Micro: Viral Exanthems Flashcards
What are some descriptors for viral exanthems?
morbilliform = measles like rash - erythematous macules and papules scarlatiniform = scarlet fever like rash - pinpoint sandpapery papules
What are some suspicious clues that can suggest a viral etiology for a rash?
spring or summer onset
kids > adults
petechial or vesicular component
What is the microbiology of measles?
ssRNA, nonsegmented, helical nucleocapsid
morbillivirus of family paramyxoviridae (parainfluenza, RSV, Measles, Mumps)
enveloped, 1 serotype
How is the measles virus transmitted?
respiratory droplets, direct contact w nose or throat secretions of infected person
incubation = 7-8 days preceding rash, highly contagious from 1st respiratory symptoms - 4 days after rash onset
What is the pathogenesis of measles?
infects epithelial cells in URT - primary multiplication - enters bloodstream and spreads to reticuloendothelial cells - replicates again - secondary viremia –> inf of WBCs (monocytes), spread to skin and respiratory tract = febrile prodrome
infected cells become multinucleated giant cells w inclusion bodies in nucleus and cytoplasm
What are the disease manifestations of measles?
three C’s = cough, conjunctivitis, coryza
febrile prodrome, then Koplik spots (small blue and white spots w bright red background on buccal mucosa) and morbilliform rash (cephalo-caudal spread) - whole body involved in 3 days, fades in 3-4, lasts 6-7
rash may have transient petechiae and purpura
Ag-Ab complex vasculitis
How does measles resolve?
faint post-inflammatory hyperpigmentation
leukopenia
acquired immunity after natural inf is permanent
if defective cell immunity (HIV) can progress to giant cell pneumonia, otitis media and subacute sclerosing panencephalitis (yrs later)
How is measles diagnosed?
isolation from clinical specimens or serology - syncytial keratinocyte giant cells
presence of specific IgM indicates acute, more than 4x increase in IgG indicates recent inf
Ab-capture IgM assay highly sensitive and specific
What is the treatment and prevention of measles?
treatment is supportive
immunization - 2 dose MMR, live attenuated viruses
contraindicated in immunosuppressed, pregnant
immunization w/i 72 hrs of exposure may proved post exposure protection
What is the microbiology of rubella?
togavirus family, enveloped
ssRNA, 1 serotype
How is rubella transmitted?
droplet spread or direct contact
transplacental can result in congenital rubella syndrome
How is the rash of rubella different than measles?
distribution is the same
lesions less intensely red, “blueberry muffin” lesions
exanthem spreads quicker, w/i 24 hrs
enanthem has characteristic petechiae in mouth
What is the pathogenesis of rubella?
same as measles:
virus specific T cells attack vascular endothelial cells, vasculitis, rash follows prodromic febrile stage
What is the timing of rubella?
infected shed virus 1 week before and 2 weeks after rash
rash appears 14-17 days post exposure
What can infection w rubella during pregnancy cause?
death, miscarriage
congenital rubella syndrome: sensorineural deafness, mental retardation, eye abnormalities, congenital heart dz (PDA), dermal hematopoiesis
What is the treatment and prevention for rubella?
same as measles
How is rubella diagnosed?
isolation of virus from sample or serology
specific IgM for acute, 4 fold increase IgG for recent
amnio and culture for pregnant women
IgM between 2 wks - 3 mos after birth for congenital
What is the microbiology of parvovirus B19 (erythema infectiosum)?
parvoviridae family, no envelope, small ssDNA
replicates in erythroid progenitor cells
more common in kids, most adults are seropositive
How is parvovirus B19 transmitted?
respiratory droplets, direct contact w secretions, percutaneous exposure to blood or blood products, vertical transmission
winter-spring epidemics
household contact spread very common
erythema infectiosum most contagious before rash onset
What are the disease manifestations of erythema infectiosum?
prodrome: nonspecific, child not that sick
rash has 3 phases: slapped cheek, reticular rash on trunk and limbs, intermittent flare from environmental stimuli
What are the possible complications of parvovirus?
hemolytic anemias - can cause crisis in sickle cell or chronic anemia due to further halting of RBC maturation
immunocompromised can get chronic anemia or pneumonia
during pregnancy - hydrops fetalis, growth retardation, effusions, death
papular-purpuric gloves and socks syndrome = symmetric, rapidly progressive, sharp demarcation at wrists and ankles
How is parvovirus B19 diagnosed?
