Biomedical Engineering Reference
In-Depth Information
many of these diseases a diagnosis can be made by immunofluorescence staining of smears
with virus-specific antibodies. This approach to diagnosis is used most widely for detection
of respiratory virus (RSV, Influenza A and B virus, and parainfluenza virus) in smears of
nasopharyngeal cells collected by aspiration or swab. Advantages of immunofluorescence
staining are that they have rapid turnaround time, high specificity, and the ability to assess
specimen adequacy. For RSV, the sensitivity of immunofluorescence staining is equal to or
greater than that of other available diagnostic tests (enzyme immunoassay and cell culture)
[50-55]. In contrast, cell culture is more sensitive than immunofluorescence staining for
detection if the immunofluorescence test is negative [50,52,56,57]. Other uses of virus-
specific antibodies include rapid diagnosis of measles by detection of viral antigen in smears
of nasopharyngeal cells [58], diagnosis of CMV pneumonia by detection of virus-infected
cells in smears of bronchoalveolar lavage fluid [59], and differentiation of asymptomatic
shedding of CMV during reactivation from active disease. The last is based on detection and
quantitation of antigenemia by staining smears of peripheral leukocytes (buffy coat) with a
monoclonal antibody against CMV pp65 structural antigen [60,61].
21.1.7
Detection in Tissue Sections
The first step in the routine diagnosis of any infectious disease from tissue specimens is
the examination of sections stained with hematoxylin and eosin (H&E). Although the indi-
vidual virus cannot be seen, many induce easily recognizable cytopathic changes that in
most cases are sufficient for diagnosis [62,63]. Other features of viral infection are cell
necrosis, which occurs during release of viral particles after replication, and an inflamma-
tory infiltrate predominantly composed of lymphocytes; macrophages generally appear
later in the infection cycle. In certain viral infections, such as HSV bronchopneumonia or
bronchitis, polymorphonuclear leukocytes (PMN) may be present, even in the absence of
secondary bacterial infection. The composition and degree of the inflammatory response
to any infectious agent, however, depends primarily on the host immune status.
Occasionally, the changes observed in H&E-stained sections are insufficient for diagnosis
and additional stains or other tests are necessary. Only a few nonspecific “special stains”
have been useful for diagnosis of viral infections. Lendrum's phloxine-tartrazine method
improves detection of viral inclusion bodies, staining them red against a yellow back-
ground [64], and Parson's stain and Schleifstein's method have been used for detection of
Negri bodies. Orcein, modified trichrome, or Victoria blue-nuclear fast red were once used
for confirmation of chronic hepatitis B virus (HBV) infection, apparently on the basis of the
presence of disulfide bonds in HBV surface antigen [65-67]. Today, however, immunohis-
tochemical assays with commercial virus-specific antibodies are preferred.
21.1.8
Foodborne Illness
Several groups of virus may infect persons after ingestion and then shed via stool. Of
these, the norovirus (NoV) and hepatitis A virus (HAV) are currently recognized as the
most important human foodborne pathogens with regard to the number of outbreaks and
people affected in the Western world. NoV and HAV are highly infectious and may lead
to widespread outbreaks [68]. Secondary infection of populations in countries with high
standards of hygiene can take place. Molecular-based methods can detect virus in shell-
fish but are not yet available for other foods. The applicability of the methods currently
available for monitoring foods for viral contamination is unknown. No consistent correla-
tion has been found between the presence of indicator microorganisms (i.e., bacterio-
phages,
Escherichia coli
) and virus.
