JOURNAL
OF
INVERTEBRATE
Rickettsiales-like
PATHOLOGY
56, 135-138 (1%))
Infection in the Gills of Tridacna crocea from the Great Barrier Reef
Tridacnid clams are cultured throughout Asia and the Pacific for human consumption but their commensals, parasites, and diseases are little known. As rickettsiae are potentially pathogenic to humans (causing Q fever and typhus), the occurrence of a rickettsiales-like infection in tridacnid clams warrants attention. Spherical, cream-colored cysts were found in the gills of 7 among 30 burrowing clams, Tridacna crocea, in May 1987 and 20 among 30 T. crocea in September 1988 collected from the reefs around Lizard Island, Great Barrier Reef. No cysts were found in 30 giant clams, T. maxima, collected from the reefs around Heron Island,
FIG. 1. Rickettsiales-like Reef. Bar = 120 pm.
Great Barrier Reef, in December 1987. In histological sections, the cysts ranged between 60 and 230 p,rn in diameter (mean = 137 pm, SD = 10.72 urn, n = 15) (Fig. 1). Up to 15 cysts were visible in one histological section. Cysts contained finely granular, basophilic material enclosed within a membrane, presumably the wall of the parasitized cell. Outside this was an eosinophilic, hyaline layer, 1 urn thick and PAS positive. This was covered by a thin layer of connective tissue and a layer of gill epithelium. Individual rickettsial bodies were visible in some sections. With transmission electron microscopy, prokaryotic organisms could be seen within the cysts. They
cyst in gill tissue of Tridacna cr~cea from Lizard Island, Great Barrier
0022-201 l/90 $i so copyright Au rights
Q 1990 by Academic Press, la. of reproductiml in my form reserved.
136
NOTES
FIG. 2. Transmission electron micrographs of rickettsiales-like inclusion in gill of T. crocea. (a) Edge of the cyst. Bar = 1 pm. (b) Center of the cyst. Bar = 2 pm.
were 0.61 pm (SD = 0.01 pm, n = 15) in diameter and up to 1.6 pm long with a double membrane. The center of the cells was less electron dense than the margins (Fig. 2). The cysts from T. crocea are larger than those found in Mya arenaria, which were up to 100 pm in diameter (J. C. Harshbarger, S. C. Chang, and S. V. Otto, Science 1%,66(X68, 1976) and Teffina tenuis, which were 25-35 pm in diameter (J. S.
Buchanan, J. Fish. Dis. 1, 2743, 1978). The organisms within the cysts, however, are of similar size to those from the gills of Placopecten magellanicus (1.9-2.9 X 0.5 pm: G. Gulka, P. W. Chang, and K. A. Marti, .I. Fish. Dis. 6, 355-364. 1983), M. arenariu (0.3 x 2.0 urn: J. C. Harshbarger, S. C. Chang, and S. V. Otto, Science 196, 666-668, 1977), Tapes japonica, and Patinopecten yessoensis (0.4-0.6 X 2.4 km: R. Elston, J. Fish. Dis. 9,69-71, 1986) and the
137
NOTES
FIG.
2.-Continued
digestive gland of Tellina tenuis (0.34.5 urn: J. S. Buchanan, J. Fish. Dis. 1, 2743, 1978) and Crassostrea gigas (1.5-2.5 x OS0.6 pm: M. Comps, J.-R. Bonami, and C. Vago, C.R. Acad. Sci. Paris Ser. D 285, 427-429, 1977). Rickettsiales-like infections are widespread in marine bivalves, particularly in the digestive and branchial epithelium (R. A. Elston and M. G. Peacock, J. Znvertebr. Pathol. 44,84-96, 1984). They are not usually associated with host mortality, al-
though G. Gulka, P. W. Chang, and K. A. Marti (J. Fish. Dis. 6, 355-364, 1983) reported a rickettsiales-like infection in the gills of Placopecten magellanicus from Rhode Island which was associated with extensive myodegeneration and mortality. G. Le Gall, D. Chagot, E. Mialhe, and H. Grizel (Dis. Aquat. Organ. 4, 229-232, 1988) found that Pecten maximus with branchial rickettsiales-like inclusions died during the winter more rapidly than uninfected animals. T. ten&s with a rickettsi-
138
NOTES
ales-like infection in the digestive gland exhibited necrotic digestive gland cells and thin, chalky shells (J. S. Buchanan, J. Fish. Dis. 1, 27-43, 1978). The pathogenicity of the rickettsiales-like infection from T. crotea is not known, but the large size and number of cysts found in some clams suggest that the parasites are likely to compromise the function of the gills, particularly when the host is under stress. It is not known if humans may be infected by the rickettsiales-like inclusions from T. crocea. This is the first record of a rickettsialeslike infection from tridacnid clams and from Australian waters but further information on the biochemistry and antigens of the parasite is required to clarify its taxonomy.
KEY WORDS: Tridacna;
infection;
rickettsiales-like
parasite; clam.
We thank Mrs. M. Barrett and Ms. E. Rousseau for preparation of sections for light and electron microscopy. This work was funded by the Australian Research Council (ARC 785).
