| Parasite | Parvatrema sp. |
|---|---|
| Taxonomy | Plathyhelminthes, Trematoda, Digenea |
| Hosts | Manila clam (Ruditapes philippinarum) forParvatrema sp. Several bivalves including Manila clam, Laternula limicola, Glauconome chinensis, Tellina sp., Mediterranean mussel Mytilus galloprovineulis, Brachydontes minimus forParvatrema duboisi. Waterfowls including ducks as the definitive host. |
| Infection site | Around the mantle and the hinge |
| Clinical sign | Pearl-like particles (ca. 1 mm) are observed in the mantle (Fig. 1). Infected shells lose the marketability because of their sandy texture when eaten. |
| Parasitology | A particle includes a metacercaria utilizing the bivalves for the intermediate host (Fig. 1). This metacercaria is not encysted, but it induces the host reaction, and encased by gelatinous or calcareous matters resulting in the pearl-like particle (Fig. 2). It is elucidated by experimental infection that the parasite becomes an adult in mammal (Fig. 3). |
| Pathology | The calcareous particles exist as foreign bodies in bivalves, but are not harmful to host health. |
| Health hazard | Cook before eating because human infections are possible. |
| Diagnosis | Observe the morphology of the parasite in a flattened preparations and iron hematoxylin stained specimens by microscopy. It is necessary to get adults by the experimental infection because of its difficulty to identify the species by metacercariae. |
| Other information | In Japan, this infection was reported from the Tokyo Bay and the Lake Hamana. Ogata (1994) identified this parasite as Gymnophallus bursicola according to a morphological observation. However, Endo and Hoshina (1974) reassigned it to Parvatrema duboisi (=Parvatrema timondavidi). Shimura et al. (1982) reported that the parasite caused the calcareous depositions, but the causal relationship cannot be confirmed. It is possible that the trematode infecting to the mantle is different species from that infecting to the hinge. |
| References |
Ogata, T. (1944): On
the morphology, ecology and life history of an Agamodistome parasitic in a
bivalve, Paphia (Ruditapes) philippinarum
(Adames et Reeve). Sci. Rep. Tokyo
Bunrika Daigaku, Sec. B, 7, 1-24 Endo, T. and T. Hoshina (1974): Redescription and identification of a Gymnophallid trematode in a brackish water clam, Tapes (Ruditapes) Philippinaraum. Jap. J. Parasit., 23, 73-77. Shimura, S., T. Yoshinaga and H. Wakabayashi (1982): Two species of marine metacercariae, Parvatrema duboisi (Gymnophallidae) and Proctoeces sp. (Fellodistomidae), in the clam Tapes philippinarum from Lake Hamana, Japan: morphology and level of infection. Fish Pathol., 17, 187-194. (In Japanese) |
Fig. 2. A metacercaria of Parvatrema sp. from the mantle of Manila clam.
Fig. 1. Pearl-like bodies from Manila clam.
(Photos by T. Yanagida)
Fig. 3. Adult of Parvatrema sp. obtained by infection
experiment