An investigation into occasional White Spot Syndrome Virus outbreak in traditional paddy cum prawn fields in India

A review on molecular detection techniques of white spot syndrome virus: Perspectives of problems and solutions in shrimp farming

This review aims to provide an update on the current scientific understanding of various aspects of White Spot Syndrome Virus (WSSV) formation, diagnostic procedures, transmission, ecological effects, pathophysiology and management strategies. In terms of production and financial benefits, the WSSV has been the most virulent in shrimp and several other crustacean sectors around the globe. It spreads vertically from diseased broodstock to post-larvae and horizontally by cannibalism, invertebrate vectors, freshwater and sediments. In the transfer of white spot disease (WSD) in newly stocked ponds, the survivability of WSSV in sediment is the most important variable. In typical cultural conditions, it is a highly infectious pathogen capable of inflicting total death within 3-10 days after an outbreak. Some of the current biosecurity strategies used to keep diseases out of shrimp ponds such as pond water disinfection, quarantine of new stocks before stocking and broader usage of specific pathogen-free shrimp. The sequencing and characterisation of various WSSV strains have provided details about pathogen biology, pathogenicity and disease. To develop successful control methods, knowledge of these characteristics is essential. In several shrimp-producing countries in Asia and the Americas, the infections produced by the WSSV have had disastrous socio-economic consequences. As a result of international trade or migration of diseased species, the World Animal Health Organization recognised several illnesses as posing a substantial hazard to farmed shrimp. WSD is receiving much scientific research due to the potential economic effects of the virus. Research is now being done to understand better the molecular biology and pathophysiology of WSSV, as well as how to treat and prevent the virus. However, further study should be conducted in countries with more resilient host species to understand their role in mitigating disease impacts since these revelations may aid in developing a WSD treatment.

How do abiotic environmental conditions influence shrimp susceptibility to disease? A critical analysis focussed on White Spot Disease

White Spot Syndrome Virus (WSSV) causes White Spot Disease (WSD) and is historically the most devastating disease in the shrimp industry. Global losses from this disease have previously exceeded $3 bn annually, having a major impact on a global industry worth US$19 bn per annum. Shrimp are cultured predominantly in enclosed ponds that are subject to considerable fluctuations in abiotic conditions and WSD outbreaks are increasingly linked to periods of extreme weather, which may cause major fluctuations in pond culture conditions. Combined with the intensity of production in these systems, the resulting suboptimal physicochemical conditions have a major bearing on the susceptibility of shrimp to infection and disease. Current knowledge indicates that pond temperature and salinity are major factors determining outbreak severity. WSSV appears to be most virulent in water temperatures between 25 and 28 °C and salinities far removed from the isoosmotic point of shrimp. Elevated temperatures (>30 °C) may protect against WSD, depending on the stage of infection, however the mechanisms mediating this effect have not been well established. Other factors relating to water quality that may play key roles in determining outbreak severity include dissolved oxygen concentration, nitrogenous compound concentration, partial pressure of carbon dioxide and pH, but data on their impacts on WSSV susceptibility in cultured shrimps is scarce. This illustrates a major research gap in our understanding of the influence of environmental conditions on disease. For example, it is not clear whether temperature manipulations can be used effectively to prevent or mitigate WSD in cultured shrimp. Therefore, developing our understanding of the impact of environmental conditions on shrimp susceptibility to WSSV may provide insight for WSD mitigation when, even after decades of research, there is no effective practical prophylaxis or treatment.

Characterization of blooming algae and bloom-associated changes in the water quality parameters of traditional pokkali cum prawn fields along the South West coast of India

In tropical shrimp farms, especially in traditional pokkali shrimp ponds, poor water quality management can lead to serious threats like heavy algal blooms and frequent disease outbreaks. An investigation regarding the frequent disease outbreaks in selected pokkali shrimp pond adjoining the Cochin backwaters has been conducted. Water quality parameters were analyzed during the study period. Results indicate a considerable fluctuation in the concentration of dissolved oxygen (DO) in the study in the shrimp farm where the algal bloom was observed. Poor water exchange along with nutrient loading from adjacent housing areas resulted in heavy algal bloom in the pond which led to hypoxic conditions in early morning and supersaturation of DO in the afternoon. It also led to considerably high alkaline pH. High levels of total ammonia nitrogen (TAN) were recorded in the sampling sites. Heavy algal bloom was observed throughout the study period in the selected pond especially in the summer. Anabaenopsis elenkinii and Merismopedia elagans which were the dominant species from the culture pond caused the bloom. Characterization and percentage distribution of bacteria present in the water and those associated with the algal blooms were carried out. The algae were found to support greater diversity of bacteria when compared to water. Pathogenic species like Aeromonas hydrophila and Vibrio parahaemolyticus were encountered in the study. Experimental challenge studies using Artemia as a model showed that the V. parahaemolyticus isolates were highly pathogenic. Hence, this study reveals how algal growth supports opportunistic pathogens in great diverse in a shrimp pond and causes frequent disease outbreaks under favourable conditions.

Globalization and Livestock Biosecurity

Globalization has resulted in enhanced trade in livestock and livestock products leading to increased risk of diseases to livestock and human beings. The emergence of highly contagious viral diseases of livestock and poultry such as foot-and-mouth disease, peste des petits ruminants, African swine fever (ASF), Newcastle disease, avian influenza and zoonotic diseases caused by viruses like Ebola, West Nile, Nipah, Hendra and swine influenza (H1N1) have necessitated the formulation of policies and regulatory frameworks for preventing ingress of exotic diseases and controlling dissemination of endemic diseases within the country. Biosecurity measures are important to maintain and improve animal health and reduce the risks. In this review, the risks of introduction of infections through livestock and livestock products, routes of transmission and general biosecurity measures to reduce these risks have been discussed.