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Infection with Perkinsus Olseni

What is it?

For the purpose of guide, infection with Perkinsus olseni is considered to be infection with P. olseni. Perkinsus atlanticus is considered to be a junior synonym.

Where and When Might This Occur?

The infection is widespread throughout the tropical Pacific Ocean, Australia, North Island of New Zealand, Viet Nam, Korea (Rep. of), Japan, China (People’s Rep. of), Portugal, Spain, France, Italy, and Uruguay.

The Perkinsus sp. reported from Thailand in the undulated surf clam Paphia undulata is almost certainly P. olseni based on DNA sequence similarity of the ITS1 (internal transcribed spacer) and ITS2 locus. Perkinsus olseni is not known from North America.

The annual cycle of P. olseni is controlled by temperature. In Tapes decussatus in Spain, P. olseni infection intensity peaked in spring as temperature increased to about 15°C, remained high through the summer and early autumn when temperatures were 19–21°C, and then declined through winter and early spring coinciding with temperatures of 9–10°C.

Highest host mortality occurred in early autumn during a period of maximum annual temperature.

The salinity tolerance of P. olseni is poorly understood. Salinity remained above 15 practical salinity units (psu) during the study in Spain.


Clinical signs are dead or gaping molluscs but these clinical signs are not specific to infection with P. olseni.

Individual bivalves with late stage infections may also be slow to close their valves, but agaian, these changes are not specific for P. olseni.

Infections in clam hosts can be lethal depending on environmental conditions, and death may occur one or two years after infection. Infections in abalone in Australia appear not to cause mortality even though prevalence can be high.


No vaccination is currently available but a low stocking density may reduce transmission of the pathogen.


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