Pet dogs as sentinels for environmental contamination

Our plain-English summary of Pet dogs as sentinels for environmental contamination, by L.C. Backer, C.B. Grindem, W.T. Corbett, et al (The Science of the Total Environment, 2001).

The study

• Authors: L.C. Backer, C.B. Grindem, W.T. Corbett, L. Cullins, J.L. Hunter
• Journal: The Science of the Total Environment
• Published: 2001;274(1-3):161-9
• Cited by: 69 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

The presence of environmental contaminants in air, water and food may pose significant health risks to the exposed human population. However, problems associated with assessing chronic exposure to low doses of environmental chemicals, multiple exposure routes, diseases with long latency periods, and non-specific health outcomes make it difficult to conduct the appropriate human epidemiologic studies. It may be useful to complement human epidemiology with animal studies. Animals monitored or evaluated in situ for the appropriate suite of endpoints can provide information about both exposure levels and potential adverse health effects. Animals have served as sentinel indicators for health effects associated with a number of environmental exposures, including pesticides and asbestos. Pet dogs may be particularly valuable sentinels because they share the human environment. In addition, dogs respond to many toxic insults in ways analogous to humans, they have physiologically compressed life spans, and they are free from some important lifestyle risk factors for disease. An example of how pet dogs may be used as sentinels for potential human health hazards involves a study of the genotoxic effects resulting from exposure to a mixture of chemicals from nearby Superfund sites. We conducted a cross-sectional study of exposed dogs (living in the community with the Superfund sites) and controls (living in a nearby community). The pet owners completed a questionnaire, and we collected a blood sample from each dog. The blood samples were analyzed for standard clinical parameters and assays for possible genotoxic effects (peripheral blood lymphocyte micronucleus frequency and lymphocyte subtyping). Pet dogs living near the Superfund sites had a higher micronucleus frequency than control animals, suggesting that the dogs may have been exposed to environmental contaminants from these sites.

In plain English

This cross-sectional study asked whether pet dogs could act as sentinels for human exposure to two Superfund hazardous waste sites in a North Carolina town of 2700 people. The sites were contaminated with organochlorine pesticides, including DDE, DDT and lindane, and with volatile organic chemicals. Asbestos was not studied; it appears only in the authors' review of earlier research. Blood was taken from 20 dogs living in the town and 21 control dogs from a similar nearby town, recruited through local veterinarians from June to September 1992. Routine blood counts and serum chemistry were within the normal range for all dogs. The exposed dogs had significantly more micronuclei, a marker of possible genetic damage, in their lymphocytes: on average 24.2 per 1000 binucleated cells, compared with 11.0 in controls. Their relative risk of an abnormally high micronucleus percentage was 7.9 (95% CI 2.06 to 30.2) or 14.7 (2.1 to 101), depending on the cutoff. Lower CD4/CD8 ratios in exposed dogs were not statistically significant. The authors concluded that pet dogs can be an early warning sentinel for human exposure. They noted that each dog was tested only once and that exposure was assessed qualitatively.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Cross-sectional study comparing exposed and unexposed pet dogs, preceded by a brief literature review
• Who was studied: 20 exposed pet dogs living in a North Carolina town of 2700 people with two Superfund sites, and 21 control dogs from a similar nearby town. The dogs were clinically healthy, at least 5 years old, had lived in the area at least 4 years, and were recruited through local veterinarians between June and September 1992.
• Exposure: Living in the town with the Superfund sites, where all residents lived within 1.5 miles of one or more sites. The sites were contaminated with organochlorine pesticides (including DDE, DDT and lindane) and volatile organic chemicals. No asbestos exposure was studied.
• Main results:
  • Complete blood counts and serum chemistry panels were within the normal range for all dogs in both groups.
  • Exposed dogs (n=20) had a mean of 24.2 (SD 10.39) micronuclei per 1000 binucleated lymphocytes, compared with 11.0 (SD 3.29) in control dogs (n=21). The authors reported this difference as statistically significant.
  • Exposed dogs had significantly more micronuclei than control dogs.
  • Compared with control dogs, the relative risk for exposed dogs of an abnormally high percentage of micronucleated binucleates was 7.9 (95% CI 2.06 to 30.2) using a cutoff of the control mean plus 1 SD.
  • Using a cutoff of the control mean plus 2 SD, the relative risk for exposed dogs of an abnormally high percentage of micronucleated binucleates was 14.7 (95% CI 2.1 to 101).
  • In exposed dogs, the relative risks for abnormally high alkaline phosphatase, abnormally high alanine aminotransferase, or an abnormally low CD4/CD8 ratio were not statistically significant.
  • Average CD4/CD8 lymphocyte ratios were lower in exposed dogs (mean 1.50) than in control dogs (mean 2.02), but the difference was not statistically significant.
  • The micronucleus test appeared to be a very sensitive and specific screening test for this exposure, with sensitivity 0.75 and specificity 0.90 at one cutoff, and 0.70 and 0.95 at the other. Liver enzymes and CD4/CD8 ratios were not sensitive enough to serve as screening tools.
• The authors' conclusion: The authors concluded that pet dogs can be an early warning sentinel for human exposure to environmental contaminants. They also concluded that further investigation is needed to assess the sensitivity and reliability of biomarkers in sentinel animals.
• Limitations the authors state:
  • Each dog was examined only once, so trends in biomarkers could not be determined.
  • Exposure was assessed qualitatively, based on historical evidence of widespread contamination in the area.
  • Higher past exposures may have caused biomarker changes that were no longer detectable at the time of the study.

Topics

Medical terms in this study, explained in our Lexicon: Latency, Epidemiology, Environmental Exposure, Superfund.

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