Lake Titicaca is the main area of rainbow trout aquaculture in Peru, responsible for over 80% of trout production mainly made up of small and medium size farms. The growing trout production, large number of farms, acquisition of egg without adequate control of the country’s health authority and increasing of temperature (up to 20°C in summer) could be important factors for the appearance of recent outbreaks of Weissella tructae. Reported since 2019, in a few years it has become the main disease that affects trouts, mainly in growing, adults and breeding fish, which has, which produces a greater impact due to the losses of farmers. The aim of this study was to characterize Weissella tructae infection and tested some vaccine protocols against this bacterium.
One hundred and twenty trouts were infected (60 fry and 60 juveniles) using 8.2 x 106 CFU at 14 and 17°C. After 96h, fish were sacrificed, and bacteria were recovered from spleen and brain (figure 1).
In a second trial, vaccines were administered by intraperitoneal injection (0.1 mL= equivalent to 8 × 107 CFU per fish). For vaccination, the bacterium was inactivated with formaldehyde and fish (200) were placed in 250L-tanks (25 fish per tank). Finally, fish were distributed in four groups. G1: bacterin + adjuvant; G2: bacterin; G3: adjuvant; G4: PBS. After 30 days, fish from each treatment were intraperitoneally infected with 0.1 mL of bacterial inoculum and returned to the previous tanks. Survival was registered for 30 days (figure 2).
Besides, DL50 trial, and histopathology assays were also performed to characterize the weissellosis in trouts.
Finally, this study shows that is possible to control this infection using vaccines in controlled conditions and that the temperature plays an important role in the pathogenesis of the disease. Intraperitoneal vaccines are a good strategy, however, it is necessary to perform field trials using intraperitoneally vaccines.