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viruses are easy to propagate (Enteroviruses), some are difficult (Rotavirus
and Hepatitis A virus) and for some no cell line is available.
25
Cell culture propagation of wild-type strains of hepatitis A virus (HAV)
is a complex and tedious task, which requires virus adaptation before its
effective growth. Even then, the virus usually establishes persistent infec-
tions, which results in low virus yields. In 2006, the use of a cell line that
allows the growth of a wild-type HAV isolate from stool was reported by
Konduru and Kaplan,
27
although its validity for broad spectrum isolation of
HAV has not yet been demonstrated. For NoV, the prospects for cell culture
are even worse and, in spite of numerous attempts, NoV propagation has
only been shown in a intestinal epithelium, which provided unconfirmed
expectations for infectious NoV detection.
28
Typically the cell cultures are monitored daily by microscopy for cyto-
pathogenic or cytopathic effect (CPE) for up to 1-3 weeks.
25
CPE can
be manifested in a variety of ways such as swelling, shrinking, rounding of
cells or any clustering or destruction of the monolayer (
Fig. 3.5a
). Quanti-
fication of the virus can be carried out by using serial dilutions of the virus
inoculated into cell cultures and counted using a most probable number
or plaque assay method.
25
Standard methods for enteric viral detection
are available and used by laboratories that are equipped to handle such
analysis.
20-22
A major limitation of using standard cell culture assays for
routine pathogen detection in water is that they are laborious, expensive
and the conditions for propagation or cell lines not well established for
some pathogenic strains.
Nucleic acid amplification techniques are currently the most widely
used methods for detection of viruses in water and food (
Fig. 3.5b
). The
advent of molecular methods enabled the development of diagnostic tools
with exquisite sensitivity for detection of human pathogenic viruses that do
now grow in cell cultures. In this way, the significance of the enteric viruses,
for which cell culture methods were troublesome, such as hepatitis A and E
viruses, rotaviruses and, particularly, NoVs as water and food borne agents,
could be ascertained.
29
Immunological detection systems for NoV detection
in fecal specimens do exist.
30
However, even when kits for antigen detection
are available, their sensitivity is not high enough to be employed in
scenarios of low virus concentration, such as water samples. A 2012 review
of both molecular methods and other approaches is given in Ref 25 cover-
ing both established and developing techniques. A table summarizing the
cost, turnaround time, advantages and disadvantages of the different virus
detection approaches can be found in Ref 37.
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