Marteiliosis here refers only to the diseases caused by Marteilia refringens and M. sydneyi. Other Marteilia spp. infect oysters and other bivalves. Until more is known about the identity and biology of these other Marteilia spp., their presence in any bivalve should be regarded as potentially serious and the OIE Reference Laboratory should be consulted.
Marteiliosis is primarily caused by two protistan parasites of the genus Marteilia: M. refringens and M. sydneyi( phylum Paramyxea )( 3, 11, 12, 26, 30 ) . Marteiliosis is also known as Aber disease (M. refringens), and QX disease (M. sydneyi).
The type species of the genus, M. refringens , is a lethal parasite of the European flat oyster, Ostrea edulis( 12 ) . Marteilia sydneyi infects Saccostrea glomerata (= commercialis) and possibly also Saccostrea echinata( 30, 31 ) .
In addition, M. maurini( 9 ) in Mytilus galloprovincialis and Mytilus edulis has been described from France, Italy and Spain ( 21 ) . Because M. maurini is not easily distinguished from M. refringens, detection of the parasite in mussels would require confirmatory diagnosis as described in this chapter. Marteilia lengehi( 7, 16 ) in Saccostrea cucullata from the Persian Gulf and Western Australia, and M. christenseni( 8 ) in Scrobicularia plana from France can apparently be differentiated from other species by the characteristics of the cytoplasmic contents of sporangia and spore morphology. Marteilia spp. has also been described in the following species: Tiostrea chilensis( 13 ) , Ostrea angasi( 5 ) , O. puelchana( 25 ), Cerastoderma (= Cardium) edule( 10 ), Mytilus edulis( 10, 22 ) , Mytilus galloprovincialis( 29 ) , Crassostrea gigas( 6 ) and C. virginica( 27 ) . A protistan similar to M. sydneyi was reported in giant clams Tridacna maxima( 24 ) . The scallop Argopecten gibbus is infected by a nonspecified Marteilia sp. in Florida, United States of America ( USA ) that has not been identified to species level ( 23 ).
The geographical distribution of M. refringens is: France, Greece, Italy, Morocco, Portugal, and Spain. Marteilia sydneyi is found in New South Wales, Queensland and Western Australia.
Marteilia refringens and M. sydneyi sporulate in the epithelia of the digestive gland, where infection is associated with poor condition index, emaciation of the oyster and exhaustion of its reserves of energy ( glycogen ) , discoloration of the digestive gland, cessation of growth, and mortalities. Mortality appears to be related to the sporulation of the parasite ( 12 ) . The initial site of infection of M. sydneyi is in the epithelia of the palps and gills and presporulating stages are found throughout the connective tissue and in digestive gland epithelia ( 18 ) . Presporulating stages of M. refringens occur in the epithelia of the palps, stomach, digestive ducts and possibly the gills. Oysters infected with M. sydneyi and M. refringens are in poor condition with completely resorbed gonads ( 28 ) . Massive invasion by M. sydneyi leads to complete disorganisation of the digestive gland epithelia. Death results from starvation in under 60 days after initial infection
The period of infection for M. refringens in Ostrea edulis is confined to spring and summer, when water temperature is greater than 17°C ( 1, 12, 14 ) . Oysters may become infected with M. sydneyi in summer and early autumn. However, the disease is not seasonal, heavy mortality occurs and spores may be found all year round. High salinities limit the development of Marteilia spp.
The mode of infection and the life cycle outside the host are unknown. Because it has not been possible to transmit the disease experimentally in the laboratory, possible intermediate hosts are suspected ( 2, 4, 14, 22, 28 ) .
For diagnosis, the recommended guidelines for sampling are those stated in Chapter 1.1.4 and Chapter I.2. of this Aquatic Manual .