Measles, Rubella, Varicella Flashcards
Members of the Paramyxovirus family of viruses - features
negative sense
single-stranded RNA virus
Large, helical
Enveloped
Parainfluenza virus is part of Paramyxovirus and orthomyxovirus is inflluenza (T/F)
True
Paramyxovirus is segmented and influenza is non segmented (T/F)
False; Paramyxovirus is non segmented and influenza is segmented
The family is divided into 3 genera
- Parainfluenzavirus
- Pneumovirus
- Morbillivirus
Pneumonia, bronchitis and croup, especially in children, and Mumps - under which genera of Paramyxovirus?
Parainfluenzavirus
Measles; Canine Distemper Virus - which genera of Paramyxovirus?
Morbillivirus
Respiratory Syncytial Virus (RSV), causes pneumonia - which genera of Paramyxovirus?
Pneumovirus
Is replication basically the same for all viruses in paramyxovirus group?
Very similar for all viruses in this group.
What is the diff in replication for viruses in paramyoxvirus group compared with influenza in same group?
All the action occurs in the cytoplasm for the other viruses
Unlike influenza, Paramyxovirus replication is resistant
to ________ _
Actinomycin D
Nucleocapsid - define
Viral genome encapsulated by the nucleocapsid protein; it is generally inside the cytoplasm.
Syncytium - define
a single cell or cytoplasmic mass containing several nuclei, formed by fusion of cells or by division of nuclei.
What occurs due to the syncytium formation in Measles Virus (MV)?
What are the MV cells referred to as?
A large excess of nucleocapsids are produced in infected cells, which form characteristic cytoplasmic inclusion bodies
Warthin Finkeldey cells
Measles virus (MV), a paramyxovirus, has two glycoproteins which are?
haemagglutinin (HA) and fusion (F) protein
Role of MV glycoproteins
responsible for virus attachment and entry
During MV infection, both the viral _________ are
synthesized in the ________ _________ and are
_______ to the cell surface where they cause _____ with the neighbouring cells
During MV infection, both the viral glycoproteins are
synthesized in the endoplasmic reticulum and are
transported to the cell surface where they cause fusion
(syncytium formation) with the neighbouring cells
Syncytium is rare in MV (T/F)
False; Syncytium is very common
Name one of the most infectious diseases known
Measles
Before ____ almost everyone contracted measles
1963
Known hosts for MV
Humans, monkeys, rodents
MV is the single leading cause of _______ _________
death among children in _____ - more than
AIDS, tuberculosis, and malnutrition
MV is the single leading cause of vaccine-preventable
death among children in Africa - more than
AIDS, tuberculosis, and malnutrition
Neuraminidase spikes absent in MV morphology (T/F)
True
Neuraminidases are enzymes that cleave sialic acid groups from glycoproteins, thereby freeing the virus to infect other cells in the host organism.
Pleomorphic – define
A term used in histology and cytopathology to describe variability in the size, shape and staining of cells and/or their nuclei.
MV - structural features
- pleomorphic spherical structures
- 100-250nm diameter
- Inner nucleocapsid contains coiled helix of ssRNA and three proteins
- Outer envelope contains three other proteins
Terminus
One end of a protein molecule
Capsid structure involving helical core and N terminus
Capsid has an interior helical core around which the RNA is wound
N-terminus domain of the capsid protein forms an exterior helical covering that protects the viral genome.
– Researchers wishing to design antiviral drugs may want to disrupt the assembly of this helical capsid
Function of N protein in MV
The N protein encapsidates (surrounds) genomic RNA to shield RNA from nucleases and RNA-mediated silencing
– a function reflected in its ability to self-assemble into nucleocapsid particles in the absence of other viral proteins
RNA synthesis by nonsegmented negative-stranded RNA viruses (nsNSVs) is carried out by an interplay between at least four components which are?
the genomic RNA,
the nucleoprotein (N),
the phosphoprotein (P),
and the polymerase or large protein (L).
Viral polymerase complex made of the polymerase L associated with its cofactor P performs what function in MV?
Transcription and replication
Cofactor, P protein, plays a central role in nsNSV RNA synthesis (transcription)- how?
