Abstract
Quahog Parasite Unknown (QPX) was identified in aquacultured hard clams grown in Provincetown and Duxbury, MA, USA in the summer and fall of
19951. The disease continues to devastate the clam industry in those areas. Recently, disease and resultant mortality in hard clams were identified in
Virginia2 and New Jersey3 cultured animals demonstrating that the disease is not limited to the Northeast.
QPX is a protistan organism that has been placed in the phylum Labyrinthomorpha4,5. Only rarely have organisms in this group caused
disease in animals. In both infected tissues and cultures of QPX four life forms can be identified including: thalli, sporangia, endospores and flagellated
zoospores.1,6.
The disease caused by QPX is slowly progressive. Animals do not die until approximately 22 years after infection, just below market size.
Mortality is most severe in the spring and summer as moribund clams unearth themselves and lie on the top of the sediment. Nodules up to 1 cm can be noted in the
mantle edges of severely infected animals. Microscopically, infections are most common in the mantle and gills suggesting QPX invades those organs directly
exposed to seawater.
Little is known about the life cycle of QPX, pathogenic components of the organism or methods of amelioration of its effect on cultured
animals in endemic areas. Our present studies are examining methods of control and disease reduction by developing possible resistant strains of clams, rotation
of plots, plot pretreatment, and laboratory studies of the organism's ability to cause disease in clams. Results of these studies to date will be presented.
References
1. Smolowitz R, D Leavitt, F Perkins. 1998. Observations of a protistan disease similar to QPX in Mercenaria mercenaria (hard
clams) from the coast of Massachusetts. Journal of Invertebrate Pathology 71: 9-25.
2. Ragone Calvo LM, JG Walker, EM Burreson. 1998. Prevalence and distribution of QPX, Quahog Parasite Unknown, in hard clams
Mercenaria mercenaria in Virginia, USA. Diseases of Aquatic Organisms 33: 209-219.
3. Kraeuter J. Haskins Shellfish Lab., Rutgers University, personal communication.
4. Whyte SK, RJ Cawthorn, SE McGladdery. 1994. QPX (Quahog Parasite X), a pathogen of northern quahog Mercenaria mercenaria
from the Gulf of St. Lawrence, Canada. Diseases of Aquatic Organisms 19: 129-136.
5. Moss P, R Smolowitz, S Kleinschuster, M Dykstra. Molecular identification of QPX (Quahog Parasite Unknown), a pathogen of
Mercenaria mercenaria. In preparation.
6. Kleinschuster SJ, R Smolowitz, J Parent. 1998. In vitro life cycle and propagation of quahog parasite unknown. Journal
of Shellfish Research 17: 75-78.