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Description

At a low level of infection, fish might not display any symptoms. As the infection becomes greater, however, fish will display widespread hemorrhages (bleeding) throughout body surface (eye, skin and fins) and within the internal organs (swim bladder, intestine, kidney etc.). Because of the bleeding, gills and liver might appear pale. Sick fish will often be listless, swim in circles, and are frequently observed at the surface of the water.

*Confirming VHS infection requires sophisticated laboratory testing. A diagnosis cannot be made based solely on observation because many different diseases of fish have very similar symptoms.*

Ecological Threat

Over 40 species of fish are known to be susceptible to VHS and massive die-offs of freshwater drum, muskellunge, round goby, gizzard shad, and other species have occurred in the Great Lakes. It can easily spread to the Northeastern United States via drainages off of the St. Lawrence River; and there’s the impending threat of VHS making it to the Mississippi River system. Even though Texas has a warmer climate that may offer some natural resistance to VHS infections, the presence of susceptible fish species, renowned fisheries that bring in visitors from across the US, and unregulated fish movements make Texas an at risk state to this severe disease.

Biology

VHS is a single-stranded RNA virus and a member of Rhabdoviridae and has an incubation period of 7 to 15 days depending upon water temperatures. Fish mortality from VHS can reach 80-90% and is most successful at temperatures of 37 - 54°F. It's not a threat to people who handle infected fish or want to eat their catch (stated by the Department of Health and Family Services), but it is threat to more than 40 species of fish that it can kill. This is the first time a virus has affected so many different fish species from so many fish families in the Great Lakes. The disease can be spread to other waterways through live baitfish, fresh fish eggs, live fish, bilge and bait bucket water and un-cleaned fishing gear or boats. Although fish may appear healthy, they can still carry and spread VHS.

History

VHS was first discovered in the mid-20th Century in Europe where it was originally a significant and costly disease of cultured rainbow trout. Since its initial discovery in Europe, four strains of the VHS virus have been identified, including both freshwater and marine strains. In 1988, VHS was reported in spawning salmon in the Pacific Northwest and was determined to be a new strain of the virus (Type IV) that appears to be a North American strain. It is widespread in the Pacific herring and Pacific cod populations in the Pacific Northwest and has also been found in Atlantic herring and Greenland halibut in the Atlantic Ocean. In 2005, a very large die-off of freshwater drum in Lake Ontario and a muskellunge kill in Lake St. Clair were linked to VHS, representing the first documentation of the disease in freshwater in the western hemisphere.

Native Origin

Japan, Korea and Europe

Current Location

U.S. Habitat: Different strains of VHS are native to Europe, Japan, and the Pacific (from California to Alaska) and North Atlantic coasts of North America. In 2006 using genetic data, scientists determined that the Great Lakes strain probably originated from the Atlantic coast of North America, specifically the Maritime Provinces of Canada. Since a wide variety of fish species can be susceptible it could even spread to Texas waters and impact native and sporting fishes.

Distribution

U.S. Present: Lake Huron, Lake St. Clair, Lake Erie, Lake Ontario and the St. Lawrence River affecting these states MI, MN, NY, OH, PA and WI.

Management

Since there is no treatment for VHS, the key is prevention. There are several ways to be responsible and do your part to not help the spread of VHS:

Do not transport leftover baitfish, fresh fish eggs or live fish to other waterways.
Empty live wells and bilges drawn from the body of water back into that same body of water before leaving.
Dump bait bucket water on dry land after fishing and do not release bait into water at end of fishing trip.
Thoroughly clean, dry (at least 5 days) and disinfect (with bleach) all fishing gear, boats and boat trailers before fishing a different lake or stream.

In an effort to control the spread of VHS, the USDA Animal and Plant Health Inspection Service issued orders restricting the movement of some fish species from the affected areas. If you notice any fish kills please contact your state wildlife entity; for Texas click here or here.