Lactococcus garvieae is considered the main etiological agent of lactococcosis, a globally distributed disease characterized by haemorrhagic septicaemia in aquaculture species, leading to significant economic losses. The history of pathogenic Lactococcus garvieae clones for fish, dates back more than three decades, when it was first described following a septicaemic outbreak in Japan in marine Seriola fish farms (Seriola quinqueradiata), initially classified as a new enterococcus species (Enterococcus seriolicida).

Subsequently, outbreaks began to appear in freshwater fish farms in Japan (Japanese eel, Anguilla japonica) (Kusuda et al. 1991) and in Europe in rainbow trout (Oncorhynchus mykiss). The disease caused by this bacterium in fish showed signs like exophthalmia, petechiae on the opercula, and congestion of the pectoral and caudal fins. The similarity in clinical presentation and characteristics of this new strain with infectious outbreaks in freshwater fish farms in Spain, led to a comparative analysis of the bacterial culture characteristics, biochemical profile, and protein composition of both bacteria. This analysis provided phenotypic and phylogenetic evidence for reclassifying Enterococcus seriolicida as Lactococcus garvieae (Doménech 1993).

Several co-authors of this study belonged to the Department of Animal Health at the Veterinary Faculty of the Complutense University of Madrid. It was in this department, and later also at the Veterinary Health Surveillance Centre (VISAVET – UCM), where the first autogenous vaccines against L. garvieae were successfully developed. These vaccines were distributed in collaboration with DIBAQ Group to many freshwater fish farms in Spain where this infectious disease was present, significantly reducing its prevalence through this prophylactic measure. This work in vaccine development and the epidemiological and molecular characterization of L. garvieae was recognized and awarded with the first Jacumar Award for Research in Aquaculture by the Ministry of Agriculture, Fisheries and Food in 2001. Since then, numerous studies on this pathogen have been conducted by the research group from the Department of Animal Health, VISAVET, and DIBAQ Group, focusing on its phenotypic and molecular characterization (Vela 2000, Aguado-Urda 2010), its isolation from different animal species (Garcia 2001, Tejedor 2004, Tejedor 2008), comparison of isolates from different animal species and countries (Tejedor 2011), its zoonotic potential (Reguera-Brito 2016, Gibello 2016), development of detection techniques (Tejedor 2009, Perez-Sancho 2015), and studies on antimicrobial sensitivity (San Martin 2017, 2018, 2019).

At the international level, the publication of studies on this pathogen in the aquaculture sector is extensive, with publications confirming its worldwide distribution (Eldar 1999), studies on the epidemiology of the infection in relation to isolated strains (Eyngor 2004), immune response to the infection and comparisons among asymptomatic, symptomatic, and vaccinated animals (Ooyama 1999, Khalil 2023), various studies on genetic and phenotypic characterization (Morita 2011, Shahi 2020, Rao 2022), antimicrobial resistance (Maki 2008, Akmal 2023), susceptibility to infection (Algöet 2009), development of detection techniques (Tsai 2013), supplementation with probiotics or bacteriocins as a preventive measure (Sequeiros 2015, Baños 2019), vaccination (Hussein 2023), and review articles establishing L. garvieae as an emerging pathogen in aquaculture (Meyburgh 2017).

The concern created by this pathogen in aquaculture is further compounded by the description of Lactococcus petauri in 2017 from an abscess in a sugar glider (Goodman 2017). Since then, numerous publications have identified this new species as responsible for lactococcosis outbreaks in continental fish farms instead of the previously isolated L. garvieae (Kotzamanidis 2020, Altinok 2022, Vela 2024). Consequently, studies on L. petauri have focused on its identification (Catao 2023, Stoppani 2023), characterization at different levels, mainly to find differences between L. petauri and L. garvieae (Saticioglu 2023), pathogenicity (Catao 2023), vaccination strategies (Ruyter 2023), and evaluation of its zoonotic potential (Vendrell 2006, Martinovic 2021).

Recently, outbreaks of lactococcosis caused by L. garvieae in marine species such as sea bass (Salogni 2024), have set off the alarm about a new emergence of this pathogen. The genetic differences from other epidemiologically related strains and the pathogen’s resistance to antimicrobial treatment, underscore the importance of vaccination against L. garvieae as a crucial tool for controlling this disease. And once again, at DIBAQ, we are prepared to take on the challenge and provide scientific solutions to the problems that Aquaculture has to face.