Quantifying Circulating IgY Antibody Responses against Select Opportunistic Bacterial Pathogens and Correlations with Body Condition Factors in Wild American Alligators, Alligator mississippiensis .

Little is known about the disease ecology of American alligators ( Alligator mississippiensis ), and especially how they respond immunologically to emerging infectious diseases and zoonotic pathogens. In this study, we examined serum samples collected from wild alligators in Florida (2010-2011) and South Carolina (2011-2012, 2014-2017) for antibody responses to multiple bacteria. Immunoglobulin Y (IgY) was purified from serum to generate a mouse monoclonal antibody (mAb AMY-9) specific to the IgY heavy chain. An indirect ELISA was then developed for quantifying antibody responses against whole cell Escherichia coli, Vibrio parahaemolyticus , Vibrio vulnificus, Mycobacterium fortuitum, Erysipelothrix rhusiopthiae , and Streptococcus agalactiae . In Florida samples the primary differences in antibody levels were between January-March and late spring through summer and early fall (May-October), most likely reflecting seasonal influences in immune responses. Of note, differences over the months in antibody responses were confined to M. fortuitum , E. rhusiopthiae , V. vulnificus , and E. coli . Robust antibody responses in SC samples were observed in 2011, 2014, and 2015 against each bacterium except E. coli . All antibody responses were low in 2016 and 2017. Some of the highest antibody responses were against V. parahaemolyticus , M. fortuitum , and E. rhusiopthiae. One SC alligator estimated to be 70+ years old exhibited the highest measured antibody response against V. parahaemolyticus and M. fortuitum. By combining data from both sites, we show a clear correlation between body-mass-indices (BMI) and antibody titers in all six of the bacteria examined. Our study provides a critical antibody reagent and a proof-of-concept approach for studying the disease ecology of alligators in both the wild and in captivity.