Paramoeba perniciosa (Paramoebiasis) of Lobsters


Category 1 (Not Reported in Canada)

Common, generally accepted names of the organism or disease agent


Scientific name or taxonomic affiliation

Paramoeba perniciosa

Mullen et al. (2005) used molecular analysis to identify the amoeba in diseased lobsters collected during the 1999 die-off in Long Island Sound, USA as Neoparamoeba pemaqueidensis (originally described as the aetiological agent of amoebic gill disease in aquaculture-reared finfish).

Geographic distribution

East coast of the United States from Connecticut to Florida including high salinity areas of Chincoteague Bay and Chesapeake Bay.

Host species

Reported from Homarus americanus but is principally a disease of crabs (Callinectes sapidus and Cancer irroratus).

Impact on the host

Paramoebiasis was proposed as the primary cause of the mass mortality of American lobsters from western Long Island Sound, USA in 1999 (Mullen et al. 2004). The collective findings of more than 20 research efforts that investigated the effects of anthropogenic and environmental stressors and disease on the lobsters from Long Island Sound, during a 3 year period associated with the mortality event, indicated that lobsters stressed by all-time high population abundance and sustained, stressful environmental conditions, including above average water temperatures, were unable to fend off paramoebiasis (Pearce and Balcom 2005).

Signs of paramoebiasis include general sluggishness or flaccid paralysis ("limp"), reduced or absence of clotting of the haemolymph, and poor survival after handling or holding in tanks. A parasite of the connective tissues and haemal spaces, invading the circulating blood only when the infection is terminal. In heavy infections, pathological changes caused by large numbers of amoebae include: tissue displacement, probable lysis of some types of tissue including haemocytes, and significant decreases in protein, haemocyanin and glucose (Sawyer and MacLean 1978).

Diagnostic techniques

Gross Observations: Greyish discolouration of the ventral exoskeleton.

Squash Preparations: In light infections, connective tissues along the midgut, antennal gland, and Y organ harbour amoebae. Before the amoebae appear in the circulation, they may be observed in subepithelial connective tissue examined with phase contrast if the infection is sufficiently advanced.

Wet Mounts: Observe amoebae in the blood with phase contrast either live or fixed in 5% formalin seawater and stained with dilute methylene blue.

Smears: Infection is diagnosed easily only in the terminal phase when numerous amoebae and virtually no haemocytes are present in the circulating blood. For permanent preparations, haemolymph smears can be fixed in Bouin's, Davidson's, Hollande's, or 10% formalin solutions and stained with iron haematoxylin or Giemsa's stain. Amoeba (round to elongate, 3-35 µm) contain a well-defined nucleus with a large central endosome plus a characteristic, morphologically-different secondary nucleus-like body in the cytoplasm.

Histology: Haemal spaces in the gills are usually invaded in medium and heavy infections and eventually the infection becomes systemic.

DNA Probes: Primers designed to SSU r RNA sequences of the amoeba in lobsters and other paramoebid/vexilliferid amoeba were used in a nested polymerase chain reaction (PCR) prtotocol to amplify parasite DNA in formalin-fixed paraffin-embedded tissues from infected lobsters (Mullen et al. 2005).

Methods of control

No known methods of prevention or control. Contact transmission experiments conducted in laboratory tanks resulted in transmission of paramoebiasis to uninfected lobsters within 15 days of co-habiting diseased and healthy lobsters (Mullen et al. 2004).


Couch, J.A. 1983. Diseases caused by protozoa. In: A.J. Provenzano Jr. (ed.). The Biology of Crustacea. Volume 6, Pathobiology. Academic Press, New York, p. 79-111.

Mullen, T.E., S. Russell, M.T. Tucker, J.L. Maratea, C. Koerting, L. Hinckley, S. De Guise, S. Frasca Jr, R.A. French, T.G. Burrage and C. Perkins. 2004. Paramoebiasis associated with mass mortality of American lobster Homarus americanus in Long Island Sound, USA. Journal of Aquatic Animal Health 16: 29-38.

Mullen, T.E., K.R. Nevis, C.J. O'Kelly, R.J. Gast and S. Frasca Jr. 2005. Nuclear small-subunit ribosomal RNA gene-based characterization, molecular phylogeny and PCR detection of the neoparamoeba from western Long Island Sound lobster. Journal of Shellfish Research 24: 719-731.

Pearce, J. and N. Balcom. 2005. The 1999 Long Island Sound lobster mortality event: findings of the comprehensive research initiative. Journal of Shellfish Research 24: 691-697.

Sawyer, T.K. 1976. Two new crustacean hosts for the parasitic amoeba Paramoeba perniciosa. Abstract, Transactions American Microscopical Society 95: 271.

Sawyer, T.K. and S.A. MacLean. 1978. Some protozoan diseases of decapod crustaceans. Marine Fisheries Review 40: 32-35. (MRF Paper 1342).

Citation Information

Bower, S.M. (2007): Synopsis of Infectious Diseases and Parasites of Commercially Exploited Shellfish: Paramoeba perniciosa (Paramoebiasis) of Lobsters.

Date last revised: August 2007
Comments to Susan Bower

Date modified: