Research News from the College of Veterinary Medicine

Researchers launch three-year study of largemouth bass virus
by Jim Barlow

Officials of the Illinois Department of Natural Resources went fishing last August to collect samples. The largemouth bass they caught at four lakes and two fish hatcheries were infected with a virus the officials were seeking but didn’t expect to find.

The virus—now confirmed in 17 states—is called the largemouth bass virus (LMBV) because only this species is dying from it. That no fish kills have been reported in Illinois is good news, but it also deepens the mystery as to the virus’s origin and variability.

“It was found in all four lakes and both state hatcheries—the only places we looked,” says Dr. Tony Goldberg, veterinary pathobiology. “This surprised everybody. It was shocking, because we hadn’t experienced any of the clinical signs typically linked with the virus.”

When active, usually in summer months, the virus attacks both sexes and all ages of largemouth bass; they lose equilibrium, float to the surface and die.

“One of the most interesting things about this virus is its clinical variability,” Dr. Goldberg says. “Some fish populations experience large-scale fish kills, but others appear perfectly normal. Nobody knows why some die and some do not.”

To find out, Dr. Goldberg and David Philipp, a scientist with the Illinois State Natural History Survey Center for Aquatic Ecology, have launched a three-year national study. They will do on-site examinations in affected areas and laboratory experiments in which they will raise largemouth bass and expose them to environmental stressors and to the virus.

Preliminary data suggest the virus in Illinois is not as deadly as that found in South Carolina lakes, he said. No bass deaths had been noted in the Illinois lakes sampled.

LMBV is an iridovirus, a family of virus that only affects fish, amphibians, and reptiles. Genetically, it is similar to a pathogen of aquarium fish from Southeast Asia, suggesting the virus may have been imported, Dr. Goldberg says. While found in other fish, LMBV so far has only caused mortality in largemouth bass. The virus poses no health risk to people who eat infected fish.

The virus was discovered in 1995 in the Santee Cooper Reservoir of South Carolina, where it killed 1,000 largemouth bass. It has since been found elsewhere, including last year in Indiana and Michigan. Not all states have tested for the presence of the virus. A mysterious 1991 Florida fish kill may have been from LMBV, scientists now theorize.

The UI research is funded by the Illinois Council on Food and Agricultural Research and the Conservation Medicine Center of Chicago, a consortium of the Brookfield Zoo, Loyola College of Medicine, and the College of Veterinary Medicine. The national survey is being done in collaboration the U.S. Fish and Wildlife Service’s Warm Springs Regional Fisheries Center in Georgia.

Dr. Goldberg has written a chapter on LMBV for Black Bass 2000: The Ecology, Conservation and Management of Black Bass in North America, to be published later this year by the American Fisheries Society.

 

Soy Component May Cause Immune Changes

Estrogens can have negative health effects, including, at high doses, atrophy of the thymus gland, which is needed early in life for development of normal immune functions. Genistein is a plant estrogen present in soybeans and found in infant soy formulas at high levels. In fact, soy-fed infants may ingest 10 times as much genistein per kilogram of body mass as do adults on high-soy diets.

Given the possible implications for soy-fed infants, Dr. Paul Cooke, veterinary biosciences, doctoral student Dr. Srikanth Yellayi, and other researchers from the University of Illinois at Urbana-Champaign investigated whether genistein could have a negative effect on the development of the immune function.

Results of their investigation, which was supported by grants from the United Soybean Board and Illinois Council on Food and Agricultural Research, were published recently in the Proceedings of the National Academy of Sciences.

In a series of studies using mice, researchers looked at the effects of injected or ingested genistein on various aspects of the immune system, such as the size of the thymus and the number of immune cells associated with the thymus. Their work provided evidence that serum genistein in mice at levels comparable to those reported in soy-fed human infants caused significant thymic and immune changes in mice.

These results raise the possibility that serum genistein concentrations found in soy-fed infants may be capable of producing thymic and immune abnormalities. The findings suggest that the use of soy formula for infant nutrition—and of high soy/isoflavone intake by adults through the use of supplements—needs to be approached with caution.