Viral Exanthems Flashcards
Important properties of Varicella–Zoster virus
- Large viruses
- Icosahedral core surrounded by lipoprotein envelope
- Linear double stranded DNA
- No polymerase
- Tegument
- Replicate in nucleus
- Form intranuclear inclusions
How VZV is transmitted ?
- Respiratory droplets
2. Direct contact with skin lesions
Explain pathogenesis of VZV
VZV infects mucosa of upper respiratory tract
- VZV spreads via blood to skin, where papulovesicular rash appears in crops on trunk & spreads to head & extremities (Varecella).
- Multinucleated giant cells with intranuclear inclusions are seen in base
of lesions.
VZV infects into cells of ……. neurons & carried by …….. axonal flow …………….ganglia (where VZV becomes latent).
Sensory neuron , retrograde axonal flow & dorsal root ganglia
Where is VZV DNA located in latency infected cell ?
Nucleus
What does each of varicella & zoster in VSV represents ?
- Varicella ——-> VZV spreads via blood to skin, where papulovesicular rash appears in crops on trunk & spreads to head & extremities
- Zoster ——-> painful vesicular lesions along course of sensory nerve of head or trunk
How zoster happens ?
Later in life, at times of reduced cell-mediated immunity or trauma, virus is activated ——-> zoster
Which Laboratory Diagnosis is done to identify VZV ?
- Tzanck smear ( Presumptive diagnosis)
- isolation of virus in cell culture
- identification with specific antiserum
Both are definitive diagnosis
- Rise in antibody titer:
diagnose of varicella
Important properties of Coxsackie Viruses
- RNA Viruses
- Picornavirus Family
- Enteroviruses
- Small nonenveloped
- Icosahedral nucleocapsid
- Positive Single-stranded RNA
- No polymerase
- replicate in cytoplasm of cells
Transmission of coxsackie viruses
- Fecal–oral
2. Respiratory aerosols
Classification of coxsackie
- Group A
- Group B
- Group A & B
Mention the diseases site associated with each group of coxsackie
- . Group A ———-> In skin & mucous membranes
- Group B ————> various organs such as heart, pleura, pancreas & liver
- Group A & B————> Meninges & motor neurons (anterior horn cells) causing paralysis
What is the original site of replication in coxsackie ?
oropharynx & gastrointestinal tract———-> disseminate via bloodstream
What are the group A diseases & their manifestations?
- Herpangina
- fever
- sore throat
- Tender vesicles in oropharynx
- Hand-foot-and-mouth ( mainly children)
- Vesicular rash on hands& feets
- ulceration in mouth
What are the group B diseases & their manifestations?
- Pleurodynia (Bornholm disease, epidemic myalgia, “devil’s grip”)
* Fever
* severe pleuritic-type chest pain - Myocarditis & pericarditis
* Fever
* chest pain
* congestive failure signs - Coxsackie virus B4
* plays a role in juvenile diabetes
What are the diseases caused by both groups A & B ?
- Aseptic meningitis:
* mild paresis
* acute flaccid paralysis - Upper respiratory infections
- Pharyngitis
- Minor febrile illnesses with or without rash
How to diagnose coxsackie virus ?
- Isolating virus
* cell culture or suckling mice - Rise in titer
* neutralizing antibodies - PCR ( diagnosis of viral meningitis)
* enteroviral RNA in spinal fluid
Important properties of measles virus
- Lipoprotein envelope studded with spikes of 2 transmembrane glycoproteins
- Helical nucleocapsid
- Negative single stranded linear non segmented RNA
- Has RNA dependent RNA polymerase
- Single stereotype
What are the 3 proteins complexed with viral RNA in measles?
- Nucleocapsid (N) protein:
* forms helical nucleocapsid
* represents major internal protein - P (Phosphoprotein) & L (Large polymerase) proteins
- L & P proteins & nucleocapsid
- has RNA-dependent activity
- RNA transcriptase activity
What are the 3 proteins that participate in formation of viral envelope of measles ?
- Matrix (M) protein:
* underlies viral envelope
* important in viron assembly
Two transmembrane glycoproteins:
- Hemagglutinin (H) :
* Hemagglutination activities
* Attachment to host cell - Fusion (F) glycoproteins
* Membrane fusion
* Hemolysin activities
Transmission of measles virus
Respiratory droplets
produced by coughing & sneezing
Explain pathogenesis of measles virus
virus enters blood & infects reticuloendothelial cells, where it replicates again
Then spreads via blood to skin
How rashes occur in measles?
- Cytotoxic T cells ——-> attack virus–infected vascular endothelial cells in skin
- Antibody-mediated vasculitis
- Multinucleated giant cells:
* form as result of fusion protein in spikes - Lifelong immunity occurs
- Maternal antibody passes placenta :
* infants are protected for first 6 months of life
How reactivation of dormant organisms & clinical disease is executed by measles virus?
Measles virus can transiently depress cell-mediated immunity against other intracellular microorganisms
Why measles binds to receptor (CD46) on surface of macrophages?
For suppression of interleukin-12 production
(necessary for cell-mediated immunity)
What is the Incubation period of measles virus?
10 to 14 days
What are the symptoms during Prodromal phase of measles?
- Fever
- conjunctivitis
- Running nose
- Coughing
Clinical manifestations for measles virus
- Koplik’s spots
* bright red lesions with white , central dot on buccal mucosa - Maculopapular rash
* appears on face & proceeds gradually down body
* lower extremities, including palms & soles
What are the complications of measles?
- Encephalitis
- Primary measles (giant cell) pneumonia & secondary bacterial pneumonia
- Bacterial otitis media
- SSPE ( Subacute sclerosing panencephalitis) :
* rare fatal disease of CNS
* several years after measles - Measles in pregnant woman leads
to risk of stillbirth ( birth of an infant that has died in the womb)
Diagnosis of measles virus
- Clinically
- Cell culture ( isolation of virus )
- Rise antibody titer > fourfold to diagnose difficult cases
- PCR
