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Human parvovirus is a member of the
family Parvoviridae, a group of single-stranded DNA viruses.
Parvovirus B19 is the type most often implicated in human disease.
Lesions caused by Parvovirus:
Lesions in the Placental tissue:
The placental tissue
looks hypercellular on the low power. It is mid-trimester in type,
without vasculo-syncitial membranes. The cellularity is partly an
excess of Hofbauer cells, and partly the prominent nucleated blood
cells in the villous vessels. These are erythroid precursors (pronormoblasts)
with purple homogeneous intranuclear viral inclusions. This picture is
pathognomonic of B19 parvovirus infection.
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Transplacental infection in early pregnancy infects the erythroblasts
causes fetal anaemia, and hydrops.
Hematological lesions:
It also produces a transient red cell hypoplasia via marrow infection.
In normal people this is of little consequence, but in haemolytic
anaemia it may induce fatal aplasia - Eg. aplastic crisis in sickle
cell disease.
Parvovirus
B19 is also a cause of haemophagocytic syndrome.
Skin
lesions :
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Purpura,
vasculitis, erythema multiforme, dermatomyositis
, a sweet’s
syndrome-like eruption, lupus erythematosus-like syndromes, an
asymptomatic papular eruption, livedo reticularis, acral pruritus, the
papular-purpuric (petechial) ‘gloves-and-socks’ syndrome and erythema
infectiosum (fifth disease).
Erythema infectiosum (fifth
disease):
Parvovirus infections causes
erythema infectiosum in children
(fifth disease).
Erythema infectiosum (fifth
disease) is an exanthem
which may be difficult to distinguish from rubella. A well demarcated
rash often appears on the face a few days after the onset of prodromal
symptoms.
The ill child typically
has a "slapped-cheek" rash on the face and a lacy red rash on the
trunk and limbs. Occasionally, the rash may itch.
The rash usually becomes more generalized after a few days. It is
accompanied by
low-grade fever,
malaise, or a "cold" a few days before the rash breaks out.
Papular-purpuric ‘gloves-and-socks' syndrome:
It is a self-limited infection characterized by pruritic,
erythematous papules with petechiae and edema involving predominantly
the hands and feet.
Fever, arthralgias and oral lesions may be
present. This exanthem usually occurs in adults.
Immunocompromised
patients :
People
who have leukemia or cancer, who are born with immune deficiencies,
who have received an organ transplant, or who have human
immunodeficiency virus (HIV) infection are at risk for serious illness
due to parvovirus B19 infection.
In immunocompromised patients,
persistent skin lesions and anemia often develop.
Mode of
infection:
Parvovirus B19 is spread by a
respiratory droplet.
Incubation period:
Incubation
period of 5-14 days.
Diagnosis:
Serological confirmation may be used to
confirm the diagnosis.
The
receptor for the virus is the erythrocyte P antigen which is also
expressed on endothelial cells.
The virus has been demonstrated in
endothelial cells in lesional skin by several methods, including PCR.
It has also been identified in keratinocytes.
Approximately 50% of the adult
population is immune.
Histopathology:
- Mild perivascular infiltrate of
lymphocytes together with exocytosis of lymphocytes and mild basal vacuolar
change.
-Apoptotic keratocytes
may be present.
- Extravasaytion of red cells.
- Eosinophils and
occasional neutrophils may be present.
- Changes
resembling incomplete granuloma
annulare may be present. This may be a late manifestation of a previous lymphocytic vasculitis.
It is characterized by a hypercellular interstitium (‘busy’
dermis) and mucin.
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