It binds to and stabilizes both L and N in an RNA-free form;
It tethers the polymerase onto the nucleocapsid, thus giving access to the shielded RNA template;
It regulates RNA synthesis
F protein function in MV
F proteins expressed at the plasma membrane of infected cells could mediate fusion with adjacent cells to form syncytia (a cytopathic effect that could lead to tissue necrosis)
H protein function in MV
Attaches the virus to cell receptors and thereby initiating infection.
Binding of H protein to the receptor induces a conformational change that allows the F protein to trigger virion/cell membranes fusion.
M protein function in MV
2D array associated with the membrane.
Virus development
– Incorporation of the surface glycoproteins and the RNP (ribonucleic complex) at sites of virus assembly.
Measles Virus environmental stability
- Can live up to two hours on surfaces
- 30 minutes in aerosol form
- Heat sensitive
- Survives freezing well
- Can survive when freeze-dried with a protein stabilizer for decades
- Inactivated by solvents like ether, disinfectants, by acids (pH<5), bases (pH>10), and by UV and visible light.
MV is heat sensitive but can survive freezing well (T/F)
True
Transmission for MV
Mode of transmission
Large respiratory droplet
Airborne
Can also infect via the eye and multiply in the conjunctivae
Most infectious in early stage before rash appears but can still be transmitted a week after rash is gone
Incubation period (asymptomatic) - MV
Incubation period lasts between 7 – 10 days
Droplet nuclei - define
Aerosols formed from the evaporation of respiratory droplets.
Generally smaller than 5 μm in diameter.
Formed by the “dried residua of larger respiratory droplets”.
MV pathogenesis
- Transmission via respiratory droplets or aerosolized small droplet nuclei
- Enters cells; can start infection anywhere along respiratory tract from nose to lower airways
- Along the mucociliary epithelium (cilia of mucous membranes in tissues of resp system), dendritic cells can poke through tight junctions to pull in measles cells from lumen (space inside tubular structure)
- MV uses glycoproteins H & F to bind to dendritic cell receptors
In the alveolar space, macrophages can be infected with measles virus - Both DCs and MACs carry MV to lymph nodes; MV now infects lymphocytes (T and B cells)
- They replicate making more measles viruses - amplification
- Spleen and tonsils become infected due to lymphocytes moving to secondary lymphoid organs
- MV can disseminate to skin, resp tract, liver, brain, intestines
- Infected lymphocyte brings MV to basal side of epithelial cells, MV replicates inside cell and exits via budding on apical side
- Damaged epithelial cells cause irritation and virus is expelled by coughing and sneezing
MV causes transient immunosuppression in what ways?
- Inhibits toll like receptor signalling
- inhibits synthesis and signalling of interferons
- Causes lymphopenia (low lymphocyte counts due to infection of lymphocyte cells)
- Interferes with antigen presentation to T cells thus T cell activation
Denoting the period between the appearance of initial symptoms and the full development of a rash or fever - definition for what term?
Prodromal
Timeline of signs and symptoms for MV
Incubation : 7-10 days Prodromal : before rash, after incubation -- Fever 2-10 days -- Cough 2-16 days -- Coryza 2-6 days -- Conjunctivitis 2-6 days Koplik spots 2-4 days (lesions on buccal mucosa) - appears 4 days before skin rash and resolve before skin rash is seen Rash 4-8 days
Skin rash is associated with T cells attacking infected epithelial cells in small BVs. After 1-2 days it’s difficult to isolate replicating MV.
Many clinical signs and symptoms start to resolve also.
All except cough resolve.
