More than half of 135 Louisiana crawfish ponds tested for white spot syndrome virus so far have shown up positive, according to an LSU AgCenter aquaculture expert.

“This means it’s much more widespread than anyone thought,” said Ray McClain, crawfish researcher at the LSU AgCenter Rice Research Station, who was among speakers at the Evangeline Parish Rice Field Day July 10.

The virus has been detected in more than 88 samples. But McClain said fewer than 10 ponds reported dying crawfish. It also has been found in three of nine samples from Atchafalaya Basin crawfish.

In addition, McClain said, crawfish tissue samples at the LSU School of Veterinary Medicine from two years ago tested positive, he said.

“It looks as if it’s been around a while,” McClain said. “It does not appear to be as devastating in crawfish farms as it was in shrimp farms.” A crawfish pond where the virus was found earlier this year appears to have recovered somewhat, he said.

The virus was first found in the United States among Texas shrimp farms in 1995, and the affected shrimp died rapidly.

Several crawfish ponds were quarantined this spring after the virus was found in St. Martin Parish and Vermilion Parish ponds. Crawfish from the affected ponds have to be tagged and sold only to a processor. McClain said the quarantine is still in effect, but that could change, depending on future decisions by state and federal agencies.

Symptoms of the virus include lethargic and sluggish crawfish that eventually die. Affected shrimp usually have a white spot, but not crawfish.

The virus is not a threat to humans, McClain said.

McClain said the virus was detected recently in crawfish from North Carolina, where farmers keep the crustaceans in large holding tanks just before they are sold. He said the virus also was found in crabs and shrimp along the South Atlantic coast.