MSD Animal Health, which is known as Merck Animal Health in North America, has obtained approval from Indonesian authorities to begin marketing an inactivated vaccine that aids in the protection against Streptococcus agalactiae infections in tilapia.
AQUAVAC Strep Sa, the world’s first oil-adjuvanted vaccine for tilapia, is administered intraperitonealy as a single-injection dose to fish weighing no less than 15 grams. Vaccinated fish develop protection within 3 weeks of injection and laboratory challenge studies have demonstrated that this protection lasts for at least 30 weeks.
“AQUAVAC Strep Sa represents a major breakthrough that will help Indonesia’s tilapia producers reduce losses from this disease while helping to improve the long-term sustainability of Indonesia’s fish farms,” said Neil Wendover, technical director for warmwater aquatic species at MSD Animal Health. He noted that the vaccine — the first of its kind in the industry — was registered successfully in Brazil in late 2011 and subsequently in several Central American countries.
“The tilapia industry is quickly adopting vaccination as a disease management tool because it fits with its strategy to produce healthy, profitable, high-quality fish for local and export markets,” Wendover added, noting that vaccinated fish often show significant performance improvements when compared to unvaccinated controls. MSD Animal Health is pursuing registrations for AQUAVAC Strep Sa in other major tilapia markets.
S agalactiae is a bacterial disease that strikes tilapia at all stages of the production cycle, but disease outbreaks late in the grow-out period are the most economically significant because, at that point, tilapia farms have already made considerable investments in feed, energy and other production inputs.
According to Wendover, streptococcus thrives at temperatures from 28-32°C. Fish stressors such as rapid increase in temperatures, fluctuating water quality and high competition and stocking densities have made fish more susceptible to the disease. Streptococcosis typically causes bulging eyes and a swollen belly. Infected fish swim in an erratic circular motion and often experience high mortality. “If left uncontrolled, S. agalactiae Biotype II infection could cause mortality rates of up to 90 percent in pre-market age fish,” Wendover said. “The disease also results in significant declines in feed conversion and growth in tilapia. Surviving infected fish may also be damaged and produce lower quality and lower yielding fillets.”
Epidemiological surveys conducted by MSD Animal Health in major tilapia-producing markets have collected over 1,000 bacterial isolates from tilapia reared at 74 sites in 14 countries.
“Streptococcal species were the dominant bacterial pathogens, accounting for more than half of all bacteria identified. S agalactiae was more prevalent than S iniae,” reported Siow Foong Chang, site manager at MSD Animal Health’s aquaculture research facility in Singapore. Of the S agalactiae isolates collected globally, Biotype II accounted for 56 per cent compared to 26 per cent for Biotype I. “These data showed an unexpected geographical segregation of the biotypes, with S agalactiae Biotype II being the only strain isolated from Indonesia and Latin America,” he added.