Timeline of virus involvement inside host
Virus growth in lymph tissue (1-5 days) Virus goes to body surface (3-6 days) Virus grows on body surface (6-10 days) Respiratory disease (9-14 days) Infectious period (8-16 days)
Antibody titer = low for infectious period but high for every other aspect
People with measles are contagious for _ ____ before and at least _ ____ after the ____ begins
People with measles are contagious for 1 week before and at least 4 days after the rash begins
Other signs and symptoms of MV
Depends on where virus infects
Infection of intestinal epithelial cells:
Diarrhoea, vomiting, abd pain
Dissemination of infected lymphocytes Cervical lymphadenopathy (enlarged lymph nodes), splenomegaly (enlarged spleen)
Infection of mucosal epithelial cells
Pharyngitis (sore throat)
Infection of resp epithelial cells
Viral pneumonia/bronchiolitis
Encephalitis (inflammation of brain tissue)
Complications - MV
Secondary bacterial infections
Pneumonia
Otitis media (inflammation of middle ear) or any other resp tract infection
Subacute schlerosing pan encephalitis (SSPE)
is very uncommon
- chronic infection where virus multiplies in the
brain with the expression of a limited repertoire of
virus genes
- Risk factor - acquiring MV before 2 yrs old
- Occurs 4-8 yrs after contracting acute measles infection
Lab ID
Specimens: nasal secretions, nasopharygneal aspirate, urine
- Direct virus demonstration
In smears of nasal secretions - intranuclear inclusion bodies and syncytial giant cells
Enzyme Immunoassay (EIA) can be used if needed, to detect IgM or IgG levels
Treatment - MV
No treatment, only supportive care (treat symptoms)
Vitamin A supplementation (reduces morbidity)
Ribavirin (reduces complications)
Vaccines - MV
Both live and killed vaccines exist.
Vaccination with the live attenuated vaccine has
been practiced in the US since the 1960’s with a
dramatic decline in the incidence of the disease,
but has only been used more recently in the UK.
Trivalent (3’s) live attenuated vaccine (MMR) usually
given - all of these viruses best avoided during
pregnancy!
When should 2nd dose of MMR vaccine be given?
• 2nd dose between 5-19 years of age
No large preschool-type outbreak of MV has been reported since 1992 (T/F)
True
Report of MV prevlance in US, UK, Latin America and Caribbean
March of 2000, CDC concluded that Measles are no longer an epidemic in the U.S.
• All cases are importations
• Europe and Asia
Pan American Health Organization
• measles incidence is now very low in Latin America and the Caribbean
81% vaccination rate in a community is needed to avoid virus circulation outbreaks (T/F)
False; 93% vaccination rate in a community is needed to avoid virus circulation outbreaks
Rubella agent
Rubella Virus
RV - morphology
ssRNA
Envelope containing lipid layer (Enveloped)
Spike like glycoproteins (E1 and E2)
One serotype
Humans are only known reservoir for RV (T/F)
True
Variation of size and shape as well as the protein copy number that constitute the virus particle - is the definition for what term?
Pleomorphic
+ve 40S RNA consists of 3 structural proteins which are?
- E1, E2 membrane bound glycoproteins, and C capsid protein
• E1 has 6 distinct antigenic determinants; Associated with
haemagglutination, and neutralization
Vero cells
derived from the kidney of an African green monkey (commonly used)
RV induces a CPE only in continuous cell lines, what are some examples of cell lines used?
RK13 (rabbit kidney) and Vero.
What is used to identify the presence of the virus in culture?
Immunofluourescense
Rubella virus infects various primates and other mammals such as?
Monkeys, chimpanzees, rabbits and mice.
Substances that may cause birth defects via a toxic effect on an embryo or fetus are?
Teratogens
ToRCHeS
Toxoplasma gondii Rubella CMV HSV, Herpes Zoster, Hepatitis C,D,E Syphilis
Attempts to reproduce the teratogenic effects of Rubella virus in animal models have produced what kind of results?
inconsistent and irreproducible results.
Before the introduction of vaccination outbreaks
tend to occur in which seasons?
Spring and Summer
Despite the vaccination program ______ % of
women that reach ____ ________ age are susceptible to Rubella infection.
Despite the vaccination program 5-10 % of women reach child bearing are susceptible to Rubella infection.
Transmission of RV is by
the respiratory route
Viremia
viruses present in the bloodstream.
Incubation period for RV is for how many days? What can occur during this time?
IP is 13 to 20 days, during which a viraemia occurs
and virus disseminates throughout the body.
Onset of RV in kids
•Onset is abrupt in kids with the appearance of the
rash. In adults
Onset of RV in adults
a prodromal phase may be present with fever and malaise for a day or two before the rash develops
Characteristics of rash
maculopapular (flat, discoloured lesions) rash, which first appears on the face and then spreads to the trunk and the limbs, seldom lasts > 3 days
How long can lymphadenopathy last and when does it occur in RV?
