Transmission and pathology of Streptococcus inane in monosex Nile tilapia (Oreochromis niloticus) in aquaculture of Bangladesh

Abstract

Streptococcus iniae is a major fish pathogen, recently emergent outbreaks were recorded in commercially cultured monosex Nile tilapia (Oreochromis niloticus) result in significant losses termed “streptococcosis”-causes unusual appearances with multi-focal pin-point haemorrhages, abscesses, necrosis and ascites in skin, fin, muscle, liver, spleen, kidney, blood, interstitial fluid specially in central nervous system and brain. This disease was more prevalent (>26%) at summer when the water temperature was approximately >25oC, percentage of mortality was higher >41% during the overcrowding and improper water chemistry. Raised levels of glucose and ammonium in blood serum causes reduced number of free blood cells released into the haemolymph to stomach and gut, result in refrain from eating in diseased tilapia. Stocking density (200 fish/decimal; class IV) had significant effect (P<0.01) on the total production (5,000 to 5,500 kg/ha). S. iniae in the circulating blood cells, extra-tubular haemal spaces containing blood vessels, fixed phagocytes in the hepatopancreas (gastrointestinal tract), bacteria-like particles in the brain tissue, vacuum and necrosis in hepatocytes revealed with histopathology. In vitro study revealed that cohabitation of dead or infected fish with healthy fish resulted infection (horizontal transmission mechanism) to the healthy fish.

Pathomorphology of experimental Streptococcus iniae infection in tilapia (Oreochromis niloticus)

“…Haemorrhages and macrophage infiltrations have also been identified in the digestive tract (Hossain et al, 2014). The changes that we observe for the liver, kidney and digestive tract were in like with previous studies except for a few.…”

First identification and characterization of Streptococcus iniae obtained from tilapia (Oreochromis aureus) farmed in Mexico

“…Importantly, streptococcosis in tilapia is primarily attributed to S. agalactiae (Li et al., , ; Zamri‐Saad et al., ), including in Latin America (Conroy, ; Ortega, Barreiro, et al., ; Sheehan, ). However, the majority of S. iniae reports also originate from infections in tilapia (Hossain, Ehsan, Rahman, Haq, & Chowdhury, ; Sheehan, ; Shoemaker, Evans, & Klesius, ; Weinstein et al., ; Zhou et al., ).…”

Dietary supplementation of garlic ( Allium sativum ) modulates gut microbiota and health status of tilapia ( Oreochromis niloticus ) against Streptococcus iniae infection

“…Streptococci infection in fish is widespread in tropical and subtropical countries, especially during summer (Pourgholam et al., ). Streptococci associated diseases in fresh and saltwater fish cause an estimated US$150 million production losses in each year (Hossain, Ehsan, Rhaman, Haq & Chowdhury, ). The infection was first reported in Amazon freshwater dolphins ( Inia geoffrensis ) in New York and San Francisco, USA (Amal & Zamri‐Saad, ).…”

“…Tilapia is one of the most popular fish consumed in Bangladesh. However, different factors including high stocking density, warm and humid weather, low‐quality feed, etc., influence the rapid spread of bacteria into the pond results in streptococcosis outbreaks (Hossain et al., ). Antibiotics are often used to treat streptococci infection, but the widespread use of commercial drugs cause the transmission of multidrug‐resistant bacteria into the pond (Park et al., ).…”