Does Herd Immunity Exist in Aquatic Animals?

• Main Authors: Isaac F. Standish, Travis O. Brenden, Mohamed Faisal
• Format: Article
• Language: English
• Published: MDPI AG 2016-11-01
• Series: International Journal of Molecular Sciences
• Subjects: DNA vaccine; herd immunity; fish; muskellunge
• Online Access: http://www.mdpi.com/1422-0067/17/11/1898

Viral hemorrhagic septicemia virus genotype IVb (VHSV-IVb) is presently found throughout the Laurentian Great Lakes region of North America. We recently developed a DNA vaccine preparation containing the VHSV-IVb glycoprotein (G) gene with a cytomegalovirus (CMV) promoter that proved highly efficacious in protecting muskellunge (Esox masquinongy) and three salmonid species. This study was conducted to determine whether cohabitation of VHSV-IVb immunized fishes could confer protection to non-vaccinated (i.e., naïve) fishes upon challenge. The experimental layout consisted of multiple flow-through tanks where viral exposure was achieved via shedding from VHSV-IVb experimentally infected muskellunge housed in a tank supplying water to other tanks. The mean cumulative mortality of naïve muskellunge averaged across eight trials (i.e., replicates) was significantly lower when co-occurring with immunized muskellunge than when naïve muskellunge were housed alone (36.5% when co-occurring with vaccinated muskellunge versus 80.2% when housed alone), indicating a possible protective effect based on cohabitation with vaccinated individuals. Additionally, vaccinated muskellunge when co-occurring with naïve muskellunge had significantly greater anti-VHSV antibody levels compared to vaccinated muskellunge housed alone suggesting that heightened anti-VHSV antibodies are a result of cohabitation with susceptible individuals. This finding could contribute to the considerably lower viable VHSV-IVb concentrations we detected in surviving naive muskellunge when housed with vaccinated muskellunge. Our research provides initial evidence of the occurrence of herd immunity against fish pathogens.