It cut a thick swathe down the coast: an elusive beast that bumped off a full year's crop.

The symptoms were the same everywhere. The prawns developed white spots on their dorsal side, which began to degenerate. As the pathogen spread to the intestines, the shrimp lost appetite and growth.

Scientists at the Central Institute of Brackish Water Aquaculture (CIBA) say that their initial guess was the Infectious Hypodermal Hematopoietic Necrovirus (IHH-NV). An expert group from the Philippines shares this view.

The leading Thai technical consultancy, Chareon Pokaphand, concluded that the pathogen was sembv (a type of Baculovirus). Japanese studies have shown that the virus was similar to the one that caused great losses in 1993 and 1994 in cultured P chinensis and P japanicus in Korea, Japan and China.

A paper presented by Yukinoi Takahashi of Shimonseki University of Fisheries notes that the significant symptoms of the sickness in both P chinensis and P japanicus were similar to the monodon disease. The study says: "From histopathology, it seems that the virus is a new species belonging to either family Baculovirus or family Polydravirus."

The Indian Council of Agricultural Research's deputy director (fisheries), Padmakar Dehadrai, says that the stressed, unhygienic condition helped the virus spread: "The virus might have come in through imported contraband shrimp larvae or through imported rancid feed." He claims that a month before the disease broke out, shrimp larvae were clandestinely imported from Thailand by some Andhra Pradesh farms. He doesn't rule out sabotage.