C. L. GOGGIN AND R. J. G. LESTER Department of Parasitology University of Queensland St. Lucia Brisbane, QLD 4067 Australia Received August 3, 1989; accepted November 13, 1989
OF
INVERTEBRATE
Rickettsiales-like
PATHOLOGY
56, 135-138 (1%))
Infection in the Gills of Tridacna crocea from the Great Barrier Reef
Tridacnid clams are cultured throughout Asia and the Pacific for human consumption but their commensals, parasites, and diseases are little known. As rickettsiae are potentially pathogenic to humans (causing Q fever and typhus), the occurrence of a rickettsiales-like infection in tridacnid clams warrants attention. Spherical, cream-colored cysts were found in the gills of 7 among 30 burrowing clams, Tridacna crocea, in May 1987 and 20 among 30 T. crocea in September 1988 collected from the reefs around Lizard Island, Great Barrier Reef. No cysts were found in 30 giant clams, T. maxima, collected from the reefs around Heron Island,
FIG. 1. Rickettsiales-like Reef. Bar = 120 pm.
Great Barrier Reef, in December 1987. In histological sections, the cysts ranged between 60 and 230 p,rn in diameter (mean = 137 pm, SD = 10.72 urn, n = 15) (Fig. 1). Up to 15 cysts were visible in one histological section. Cysts contained finely granular, basophilic material enclosed within a membrane, presumably the wall of the parasitized cell. Outside this was an eosinophilic, hyaline layer, 1 urn thick and PAS positive. This was covered by a thin layer of connective tissue and a layer of gill epithelium. Individual rickettsial bodies were visible in some sections. With transmission electron microscopy, prokaryotic organisms could be seen within the cysts. They
cyst in gill tissue of Tridacna cr~cea from Lizard Island, Great Barrier
0022-201 l/90 $i so copyright Au rights
Q 1990 by Academic Press, la. of reproductiml in my form reserved.
136
NOTES
FIG. 2. Transmission electron micrographs of rickettsiales-like inclusion in gill of T. crocea. (a) Edge of the cyst. Bar = 1 pm. (b) Center of the cyst. Bar = 2 pm.
were 0.61 pm (SD = 0.01 pm, n = 15) in diameter and up to 1.6 pm long with a double membrane. The center of the cells was less electron dense than the margins (Fig. 2). The cysts from T. crocea are larger than those found in Mya arenaria, which were up to 100 pm in diameter (J. C. Harshbarger, S. C. Chang, and S. V. Otto, Science 1%,66(X68, 1976) and Teffina tenuis, which were 25-35 pm in diameter (J. S.
Buchanan, J. Fish. Dis. 1, 2743, 1978). The organisms within the cysts, however, are of similar size to those from the gills of Placopecten magellanicus (1.9-2.9 X 0.5 pm: G. Gulka, P. W. Chang, and K. A. Marti, .I. Fish. Dis. 6, 355-364. 1983), M. arenariu (0.3 x 2.0 urn: J. C. Harshbarger, S. C. Chang, and S. V. Otto, Science 196, 666-668, 1977), Tapes japonica, and Patinopecten yessoensis (0.4-0.6 X 2.4 km: R. Elston, J. Fish. Dis. 9,69-71, 1986) and the
137
NOTES
FIG.
2.-Continued
digestive gland of Tellina tenuis (0.34.5 urn: J. S. Buchanan, J. Fish. Dis. 1, 2743, 1978) and Crassostrea gigas (1.5-2.5 x OS0.6 pm: M. Comps, J.-R. Bonami, and C. Vago, C.R. Acad. Sci. Paris Ser. D 285, 427-429, 1977). Rickettsiales-like infections are widespread in marine bivalves, particularly in the digestive and branchial epithelium (R. A. Elston and M. G. Peacock, J. Znvertebr. Pathol. 44,84-96, 1984). They are not usually associated with host mortality, al-
though G. Gulka, P. W. Chang, and K. A. Marti (J. Fish. Dis. 6, 355-364, 1983) reported a rickettsiales-like infection in the gills of Placopecten magellanicus from Rhode Island which was associated with extensive myodegeneration and mortality. G. Le Gall, D. Chagot, E. Mialhe, and H. Grizel (Dis. Aquat. Organ. 4, 229-232, 1988) found that Pecten maximus with branchial rickettsiales-like inclusions died during the winter more rapidly than uninfected animals. T. ten&s with a rickettsi-
138
NOTES
ales-like infection in the digestive gland exhibited necrotic digestive gland cells and thin, chalky shells (J. S. Buchanan, J. Fish. Dis. 1, 27-43, 1978). The pathogenicity of the rickettsiales-like infection from T. crotea is not known, but the large size and number of cysts found in some clams suggest that the parasites are likely to compromise the function of the gills, particularly when the host is under stress. It is not known if humans may be infected by the rickettsiales-like inclusions from T. crocea. This is the first record of a rickettsialeslike infection from tridacnid clams and from Australian waters but further information on the biochemistry and antigens of the parasite is required to clarify its taxonomy.
KEY WORDS: Tridacna;
infection;
rickettsiales-like
parasite; clam.
We thank Mrs. M. Barrett and Ms. E. Rousseau for preparation of sections for light and electron microscopy. This work was funded by the Australian Research Council (ARC 785).
C. L. GOGGIN AND R. J. G. LESTER Department of Parasitology University of Queensland St. Lucia Brisbane, QLD 4067 Australia Received August 3, 1989; accepted November 13, 1989
