjunctivitis
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Complications of measles
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Secondary bacterial infections: otitis media, eye
infections, and more
General depression of cellular immunity: e.g.,
herpes simplex reactivation
Respiratory tract: several types of pneumonia
(bacterial or viral, measles, giant-cell)
Central nervous system: encephalitis, SSPE
(subacute sclerosing panencephalitis)
(Atypical measles)
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CNS complications in measles
(affinity for central nervous system)
SSPE
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SSPE symptoms and prognosis
SSPE diagnosis (serology: high titers; EEG: slow waves)
SSPE epidemiology (massive exposure, young age)
Effect of measles vaccine on incidence of SSPE
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Measles virus outbreaks
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The need for a second immunization
Possible subclinical infection in partially
immune persons
What is the earliest age at which one can
immunize?
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Individual viruses and their illnesses:
(2) Mumps
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Mumps
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Mumps
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Incubation period relatively long (2.5 wks)
Virus replicates rather slowly…
Rather mild illness (usually low fever, swelling of
parotid glands)
One third of infections are asymptomatic
Contagiousness: Virus is secreted in saliva 6
days before appearance of symptoms
There is an effective vaccine—developed
because of complications of mumps infection
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Complications of mumps infection
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Nervous system
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Meningitis – usually benign
Meningoencephalitis – can be dangerous
Deafness
Pancreatitis — diabetes (IDDM, type I)?
Orchitis and oophoritis—sterility, rarely
Myocarditis
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Rubella (German measles, 3-day measles)
Rubella is a Togavirus (RNA+)
Mature rubella virion in cytoplasmic vacuole. Note central capsid
and lipid-containing outer envelope; bar = 100 nm
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Togaviridae: Enveloped + Strand RNA
Viruses
Alphaviruses –
a) Eastern Equine Encephalitis
b) Western Equine Encephalitis
c) Venezuelan Equine Encephalitis
Rubiviruses –
a) Rubella
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Rubella infections
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The virus is extremely labile
Incubation period relatively long (~2.5 weeks)
Generally mild illness: sometimes low fever,
maculopapular rash, lymphadenopathy,
specifically posterior cervical and suboccipital
l.n., conjunctivitis, and sore throat
One quarter of infections are subclinical
Arthralgia is common in infections of adolescents
and adults (virus in joints)
Vaccine developed because of teratogenicity
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Rubella exanthem
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Simple rubella
Congenital rubella
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Rubella congenital infection
cataracts
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These defects are fairly
common. Others are possible
but are rather rare.
Some defects are noticed only
with time (developmental)
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Spread of rubella in the host
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Excretion of rubella in urine
after congenital infection
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Mechanism of damage to fetus
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Inflammation of blood vessels
of the placenta—lack of O2 for
fetus?
Chromosome breaks??
Slowing of cell division (in
vitro, infected human embryo
cells respond less to epidermal
growth factor and synthesize
less collagen)
Focal cellular necrosis (lens)
Damage to blood vessels (and
nearby neural tissue)
Immune complexes?
Timetable of fetal
damage
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1st 8 weeks of pregnancy:
67-85% chance for fetal
damage
Average for 1st trimester,
30%
2nd trimester on: about
10% chance for
damage—mostly auditory
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Molecular mechanisms of cellular and fetal
damage
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Viral p90 (replicase)
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Binds cellular RB (retinoblastoma) protein (cf. IE2 86
of CMV) causes premature cellular DNA synthesis,
yielding chromosomal damage and mitotic arrest)
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Binds cellular citron-k kinase (CK), a cytokinesis
regulatory protein
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Deletion of the RB binding motif is lethal to the virus
Problem of cellular location (RB vs virus)
CK knockout: pcd (programmed cell death) of neuroblasts,
malformation syndromes of the CNS; apoptosis?
Will new drugs be developed to prevent these
interactions?
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Diagnosis of congenital rubella
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Prenatal—exposure/illness
Postnatal
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Viral culture from urine
Infant IgM or IgA
Importance of diagnosis
-for genetic counseling
-for protection of pregnant women
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Simple rubella infection
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Eradication of these viruses?
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Lack of animal reservoir
Existence of effective vaccine
Inapparent infections?
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High rate of asymptomatic infections in
mumps and rubella
Asymptomatic infection in partially immune
individuals (measles)?
