The Epidemiology of Human Animal Interactions Part III Animals as Sentinels of Environmental Hazards

The Epidemiology of Human-Animal Interactions Part III: Animals as Sentinels of Environmental Hazards Larry Glickman, VMD, DrPH and Nita Glickman, MS, MPH Purdue University School of Veterinary Medicine The Epidemiology of Human-Animal Interactions: Animals as Sentinels of Environmental Health Hazards  Larry Glickman and  Nita Glickman Instructional Objectives  Describe the risk assessment process  Explain the „sentinel‟ concept  Provide a rationale for using pet animals in risk assessment  Explain how pet animals can be used as sentinels for environmental causes of human disease Risk Assessment  The process by which scientific evidence is accumulated and used to define the health effects resulting from the exposure of individuals or populations to hazardous chemicals or situations Usual Sources of Data for Risk Assessment  Human epidemiological studies  Laboratory animal toxicological studies Suggested Complementary Approach to Risk Assessment  Naturally occurring diseases in animals • Epidemiological studies of animal populations • In situ studies Sentinel:  „Sentinel‟ is derived from the French word „sentinelle‟ meaning watch tower  Sentinels provide early warning  A sentinel is like a guard dog on patrol “Classical” Example of Animals as Sentinels  Canaries in the coal mines - 1916 • Canaries were taken into the coal mines to warn of noxious gases • Canaries are more sensitive to the effects of odorless coal gas than humans “Modern” Example of Animals as Sentinels  Bioterrorism in Japan in 1995 • A Japanese cult released poisonous gas into the subway system • Japanese police used canaries as detectors for poisonous gas during a raid on the cult‟s premises  Mercury poisoning at Minamata, Japan (1956) & Niigata, Japan (1965) An Example of a Potential Animal Sentinel That Was Overlooked • Strange, erratic behavior of local cats that consumed mercury contaminated fish • This behavior in cats preceded similar changes in humans • Unfortunately, the value of this animal sentinel was not recognized early enough to prevent significant human morbidity • Supercourse Lecture on Minamata disease One Approach to Environmental Monitoring: Animal Sentinel Systems  Systems in which health information on animals exposed to environmental contaminants are regularly and systematically analyzed to identify potential hazards to other animals or humans. Primary Objectives of Animal Sentinel Systems  Facilitate assessment of human exposures to environmental contaminants  Facilitate assessment of health hazards resulting from such exposures  Indicate relationships between exposure & hazard, eg., dose-response Animal Sentinel Systems Can Be Classified By:  1) What is being monitored, i.e., exposure or effect  2) Species of animals used  3) Environment in question  4) Natural habitat (observational) vs. purposely placed (experimental or in situ) Selection of an Animal Species:  An ideal animal sentinel species for human health risk assessment is one that is exposed to chemical contaminants in habitats shared with humans or comparable with human habitats and at similar concentrations (e.g., pet animals) Desirable Features of Animal Sentinel Species  Abundance & availability  Example: pet animals 41% 59% Pet-Owning Households Non-Pet Owning Households Selected Diseases in Household Dogs Associated with Environmental Hazards Environmental Contaminant Lead Disease in Dogs Acute toxicity Method of Diagnosis Clinical signs & blood lead level Mesothelioma Histopathology Bladder cancer Histopathology Asbestos Insecticides Example of a Veterinary Sentinel Event: Lead Poisoning Comparison of Blood Lead Concentrations (BLC) of 119 Children and 94 dogs from 83 Low-Income Suburban Illinois Families Factor Families with dog Families with dog BLC* elevated BLC low # Families 12 71 # Children # (%) BLC >40ug% Children Families 21 8 (38.1) 6 (50.0) 98 9 (9.2) 6 (8.3) *BLC – blood lead concentration Example of a Veterinary Sentinel Event: Lead Poisoning (con‟t)  Family dogs can be sensitive sentinels of lead poisoning in children.  Veterinarians diagnosing lead poisoning in dogs have a responsibility to protect public health as well. Example of a Veterinary Sentinel Event: Asbestos & Mesothelioma  Mesothelioma is a highly fatal cancer of humans and dogs caused by asbestos exposure  The latency period between asbestos exposure and mesothelioma may be >25 years in humans  Pet dogs with spontaneous mesothelioma were used to identify environmental exposures that might increase their owner‟s risk of asbestos-related diseases  Dogs share their owner‟s home environment but do not have occupational exposures that could confound interpretation of human epidemiologic studies Example of a Veterinary Sentinel Event: Asbestos & Mesothelioma (con‟t) Summary of a Veterinary Sentinel Event : Asbestos & Mesothelioma Mesothelioma 5 years ALERT Asbestos Exposure Preventive Action Mesothelioma 25+ Years Example of a Veterinary Sentinel Event: Insecticides & Bladder Cancer in Pet Dogs  Pet dogs were used to test for an association between spontaneous bladder cancer and commonly used insecticides for flea & tick control Example of a Veterinary Sentinel Event: Insecticides & Bladder Cancer in Pet Dogs (con‟t)  Risk of bladder cancer was significantly increased by topical insecticide use & followed a doseresponse pattern 3.5 3 2.5 Odds 2 Ratio 1.5 1 0.5 0 0 1-2 >2 Number of Applications Per Year Further Implications of a Veterinary Sentinel Event: Insecticides & Bladder Cancer in Pet Dogs  Pet owners and dog groomers are often heavily exposed to topical insecticides during their application  The latent period for bladder cancer is < 10 years in dogs, but probably > 25 years in humans  Question: Is canine bladder cancer a sentinel health event? Summary of a Veterinary Sentinel Event: Insecticides & Bladder Cancer Bladder Cancer 8 years ALERT Insecticide exposuretick & flea dips, sprays Preventive Action Bladder Cancer 25+ Years Conclusions  Pet animals can serve as valuable sentinels for hazards in the home environment  Diseases of animals only make useful sentinels if they are recognized & reported in a timely manner  Sentinel systems require cooperation between human and veterinary health specialists