Pathogenicity, diagnosis, prevention strategies and immune response of bacterium Nocardia seriolae : A critical review

Nocardia seriolae, an opportunistic and facultative intracellular Gram-positive bacterium, is mainly responsible for nocardiosis in fish. Nocardiosis is a chronic, granulomatous and systemic disease in which lesions are found in the skin as well as several internal organs such as the kidney, liver and spleen with the distinctive nodular granuloma structure. N. seriolae is capable of infecting a wide variety of fish species which poses a devastating impact on the aquaculture sector around the globe, particularly in Asia. Due to the lack of appearance of nocardiosis symptoms at the earlier stages, multiple epidemics of nocardiosis causing high mortality have been recorded. To this end, numerous epidemiological studies have been carried out to characterize and identify Nocardia spp. through several detection techniques, which have favoured the formulation of a multitude of antibiotics and vaccines. After bacterial resistance to antibiotics, nowadays, vaccination has been considered the more appropriate strategy to treat nocardiosis. For valuable information related to N. seriolae and to combat fish nocardiosis, this review extended the existing knowledge, including pathogenesis, virulence characteristics, rapid detection techniques, host immune response and prevention strategies against N. seriolae infection in fish species in aquaculture.