This virus appears to have mutated from strains that affected marine fish; the strain found in the Great Lakes is called Type IVb, and is the strain for which most surveillance efforts have been directed. VHSV can have devastating effects on a wide variety of species of fresh-water fish, with disease ranging from cases of acute high mortality to low-grade infections and carrier states.
In 2008, the state of Colorado entered into a Cooperative Agreement with the USDA-APHIS and received $45,000 to conduct statewide surveillance for the virus in free-ranging fish. From May 21 through November 4, 2008, 4,121 fish from 20 major watersheds within the state were sampled, and no VHSV was detected in any of the samples.
Monies were not available from USDA-APHIS for further surveys in 2009, and grants were delayed in 2010. However, another $30,000 was obtained in 2011 for continued surveillance within the state. In this latest grant, greater latitude was given to the cooperators (Colorado Parks and Wildlife) for use of the money. It was decided that one priority would be to perform surveillance testing in watersheds not sampled in 2008. In addition, frozen baitfish were tested for the virus, and an educational brochure was developed for state-wide dissemination.
In 2011, 928 samples from free-ranging fish in six major watersheds were collected under the APHIS grant. In addition, 606 fish from seven major watersheds, including two fish kills, were tested for VHSV by the Colorado Parks and Wildlife Aquatic Animal Health Lab (AAHL), independent of the APHIS grant. No VHSV was detected in any samples. The AAHL also performed testing for largemouth bass virus on samples of tissues from appropriate species of fish, and there were no detections of that virus. It is important to point out that in addition to the free-ranging VHSV testing, all public and private aquaculture facilities in the state receive annual disease testing, which includes VHSV, and there have never been detections in that sector.
A concern exists about the use of frozen baitfish imported from the Great Lakes. It has been proven that the VHSV virus can be detected in fish that have been frozen, but questions remain about whether the virus is still capable of replicating and causing disease in bodies of water where these baitfish are used. Frozen rainbow smelt (Osmerus mordax) from the Great Lakes are readily available in grocery and angling stores in Colorado, and are used as bait by fishermen throughout the state, particularly for ice-fishing. Therefore, as part of the APHIS grant, 180 samples from frozen Great Lakes smelt were tested for presence of the virus via molecular methods. No virus was detected, but the sample number was small.
Statewide surveillance is very important, but angler education is extremely useful in order to try to prevent introduction of this virus into the state. Toward that end, an educational brochure was produced which covered information about clinical signs and how to report moribund or dying fish; restrictions for movement of fish, bait and fish offal; and proper disinfection techniques. Ten thousand copies were sent to all Colorado Parks and Wildlife offices, commercial angling/bait shops that sell fishing licenses, professional fishing guide services, and other stakeholders. A copy of the brochure can be found on the Colorado Parks and Wildlife website at http:// wildlife.state.co.us/SiteCollectionDocuments/DOW/ Fishing/AAHL/ViralHemorrhagicSepticemiaBrochure. pdf. Colorado Trout Unlimited disseminated copies to their membership.
Continued surveillance of free-ranging fish is important as early detection is the best method by which to contain an outbreak. Currently, no funds are available from the USDA-APHIS for surveillance efforts in 2012. However, the Aquatic Animal Health Lab will continue to test for this virus at all private, public and freeranging sites during annual health inspections, and for unexplained fish-kills in the state. All live fish entering the state must have a current health certificate indicating that the fish have tested negative for the virus.
February 2012
