A disease that can wipe out oyster populations has spread in Eastern Canada, federal fisheries scientists said Monday.

For the first time, the microscopic parasite MSX has spread beyond the Bras d'Or Lakes area of Cape Breton. Scientists said the disease has been confirmed in four of nine sites sampled in Cape Breton.

Oysters in two areas in Prince Edward Island are also affected.

Scientists have been studying the parasite and testing oysters from 22 sites across the Maritimes since it was first found in Canadian waters last month.

"The reason we jumped on it so soon is we considered it a serious threat and wanted to get a handle on it as quickly as possible," said Sharon McGladdery, of DFO's Aquaculture Science Branch.

The disease does not appear to be spreading to other provinces, the scientists said. If it were to spread, the disease could threaten the whole multimillion-dollar maritime industry, said federal Fisheries Minister Robert Thibault.

The disease has severely damaged the local oyster industry in the Bras d'Or Lakes region.

Fisheries officials stressed the oysters found outside the Bras d'Or Lakes area were in the early stages of the illness, and there was no evidence of widespread mortality rates.

Growers in P.E.I. aren't panicking, according to Crystal McDonald of P.E.I. Aquaculture Alliance.

"They're not happy to know that MSX is in P.E.I. water," said McDonald. "But the good news that they received is the fact that anything that came back positive was linked to Nova Scotia product that was brought into P.E.I."

Fisheries officials are limiting the movement of oysters, but they add there's no sign of MSX in New Brunswick or along the gulf shore of Nova Scotia.

Scientists plan to take more samples to better assess the scope of the problem.