Streptococcosis in farmed Litopenaeus vannamei: a new emerging bacterial disease of penaeid shrimp

Abstract

Presumptive systemic streptococcal infections were detected histologically in farmed Litopenaeus vannamei juveniles submitted from a Latin American country and the bacteria isolated. Characterization work demonstrated that the Gram-positive cocci form chains, grow aerobically and anaerobically, are oxidase-and catalase-negative, non-hemolytic, non-motile, Lancefield Group B positive and PCR positive when amplified with a universal streptococcal primer set. Differing Streptococcus identifications were obtained using API 20 Strep and Biolog systems, the former identifying the isolate as S. uberis and the latter as S. parauberis. Injection of specific pathogen-free (SPF) L. vannamei with the bacteria resulted in 100% mortality by 3 d post-injection with successful recovery of the agent from moribund test shrimp hemolymph samples. The recovered isolate was used in per os and waterborne exposure studies of SPF L. vannamei with mortalities ranging from 40 to 100% and 80 to 100%, respectively. Histologic analysis of 5 to 8 moribund shrimp from each exposure method demonstrated that all contained a severe bacteremia characterized by numerous free cocci within the hemolymph and aggregates of vacuolated hemocytes with notable intravacuolar cocci. This unique lesion type was most pronounced within the lymphoid organ and considered pathodiagnostic for this disease. Experimentally induced lesions were identical to those in naturally infected farmed shrimp and the Streptococcus sp. responsible was re-isolated, fulfilling Koch's postulates. Five freeze/thaw cycles of 10 experimentally infected shrimp were performed over a 2 mo period and the bacteria successfully cultured from all shrimp at each interval. These collective findings describe the first reported case of streptococcosis in marine penaeid shrimp in the Western Hemisphere and indicate that the agent may be disseminated via live or frozen infected shrimp.

Milky hemolymph syndrome (MHS) in spiny lobsters, penaeid shrimp and crabs

“…Noteworthy examples of recently described crustacean diseases in which milky hemolymph has been reported include systemic infection by Streptococcus sp. (Hasson et al 2009), a herpes-like virus (Shields & Behringer 2004) and a parasitic dinoflagellate in the genus Hematodinium (Xu et al 2010). Like the rickettsia-like bacteria discussed in the present paper, Hematodinium spp.…”

“…affect a wide range of crustaceans, including shrimp, crabs and lobsters and generally present similar gross signs including lethargy, discolored carapace and hemolymph that is milky and does not clot (Field et al 1992, Li et al 2008, Xu et al 2010. The streptococcal infection of Litopenaeus vannamei characterized by Hasson et al (2009) caused the hemolymph to appear opaque and milky as a result of the high concentrations of circulating bacteria, which prevented the hemolymph from clotting.…”

Historic emergence, impact and current status of shrimp pathogens in the Americas

“…Hemocyte accumulations or nodules are sometimes present. Similar, but less conspicuous lesions may be present in the heart lumen, gills, and diffusely distributed systemically in the connective tissues (Hasson et al, 2009;Lightner et al, 2009b).…”

“…Streptococci are the cause of an emerging disease in penaeid shrimp in the Americas and in regions of east Africa (Hasson et al, 2009;Lightner et al, 2009b). Severe mortalities due to Streptococcus spp.…”

Advances, challenges, and directions in shrimp disease control: the guidelines from an ecological perspective

“…Therefore, the traditional application of Vibrio pathogens as surrogates for disease prediction and targeting is unwarranted, as newly identified pathogenic bacteria, such as Streptococcus sp. (Hasson et al 2009), Nautella italica, and Pseudoalteromonas piscicida (Zheng et al 2016), have been regularly isolated from shrimp ponds. The relative abundance of Vibrio species accounts for a small portion (<0.2 %) of the bacterioplankton community, which is unchanged between ponds with healthy and diseased shrimp (Zhang et al 2014).…”