Theses and Dissertations


Title: PATHOGENESIS OF LARGEMOUTH BASS VIRUS: INFECTION BY IMMERSION, CLINICAL SIGNS OF DISEASE, AND VIRUS DISTRIBUTION

Name: Beck, Benjamin Hester

Degree: MS

Chair: John M. Grizzle

Resides: FAA Library

University: Auburn

Location: Auburn, Alabama

Date: 2005

Pages: 62

Keywords: largemouth bass virus, infection, detection

Abstract:

Largemouth bass virus (LMBV) can cause a fatal disease in Largemouth bass Micropterus salmoides. LakeWeir, Florida, was the source of the first isolate of this virus, and the first fish die-off attributed to LMBV occurred during 1995 in Santee-Cooper Reservoir, South Carolina. While several additional fish kills have been caused by LMBV, the pathogenicity of LMBV appears to be variable because infected largemouth bass are often found where there have been no reports of fish kills. In previous laboratory studies, largemouth bass were infected with LMBV by injection, oral administration, or immersion into water containing LMBV. While injection causes the highest mortality, oral and immersion infection routes are considered the most likely routes of transmission in the wild.

In the present study, we immersed largemouth bass (mean weight 79 g; mean Length 181mm )for 1 h in water containing LMBV (1.7x103 plaque forming units/mL) and then necropsied fish daily for 27 d. Cell culture was used for detection of LMBV in the following organs: gill, liver, spleen, trunk kidney, head kidney, swim bladder, heart, brain, gonad, intestinal cecum, and intestine. Of the 225 fish exposed to LMBV, 2 dead and 5 moribund fish were collected during the 27 d after immersion. There were 192 virus-exposed fish tested for LMBV
(moribund and clinically normal), and 33% were infected with LMBV. The dead fish Were not necropsied because of their advanced state of decomposition, but all five of the moribund fish tested positive for LMBV. Largemouth bass virus was detected systemically at the end of the l-h exposure period and for up to 24 d postexposure. The gill, swim bladder, and trunk kidney were the organs most frequently infected with LMBV and had the highest titers of LMBV. Fish collected during days 0 through 8 postexposure had a greater average number of LMBV infected organs than fish collected on days 9 through 27. Moribund fish had significantly lower total length and weight than LMBV negative fish. There were no lesions observed histologically that could be attributed to LMBV.

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