Potential Implications of the Hygiene Hypothesis on Cetacean Management Systems
Modern facilities housing cetaceans strive to maximize husbandry efforts in order to minimize disease, optimize animal comfort, and provide an educational and enjoyable visitor experience. Veterinary professionals working with cetaceans in these facilities have noted different patterns of diseases between free-ranging and captive cetaceans. Emerging hygiene hypothesis research in the human medical literature may provide an explanation for these observations and raises many questions regarding the current housing recommendations for cetaceans.
The hygiene hypothesis was first proposed in 1989 by an epidemiologist who documented an inverse relationship between family size and the development of atopic disorders (Stanwell-Smith and Bloomfield 2004, Strachan 2000, Kemp and Bjorksten, 2003). The current hypothesis explores the relationship between the increased emphasis placed on hygienic practices (and the subsequent decrease in exposure to microorganisms) in urbanized societies and immune system changes, which favor the development of allergic and autoimmune responses in people. Exploration of this concept in veterinary literature is lacking, although one recent study demonstrated altered levels of IgE and autoreactive IgG in wild-type rodents housed in controlled (hygienic) and natural conditions (Devalapalli et al, 2006).
The John G. Shedd Aquarium (Chicago, IL) houses two species of cetaceans (Lagenorhynchus obliquidens and Delphinapterus leucas) in a closed water system. Aquaria such as this are examples of controlled environments where hygiene is maximized. Members of the Shedd veterinary staff have noticed changes in the monthly, routine blood work values for both of these groups of animals. Medical records were examined for six pacific white-sided dolphins (Lagenorhynchus obliquidens) and six beluga whales (Delphinapterus leucas) cared for at the Shedd Aquarium. These medical records contained data for an average of thirteen years for the dolphins (range: 3-19 years) and eleven years for the beluga whales (range: 6-17 years). Eight out of twelve (66.7%) cetaceans showed a clear negative trend in total white blood cell count (unpublished data). Animals that did not show this trend were either aquarium-born or experienced documented inflammatory processes later in life.
One potential explanation for this negative trend is a relative lack of immune stimulation created by the altered amounts and types of microorganisms found in the water of controlled systems versus the world's oceans. There are several other disease processes common in veterinary medicine that have a disuse component to their pathophysiology. Disuse atrophy of skeletal muscle, post-parturient hypocalcemia (milk fever) of dairy cattle, and iatrogenically induced hypoadrenocortical crisis are all examples of these types of diseases. Existing medical research supporting the relationship between microbial exposure and immune system function raises questions regarding the possible link between husbandry protocols and captive cetacean immune systems.
There are significant differences in the human hygiene hypothesis and the hypothesis regarding cetaceans proposed via this preliminary review. However, the premise that altered exposure to microorganisms may influence the development and/or function of an immune system is currently being widely investigated in the human medical field. Animals housed in controlled environments may serve as a resource for these investigations and the results may have clinical implications for an innovative branch of preventative medicine.
The authors would like to thank the John G. Shedd Aquarium for supporting this work.
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