Lymphadenopathy (swollen lymph nodes) may precede the rash by up to a week and persists up to 2 weeks after the rash has gone
Most common complication in RV
•Joint pain (arthralgia) is the commonest complication
and occurs in up to 60% of adult females.
E.g. fingers, wrists knees and ankles are most
frequently affected.
Encephalitis develops in 1 /_____ but the prognosis is good
Encephalitis develops in 1 /10000 but the prognosis is good
Thrombocytopenic purpura
abnormal decrease in the number of platelets
Purpuric rash
Purplish bruises on the skin or mucous membranes (such as in the mouth)
Hemorrhage
an escape of blood from a ruptured blood vessel
Epistaxis
Acute hemorrhage from the nostril, nasal cavity, or nasopharynx.
How does Thrombocytopenic purpura present in MV complication?
Purpuric rash, epistaxis, haematuria (blood in urine) and GI bleeding
Transient (lasts for short time) effects of Congenital Rubella Syndrome (CRS)
Intra uterine growth retardation (IUGR), thrombocytopenic purpura, hepatosplenomegaly and haemolytic anaemia.
These abnormalities are present during the first few
weeks of life and are not associated with permanent
sequelae.
Transient bone lesions occur in 20% of congenitally infected infants.
25% have a meningoencephalitis which may or not
leave neurological sequelae.
Jaundice is commonly present
Developmental effects of congenital rubella syndrome
Sensorineural deafness, mental retardation, insulin-dependent diabetes (IDDM). Developmental defects may take months before they become apparent but persists permanently.
Rubella deafness may be unilateral or bilateral and varies considerably in severity.
• IDDM is actually a common manifestation of CRS ( up to 20%).
However onset may be delayed till adolescence or adulthood.
High mortality developmental congenital rubella syndrome
Autoimmune mechanisms may be involved. Between 3 - 12 months some infants develop a rubbelliform rash, persistent diarrhoea and pneumonitis which is referred to as “late onset disease”. This carries a high mortality.
Permanent effects of CRS
- Heart defects (patent ductus (ductus arteriosus fails to close after birth), VSD (hole in the heart), pulmonary valve
stenosis (deformity on or near your pulmonary valve narrows the pulmonary valve opening and slows the blood flow)), - Eye defects (retinopathy (damage to retina), cataract, microopthalmia (abnormally small eyeballs), glaucoma (optic nerve connecting to brain damaged due to fluid build up), severe myopia (near sightedness)),
- CNS defects (microcephaly (abnormally small head), psychomotor retardation (visible slowing of physical and emotional reactions)).
Late sequelae, especially those affecting the heart were commonly seen
How does CRS occur
When a woman is infected with the rubella virus early in pregnancy, she has a 90% chance of passing the virus on to her fetus. This can cause the death of the fetus (b/c rubella inhibits cell division), or it may cause CRS.
The rubivirus can be spread from a pregnant mother to her fetus through the bloodstream.
Serological diagnosis of rubella infection
Serology is the mainstay of diagnosis of rubella infection.
A recent rubella infection can be diagnosed by:
(a) detection of rubella-specific IgM,
(b) rising titres of antibody in HAI and ELISA tests,
(c) seroconversion.
It is essential to obtain accurate information relating to the ____ ___ ____ of ________, the date of ____ of illness.
It is essential to obtain accurate information relating to the date and time of exposure, the date of onset of illness
What serological ID method is best for diagnosis of rubella infection?
Haemagglutination inhibition (HAI) assay remains the mainstay test for diagnosis of rubella infection.
Detection of rubella-specific IgM by EIA or RIA. The most sensitive and reliable techniques in use are
WWhat can be detected on first day of rash in HAI?
HAI Abs may be detected on the first day of the rash and rise rapidly to peak titres.
Most sensitive and reliable detection techniques for rubella infection
antibody capture ELISA and radioimmunoassay
Serological techniques used for rubella antibody screening
- Single Radial Haemolysis (SRH) and latex agglutination (LA), and ELISA are used for screening for immunity against rubella. SRH is reckoned to be slightly less sensitive than LA or ELISA.
Virus isolation is now seldom used for diagnosing postnatally acquired rubella infection. (T/F)
True
Diagnosis of congenital acquired infection: This is made by:
(a) The presence of rubella ___ in cord ____ or serum samples taken in infancy.
