VHS has been known for many years primarily as a disease of salmonids in Europe and the US Pacific Northwest. Recently, a new strain of the virus, VHS IVb, has emerged in the Great Lakes of the US and Canada. This new strain is a serious pathogen of many species of marine and freshwater fish. Among the susceptible species are popular Texas sport fish such as largemouth bass, bluegill, channel catfish, and white bass.
Symptoms: Signs of diseased fish typically include dark color, exophthalmia (popeye), anemia, and hemorrhaging in the eyes, skin, gills, bases of fins, skeletal muscles, and viscera. The abdomen may be distended from internal swelling and the liver and kidney often appear pale. Fish may swim erratically but some infected fish may appear normal. Positive identification requires laboratory procedures including cell culture and molecular tests. VHS has been called “fish Ebola” in the popular press but VHS is not closely related to the Ebola virus..
Host(s): Black crappie, Bluegill, Bluntnose minnow, Brown bullhead, Brown trout, Burbot, Channel catfish, Chinook salmon, Emerald shiner, Freshwater drum, Gizzard shad, Lake whitefish, Largemouth bass, Muskellunge, Shorthead redhorse, Northern pike, Pumkinseed, Rainbow trout, Rock bass, Round goby, Silver redhorse, Smallmouth bass, Spottail shiner, Trout-perch, Walleye, White bass, White perch, Yellow perch
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. VHS IVb is believed to have been introduced to the Great Lakes from the Atlantic through either ballast water or migrating fish. Aquaculture activities, including movements of bait fish, have been implicated in the spread of the virus, which has been recovered from frozen fish. Waterfowl may also contribute to the spread of VHS. The virus can remain infective in water for 1 to 5 days depending upon temperature.
Although the warm climate of Texas may offer some natural resistance to VHS infections, the presence of susceptible fish species, nationally renowned fisheries attracting visitors from across the US, and unregulated fish movements make Texas vulnerable to this serious disease.
Biology: VHS is a single-stranded RNA virus and a member of Rhabdoviridae. The name is derived from the Greek rhabdos meaning rod and refers to the shape, which is bullet-like in VHS. VHS has an incubation period of 7 to 15 days depending upon water temperatures. Fish mortality from VHS is greatest at temperatures of 3-12°C (37 - 54°F) and can reach 80-90%. VHS is not harmful to humans even if infected fish are handled and eaten.
History: VHS was first described in 1963 as a viral disease affecting primarily rainbow trout in Europe where it caused massive mortality among cultured fish. In 1988, VHS was reported in spawning salmonids in the Pacific Northwest. The virus became widespread among several species of marine fish and also became established in the Atlantic Ocean in Atlantic herring and Greenland halibut. A new strain of the virus, VHS IVb, was apparently introduced into the Great Lakes in 2003 and large, multispecies fish kills were reported in 2005 and 2006. 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.
U.S. Habitat: VHS is considered indigenous to the Pacific coast (California to Alaska) and North Atlantic coast of North America. The VHS IVb strain is considered an emerging disease and aquatic nuisance species since its 2003 arrival in the Great Lakes. A wide variety of fish species are susceptible, including many popular sport fish in Texas, although the disease has not yet been recorded in Texas waters.
Native Origin: Europe, North America, Japan and Korea.
U.S. Present: The North American strain of VHS virus is present in Lake Huron, Lake St. Clair, Lake Erie, Lake Ontario, and the St. Lawrence River.
Distribution: The North American strain of VHS virus is present in Lake Huron, Lake St. Clair, Lake Erie, Lake Ontario, and the St. Lawrence River.
Currently, there is no treatment for VHS and efforts to minimize the effects of VHS focus on prevention. Recommended prevention methods include the following:
- Never move fish or other aquatic organisms from one body of water to another
- Drain water from bait bucket, live well, bilge and motor before leaving any waterbody
- Dispose of unwanted bait, fish parts, and worms in the trash
- If purchasing fish for bait, verify that the bait is from VHS-free waters
- Spray/wash boat, trailer, and equipment with high pressure hot water or
- Disinfect fishing equipment between water bodies by allowing equipment to dry thoroughly (for at least 5 days) between uses or using bleach (1/2 cup of bleach in 5 gallons of water).
NAS - Nonindigenous Aquatic Species
Great Lakes Aquatic Nonindigenous Species
Wisconsin Department of Natural Resources
Centre for Environment, Fisheries & Aquaculture Science
Viral Hemorrhagic Septicemia-Iowa State University
Fish Disease Leaflet 83 - USGS
Animal and Plant Health Inspection Service