The Zebrafish Science Monitor Vol 3(4)
INTESTINAL CAPILLARIASIS IN ZEBRAFISHBy M. Pack, J. Belak, C. Boggs, M. Fishman and W. Driever.
Cardiovascular Research Center, Massachusetts General Hospital and Harvard Medical School, 149 Thirteenth Street, Charlestown, MA 02129, USA.
In 1994, a progressive wasting illness associated with the presence of intestinal Nematodes was noted in our facility. Fish which appeared healthy were also infected and often infertile. In this report we provide details of our experience with this condition.
Fish raised in our facility during the first months of 1994 developed a progressive wasting illness soon after reaching sexual maturity. Pathological evaluation performed outside of our facility was normal. Because of the sporadic occurrence of elevated copper levels in Boston water a reverse osmosis water purification system was installed. Snails were introduced into all aquaria to remove excess food and prevent fungal growth. Despite these measures the percentage of affected fish increased over several months. In the summer of 1994 we repeated the pathologic evaluation and found live Nematodes in the intestinal bulb of all fish examined. Microscopic examination of eggs identified the worm as a member of the Capillaria species.
Capillarids are thin and transparent worms that can reach one centimeter length. The eggs have a characteristic oval shaped appearance with a plug-like structure at either end and are visible in the adult worm, and the gut or feces of infected fish. Photographs and a good description of Capillarids at different developmental stages can be found in the Handbook of Fish Diseases, Dieter Untergasser, Editor (TFH publications, 1989, p104-5). Worms in the intestinal bulb of adult zebrafish are motile and can be easily seen when the dissected gut, in egg water (0.03% Instant Ocean) is viewed with transmitted light using a high power (50X) dissecting microscope. Outside the fish gut Capillarids are no longer motile.
To rid fish and aquaria of the Nematodes, snails, which may act as storage for Capillarid eggs, were removed, and treatment with anti-helminthic drugs was begun. We tried Levamisol (9mg/ml) first, but two treatments were ineffective. Next we tried a combination of two drugs, Trichlorfon and Mebendazole ("Fluke-tabs"; Aquarium Products, 180-L Penrod Court, Glen Burnie, MD 21061). This combination of drugs has been reported to be extremely efficacious for removing monogenetic trematodes from fresh water fish. Trichlorfon is an insecticide with anti-cholinergic activity that is considered toxic to humans. Mebendazole, a common anti-helminthic used to treat human intestinal infections, inhibits glucose uptake and is cidal for adult helminths and embryos.
We used the dosage recommended by the supplier; one tablet per 38 liters once trials to assess toxicity were completed. The drugs were added to our recirculating system (volume of tanks, reservoirs, filters and pipes included) as a slurry (100 tablets per one liter water-let stir 10 minutes) since they are poorly soluble in water. The treatment was repeated after 24 and 48 hours with a 10% water change every day thereby increasing the effective concentration. Carbon filters were removed during treatment. UV filters were not. Fish facility personnel were required to wear plastic gloves to avoid contact with water. Carbon filters were re-installed at 72 hours which removed the drugs from the system. The treatment protocol was repeated at 10 days since the cidal effect of these drugs on freshly fertilized eggs or dauerlarvae is not reported.
A beneficial effect from the treatment was evident within one week as fish gained weight and regained fertility. Fish sacrificed for pathological examination were free of worms. No widespread recurrence has been noted three months after treatment and fish remain healthy. However, after four months, isolated appearance of Capillaria was observed in few tanks. The treatment was repeated. No significant adverse effects of treatment were observed.
The youngest fish in the system which received medication had been feeding on brine shrimp for at least five days. Larvae still feeding on paramecia received one treatment (one tablet per 38 liters) 24 hours before their first dose of brine shrimp and were introduced into our recirculating system 30 hours later. No toxicity was observed.
Parasitic infections are common in fresh water fish and heavy infestations can be lethal. We feel the wasting illness and reduced fertility seen in our fish was the result of nutritional deprivation since the intestinal bulb of all fish examined was fully occupied by live worms. Eradication of the parasite was coincident with weight gain and a dramatic improvement in fertility. Within a large facility, recurrence even after several months is possible, and fish with wasting syndrome should be routinely checked for parasites.
We thank Drs. B. Dixon (Haywood, CA), D. Grunwald (Salt Lake City), C. Nuesslein-Volhard (Tuebingen), J. McBain (San Diego) and R. Bullis (Woods Hole) for their assistance.
References:
Goven, B.A. and Amend D. F. (1982). Mebendazole/trichlorfon combinations: A new anti-helminthic for removing monogenetic trematodes from fish. Journal of Fish BIology. 20, 373-378.
Zebrafish Science Monitor Vol 3(4)
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