Nuclear Inclusion X (NIX) of Pacific Razor Clams

Category

Category 2 (In Canada and of Regional Concern)

Common, generally accepted names of the organism or disease agent

Nuclear inclusion X, NIX.

Scientific name or taxonomic affiliation

Highly specialized and very large type of Rickettsia-like organism.

Geographic distribution

Washington, as well as some populations in Oregon, USA and British Columbia (Haida Gwaii), Canada.

Host species

Siliqua patula.

Impact on the host

Rickettsia-like organism resides in the nucleus of epithelial cells of the gills causing gross hypertrophy such that infected cells are visible as protrusions on the gills. The disease persists at a low level in clams during the winter and spring. In some years the infection can greatly increase in intensity during the summer and fall, when mortalities associated with the disease usually occur. Prevalence and intensity of infection in razor clams from the Haida Gwaii, British Columbia appears to be low. None of 10 clams examined in 1983 and 13 of 50 clams examined in August 1990 were infected and all infected clams had very low levels of infection (Ralph Elston, personal communications).

Diagnostic techniques

Gross Observations: Presumptive diagnosis by observing nodules on the gills.

Histology: Observation of hypertrophied gill epithelia nuclei (about 25 µm wide compared with 4-6 µm in normal gill epithelia). Occlusion of the water channel spaces and disruption of normal tissue structure occurs in heavy infections.

Electron Microscopy: Large, presumptively prokaryotic organisms occurring exclusively within the greatly enlarged cell nuclei of nonciliated branchial epithelium. These organisms, with partially cleaved forms, are membrane rich, complexly folded, and have ultrastructural features typical of prokaryotic cells except for their size (16 x 25  µm) which was larger than any known bacterium.

Methods of control

Control or management consists of harvesting populations with a high prevalence of the disease prior to onset of mortalities.

References

Elston, R.A. 1986. An intranuclear pathogen [Nuclear Inclusion X (NIX)] associated with massive mortalities of the Pacific razor clam, Siliqua patula. Journal of Invertebrate Pathology 47: 93­104.

Elston, R.A., A.S. Drum and M.T. Wilkinson. 1990. Pathology of razor clams. Report prepared for State of Washington, Department of Fisheries, by Battelle, Pacific Northwest Laboratories, Richland, Washington. 17 p.

Elston, R.A., A.S. Drum, Wilkinson, M.T. and J.R. Skalski. 1988. Pathology of razor clams. Report prepared for State of Washington, Department of Fisheries, by Battelle, Pacific Northwest Laboratories, Richland, Washington. 19 p.

Olson, R.E. and J. Pierce. 1988. Occurrence of the nuclear inclusion parasite in Oregon razor clams (Siliqua patula). Journal of Invertebrate Pathology 52: 198­199.

Citation Information

Bower, S.M. (2001): Synopsis of Infectious Diseases and Parasites of Commercially Exploited Shellfish: Nuclear Inclusion X (NIX) of Pacific Razor Clams.

Date last revised: July 2001
Comments to Susan Bower

Date modified: