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Date: 24 Jun 2011
Source: Hartland Patch [edited]

Spring viremia of carp is the likely cause of death of 200 to 500 fish
DNR [Department of Natural Resources] biologist believes he has pinpointed the cause of a mass fish die-off that occurred at Kent Lake last weekend. A new estimate of 200 to 500 carp died, likely due to a virus called spring viremia of carp, said DNR fisheries biologist, Jim Francis.

Francis said that conditions were favorable for the spread of the virus, with the lake's temperature being under 65 degrees. "All of the reports we have received are consistent with the virus," Francis said.

Concerns that the fish had been poisoned by a water treatment or were victims of oxygen turnover can be laid to rest since either of those scenarios would have killed many different species indiscriminately, Francis said.

Other area lakes have been affected by the same virus, including Woodland Lake in Brighton.

"It's not the worst thing in the world when some carp die off,"
Francis said. "They aren't good for the ecosystem. They do harm to lakes." Francis said. Though 500 fish sounds like a big number, Francis said it only represents a small percentage of the population in Kent Lake. He says the die-off is likely over now that the lake's temperature is just above 65 degrees.

Clean-up crews at Kensington Metropark are currently hard at work trying to clean the lake and shoreline of the dead fish carcasses, said metropark superintendent Kimberly Jarvis. She said she anticipates a quick clean-up.

"If the die-off is over, it will be no later than the end of the week," Jarvis said. Many of the dead carp will be used in Kensingtons community service garden as fertilizer. "When we can use no more they will be disposed of appropriately," Jarvis said.

[byline: Johnny Branstetter]

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[While they believe it is spring viremia, I haven't seen a laboratory report on necropsy findings that indicate it is spring viremia or koi herpes virus.

Spring viremia of carp is caused by the spring viremia of carp virus (SVCV), which is also known as Rhabdovirus carpio. This virus is a member of the family Rhabdoviridae and has been tentatively placed in the genus Vesiculovirus. SVCV is closely related to pike fry rhabdovirus, and these 2 viruses cross-react in some serologic tests.

SVCV strains vary in their pathogenicity. Isolates can be divided into 4 genetic groups. Genogroup Ia viruses originate from Asia.
Genogroups Ib and Ic are comprised of isolates from Russia, Moldova, and Ukraine. Genogroup Id mainly contains viruses from the United Kingdom, although a few isolates in this group are from the former Soviet Union. SVCV strains from recent outbreaks in the United States appear to be most closely related to genogroup Ia.

Fish can carry SVCV with or without symptoms. Fish up to a year old are most likely to be affected, but illness also occurs in older animals. The clinical signs are nonspecific. In carp, the most common symptoms include abdominal distension, exophthalmia, inflammation or edema of the vent (often with trailing mucoid fecal casts), and petechial hemorrhages of the skin, gills and eyes. The body is often darkened with pale gills. Diseased fish tend to gather at the water inlet or sides of the pond, swim and breathe more slowly than normal, and react sluggishly to stimuli. Loss of equilibrium, with resting and leaning, are seen in the late stages. Concurrent bacterial infections (carp-dropsy complex) or parasitic infections influence the symptoms and mortality rate.

SVC outbreaks are most common in farmed carp, but can also occur in wild fish. Although fish of any age can become ill, disease is most common in young fish up to a year of age. The morbidity and mortality rates vary with stress factors and population density, as well as the species, age and condition of the fish. Water temperature affects the development of disease. In Europe, susceptible species usually become infected in the fall and winter as the water temperature falls. Some populations may become ill then, but most outbreaks occur in the spring as temperatures rise. Although the relationship between water temperature and illness is complex, clinical signs are most common at
17 deg C (63 deg F) or below. Fry may become ill at temperatures as high as 22-23 deg C (71-73 deg F).

The mortality rate is highest in young fish. Mortality rates up to 70 per cent have been reported in young carp during outbreaks. In experimentally infected fish, the mortality rate can be as high as 90 per cent. Yearly losses in older fish are usually under 30 per cent.
Water temperatures affect the mortality rate. In experimental infections, the cumulative mortality rate is similar at all temperatures from 11 deg C to 17 deg C (52 to 63 deg F), but the fish die more quickly at 17 deg C than 11-15 deg C (52-59 deg F). The mortality rate decreases at temperatures between 17 deg C and 26 deg C
(78.8 deg F). Recovery from infection usually results in strong immunity.

SVC should be suspected in cyprinid fish with signs of a systemic infection and an increased mortality rate, when water temperatures are below 20 deg C (68 deg F). A particularly high incidence of disease in common carp, with reduced susceptibility in carp hybrids and lower disease prevalence in other cyprinids, is also suggestive. The clinical signs and lesions are not pathognomonic and must be confirmed by laboratory diagnosis.

Spring viremia of carp is generally a reportable disease in most states and should be reported the federal authorities, generally the area veterinarian in charge (AVIC) is the one to receive the report.

Portions of this comment have been extracted from:
- Mod.TG

The state of Michigan can be located on the HealthMap/ProMED-mail interactive map at <http://healthmap.org/r/0_ua>. - Sr.Tech.Ed.MJ]

[see also:
Die-off, carp - USA: (MI) 20110622.1907 2010
Undiagnosed fish die-off - USA (02): (NJ) koi herpesvirus susp.
Koi herpesvirus, carp - USA: (CA) 20100523.1707
Koi herpesvirus, carp - USA: (AZ) 20090703.2395 Koi herpesvirus disease - USA (AZ) 20090613.2186
Koi herpesvirus - USA (TX) 20060707.1867
Spring viremia & Koi herpesvirus, carp - UK 20040907.2497 Spring viremia, carp - USA: OIE 20040612.1579
Spring viremia of carp - UK (England) 20021201.5941 Spring viremia, carp - USA (Wisconsin) 20020812.5028 Spring viremia, carp - USA (North Carolina)20020714.4758
Spring viremia of carp - UK (Suffolk) 20010626.1210] .................................................sb/tg/ejp/sh/ll
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