Lactococcosis is a well-known infectious disease that affects aquaculture farming systems.
It is caused by Lactococcus garvieae, a warm-water pathogen, responsible of significant economic losses in aquaculture worldwide, in particular for rainbow trout.
The loss due to this infection is around 10-60% of the total rainbow trout production; increased mortalities are reported when water temperature exceeds 15 °C. L. garvieae has been traditionally considered the unique responsible of lactococcosis, but recently Lactococcus petauri has been linked to lactococcosis outbreaks in Europe and North America.
L. petauri shares high similarity in its genome sequence, morphological characteristics and biochemical profile with L. garvieae, which makes the diagnosis extremely difficult.
Currently available molecular diagnostic tools fail to distinguish L. petauri from L. garvieae. Average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) are commonly used for differentiating species.