Biomedical Engineering Reference
In-Depth Information
herpesviruses 6 and 7 (Chapter 39) cause the sixth childhood rash, “sixth dis-
ease”. The rash of fifth disease results from an immune response of the host
to the virus particles. Essentially, fifth disease is an allergic phenomenon,
and not the direct, cytopathic effect of the virus.
Infection by parvovirus occurs from contact (usually via respiratory dro-
plets) with actively infected hosts. The virus is known to infect humans and
dogs. Serologic evidence indicates that at least half of the human population
has been infected with parvovirus B19.
Members of Class Parvoviridae characteristically infect rapidly dividing
host cells, using host processes to support their own replication. The target
cells for parvovirus B19 are the dividing precursor erythroid cells. Another
name for parvovirus B19 is erythrovirus B19, indicating the target cell for
the virus. In the active stage of infection, huge amounts of virus are pro-
duced. Death or dysfunction of the target hematopoietic (blood precursor)
cells can lead to a transient pancytopenia (i.e. anemia of all blood cell
lineages). In rare cases, aplastic anemia may occur, in which most of
the precursor erythroid cells are destroyed, leading to a massive decline in
circulating mature forms. When aplastic anemia occurs, it usually occurs in
individuals who have a concurrent condition that requires an excessive pro-
duction of blood cells to maintain the normal blood profile of mature cells.
These conditions include: autoimmune hemolytic anemia, sickle cell anemia,
and inherited blood dyscrasias that increase the fragility of red blood cells or
that decrease the life-span of red blood cells. Basically, a co-infection with
parvovirus B19 is the last straw for bone marrows that are barely keeping
pace with the body's demand for erythrocytes.
The intense viremia that occurs in parvovirus B19 infection, and the
small size of parvovirus particles, may predispose to cross-placental trans-
mission occurring in some cases of infection in pregnant women. Though
rare, parvovirus may cause miscarriage or hydrops fetalis (fluid accumulation
in the fetus) with anemia.
Bocavirus has been associated with some cases of respiratory disease and
diarrhea in young children. Though it is rarely detected in healthy persons,
there is indication that it can occur in up to 9% of pediatric patients hospital-
ized with lower respiratory infections [131]. Bocavirus should not be con-
fused with Bocas virus, a type of Coronavirus (Group IV, Chapter 42).
SEN virus (SEN-V) is a newly discovered single-stranded non-enveloped
DNA virus that has been found in the blood of donors and recipients of
transfusion blood [132]. In addition, another Group II virus, TT virus, also
known as transfusion transmitted virus or Torque teno virus, has been iso-
lated from transfusion blood. TT virus is currently a suspected hepatitis
virus. At this time, the pathogenicity of both SEN-V and TT viruses are in
doubt; hence neither virus is included in the list of Group II virus pathogens.
