Clinicopathological features and immunohistochemical detection of antigens in acute experimental Streptococcus agalactiae infection in red tilapia (Oreochromis spp.)

Syuhaidah Abdullah,Jamil Samad,Latifah Hanan,Tanko Polycarp Nwunuji,Emikpe Benjamin Obukwho,Noraini Omar,Sabri Mohd Yusoff

doi:10.1186/2193-1801-2-286

Abstract

This study investigates the clinicopathological features of acute experimental streptococcosis in red tilapia using various routes of infection; intraperitoneal (IP), immersion (IM) and immersion cut (IC). Twenty four red tilapia in duplicates were inoculated intraperitoneally with 109 CFU/ml of S. agalactiae while another sets: intact, one with sharp cut at the tail end were exposed to bacterial inoculums 109 CFU/ml diluted in water while two groups of control fish were similarly manipulated. Clinical signs were recorded; samples from the gills, brain, eyes and kidneys were also taken for bacterial isolation and histopathology. Immunohistochemistry (IHC) and polymerase chain reaction (PCR) were employed to detect the antigen. The diseased fish showed skin, fin haemorrhages and exophthalmia with obvious signs in IP at 2 hpc followed by IC and IM at 4 hpc. The lesions were noticed earlier in the kidney and most severe in IP. IHC detected antigen as early as PCR and isolation with intense staining in blood vessel lumen and wall, macrophages in choroid, focal haemorrhage in the renal interstitium and meninges especially in IP followed by IC and IM. The immunolocalisation of the antigen described for the first time further explain the pathogenesis of streptococcosis in red tilapia.

Highlights

Tilapia (Oreochromis spp.) are reported to be among the most cultured food fish worldwide (Klesius et al 2008)
Clinical and macroscopic findings The clinical signs observed during 24 hpc with S. agalactiae demonstrated haemorrhage around the eyes, operculum, fin and/or body, erratic swimming, c-shaped body curvature, imbalance, some were dull and were isolated from the others
The clinical signs were most obvious in fish that were challenged IP followed by immersion cut (IC) and lastly by IM bath of live S. agalactiae

Summary

Introduction

Tilapia (Oreochromis spp.) are reported to be among the most cultured food fish worldwide (Klesius et al 2008). About 80% of the global farmed tilapia production in 2002 showed Asia as the largest world producer. Among the Asian countries, Malaysia is listed among the top ten producers of farmed tilapia (El-Sayed 2006). Known as “aquatic chicken” are fast growing with ability to survive in poor water conditions. They are white flesh, eat variety of food, easy to breed with simple and noncomplicated hatchery technology (Nandlal and Pickering 2004).

Methods

Results

Conclusion