Use of DNA sequencing to map Streptococcus agalactiae and Streptococcus iniae infections in farmed Nile Tilapia (Oreochromis niloticus) on Lake Kariba in Zambia
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1
Ministry of Fisheries and Livestock, Zambia, Veterinary Services, Zambia
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2
University of Zambia School of Veterinary Medicine, Zambia
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3
Norwegian University of Life Sciences Faculty of Veterinary Medicine and Biosciences, Department of Basic Science and Aquatic Medicine, Norway
Fish farming in Zambia dates back to the early ‘70s where the practice was to rear fish in ponds, a practice predominated by small-scale farmers. The main species cultivated then was tilapia (Oreochromis macrochir and Tilapia rendalli). Nile tilapia (Oreochromis niloticus), believed to be more versatile than indigenous breeds has also been introduced with time. Over the last two decades, fish farming has increased significantly, with the emergence of commercial farming in cages on lakes. Commercial farms have been established on Lake Kariba where at least some of the farmed fish are Genetically Improved Farmed Tilapia (GIFT) imported from Thailand. Importation of breeding materials of fish is a practice known to be associated with the transfer of diseases. Indeed, a number of disease outbreaks have been observed in farms on Lake Kariba typically affecting large fish (more than 200g) with increased mortalities from 2014 to date.
The present study is part of a larger study to map bacterial diseases in different fish farming systems in Zambia. The objective of the present study was to characterize the aetiology of the disease outbreaks using standard as well as molecular methods with a view of establishing the relationship with other known pathogens of tilapia world-wide.
Based on clinical symptoms of the fish that included, darkening of the skin, distended abdomen, eye opaqueness, unilateral or bilateral exophthalmia or endophthalmia, body ulcers and hemorrhagic areas on the skin and head, bacterial infections and in particular Streptococcus species infections were suspected. This was confirmed by culturing, Gram stain and biochemical tests of kidneys and liver samples from moribund fish during outbreaks of 2014 and 2015. PCR using primers designed on the basis of the 16S-23S rRNA intergenic spacer region followed by sequencing confirmed a mixed infection of S. agalactiae and S. iniae. The relationship between these and other Streptococcus species as well as the epidemiology of the disease in the lake versus ponds will be discussed.
References
Wijkstrom UN and Wahlstrom KO. 1992. Tilapia Culture by Farmers in Luapula Province, Zambia. ALCOM Field Document No.9
Mutoloki S1, Evensen Ø. 2011. Sequence similarities of the capsid gene of Chilean and European isolates of infectious pancreatic necrosis virus point towards a common origin. J Gen Virol. 2011. 92(Pt 7):1721-6.
Godoy MG, Kibenge MJ, et al. 2013.Infectious salmon anaemia virus (ISAV) in Chilean Atlantic salmon (Salmosalar) aquaculture: emergence of low pathogenic ISAV-HPR0 and re-emergence of virulent ISAV-HPR∆: HPR3 and HPR14. Virol J. 10:344.
Keywords:
Oreochromis niloticus,
Streptococcal Infections,
Streptococcus agalactiae,
Streptococcus iniae,
Lake Kariba
Conference:
AquaEpi I - 2016, Oslo, Norway, 20 Sep - 22 Sep, 2016.
Presentation Type:
Oral
Topic:
Aquatic Animal Epidemiology
Citation:
Bwalya
P,
Hang'Ombe
BM,
Mutoloki
S,
Evensen
O,
Store
S and
Store
P
(2016). Use of DNA sequencing to map Streptococcus agalactiae and Streptococcus iniae infections in farmed Nile Tilapia (Oreochromis niloticus) on Lake Kariba in Zambia.
Front. Vet. Sci.
Conference Abstract:
AquaEpi I - 2016.
doi: 10.3389/conf.FVETS.2016.02.00052
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Received:
29 May 2016;
Published Online:
14 Sep 2016.
*
Correspondence:
Dr. Patricia Bwalya, Ministry of Fisheries and Livestock, Zambia, Veterinary Services, Livingstone, Zambia/ Southern province, 10101, Zambia, trishbwalya20@yahoo.com
Prof. Bernard M Hang'Ombe, University of Zambia School of Veterinary Medicine, Lusaka, Zambia, 10101, Zambia, mudenda68@yahoo.com