Per os challenge of Litopenaeus vannamei postlarvae and Farfantepenaeus duorarum juveniles with six geographic isolates of white spot syndrome virus

White spot syndrome virus (WSSV) is one of the most important pathogens of penaeid shrimp. It is widely distributed in most Asian countries where pena eid shrimp are cultured, as well as in the Gulf of Mexico and SE USA. The v irulence of six geographic isolates of WSSV was compared using Litopenaeus vannamei postlarvae and Farfantepenaeus duorarum juveniles. The six geograp hic isolates of WSSV originated from China, India, Thailand, Texas, South C arolina, as well as from crayfish maintained at the USA National Zoo. For c hallenge studies, virus infected tissues were given per os to L. vannamei p ostlarvae and Fa. duorarum juveniles. Resultant WSSV infections were confir med by histological examination. The cumulative mortality of L. vannamei po stlarvae reached 100% after challenge with each of the six geographic isola tes of WSSV. However, the Texas isolate caused mortalities more rapidly tha n did the other shrimp isolates; the crayfish WSSV isolate was the slowest. In marked contrast, cumulative mortalities of juvenile Fa. duorarum reache d only 35-60%, and varied among the geographic isolates of WSSV. Interestin gly, in Fa. duorarum, the Texas WSSV isolate was also the most virulent, wh ile the crayfish WSSV was the least virulent. The findings suggest that sli ght differences in virulence exist among geographic isolates of WSSV, and t hat susceptibility may vary with species and lifestages of the host. (C) 19 99 Elsevier Science B.V. All rights reserved.