CSIM 1.15 Viruses Which Cause Rashes Flashcards
What are the types of viral rashes?
• Maculopapular
• Vesicular
IMG 40
What are the (learning outcome) viral causes of maculopapular rashes?
- Measles
- Rubella
- Parvovirus B19
- HHV6 & HHV7
What are the (learning outcome) viral causes of vesicular rashes?
- Herpes simplex virus
- Varicella zoster virus
- Poxviruses
Where does the virus reside in a vesicular rash and in a maculopapular rash?
Vesicular rash:
• Within the lesions
Maculopapular rash:
• Not within lesions (raised redness is just due to the immune response)
What features are looked at when clinically diagnosing the cause of a vesicular rash?
- Typical site
- Whether lesions are at the same or different stages of development
- Whether the rash is generalised or dermatomal
What features can give a clue of the causative agent when diagnosing maculopapular rashes?
- Typical prodrome
- Associated symptoms
- Lab tests
Describe the virology of measles, mumps and rubella
Mumps and Measles • Single stranded RNA viruses • Negative sense • Enveloped • Paramyxoviridae
Rubella • Single stranded RNA viruses • Positive sense • Enveloped • Togaviridae
Describe the pathogenesis of measles, mumps and rubella
- Spread by respiratory route: aerosol
* Pathology is immune mediated
What is the difference between aerosol and large droplet respiratory transmissions
The size of the droplet, and thus the range of transmission through coughing and sneezing
What is the incubation period and infectious period of measles?
Incubation: 10-14 days
Infectious:
• 2-3 days before the rash
• 5 days after the rash
What are the clinical features of measles with regard to the prodrome and the rash
Prodrome • High fever • Cough, Coryza and Conjunctivitis • Koplik spots • Miserable
Rash • Maculopapular • Face and neck • Spreads to trunk • 4-5 days duration
What is coryza?
A running nose
What are Koplik spots?
White spots on the buccal muscosa (inner cheek lining)
What are the complications of measles?
• Secondary bacterial infections due to immunosuppression
• Acute measles post-infectious
encephalitis
• Subacute sclerosing panencephalitis
How common is acute measles post-infectious encephalitis? When does this occur? How fatal is this?
1 in 1000 cases
7-10 days after rash fades
15%
How common is subacute sclerosing panencephalitis? When does this occur? How fatal is this?
1 in 100,000 cases
6-8 years after measles
100%
Who are the risk groups for measles? What is given to these groups if infected?
Immunocompromised patients
• Giant cell pneumonitis
• Measles inclusion body encephalitis
Pregnant women
• Stillbirth
Neonates
• More severe disease
These groups should be given human normal immunoglobulin treatment
How is measles diagnosed?
Throat swab of nasopharyngeal secretions
• Immunofluorescence or PCR performed
Antibody screening
• IgM for infection (present acutely 2 days after rash onset)
• IgG for past infection (present for life)
• Salivary screening
How is measles managed?
No antiviral available
Infection control precautions are taken
What form of vaccine is given for measles?
How is this administered?
Live, attenuated measles (mumps and rubella) strains
In 2 doses 12-18 months apart given to pre-school children
What is the efficacy of measles vaccine?
90% for each dose
99% total
How is rubella spread? When are patients infectious?
- Respiratory spread
- Incubation 14-21 days
- Infectious 7 days before their rash to 7 days after it appears
What are the clinical features of rubella with regard to the prodrome and the rash?
In what proportion of the population is rubella asymptomatic?
Prodrome
• Lymphadenopathy 7 days before rash: cervical, postauricular, subocciputal
Rash
• Maculopapular
• Face to trunk to limbs
Asymptomatic in 25%
What are the complications of rubella?
Arthralgia
Congenital rubella syndrome
Describe congenital rubella syndrome
If mother gets rubella before 12 weeks gestation, there is a 75% risk of severe malformation: • Jaundice • Petechia • Hepatomegaly • Cardiac and ocular defects
Before 16 weeks is sensorineural hearing loss
How is rubella diagnosed?
Antibody screening
• IgM for infection
• IgG for past infection (or vaccination)
How is rubella managed?
No antiviral available
Infection control precautions
Termination offered if rubella confirmed in
How effective is one dose of the rubella vaccine?
99% (one dose)
Describe the virology of parvovirus B19
- Single stranded DNA virus (only one that is relevant)
* Non-enveloped
Which cells do parvovirus B19 infect?
Red blood cell progenitors (not mature RBCs as these do not have nuclei)
Describe the transmission and infectious window of parvovirus B19
- Respiratory spread
- Incubation 14-21 days to rash onset
- Infectious 7 days before rash, not infectious after rash present
What are the clinical features of parvovirus B19
- Subclinical/mild
- Nonspecific prodrone
- Slapped cheek rash
- Maculopapular rash on trunk
- Arthralgia/arthritis
Who are high risk groups to parvovirus B19?
- Haemolytic disorders (because blood cell lifespan is shorter and so due to loss of progenitors anaemia can result)
- Immunocompromised (persistent anaemia because these patients cant clear the virus)
- Pregnancy
What are the pregnancy risks associated with parvovirus B19
Foetal loss
Foetal hydrops
• Virus destroys erythroid cells causing anaemia
• Heart tries to compensate leading to left ventricular failure
• Fluid accumulates
How is parvovirus B19 diagnosed?
Diagnostic tests not needed if uncomplicated
Antibody screening
• IgM for infection
• IgG for past infection
Amniotic fluid PCR
How is parvovirus B19 managed?
No antiviral available
Foetal blood transfusion
Describe the virology of enteroviruses
- Non-enveloped
* Positive sense single stranded RNA viruses
How are enteroviruses transmitted?
Faecal-oral transmission
Name the common poxviruses
- Orf
* Molluscum contagiousum
