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Taura syndrome (TS) was hypothesized to be caused by a virus and proven experimentally by meeting the criteria of Rivers' postulates. This was accomplished through 3 serial infectivity studies utilizing specific-pathogen-free Penaeus vannamei as the host for the TS virus (TSV). Test animals were infected via intramuscular injection with either a crude or cell-free suspension of the virus. The source of the crude homogenate was TSV-infected Ecuadorian P. vannarnel, which were collected during August 1993. Both types of viral inocula caused cumulative mortalities of 73 to 87'.';, among treatment groups. Diagnosis of TS was based on histological analysis of moribund shrimp collected during each experiment. All moribund shrimp, collected between 1 to 3 d post-injection, demonstrated moderate to severe pathognomonic TS les~ons. Both gross external and histological lesions, characteristic of chronic phase TS, were observed In 25 to 100"t, of all survivors. Virions with a buoyant density of approximately 1.337 g m1 ', lcosahedral morphology, and a diameter of 31 to 32 nm, characteristics which suggest that TSV is a member of either the Picornaviridae or Nodaviridae, were recovered from the dead shrimp collected during each of the 3 infectivity studies. Comparisons of TSV samples isolated from naturally infected P. vannamei from Hawaii (USA) and Ecuador indicate that the same virus was responsible for the TS epizootics in both of these shrimp growing regions.

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Among the strategies being developed to improve survival and harvest yields in the farming of Pacific white shrimp Litopenneus vannumei is breeding domesticated family lines and the selection for further development of those lines that demonstrate resistance to Taura syndrome virus (TSV) challenge in the laboratory. A standardized laboratory challenge method for measuring TSV resistance by per os exposure to the virus, relative to a reference stock of L. vannamei, was developed and used to screen a total of 176 family lines provided by five different companies over a period of several months. All challenged shrimp were exposed to TSV per os by feeding minced TSV‐positive shrimp carcasses at ∼10% of the shrimp biomass once per day for three consecutive days. Studies were carried out for a minimum of 14 d from the first day (day 0) of exposure to TSV. The survival rates obtained following TSV challenge of the selected L. vannamei families ranged from 0% to 100%, with a mean of 31%. The reference line of L. vannamei (“Kona line”) gave survival rates of 0% to 37% with a mean of 13%. The results of the present study demonstrate that the use of a relatively simple laboratory challenge procedure provides a mechanism to evaluate and compare resistance to TSV among selected L. vannamei families and to predict the performance of selected stocks in farm environments where TSV is enzootic.