(b) Detection of rubella antibodies at a time when ______ antibodies should have disappeared (approx.6 ______ of age)
(c) Isolation of rubella virus from _______ _______ in the first few months of life.
Diagnosis of congenital acquired infection: This is made by:
(a) The presence of rubella IgM in cord blood or serum samples taken in infancy.
(b) Detection of rubella antibodies at a time when maternal antibodies should have disappeared (approx.6 months of age)
(c) Isolation of rubella virus from infected infants in the first few months of life.
Prenatal diagnosis of congenital infection helps when:
- maternal infection occurred after the first trimester,
- in cases of maternal reinfection and
- in cases where equivocal serology results from the mother were obtained.
Possible methods include:
(i) The testing of fetal blood samples obtained by fetoscopy for rubella specific IgM. However the fetus does not produce sufficient IgM for detection before 22 weeks.
(ii) Virus may be isolated from amniotic fluid but the reliability of this technique has not been demonstrated.
(iii) The detection of rubella RNA or viral proteins in chorionic villus biopsies and amniotic is currently being evaluated.
Other method of ID
Molecular methods
RA 27/3 origin
The kidney tissue from fetus 27 produced the strain that was used to develop the attenuated rubella vaccine. The name RA 27/3 refers to “Rubella Abortus”, 27th fetus, 3rd organ to be harvested (the kidney).
• The first vaccines were developed in the early 60’s (HPV77.DE5 and Cendehill) , what was it replaced by?
RA 27/3
What is the Measles initiative and who does it involve?
• Control deaths by vaccinating 200 million
children and preventing 1.2 million deaths
over 5 years
• American Red Cross, United Nations
Foundation, CDC, WHO, UN Children’s Fund
Varicella-zoster virus (VZV) causes two distinct clinical
diseases
Varicella (Chickenpox) Herpes Zoster (Shingles)
Varicella is ubiquitous (present everywhere) and slightly contagious (T/F)
False, it is highly contagious
C-pox was often confused with smallpox. (T/F)
True
VZV is a member of the Herpesviridae family but does not share structural characteristics with other members
of the family (T/F)
VZV is a member of the Herpesviridae family and
shares structural characteristics with other members
of the family.
Features of VZV
- Icosapentahedral symmetry and contains centrally located double-stranded DNA with a surrounding envelope.
- The size of the virus is approximately 150 to 200 nm, and it has a lipidcontaining envelope with glycoprotein spikes.
- The naked capsid has a diameter of approximately 90
to 95 nm.
VZV replication
DNA contains 125,000 base pairs, or approximately 80 megadaltons, and encodes about 75 proteins.
Organization of the viral genome is similar to that of
other herpesviruses.
There are unique long (105-kb)
and unique short (5.2-kb) regions of the viral genome.
Each unique sequence contains terminal repeat
sequences.
With replication, the unique short region can invert
upon itself and result in two isomeric forms.
Hosts for VZV
Humans are the only known reservoir for VZV.
Seronegative
person does not have the same antibodies that a person who is “seropositive” has
Is VZV transmitted via respiratory route? Explain issues with theory
Although it is assumed that the virus is spread by the
respiratory route and replicates in the nasopharynx or
upper respiratory tract, retrieval of virus from persons
incubating VZV has been uncommon
Transmission of VZV
Transmission is likely by the respiratory route, followed by localized replication at an undefined site,
which leads to seeding (spread) of the reticuloendothelial (liver) system and, ultimately, viremia.
Effect of VZV on cells during replication
• The vesicles involve the corium (dermis = btw epidermis and subcutaneous tissue)
• As viral replication progresses, the epithelial cells undergo
degenerative changes characterized by ballooning, with the
subsequent appearance of multinucleated giant cells and
prominent eosinophilic intranuclear inclusions (foreign bodies)
(Intra = within)
The occurrence of viremia in patients with chickenpox
is supported by ?
Diffuse and scattered nature of the skin lesions and can be verified in selected cases by the recovery of virus from the blood.
Presenting manifestations of VZV
- rash, low-grade fever, and malaise
A prodrome of symptoms may occur _ to _ days ______ the onset of the ______ (widespread rash) in a few patients.
