Biomedical Engineering Reference
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immediate fixation in 95% ethanol or 70% isopropyl alcohol and the use of alternative
stains, such as Papanicolaou, modified Papanicolaou, Diff-Quik (another Romanowsky
dye preparation), or Paragon multiple stain [27-29]. Smears may also be stained with
monoclonal antibodies, which increase diagnostic sensitivity and specificity and allow the
diagnosis of infection with virus that do not induce visible cytopathic changes.
Although the Tzanck preparation is useful for rapid diagnosis of cutaneous or mucocu-
taneous lesions caused by HSV or VZV, the test has limitations. It does not distinguish
between HSV and VZV, and the sensitivity is less than 100%. Viral cytopathic changes are
most likely to be detected in smears prepared from vesicles, followed by pustules, and
then crusted lesions. When clinical impression is used as the standard, the overall sensi-
tivity of Tzanck smear is about 50-60% for diagnosis of HSV infection and 64 -100% for
VZV, whereas the sensitivity of cell culture is approximately 80% for HSV and only
26-60% for VZV [29-32]. By staining with monoclonal antibodies, using immunofluores-
cence or immunoperoxidase techniques, the sensitivity of the direct smear increases but
remains lower than that of the cell culture for HSV, and identification of the specific virus
(HSV or VZV) is possible [29,33,34].
In certain situations, examination of cytologic preparations stained with nonspecific stains
is useful for diagnosis of several viral infections other than those caused by HSV and VZV.
For example, examination of a Papanicolaou-stained smear of cells collected from the uterine
cervix is a valuable screening tool for diagnosis of infection with genital human papillo-
maviruses [35-39]. Diagnosis of molluscum contagiosum, although usually based on the clin-
ical appearance of the lesion, may be confirmed by the examination of a smear of the cellular
material collected from the central cavity and stained with lugol's iodine [40]. The carbohy-
drate-containing matrix takes up the stain, and the inclusions appear as dark-brown masses.
Evaluation of cytologic preparations of bronchoalveolar lavage fluid stained by the
Papanicolaou technique or Giemsa stain is a rapid method, used predominantly with
specimens from immunocompromised hosts, for diagnosis of pneumonias caused by
some virus, including cytomegalovirus (CMV), adenovirus, respiratory syncytial virus
(RSV), HSV or VZV, or measles virus [41,42]. For RSV, the changes are often subtle and are
found only in a small proportion of epithelial cells, so that their recognition requires care-
ful search. Prolonged RSV infection in immunocompromised hosts, however, may result
in production of multinucleate giant cells containing eosinophilic cytoplasmic inclusions.
To confirm infection with any of these virus, a smear may be stained with specific anti-
bodies [43]. Examination of a smear of Wright- or Giemsa-stained bone marrow aspirate
for characteristic erythroblast inclusions is often necessary to confirm parvovirus B19 as
the cause of chronic anemia in an immunocompromised patient, especially a person with
AIDS, because serologic tests generally are not helpful in such cases. Infection with BK
virus or CMV may be diagnosed by detection of cells showing cytopathic changes charac-
teristic of the respective virus in cytologic preparations of urine sediment stained by the
Papanicolaou technique [22,44,45]. For CMV, however, shell-vial centrifugation-enhanced
cell culture with detection of CMV nuclear antigens is a more sensitive and more fre-
quently used diagnostic test. Microscopic examination of imprints of brain tissue stained
with Seller stain (a mixture of basic fuchsin and methylene blue) for Negri bodies is a use-
ful method for rapid diagnosis of rabies, especially in dogs [46]. However, rabies in
wildlife, particularly skunks and bats, may be caused by strains of the virus that do not
produce Negri bodies, and Negri-like cytoplasmic inclusion bodies may occur in neural
tissues in the absence of rabies [47-49]. For these reasons, use of the Seller stain for diag-
nosis of rabies has for the most part been replaced by immunofluorescence staining with
specific antibodies [46].
For some viral infections, diagnosis based on visualization of characteristic morphologic
changes in cells stained with a nonspecific stain is not possible or is very difficult, but in
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