AccScience Publishing / MI / Online First / DOI: 10.36922/MI025340086
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ORIGINAL RESEARCH ARTICLE

Characterization of virulence gene profiles of Aeromonas hydrophila and Lactococcus garvieae from diseased Nile tilapia in Zambia

Kunda Ndashe1* ,  Katendi Changula1 ,  John Yabe1,2 ,  Ladslav Moonga1 ,  Bernard Mudenda Hang’ombe1,3
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1 Department of Paraclinical Studies, School of Veterinary Medicine, The University of Zambia, Lusaka, Zambia
2 Department of Veterinary Paraclinical Studies, School of Veterinary Medicine, University of Namibia, Windhoek, Namibia
3 Directorate of Research and Innovation, Copperbelt University, Kitwe, Copperbelt, Zambia
MI, 025340086 https://doi.org/10.36922/MI025340086
Received: 23 August 2025 | Revised: 29 November 2025 | Accepted: 12 January 2026 | Published online: 31 March 2026
© 2026 by the Author(s). This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution 4.0 International License ( https://creativecommons.org/licenses/by/4.0/ )
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Abstract

Fish production is threatened by frequent disease outbreaks, especially bacterial diseases that cause significant economic losses. This study characterized the key virulence gene profiles of Aeromonas hydrophila and Lactococcus garvieae isolated from diseased Nile tilapia in southern Zambia and assessed genotype–lesion associations. A total of 163 clinically affected tilapia were examined, from which A. hydrophila (43%) and L. garvieae (22%) were recovered predominantly from brain and kidney tissues. Virulence gene screening showed that A. hydrophila exhibited low-frequency profiles dominated by hemolysin A (hlyA) (20.5% in broodstock) and elastase (ela) (11.5% in grow-out), while aerolysin (aerA) and enterotoxin (act) were infrequently detected. L. garvieae displayed a hemolysin-skewed profile, with hly2 being most prevalent (27.3% in broodstock; 21.4% in grow-out), hly2 detected only in broodstock, and capsule gene cluster (CGC) and fibronectin-binding protein (fbp) genes occurring rarely. Significant gene–lesion associations linked aerA and ela with pale gills (r = 0.41, p < 0.01; r = 0.24, p = 0.05, respectively), act with skin discoloration (r = 0.27, p =0.02), and demonstrated inverse correlations between hlyA and fins (r = −0.4, p < 0.001) or hepatic hemorrhages (r = −0.27, p = 0.02) in A. hydrophila. In L. garvieae, hly3 correlated with enlarged liver (r = 0.23, p < 0.001), corneal opacity (r = 0.15, p = 0.05), and gill necrosis (r = 0.21, p = 0.01), while hly2 and capsule genes were associated with skin discoloration (r = 0.18, p = 0.02; r = 0.24, p < 0.001, respectively). Overall, virulence determinants occurred at low frequencies and in limited combinations, suggesting the circulation of less virulent strains and underscoring the value of genotype-informed surveillance for improving disease control in tilapia aquaculture.

Keywords
Nile tilapia
Aeromonas hydrophila
Lactococcus garvieae
Virulence genes
Post-mortem lesions
Funding
None.
Conflict of interest
The authors declare that they have no conflicts of interest relevant to this publication.
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Microbes & Immunity, Electronic ISSN: 3029-2883 Print ISSN: 3041-0886, Published by AccScience Publishing
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