Variability in snake venom composition has been frequently reported and correlated to the adaptability of snakes to environmental conditions. Previous studies report plasticity for the venom phenotype. However, these observations are not conclusive, as the results were based on pooled venoms, which present high individual variability. Here we tested the hypothesis of plasticity by influence of confinement and single diet type in the venom composition of 13 adult specimens of Bothrops atrox snakes, maintained under captivity for more than three years. Individual variability in venom composition was observed in samples extracted just after the capture of the snakes. However, composition was conserved in venoms periodically extracted from nine specimens, which presented low variability restricted to the less abundant components. In a second group, composed of four snakes, drastic changes were observed in the venom samples extracted at different periods, mostly related to snake venom metalloproteinases (SVMPs), the core function toxins of B. atrox venom, which occurred approximately between 400 and 500 days in captivity. These data show plasticity in the venom phenotype during the lifetime of adult snakes maintained under captive conditions. Causes or functional consequences involved in the phenotype modification require further investigations.

Streptococcus agalactiae is an important bacterial pathogen in intensive Nile tilapia production, causing high mortality rates and great economic losses. This work aimed to evaluate the Nile tilapia vaccination against S. agalactiae and fed with ration containing probiotic AQUA PHOTO® composed of Bacillus subtilis and Lactobacillus plantarum, on the immune response action and gut microbiota. The experimental design was completely randomized with five treatments (CON = control; ADJ = adjuvant; PRO = probiotic; VAC = vaccine; PRO + VAC = probiotic + vaccine) and five replicates. The vaccine (bacterin + adjuvant) was injected after 21 days (21d) of probiotic feeding and the vaccine was booster 14 days post-vaccination (35d). After 14 days of the booster (49d), the fish were challenged with S. agalactiae and observed for more than 14 days, completing 63 days. The immunized group showed a better survival rate (CON 40%; ADJ 57%; PRO 67%; VAC 87%; PRO + VAC 97%). The treatments VAC and PRO + VAC, after booster produced higher levels of IgM antibodies compared with the control from the same time. The combination of probiotic and vaccination provided better protection against S. agalactiae infection, directly affecting the gut microbiological profile. These results indicated the contribution of probiotic to the adaptive immune response through the modulation of the intestinal microbiota, improving the effect of the vaccination. In conclusion, AQUA PHOTO®, composed of B. subtilis and L. plantarum, orally administered to Nile tilapia vaccinated against and challenged with S. agalactiae increases protection from infection and modifies the intestinal microbiota profile of the host, promoting the microbiota balance and improving adaptive immune response.

Dear Editor,According to Anuário 2021 Peixe BR da Piscicultura, in 2020 the Brazilian fish culture reached 802,930 tons, maintaining growth of around 5.93% compared to the previous year. Tilapia is the most popular aquaculture species item farmed in Brazil, representing 60,6% of the national production, with 486,155 tons in 2020, an increase of 12.5% over the previous year. As a result, Brazil consolidates itself in the 4 th position among the largest Tilapia producers in the world. Among the largest producing states in Brazil, Paraná stands out, which leads the national ranking, with 166,000 tons, followed by São Paulo, with 70,500 tons, and Minas Gerais with 42,100 tons.The intensification of fish production increases outbreaks of infectious diseases that affect the aquaculture sector. Streptococcosis is a fish disease that is horizontally transmitted by direct contact between infected and healthy animals or indirect contact with water and fomites, resulting in disseminated disease in fish production systems (MIAN et al., 2009). Streptococcus species are considered the pathogenic bacterium with the highest occurrence and economic importance for intensive fish culture (MISHRA et al, 2018).One of the most used ways to treat and prevent bacterial infections in a fish farm is the administration of antibiotics; however, the abuse of these drugs represents a risk to the environment, besides causing drug resistance to future infections (CARUSO, 2016), A good alternative strategy for the control of this disease is the administration of vaccines in animals, which has proven to be a successful strategy (SECOMBES & BELMONTE, 2016). Fish immunization can be performed by intraperitoneal injection, immersion, or oral administration (DADAR et al, 2017). Although these methods have the same purpose, there are advantages and disadvantages concerning the efficiency practicality, side effects, and cost/benefit of immunization. Therefore, it is interesting for fish producers to develop methods capable of identifying and thus confirming those animals that have been immunized.In this letter, we describe the development of an immunodiagnostic assay capable of detecting specific IgM in the blood circulation of experimental Nile tilapia that received the vaccine against S. agalactiae.Rabbit immunization protocol: The Immunization procedure was approved by the Animal Ethics Committee of the Butantan Institute (CEUA Protocol number 3124080618). A female rabbit, weighing 2.5 kg, was immunized intramuscularly with a solution containing 500 μg of purified tilapia IgM/500 μL of PBS, emulsified in 500 μL of Marcol-Montanide  . After 30 days, the animal was injected intramuscularly with 500 μg of IgM, following the same protocol as before. At the end of 30 days after the second immunization, two more doses of 150 μg of previously purified IgM/300μL of PBS were injected intradermally (i.d.) at intervals of 15 days. Blood was collected after the last immunization by central artery ear bleed. The serum was separated from the red cells by centrif...

The evolution of snake venoms resulted in multigene toxin families that code for structurally similar isoforms eventually harboring distinct functions. PLA2s are dominant toxins in viper venoms, and little is known about the impact of their diversity on human envenomings and neutralization by antivenoms. Here, we show the isolation of three distinct PLA2s from B. atrox venom. FA1 is a Lys-49 homologue, and FA3 and FA4 are catalytic Asp-49 PLA2s. FA1 and FA3 are basic myotoxic proteins, while FA4 is an acid non-myotoxic PLA2. FA3 was the most potent toxin, inducing higher levels of edema, inflammatory nociception, indirect hemolysis, and anticoagulant activity on human, rat, and chicken plasmas. FA4 presented lower anticoagulant activity, and FA1 had only a slight effect on human and rat plasmas. PLA2s presented differential reactivities with antivenoms, with an emphasis on FA3, which was not recognized or neutralized by the antivenoms used in this study. Our findings reveal the functional and antigenic diversity among PLA2s from B. atrox venom, highlighting the importance of assessing venom variability for understanding human envenomations and treatment with antivenoms, particularly evident here as the antivenom fails to recognize FA3, the most active multifunctional toxin described.