Risk Assessment and Risk Management of an Epidemic of Thallotoxicosis at the Georgetown Zoo
Horace E. Walcott, DVM, MSPH, MSc
Blood and fecal specimens from 84% of a random sample of animals (n=26) at the Georgetown Zoo in Guyana were demonstrated by spectrophotometry to contain toxicologically significant levels of thallium. The topographic distributions of the mortalities and morbidities due to the thallotoxicosis were consistent with a pattern of criminal iatrogenic exposure of the affected animals. For all the animals examined by necropsy and toxicologic evaluation, the concentration of thallium in the heart was five to ten times the concentration in any other tissue. At the time of the epidemic, 1986, there were no physiologically based toxicokinetic models (PBTXKM) for thallium in non-domestic animals. The estimation of the doses of Prussian blue, the antidote of choice, was based on pharmacokinetic data from humans, laboratory rodents and domestic mammals.