1Department of Life Science, Assam (Central) University, Silchar-11, India.
2Division of Tissue Culture, National Institute of Virology, Pune.
Abstracts of Research Papers Presented during the National Symposium of Indian Virological Society at Unit of Plant Virology, Division of Plant Pathology, Indian Agricultural Research Institute, New Delhi-110 012, October 14–1.
A hitherto unknown virulent fish disease, variously called ‘Epizootic Ulcerative Syndrome or EUS’, has been sweeping, in epidemic form, the freshwater (FW) fishes of the Indian Sub-continent in particular and the Asia-Oceanea region, in general, since last more than three decades, causing large-scale mortality among them. Investigations have conducted on various aspects, including physico-chemical and biological aspects in order to ascertain the cause of the disease.
Field estimation of physico-chemical characteristics of water and soil; as well as, trace elemental quantification through atomic absorption spectrophotometry revealed that, outbreak of EUS might not be due to organic pollution of water and soil and trace elemental contaminations. On the other hand, bacterial culture revealed isolation of Aeromonas hydrophila, A. sobria, Pseudomonas aeruginosa, Staphylococcus epidermitis, Klebsiella sp, and haemolytic E. coli, all of which have been found to be sensitive to commonly available antibiotics like Chloramphenicol, Septran, Gentamycin and so on. Culture of mycotic flora revealed the isolation of Aphanomyces invadans from the EUS-affected fish tisues. These might, however, be considered as secondary invaders in view of the fact that, these microbes are known to be associated with the fishes in water normally. As such, an initial viral infection in the fishes is considered as the primary aetiology enabling the bacteria and the fungi to infect the fishes secondarily. In order to confirm the presence of virus(es), EUS affected fish tissues have been subjected to virological examination. Ulcerated tissues from EUS-affected Clarias batrachus have been homogenized in PBS, clarified in low speed centrifugation (10,000 rpm) and decontaminated through membrane filtration (0.45 μm). Monolayer cultrues of BF2 fish cell line have been grown in Leibovitz L-15 medium supplemented with 10% FCS and vitamin mixture. 50 μl aliquot of each dilution (upto 10−7 dilution) of the filtered supernatant have been added to 80% confluent monolayer of BF2 cell line grown in 96-well micro-titre plate. After 2 hours of adsorption at room temperature, the cultures were overlaid with 150 μl of maintenance medium (L-15 supplemented with 2% FCS) and incubated at 28°C. Cytopathic effect (CPE) developed between 48–72 hours post-infection; thereby, leading to the isolation of a ‘filterable Biological Agent’ (Virus ?) which was found to be passable into the subsequent cultures. Similar experiment repeated with other fish species, notably, Labeo calbasu, also resulted in isolation of a filterable biological agent with similar property of being passwable in the subsequent cultures.
Histochemical studies revealed interruption of glycogen synthesis and blockade of respiratory pathways in EUS-affected fishes. Enzymological studies revealed higher values of SGPT, SGOT and LDH in EUS-affected fishes as compared to corresponding healthy fishes. Electron Microscopic studies revealed occurrences of virus-like particles in the EUS-affected fish tissues and not in the corresponding healthy ones. Attempts are being made to characterise the suspected filterable biological agents.
