Vertical transmission and concurrent infection of multiple bacterial pathogens in naturally infected red tilapia (Oreochromisspp.)

Abstract

Horizontal transmission of various bacterial pathogens in tilapia is well described, but there is scant information regarding their vertical transmission. This study aimed to determine the possibility of vertical transmission of two commonly reported bacterial pathogens (Francisella noatunensis subsp. orientalis and Shewanella putrefaciens) in natural stocks of red tilapia (Oreochromis spp.). Vertical transmission of these pathogens via gametes was evaluated using in vitro fertilization from 10 different families and analysing for the presence of bacteria in milt, unfertilized eggs, fertilized eggs and offspring at various ages (1‐day‐old larvae, 10‐day‐old fry and 30‐day‐old fingerlings), as well as water samples using colorimetric LAMP assay. The study revealed that both F. n. orientalis (6/10) and S. putrefaciens (4/10) was transmitted vertically to the fertilized eggs. Analysis of the water samples from different water sources (brood stock tanks, hatching chamber and larval rearing tanks) showed that both the pathogens were present in water samples with highest prevalence for F. n. orientalis followed by S. putrefaciens. Analyses for the presence of two pathogens in various organs (gonads, gill, liver, spleen, kidney and brain) of the healthy tilapia broodstock without any clinical symptoms of disease demonstrated they were carriers of S. putrefaciens and F. n. orientalis. This is the first documented evidence that vertical transmission via the broodstock of tilapia may also play an important role in transmitting these problematic pathogens to their progeny and underlines the necessity to modify the current disease management strategies in tilapia aquaculture.

Development of a recombinase polymerase amplification assay for rapid detection of Francisella noatunensis subsp. orientalis

“…The tissue samples were obtained from 78 moribund and clinically healthy Nile tilapia, Oreochromis niloticus (L.) that were randomly collected from two different geographical locations including 38 fish from three tilapia farms in the UK (Farm one (Lincolnshire): 10 fish / 40±3 gm; Farm two (Lincolnshire): 10 fish /45±2 gm; Farm three (London): 18 fish / 12±5 gm) and 40 fish from a commercial tilapia farm in Prachinburi province, Thailand (10±2gm). The first and second UK farms and the Thai farm had a history of natural outbreaks of francisellosis during 2011–2012 and 2008, 2013–2014 respectively with granulomatous lesions in the affected fish and variable mortalities [ 4 , 29 , 33 ]. The third UK farm had no history of francisellosis, but it supplied red tilapia fry to an aquaponics farm in London, UK, where a natural outbreak of francisellosis occurred during spring 2017.…”

“…Nucleic acid-based methods have been applied for Fno detection, including conventional polymerase chain reaction (PCR) [ 4 , 5 , 27 – 29 ], quantitative real time PCR (qPCR) [ 5 , 21 , 22 , 30 , 31 ], duplex PCR, in situ hybridisation [ 32 ] and loop mediated isothermal amplification (LAMP) [ 33 ]. Despite the fact that, these techniques have their own points of interest, downsides, for instance, time consuming [ 22 , 33 ], labour intensive, prerequisite for skilled staff, liability to give false negative or false positive results due to low sensitivity or specificity [ 21 ], high influence with reaction inhibitors [ 34 , 35 ] and requirement of complex design [ 33 ] make them more challenging to use for pond-site diagnosis.…”

The nature and consequences of co‐infections in tilapia: A review

“…In Thailand, a natural case of vertical transmission and co‐infections with Fno and Shewanella putrefaciens was reported for the first time from red tilapia ( Oreochromis spp.) broodstock (Pradeep et al, 2017). The authors' findings showed that both Fno (6/10) and S. putrefaciens (4/10) were transmitted vertically to the fertilized eggs.…”

Vaccination of Tilapia against Motile Aeromonas Septicemia: A Review

“…Morbidity and mortality of tilapia have been reported to be caused by co‐infections with A. hydrophila and S. agalactiae (Pradeep et al. ); A. veronii and Flavobacterium columnare (Dong et al. ); A. hydrophila , A. veronii , and Streptococus agalactiae (Liu et al.…”