At long last, a vaccine offers hope of preventing Ich
Fish with Ich Credit: Dehai Xu, Ph.D
According to new research presented by Dehai Xu, Ph.D. at the 240th National Meeting of the American Chemical Society (ACS)*, a vaccine against the feared ich disease might be available in the foreseeable future.
Ich is a disease dreaded by hobby aquarists and professional fish farmers alike. It is caused by the ciliated protozoan Ichthyophthirius multifiliis (hence the name ich) and can easily kill of all the fish in an aquarium or fish pond. Fortunately, it seems to be unable to infect humans. Among aquarists, it is chiefly known as White Spot Disease since the parasites cause small white nodules to form on the skin and in the gills of infested fish.
Today, ich outbreaks in large commercial fish farms are often treated by adding hundreds of gallons of a formaldehyde solution to the water. This is far from an ideal solution, since formaldehyde can be toxic to both humans and fish. It is classified as a known human carcinogen by the WHO International Agency for Research on Cancer (IARC) and is associated with both nasal sinus cancer and nasopharyngeal cancer. And as anyone who has ever combated ich in an aquarium knows, ich treatment is something you have to do over and over again since the parasite is usually only sensitive to treatment during one of its multiple life stages. This means repeatedly adding large quantities of formaldehyde solution to the pond. Even when formaldehyde ich treatment is successful, it provides no long-lasting effects since the fish develops no immunity. If new outbreaks occur, a new treatment cycle has to be carried out.
It is therefore no surprise that the series of vaccine tests carried out by Dr. Xu and his colleagues Dr. Phillip Klesius and Dr. Craig Shoemaker, who are with the U. S. Department of Agriculture’s Agricultural Research Service (ARS) in Alabama, have sparked vibrant interest within the aquatic world. For anyone from commercial fish farmers to public aquaria and hobby fish keepers, an ich vaccine would be a dream come true.
“Outbreaks of the parasitic disease caused by Ichthyophthirius (Ich) can result in losses of 50-100 percent of fish,” Dr Xu explained while presenting the team’s findings at the ACS meeting. “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. To vaccinate against Ich, you would need much less medication, and it would not pose an apparent threat to the environment. And you would need just one treatment to make the fish immune for life.”
In their efforts to develop a vaccine, Xu and his colleagues have focused on the use of so-called trophonts.
The ich protozoa goes though three life stages:
• The ich trophozoite feeds inside the nodule (”the white spot”) on the skin or gill of the fish.
• The ich trophozoite falls off and becomes an ich tomont, i.e. it enters an encapsulated dividing stage. During this stage, the tomont is attached to plants, gravel or other objects in the environment.
• The ich parasite will then start dividing itself, producing trophonts. The trophonts will move around freely in the water, looking for fish to infect.
Trophonts burrow into the skin and fills of a fish and start to feed, thus completing the cycle. When Xu, Klesius and Shoemaker began their research project very little was known about how fish develop protective immunity to trophonts, so the researchers basically had to start from scratch.
Eventually, they were able to show that vaccination with live ich theronts and trophonts killed with high-frequency sound waves stimulated production of protective antibodies in channel catfish (Ictalurus punctatus)
“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.”
Injecting fish in a laboratory setting is one thing, administering a vaccine to thousands or even millions of fish in a huge commercial farm is another, so the next goal will be to find a way of carrying out large-scale vaccinations. It might for instance be possible to produce a large quantity of Ich antigen and then creating a vaccine that can be administered as food or in a “bath”.
For aquarists however, injecting each fish with the vaccine might actually be a feasible solution, provided of course that an injectable vaccine would be produced for the aquarium market.