Experimental host range and histopathology of white spot syndrome virus (WSSV) infection in shrimp, prawns, crabs and lobsters from India

Experimental studies were conducted by injecting or feeding white spot syndrome virus (WSSV) derived from infected shrimp, Penaeus monodon (Fabricius), collected from the south-east coast of India, to five species of shrimp, two species of freshwater prawns, four species of crabs and three species of lobsters. All species examined were susceptible to the virus. Experimental infections in the shrimp had the same clinical symptoms and histopathological characteristics as in naturally infected P. monodon. A cumulative mortality of 100% was observed within 5±7 days in shrimp injected with WSSV and 7±9 days in shrimp fed with infected tissue. Two species of mud crab, Scylla sp., survived the infection for 30 days without any clinical symptoms. All three species of lobsters, Panulirus sp., and the freshwater prawn, Macrobrachium rosenbergii (De Man), survived the infection for 70 days without clinical symptoms. However, bioassay and histology using healthy P. monodon revealed that crabs, prawns and lobsters may act as asymptomatic carriers/reservoir hosts of WSSV. This is the first report to suggest the carrier/ reservoir capacity of these hosts through histological and bioassay evidences. Ultrastructural details of the virus in experimentally infected shrimp, P. vannamei, (Boone), were also studied. Introduction White spot syndrome virus infection, with its associated mortality, is emerging as one of the most challenging problems for the global shrimp industry, especially in Asia and south-east Asia (Inouye, Miwa, Oseko, Nakano, Kimura, Momoyama & Hiraoka 1994; Nakano, Koube, Umezewa, Momoyama, Hiraoka, Inouye & Oseko 1994; Takahashi, Itami, Kondo, Maeda, Fiji, Tomonaga, Supamattaya & Boonyaratpalin 1994; Chen 1995; Chou, Huang, Wang, Chiang & Lo 1995; Wang, Lo, Leu, Chou, Yeh, Chou, Tung, Chang, Su & Kou 1995; Wongteerasupaya, Vickers, Sriurairatana, Nash, Akarajamorn, Boonsaeng, Panyim, Tassanakajon, Withyachumnarnkul & Flegel 1995). The causative viral pathogen has been named differently by various workers (Huang, Song, Yu & Yang 1994; Takahashi et al. 1994; Wang et al. 1995; Wongteerasupaya et al. 1995; Lo, Ho, Peng, Chen, Hsu, Chiu, Chang, Liu, Su, Wang & Kou 1996). However, Lightner (1996) has regrouped all the members of these non-occluded viruses under the name white spot syndrome (WSS). Accordingly, the viral pathogen is called white spot syndrome virus (WSSV) in the present paper. Although this disease was reported in India in early 1993, it was only in 1994 that adequate attention was paid to it as a consequence of its increased severity and large-scale mortality. In 1995, the causative organism of the epizootic was identified for the first time as SEMBV (Anonymous 1995). Thereafter, three reports were published on this viral epizootic from India (Manohar, Sundararaj, Selvaraj, Sheela, Chidambaram, Mohan & Journal of Fish Diseases 1999, 22, 183±191 Correspondence and present address Dr K V Rajendran, Central Institute of Fisheries Education, Jaiprakash Road, 7 Bungalows, Versova, Mumbai ± 400 061, India. E-mail: [email protected]