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Diseases of molluscs

Parasitic diseases—Infection with Marteilia sydneyi (QX disease)

CLICK ON IMAGE TO ENLARGE infection with marteilia sydneyi infection with marteilia sydneyi

Infected oyster on right shows yellowish watery body ('pale sick'). Oyster on left is normal

Source: R Adlard

Signs of disease

Important: animals with disease may show one or more of the signs below, but disease may still be present in the absence of any signs.

Disease signs at the farm level
Clinical signs of disease in an infected animal
Gross signs of disease in an infected animal

Disease agent

QX disease is caused by the haplosporidium protozoan Marteilia sydneyi of the Paramyxea phylum. In Europe, a similar disease is caused by Marteilia refringens in different species of shellfish.

Host range

Molluscs known to be susceptible to the disease:
Sydney rock oyster (Saccostrea glomerata)

Presence in Asia–Pacific

Map showing presence in Asia–Pacific

Infection with M. sydneyi has been officially reported from Australia.


For a detailed account of the known lifecycle of the parasite, see lifecycle of Marteilia sydneyi.

Differential diagnosis

The differential diagnostic table and the list of similar diseases appearing at the bottom of each disease page refer only to the diseases covered by this field guide. Gross signs observed might well be representative of a wider range of diseases not included here. Therefore, these diagnostic aids should not be read as a guide to a definitive diagnosis, but rather as a tool to help identify the listed diseases that most closely account for the gross signs.

The clinical signs of infection with Marteilia sydneyi are practically identical to those of infection with other haplosporidia (ie high mortalities associated with colourless and translucent tissues, poor condition, pale digestive gland and a shrunken body). Therefore, any presumptive diagnosis requires histological laboratory examination.

Further images

Sample collection

Because of uncertainty in differentiating diseases using only gross signs, and because some aquatic animal disease agents might pose a risk to humans, you should not try to collect samples unless you have been trained. Instead, you should phone your national hotline number and report your observations. If samples have to be collected, the agency taking the call will advise you on what you need to do. Local or district fisheries/veterinary authorities could advise you on sampling.

Emergency disease hotline

For your national emergency disease hotline number, see Whom to contact if you suspect a disease.

Further reading



These hyperlinks were correct and functioning at the time of publication. infection with marteilia sydneyi

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