A Fluorescent Antibody Test for Detection of the Rickettsia Causing Disease in Chilean Salmonids

—An indirect fluorescent antibody test (IFAT) was developed for detection of the rickettsia that was causing epizootics among salmonids cultured in seawater net-pens in southern Chile. Antiserum against the rickettsial agent was produced in New Zealand white rabbits with a preparation grown in antibiotic-free chinook salmon embryo (CHSE-214) cell cultures and partially purified by a combination of filtration and centrifugation steps. The IFAT was effectively used on blood films, tissue sections, and smears. Two gram-negative and two gram-positive bacterial pathogens of salmonids did not react in this test. Detection of the rickettsia] agent has previously been restricted to examination by light microscopy or isolation in salmonid cells. The IFAT provides a simple, rapid, sensitive method for detection of the agent and diagnosis of the disease. The rickettsia is thought to be a member of the tribe Ehrlichieae and was tested by IFAT with sera from animals infected with other rickettsial agents. An epizootic caused by a newly described rickrhynchus kisutch held at some locations in the area ettsial pathogen (Fryer et al. 1990) is ongoing (Bravo and Campos 1989). among salmonids cultured in seawater net-pens It was originally thought that the rickettsial innear Puerto Montt in southern Chile. Although fection was confined to coho salmon, because earrickettsial diseases have not previously been rely losses were reported only in that species. Howported in fish, mortality attributed to this agent ever, infectivity studies have subsequently shown reached 90% in 1989 among coho salmon Oncothe rickettsia to be pathogenic for coho salmon and Atlantic salmon Salmo salar (Garces et al. ———— 1991), and in 1990, extensive mortality oc1 To whom correspondence should be addressed. curred in Atlantic salmon cultured in the area. 229 D ow nl oa de d by [ O re go n St at e U ni ve rs ity ] at 1 5: 04 0 2 D ec em be r 20 11