White Spot Virus Invades Latin America, Hitting Shrimp Farms in Five Countries.

White spot virus (WSV), once limited to Asia, has invaded shrimp farms in at least five Latin American countries -- Honduras, Nicaragua, Guatemala, Panama and Ecuador. Yellowhead virus (YHV) has also appeared at Honduran farms.

Hurricane Mitch, which devastated Central America last fall, is being widely blamed for the viral outbreaks, although it isn't clear just where the storm would have picked up WSV and YHV in the first place. Ecuador researchers reported that polychaete worms used in feed may be a vector for WSV.

Honduras was the first country to be hit, with viruses reported in mid-January. White spot viral outbreaks were confirmed in April in Panama and Ecuador, although a later report claimed the situation in Ecuador had been "overstated." There were concerns that white spot virus might also spread to Belize.

Shrimp farm pond managers in Honduras had noticed "unusual signs of stress" in some ponds in mid-January, with wild Penaeus stylirostris the most affected, followed by wild P. vannamei. Hatchery P. vannamei were the latest affected. Samples of each species were sent to the University of Arizona, confirmed the presence of WSV and YHV.

ANDAH, the Honduran shrimp farm association, activated a crisis management system developed after an earlier Taura outbreak. Water exchange was reduced, sampling increased and oxygen levels carefully monitored to reduce stress on the shrimp. ANDAH was unable to determine the source of the infection, although it ruled out Honduran hatcheries.

The Honduran government and neighboring countries were alerted to the outbreak, but WSV nevertheless spread to Guatemala, Nicaragua and Panama. ANDAH noted that while the viral strains encountered appear to be the same as those in Asia, "the mortality they have caused is far less than that experienced in Asia" -- about the same as for the Taura outbreak which, although significant, "did not prove catastrophic."

There was a scare in Mexico at the end of April, with reports that contaminated shrimp might have wandered across the border from Guatemala. But as of May 6, there wasn't any sign of virus in shrimp farms in Quintana Roo. Shrimp farms in Tamaulipas were also virus-free -- the latter state borders on Texas, scene of a WSV outbreak in 1994 that was the first outside Asia. The National Chamber of the Fishing and Aquaculture Industry insisted that the risk of infection was low thanks to strict control measures.

El Commercio, a newspaper in Ecuador, caused a panic in early April when it predicted that WSV would cut shrimp production there by 40-60% this year. But subsequent reports claimed that the outbreak was limited to the province of El Oro, where it was causing only a 10% loss, or even that the only infected shrimp were imported nauplius larvae from Panama (Imports were banned.). Polychaete worms, cited by the Ecuadorian Center for Aquaculture and Marine Research as a source of infection, were also imported from Panama.

By sheer coincidence, the Global Aquaculture Alliance (GAA) was putting on a seminar in Panama City, "Prevention Techniques for White Spot and Yellowhead Viruses," April 8-10 -- just as the Panamanian WSV outbreak was reported. Two of the conference participants, Tim Flegel and Dan Fegan, spent several days collecting samples from wild shrimp populations, hatcheries and farms -- and confirmed the presence of the virus in broodstock, larvae and juveniles. The GAA is among the agencies now keeping watch on the situation.