The Epidemiology of Human-Animal Interactions

Part III:Animals as Sentinels of Environmental Hazards

Larry Glickman, VMD, DrPHand

Nita Glickman, MS, MPH

Purdue UniversitySchool of Veterinary Medicine

The Epidemiology of Human-Animal Interactions:

Animals as Sentinels of Environmental Health Hazards

Larry Glickmanand

Nita Glickman

Instructional Objectives

Describe the risk assessment process

Explain the ‘sentinel’ conceptProvide a rationale for using pet

animals in risk assessmentExplain 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 studiesLaboratory animal toxicological

studies

Suggested Complementary Approach to Risk Assessment

Naturally occurring diseases in animals • Epidemiological studies of animal pop

ulations

• In situ studies

Sentinel:

‘Sentinel’ is derived from the French word ‘sentinelle’ meaning watch tower

Sentinels provideearly 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 mine

s 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 policeused canaries asdetectors forpoisonous gasduring a raid on the cult’s premises

An Example of a Potential Animal Sentinel That Was Overlooked

Mercury poisoning at Minamata, Japan (1956) & Niigata, Japan (1965)• Strange, erratic behavior of local cats that

consumed mercury contaminated fish• This behavior in cats

preceded similar changes in humans

• Unfortunately, the valueof 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

SystemsSystems 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 used3) Environment in question4) Natural habitat (observational) vs.

purposely placed (experimental orin 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 & availabilityExample: pet animals

59%

41%

Pet-Owning Households

Non-Pet Owning Households

Selected Diseases in Household Dogs Associated with Environmental

HazardsEnvironmentalContaminant

Disease inDogs

Method ofDiagnosis

Lead Acute toxicity Clinical signs& blood leadlevel

Asbestos Mesothelioma Histo-pathology

Insecticides Bladder cancer Histo-pathology

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

BLC* elevated Families with dog BLC low

# Families 12 71

# Children 21 98 # (%) BLC >40ug% Children Families

8 (38.1) 6 (50.0)

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

Example of a Veterinary Sentinel Event: Asbestos & Mesothelioma

(con’t)Dogs share their owner’s home

environment but do not have occupational exposures that could confound interpretation of human epidemiologic studies

Summary of a Veterinary Sentinel Event : Asbestos & Mesothelioma

5 yearsMesothelioma

ALERT

Preventive Action

Mesothelioma25+ Years

AsbestosExposure

Example of a Veterinary Sentinel Event: Insecticides & Bladder

Cancer in Pet DogsPet 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 dose-response pattern

00.5

11.5

22.5

33.5

Odds Ratio

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

8 yearsBladder Cancer

ALERT

Preventive Action

Bladder Cancer25+ Years

Insecticide exposure-tick & flea dips, sprays

ConclusionsPet 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