Need very high vaccine coverage rate
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Newly recognized problem
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If one can’t control measles infection in
HIV-infected individuals, it will not be able
to be eliminated.
There is a lack of good animal models with
which to study the response to measles
virus infection or immunization in
immunocompromised hosts
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Parvovirus B19
Leslie Lobel
[email protected]
052-6488000
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Classification of human parvoviruses
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Subfamily Parvovirinae
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Genus Parvovirus
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Genus Erythrovirus
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Adeno-associated viruses types 1-6)
(animal viruses)
Genus Bocavirus
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B19 virus
(animal viruses)
Genus Dependovirus
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(many animal viruses)
Human Bocavirus
Bovine and canine bocavirus
Subfamily Densovirinae
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(animal viruses)
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Computer model of Parvovirus B19
Icosahedral, 32
(60) capsomeres
Diameter:
18-26 nm
Very small !
One major and
one minor coat
protein (most
parvo have 3)
ssDNA
About 5 kbp in length
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Autonomous and defective parvoviruses
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Parvovirus B19 is an autonomous parvovirus
that infects humans
Autonomous parvoviruses require growing cells
for replication
Many other autonomous parvoviruses infect
animals
AAV (adeno-associated virus) is a dependovirus
that infects man, but is not known to be
pathogenic
It requires a helper virus in order to replicate
Many other dependoviruses infect animals
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Virions of parvovirus B19 and adenoassociated virus (AAV)
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Non-structural proteins are coded at the 5’ end
of the genome.
Coat proteins coded for by overlapping in-frame
DNA sequences, at 3’ end of genome.
Virions are stable to pH (3-9) and to heating at
56 oC for one hour. (significance for blood products)
B19 cannot stimulate or turn on host DNA
synthesis in resting cells; it waits for the cell to
enter S phase.
AAV relies on a helper virus (adenovirus or a
herpes virus) to induce S phase.
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The parvovirus genome
(True for AAV)
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Parvovirus Genome
ITR
Rep
Cap
5 kb ssDNA, inverted terminal repeats (ITR)
Rep gene required for DNA replication
Cap gene encodes capsid proteins
ITR
Replication of
parvoviruses
Details may be
different for
different
parvoviruses, and
little work has been
done on B19 itself
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Viral proteins
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VP2 attaches to P antigen receptor,
(globoside P antigen), but the virus uses a
co-receptor as well
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Progenitor red cells, megakaryoblasts,
endothelial cells, kidney and heart
VP1 antibodies are neutralizing
NS1 (replication initiator) is cytotoxic
(causes apoptosis)
NS2 regulates replication
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Parvovirus B19 entry into host cells
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The viral receptor is the blood group P antigen
(globoside), and this receptor mediates attachment to
the target cell.
However, alpha5beta1 integrin is a co-receptor;
functional activation of beta1 integrin is required for viral
entry.
Therefore, erythroid progenitor cells are permissive
for replication, and non-erythroid cells that may express
the P antigen are not permissive.
Cells can be induced to permissivity by induction of highaffinity conformation of alpha5beta1 integrins.
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Disease mechanisms of B19 parvovirus
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Cell death associated with parvovirus infection
Associated
with NS1
expression
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Parvovirus pathogenesis
From Medical Microbiology, 5th ed., Murray, Rosenthal & Pfaller, Mosby Inc., 2005, Fig. 56-3.
Clinical expressions of parvovirus infection in
man (B19)
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Erythema infectiosum (EI) (Fifth disease)
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In children: light flu-like symptoms one week after
infection; at ~17 days, “slapped cheek syndrome”
and general lace-like rash. Rash disappears after 2-3
days.
In adults: arthritis, arthralgia, with or without the
rash; may persist for weeks, months or years.
Transient aplastic crisis (TAC)
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In host with underlying hemolysis (e.g.: sickle cell
disease), resulting in severe acute anemia
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Clinical expressions of parvovirus infection in
man (B19) (2)
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Pure red cell aplasia
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In immunocompromised patients
Chronic anemia and bone marrow suppression
Patients are then dependent on blood transfusions
Hydrops fetalis
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In the fetus of a mother having primary infection with
B19.
Fetal death due to severe anemia and congestive
heart failure, usually before the 20th week of
pregnancy.
