| Parasite | Perkinsus olseni |
|---|---|
| Taxonomy | Protozoan (Alveolata, Perkinsidae) |
| Hosts | Manila clam (Ruditapes philippinarum), grooved carpet-shell clam (Ruditapes decussate), ruber abalone (Haliotis rubber), whirling abalone (Haliotis cyclobates), staircase abalone (Haliotis scalaris), greenlip abalone (Haliotis laevigata) |
| Infection site | Connective tissues in the gill, mantle, etc. |
| Clinical sign | Infected shellfishes usually exhibit no external signs. Nodules are sometimes observed in the mantle and gill of heavily infected fish. |
| Parasitology | Perkinsus is considered to be a protozoan taxonomically close to dinoflagellates. Its life cycle involves vegetative proliferation within the host, by which a trophozoite undergoes successive bipartitioning, and spore formation outside of the host. A trophozoite contains a vacuole (signet-ring) (Fig. 1). Zoosporangia formation is induced by anaerobic condition resulted from host’s death, and zoospores are shed to the water (Yoshinaga, 2004). |
| Pathology | White nodules are formed due to the hemocytic infiltration around the trophozoites. Though a mass mortality of Manila clam by this parasite has not been reported, the infection could affect adversely on the growth or filtration of Manila clam (Choi et al., 2002). |
| Health hazard | Since this parasite is not infectious to human, it is harmless in food hygiene. |
| Diagnosis | Incubate in Ray's fluid thioglycollate medium (RFTM) and check the large prezoosporangia stained with Lugol’s iodine solution (Fig. 2). Histological and PCR diagnosis methods are also conducted (Hamaguchi et al., 1998; Maeno et al., 1999). |
| Other information | Since the nucleotide sequences of ITS and 5.8S rRNA regions of Perkinsus olseni in Japan are identical with those of P. olseni/atlanticus in Europe and Australia, the parasite is considered to be the same species to those Perkinsus (Hamaguchi et al., 1998). P. olseni is differentiated from P. honshuensis, which was discovered from Manila clam in Japan recently, by the size of trophozoites and sequence of ITS region (Dungan and Reece, 2006). |
| References |
Choi, K. S., K. I. Park, K. W. Lee and K. Matsuoka (2002): Infection intensity,
prevalence, and histopathology of Perkinsus sp. in
the Manila clam, Ruditapes philippinarum,
in Isahaya Bay, Japan. J. Shellfish Res.,
21, 119-125. Dungan, C. F. and K. S. Reece (2006): In vitro propagation of two Perkinsus spp. parasites from Japanese Manila clams Venerupis philippinum and description of Perkinsus honshuensis n. sp. J. Eukaryot. Microbiol., 53, 316-326. Hamaguchi, M, N. Suzuki, H. Usuki and H. Ishioka (1998): Perkinsus protozoan infection in short-necked clam Tapes (Ruditapes) philippinarum in Japan. Fish Pathol., 33, 473-480. Maeno, Y. T. Yoshinaga and K. Nakajima (1999): Occurrence of Perkinsus species (Protozoa, Apicomplexa) from manila clam Tapes philippinarum in Japan. Fish Pathol., 34, 127-131. Yoshinaga, T. (2004): Protozoan diseases in shellfish. Infectious and parasitic diseases of fish and shellfish. (eds. by Wakabayashi, H. and K. Muroga), Koseisha koseikaku, pp. 320-337. (In Japanese) |
(Photos by T. Yoshinaga)
Fig. 2. Prezoosporangia stained by Lugol's iodine after incubation in RFTM.
Fig. 1. Trophozoites pf Perkinsus olseni (arrows) in the gills of Manila clam.