A prodrome of symptoms may occur 1 to 2 days before the onset of the exanthem (widespread rash) in a few patients.
Constitutional symptoms (general symptoms)
Malaise, pruritus, anorexia, and listlessness; these gradually resolve as the illness abates.
Hallmarks of infection for VZV
Skin manifestations - consist of maculopapules, vesicles, and scabs in varying stages of evolution
- lesions initially contain clear vesicular fluid, but over a very short period of time they pustulate and scab
The diagnosis of both C-pox and shingles is
usually made by history and physical
examination. (T/F)
True
Specimen of VZV
– saliva, skin swab, blood, CSF
Microscopy of VZV
A Tzanck smear, performed by scraping the base of the lesion, can demonstrate multinucleated giant cells
Culture of VZV
Viral isolation susceptible tissue culture cell lines
Other ID methods of VZV
• Direct fluorescent antibody (DFA) staining of smears
• Antibody assays of acute and convalescent serum
specimens - immune adherence haemagglutination
assay (IAHA), Fluorescence antibody to membrane
antigen (FAMA), ELISA.
• PCR is a useful diagnostic tool; however, its expense
and lack of uniform performance standards
preclude routine diagnostic use
Where are DFAs obtained from in VZV?
obtained from scraping vesicular lesions
IAHA test explain
-detects antibodies which react with the test antigen and activate complement to form immune complexes.
IAHA tests detect immune complexes by the hemagglutination which results when the complexes bind
to the C’3b receptors found on the surface of
primate erythrocytes
Fluorescent antibody to membrane antigen (FAMA) is considered to be the gold standard for ?
assessing immunity to varicella and detects seroconversion after vaccination or natural disease
FAMA - explain
FAMA test is an immunofluorescence assay that uses unfixed varicella-zoster virus (VZV)-infected human embryonic lung fibroblast (HELF) cells incubated with serial 2-fold dilutions of sera.
The cells are then washed, incubated, and examined using fluorescence microscopy
Treatment of C-pox and Shingles
- Hygiene is important, including bathing, astringent soaks, and closely cropped fingernails.
- Pruritus can be decreased with topical dressing or the administration of antipruritic drugs. Soaks with aluminum acetate, or Burow’s solution, in the management of herpes zoster can be both soothing and cleansing.
- Acetaminophen should be used to reduce fever in patients with chickenpox because of the association between aspirin and Reye’s syndrome.
- Acyclovir – In the USA used for treating C-pox and Shingles
Who does Reye’s syndrome affect?
most commonly affects children and young adults recovering from a viral infection – for example a cold, flu or chickenpox.
What is Reye’s syndrome?
rare but serious condition that causes swelling in the liver and brain.
What happens to the body in Reye’s Syndrome?
In Reye’s syndrome, it’s thought that tiny structures within the cells called mitochondria become damaged.
Mitochondria provide cells with energy and they’re particularly important for the healthy functioning of the liver.
Can the varicella vaccine be given to immunocompromised patients?
Because the varicella vaccine is a live vaccine, it should not be administered to immunocompromised patients
Less immunocompromised individuals can receive the single-entity varicella vaccine (but not the combination varicella/MMR vaccine) (T/F)
True
Adults over 50 years - vaccine recommendations for varicella
RZV vaccine - subunit vaccine that contains recombinant varicella zoster virus (VZV) glycoprotein E in combination with a novel adjuvant (to increase efficacy)(AS01B). Shingrix does not contain live VZV.
Guidelines - immunocompromised
Two doses of recombinant zoster vaccine (RZV) (Shingrix) 2-6 months apart to adults aged 50 years or older regardless of past episodes of herpes zoster or receipt of zoster vaccine live (ZVL) (Zostavax).
Guidelines - general
Two doses of RZV 2-6 months apart to adults who previously received ZVL at least 2 months after ZVL.
Adults over 60 years - vaccine recommendations for varicella
• For adults aged 60 years or older, administer either RZV or ZVL (RZV is preferred).
Immunocompromised persons risk in developing Varicella
Second occurrence of varicella may be more likely to occur in people who are immunocompromised. As with other viral infections, re-exposure to natural (wild-type) varicella may lead to re-infection that boosts antibody titers without causing illness or detectable viremia.
