Cetacean Erysipelothrix rhusiopathae clinical disease incidence rate is reduced following water treatment changes in a closed artificial sea water system

Abstract

Cetaceans have been housed at John G. Shedd Aquarium, Chicago, Illinois, in an approximately 3 million-gallon, closed, recirculating, artificial saltwater system since March 1991. From then through September 2008 there were five clinical cases of disease caused by Erysipelothrix rhusiopathae with a case fatality rate of 40%. The incidence rate for that period was 5/173.9 (2.88%) animal-years. In September 2008, the system was entirely drained, and recommissioned in April 2009. From 2009 through 2019, there was one case of erysipelothricosis, which was not fatal: an incidence rate of 1/118.1 (0.85%) animal-years for that period. Thus, cetaceans housed in this system after the management changes were 3.39 times less likely to contract clinical disease due to E. rhusiopathae infection compared with those prior to the change. Simultaneously with the maintenance of the system and habitat, a change was made to system water sourcing and treatment. Pre-maintenance source water was entirely municipal water. Post-maintenance, source water includes approximately 30,000 gallons of water per week moved from systems housing other animals including teleost and elasmobranch fishes. The salt mixes added to the municipal water also changed and post-maintenance water temperature cycling was initiated. Diversity of the microbial communities of the water increased following the change and may in part explain the reduced erysipelothricosis incidence rate.