Page 9 - World Aquaculture Magazine - March 2011
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W
orld
A
quaculture
7
Novel and emerging trends in the
application of diagnostic technologies,
epidemiology and disease exclusion in the
aquaculture food–producing industry
T
hales
P
assos de
A
ndrade
1
Epizootic outbreaks continue to
represent one of the most important
limiting factors for the success of aqua-
culture production systems in different
countries of the world. The worldwide
movement of live and frozen aquatic
animals is necessary for the develop-
ment of aquaculture. However, it has
provided opportunities for rapid trans-
mission and transboundary spread of
disease causing adverse socio-econom-
ic losses in the aquaculture food-pro-
ducing industry (Bondad-Reantaso
et al
. 2001, OIE 2009a,b, Lightner
et
al.
2009, Walker and Mohan 2009).
In response, aquaculture researchers
and the industry have developed new
technologies and improved manage-
ment techniques, diagnostic technolo-
gies, epidemiology and disease exclu-
sion. The present paper summarizes
the state of art of novel and emerging
trends on these three areas that, taken
together, form a foundation for a more
advanced and sustainable future for
the aquaculture industry.
Diagnostic Technologies
Most currently available aquacul-
ture diagnostic technologies are based
on traditional methods used in bacte-
riology, virology, mycology and para-
sitology (OIE 2009a,b). Over the last
two decades, major efforts have been
invested in development of more ad-
vanced methods. As a result, routine
histopathology and classical microbi-
ology have now been widely supported
by a large number of immunodiagnos-
tics [immunohistochemistry (IHC),
direct or indirect florescence antibody
(FAT/IFAT), ELISA, immunocro-
matography (ICT)] and conventional
nucleic acid-based approaches such as
in situ
hybridization using pathogen-
specific gene probes, polymerase chain
reaction (PCR), reverse transcription-
PCR and quantitative real-time PCR
(qPCR; OIE 2009a,b). The last is the
latest improvement over the standard
PCR techniques. Perhaps the most re-
fined diagnostic technology currently
available is the development of qPCR,
especially using a TaqMan® probe,
because it provides quantitative detec-
tion of a specific target with higher
specificity and sensitivity. It is also less
time consuming and less prone to con-
tamination compared with conven-
tional gel-based RT-PCR (Andrade
et
al.
2007, 2009).
A limited but growing number of
protocols, reagents and kits are cur-
rently available for aquaculture patho-
gen detection. TheWorld Organization
for Animal Health (OIE [formerly the
Office International des Epizooties])
continuously updates and dissemi-
nates the normative health standards
and recommendations such as
Aquatic
Animal Health Code
and the
Manual
of Diagnostic Tests for Aquatic Animal
that serves as the `gold reference´ to as-
sist Member countries and territories
in prevention and control of aquatic
animal diseases without setting up
unjustified sanitary barriers (Bernoth
2006, 2008). In 2009, twenty-seven
diseases that pose a substantial threat
of clinical disease and production loss
to aquatic animal operations were re-
portable to the World Organization
for Animal Health, nine of them caus-
ing diseases of crustaceans, nine of
fishes, seven of molluscs and two of
amphibians. Accurate description for
their diagnosis can be accessed on-
line at
en_amanual.htm (OIE 2009a,b).
The
Manual of Diagnostic Tests
for Aquatic Animals
verifies that PCR
has become as important as tradi-
tional diagnostic methods, and it has
become the most common diagnostic
technique available to confirm findings
based on the case history, gross signs
and histopathology. On another hand,
hematology and cell culture have been
routinely applied as diagnostic tools
for fish, although currently less well
established for crustaceans and mol-
luscs (OIE 2009ab). It is important to
understand the advantages and dis-
advantages of each these diagnostic
technologies, what kind of test is the
most appropriate to apply in a specific
disease situation and the type of con-
clusion that can or cannot be drawn
from their results. Furthermore, un-
derstanding the principals behind the
diagnostic technologies will often help
avoid mistakes and improve precision.
It is likely that the rapid progress
being made in the development of
diagnostic methods will enhance the
diagnosis of disease in aquaculture in
the near future. For instance, aqua-
culture pathologists have used light-
microscopy as the main front line tool
for investigation of a potential agent