Thought to occur in <10% of primary maternal
infections
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Clinical expressions of parvovirus
infection in man (B19) (3)
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Miscellaneous
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Fulminant hepatitis
Meningitis
Encephalitis
Vasculitis
Myocarditis and cardiac allograft rejection
Glomerulopathies in renal transplant recipients
Others, see later on
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Treatment and prevention
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Vaccines are available for dog and cat parvovirus infections
Not for humans, yet. Recombinant capsid proteins with
MF59C.1 being tested in clinical trials. Neutralizing
antibodies are induced.
Immune globulin has been used to treat pure red cell
aplasia (PRCA)
Its usefulness in other persistent infections is not proven
(and often there are complications)
When used to treat hydrops fetalis, the newborn may have
congenital red cell aplasia, which is an aregenerative
chronic anemia.
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Laboratory diagnosis
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Viral DNA detection
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Most sensitive
Dot-blot hybridization of serum or tissue extracts
In-situ hybridization of fixed tissue
PCR
Serologic assays
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Use recombinant parvovirus antigens
IgM is indicative of recent infection and lasts 2-3
months
IgG lasts for years, but not always in
immunocompromised patients
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Epidemiology - summary
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Infection transmitted via the respiratory tract
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Common in childhood
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Much subclinical
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Patients with aplastic crisis are likely to be infectious
during the course of their illness.
Patients with fifth disease are probably not
infectious by the time their rash appears.
Standard infection control practices should be
followed to prevent B19 transmission to health care
workers
Blood and blood products
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“Slapped cheek syndrome”
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Pathogenesis of diseases resulting from parvovirus
B19 infection in children and adults
Transient aplastic crisis
In immunocompromised
Pure red cell aplasia
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Pathogenesis of fetal infections with
parvovirus B19
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Data re: fetal death
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Jordan and Butchko, 2002.
Apoptotic activity in villous trophoblast cells
(epithelial cells) during B19 infection correlates with
clinical outcome
Placental trophoblast cells contain globoside, but are
not permissive to B19 replication.
A MAb detecting caspase 3 activity (apoptosis)
reacted more with trophoblast cells from poor
outcome B19 infection than benign infection
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Data re: inflammatory sequelae
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Mitchell, 2002, J. Med. Virol.
Parvovirus B19 nonstructural protein
(NS1) acts as a transactivator of IL-6
synthesis.
IL-6 is a proinflammatory cytokine
promoter.
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Other putative pathologic associations
of B19 infection (not in textbooks)
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Acute onset lymphoblastic and myeloblastic
leukemia
Chronic fatigue syndrome (in association with
increased levels of INFgamma and TNF alpha)
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Improvement with IVIG and better cytokine balance
Autoimmune disease affecting joints, connective
tissue, and large and small vessels
Systemic lupus erythematosus?
Neurological manifestations? (demyelination,
HLA-DR alleles, and cytokines)
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Adeno-associated virus (AAV)
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In vitro, in the absence of a helper virus, AAV
can establish a latent infection in a cell
culture that involves integration of the viral
genome into a unique site on human
chromosome 19.
Superinfection of a cell carrying such a
provirus (by HSV or an adenovirus) rescues
the integrated genome and initiates a fully
productive infection.
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The AAV genome
TR = terminal repeat
All AAV transcripts are co-terminal at the polyadenylation
signal (poly A)
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Rescue of AAV by adenovirus
1
2
3
4
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Adeno-associated virus (AAV)
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Most AAV were found in stocks of adenovirus
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AAV do not stimulate inflammation in the host
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They do not elicit antibodies against themselves
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They can enter non-dividing cells
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These characteristics make them good
candidates for gene therapy vectors
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Some problems and possible solutions
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When injecting into an animal, most of the
material is concentrated by the liver for
discard
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But one can alter one of the coat proteins of
AAV to induce it to preferentially bind certain
types of cells in the body
AAV has a small genome – not much room
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But one can transfect (or inject) 2 or more
AAV vectors
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Trying gene therapy (not all with AAV)
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Factor VIII for hemophelia
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Adenosine deaminase for SCID
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Erythropoietin for anemia
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Insulin and promoter active in liver cells
and turned on by glucose, for diabetes
Etc.
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THANK YOU
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