IgM specific, four fold rise in IgG
PCR based viral nucleic acid detection test
bone marrow biopsy if pt develops aplastic anemia shows arrest only at proerythroblast stage
What is the treatment and prevention of parvovirus B19?
no treatment for immunocompetent, IVIG for chronic anemia and immunocompromised
children excluded from school while fever present, not infectious if cutaneous findings present
exanthem of PPGSS still infectious
What is the microbiology of roseola infantum?
due to HHV 6 and 7 inf, beta herpesvirinae
linear dsDNA, enveloped and sensitive
can re-activate in immunosuppressed
HHV-6 - almost all children seropositive by age 5
HHV-7 - almost all US adults seropositive
replicate in nucleus, cytopathic for T cells
How is roseola infantum transmitted?
respiratory secretions
virus latent in lymphocytes and salivary gland
children most likely to get acute inf
What is the prevention of roseola infantum?
no vaccine, inf results in immunity
What are the disease manifestations of roseola infantum?
mild illness in kids, high fever in otherwise well infant
after fever: pink erythematous papules and macules on trunk and spreading outwards, lasts 1-3 days (quick)
What are differentiating features among the different rashes present w these viruses?
measles - cephalo-caudal, takes 3 days
rubella - cephalo-caudal, takes 24 hrs
erythema infectiosum - “slapped cheek”
roseola infantum - spreads from trunk out, 1-3 days
What are possible complications of roseola infantum?
latency in mononuclear cells
reactivation of HHV-6 in immunosuppressed
drug hypersensitivity syndrome = reactivation due to drugs
lymphoproliferative dzs, pityriasis rosa?
How is roseola infantum diagnosed?
serology, cultures, immunohistochemistry, PCR
What is the treatment of roseola infantum?
usually just supportive
antivirals for encephalitis (NOT acyclovir)
reduction of immunosuppression if possible
What is the microbiology of VZV?
same as herpes, except single serotype
characteristic eosinophilic intranuclear inclusions and multinucleated giant cells
What are the disease manifestations of VZV?
varicella zoster = chicken pox
herpes zoster = shingles
lesions have several stages of maturity at same time
What are possible complications of reactivation of VZV?
dissemianted herpes zoster w generalized skin eruption
pneumonia: more in adults and immunosuppressed
encephalitis
Reye’s syndrome (2nd most common after flu)
Staph or GABHS superinfection most common
congenital if mom pregnant - atrophy and hypoplasia
neonatal if close to birth - high mortality
How is VZV transmitted?
late winter-early spring
inhalation of respiratory aerosol, virus in skin lesions not contagious
contagious 1-2 days before rash- 5 days after
How is VZV diagnosed?
usually clinical
complicated inf: virus from skin lesions, Tzanck smear, DFA shows viral antigen in fluid, PCR, viral culture not routinely used
What is the treatment for VZV?
acyclovir and newer versions
oral therapy not helpful once lesions have already crusted
What is the prevention of VZV?
Varivax in children - if breakthrough dz due to waning immunity, still less severe
VZIG via IM w/i 96 hrs of exposure in high risk
Zostavax - 10x more virus than Varivax, reduces zoster in ELDERLY by 50%
What is the microbiology of enteroviruses?
small ssRNA, Picornavirus family (echovirus, coxsackie, enterovirus, poliovirus)
found in respiratory secretions or stool
What illnesses has enterovirus been implicated in?
hand foot and mouth dz (HFMD) herpangina hemorrhagic conjunctivtis HSP papular acrodermatitis eruptive psuedoangiomatosis
What are the clinical manifestations of HFMD?
prodrome
self-limited exanthems, painful enanthem of vesicles and erosions
supportive treatment
What are the clinical manifestations of herpangina?
characteristic enanthem of painful vesicles and erythematous erosions on palate, uvula, tonsils
self limited
How is enterovirus transmitted?
person to person: fecal-oral or respiratory
infect epithelial tissue, replicate in lymphoid tissues, spread viremically
