Friday, August 27, 2010
Tests of the potential vaccine against "Ich" ― the dreaded
"white-spot" disease that plagues fish in commercial fish farms,
public aquariums, pet fish retail outlets, and home aquariums ― are
raising hopes for finally controlling the disease, scientists
reported here today at the 240th National Meeting of the American
Chemical Society (ACS).
"Outbreaks of the parasitic disease caused by Ichthyophthirius (Ich)
can result in losses of 50-100 percent of fish," Dehai Xu, Ph.D.,
said in presenting the results. "The disease is very common, and
almost every home fish hobbyist has encountered it. Once the
parasite infects fish, and starts growing in the skin, fins, and
gills, there is no really effective treatment. Ich causes losses
estimated at $50 million annually. It would be much better to
prevent the disease."
As an indication of the difficulty in treating Ich outbreaks, Xu
used the example of an infection that strikes a commercial fish
farming pond, which might have a surface area equal to 10 or 20
high school football fields. The typical treatment involves pouring
in a solution of formaldehyde, a potentially toxic substance.
Hundreds of gallons might be needed, and farmers might have to
repeat the treatment several times. Even after treatment, the fish
would be at risk of reinfection if they encountered the parasite
again, he said.
"To vaccinate against Ich, you would need much less medication, and
it would not pose an apparent threat to the environment," Xu
pointed out. "And you would need just one treatment to make the
fish immune for life."
Xu explained that efforts to develop an Ich vaccine have focused on
use of so-called "trophonts," which are the infective stage of the
Ich parasite's life cycle. Trophonts burrow into a fish's skin,
fins, and gills, causing the white skin spots characteristic of the
disease. Those efforts have been hindered, however, by gaps in
scientific knowledge about how fish develop protective immunity to
trophonts. Xu and colleagues, Drs. Phillip Klesius and Craig
Shoemaker, who are with the U. S. Department of Agriculture's
Agricultural Research Service (ARS) in Auburn, Al., set out to fill
those gaps.
Their study evaluated influence of vaccine formulation and doses of
vaccine on protective immunity of channel catfish against Ich. The
results showed that vaccination with live Ich theronts and
trophonts killed with high-frequency sound waves stimulated
production of protective antibodies in the catfish.
"This study demonstrated that vaccines against Ich induced
protective immunity and could provide a unique solution to prevent
this parasitic disease through vaccination," Xu said. "An Ich
vaccine would have great impact by preventing the disease,
minimizing loss of valuable fish and increasing profitability of
aquaculture."
Xu noted that the study was a small, laboratory-scale endeavor,
with unsolved problems on the road ahead to a commercial vaccine.
One, for instance, involves producing a large quantity of Ich
antigen for the vaccine and then formulating a vaccine that can be
easily administered to large numbers of fish in a "bath" or in
food, rather than by injection. In the bath approach, fish would be
kept in a container or an enclosure with water containing the
vaccine. This study is within the component of ARS National Program
106-"Aquaculture" to improve health and welfare of aquatic animals.
Xu and colleagues hope their study will bring more attention to the
research to combat this disease.
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Thanks to American Chemical Society for this
article.