INFECTIOUS DISEASES AND CONTROL STRATEGIES IN SHRIMP A brief overview of infectious diseases impacting farmed shrimp and some experimental strategies on disease control by César Marcial Escobedo-Bonilla, Instituto Politécnico Nacional - Centro Interdisciplinario de Investigación para el Desarrollo Integral Regional (CIIDIR) Unidad Sinaloa
odern shrimp aquaculture began in 1933 in Japan with the induced spawning and hatching of Marsupenaeus japonicus larvae. This technology allowed the production of shrimp larvae in hatcheries instead of using larvae from the wild to stock grow-out ponds. Shrimp farming is an important activity in several low-income countries in Asia, America and Africa as it generates employment and wealth. Nonetheless, intensification of shrimp culture increased the appearance of infectious diseases due to deviations in environmental and physiological factors. Infectious diseases caused by viruses or bacteria represent the biggest threat to development of shrimp farming due to high mortalities. Pathogens that have caused severe epizootics and high mortalities to different stages and species of shrimp include Baculoviruses, Parvo-like viruses, Dicistrovirus, Ronivirus, Nimavirus and more recently, a bacterium Vibrio parahaemolyticus (Figure 1).
Infectious hypodermal and hematopoietic necrosis virus (IHHNV)
Infectious hypodermal and hematopoietic necrosis virus (IHHNV) or Penaeus stylirostris densovirus (PstDNV), was first reported in 1981 in Hawaii affecting the species Litopenaeus stylirostris and L. vannamei. This pathogen rapidly spread to other countries in America (Mexico, Panama, Colombia, Ecuador and Argentina), Asia (Indonesia, Malaysia, Philippines, Singapore and Thailand) and French Polynesia. Its genome is organised into three open reading frames (ORFs) encoding a non-structural protein, an unknown protein and a capsid protein, respectively. IHHNV causes infection to several shrimp species. It appears that Penaeus monodon is not affected by IHHNV infection since no clinical signs and no differences in size, weight or fertility was found in IHHNV-positive animals. Clinical signs of IHHNV infection depend on the species age and size, being the early juvenile stages more susceptible to the disease. In L. stylisrostris, acute IHHNV infection includes reduced feeding and locomotion, erratic swimming and death. In L. vannamei, acute IHHNV infection showed reduced growth rate, marked size differences within a pond and deformity of the rostrum, antennae and/or cuticle which is known as 'runt deformity syndrome' (RDS). Histological lesions are Cowdrytype A inclusion bodies in infected animals. This virus became the main pathogen both in shrimp fisheries and aquaculture in the 1980s in Mexico. It was estimated that its economical impact was between 0.5 and 1 billion US dollars. This virus is still present in wild and farmed shrimp in Mexico and other countries.
Taura syndrome virus (TSV)
First reported in shrimp farms near Taura river, Ecuador in 1992, TSV soon spread to several countries in South, Central, North America and Hawaii. Since 1999, TSV was also detected in Asia (Taiwan, Thailand and Korea) which imported stocks of L. 24 | January | February 2016 - International Aquafeed