Veterinary Forensic Toxicology

What Is Veterinary Forensic Toxicology?

Forensic toxicology is defined as the application of toxicology to matters of the law. Human forensic toxicology encompasses three subfields: postmortem forensic toxicology, human performance toxicology, and forensic drug testing (Levine, 2010). Postmortem toxicology aids in the determination of cause and manner of death through identification of foreign substances within the body. Performance toxicology is focused on the identification and interpretation of the presence of substances that may impair or enhance an individual’s ability to perform a task. Forensic drug testing is the screening of body fluids or tissues from individuals to determine the presence or absence of illicit substances, such as would be conducted with workplace drug testing or court-ordered drug testing for parolees. The scope of human forensic toxicology is large enough for toxicologists to specialize in one or more of these fields. In comparison, veterinary forensic toxicology is a broader and less specialized discipline (Murphy, 2012). In addition to postmortem and performance toxicology, veterinary forensic toxicology encompasses other areas, including regulatory toxicology, insurance investigations, and wildlife toxicology (Ensley, 1995; Stroud & Kuncir, 2005). Historically, the majority of veterinary forensic toxicology focus has been regulatory toxicology, which is largely focused on policing of hazardous residues in food animals or their products (e.g., milk, eggs) that will enter the human food chain. Performance toxicology testing in the veterinary field is focused primarily on animal athletes, predominantly racing animals; this branch of veterinary forensic toxicology has been slowly declining as have the racing industries it serves. Toxicology testing for insurance purposes generally involves either the loss of large numbers of animals of significant monetary value (e.g., a herd of beef cattle) or loss of life or function of highly valuable animals (e.g., an elite racehorse). Postmortem investigations are most commonly done in situations involving loss of livestock for the purpose of identifying the source and preventing further losses. Postmortem forensic toxicology cases in companion animals most commonly relate to intentional and malicious poisonings and are less often performed, for reasons that will be discussed shortly; however, with more stringent enforcement of animal anticruelty laws, the frequency of investigations into malicious poisoning of companion animals appears to be increasing. The field of veterinary forensic toxicology is relatively small compared to human forensic toxicology, so most veterinary toxicologists tend to be “jacks-of-all-trades” and handle a variety of forensic toxicology cases as well as working in other areas of toxicology, such as research, teaching, and clinical toxicology (i.e., diagnosis and treatment of animal poisonings).

Veterinary forensic toxicology investigations are not performed as frequently as their human counterparts because of several factors unique to veterinary medicine (Gwaltney-Brant, 2016). First, suspicious animal injuries and deaths are not automatically investigated as they would be if a human were involved. While physicians are generally mandated to report suspected poisonings, there is no such mandate for veterinarians in many areas of the country; note, though, that some states do mandate that veterinarians report suspected animal abuse, which may include poisonings, depending on the statute. Unlike humans, where laws require investigation of malicious poisonings, it is generally up to the authorities whether they investigate animal poisonings, and historically many jurisdictions have chosen not to expend time and money to do so unless public health is involved, large numbers of animals are affected, or, occasionally, public outcry changes their minds. Unlike human forensic cases where governmental agencies cover the cost of the investigation and toxicology testing, in veterinary medicine those costs are usually passed on to animal owners, who may be unwilling or unable to pay for thorough forensic investigations. Often, the signs of poisonings are initially attributed to natural diseases, delaying the collection of appropriate samples for toxicological analysis; if the poisoning is finally recognized, the optimal time for collecting an appropriate and diagnostic sample may have passed.

Box 14.1 Veterinary Forensic Toxicology in the News: Selenium Toxicosis in Polo Ponies

On April 19, 2009, 20 Venezuelan polo horses attending the U.S. Polo Championships in Wellington, Florida, collapsed and died within a 6-hour time frame, with an additional horse dying several hours later. The cause of the deaths was determined to be acute heart failure due to damage to the heart muscle. Based on clinical signs and lesions found on necropsy, selenium toxicosis was suspected by veterinary toxicologists working on the case. Toxicological analysis confirmed the presence of toxic selenium concentrations in the tissues of all of the horses. The source of the selenium was found to be a vitamin and mineral supplement that had been administered by intramuscular injection to all but five horses in the Venezuelan polo horse stable. The fact that the five horses that had not been given the supplement were not affected led to the suspicion that the supplement may have been involved. It was determined that the supplement, which was formulated by a local pharmacy, contained 100 times more selenium than intended. In 2016, a jury awarded the owners of the horses $2.5 million in damages for the loss of the horses.

Since the focus of veterinary forensic toxicology is on the law, it is important to understand what those laws are. As of 2017, 12 U.S. states (Alabama, Arizona, Colorado, Delaware, Missouri, Montana, Nebraska, New Hampshire, North Dakota, Oregon, South Carolina, and Tennessee) and the District of Columbia did not specifically mention poisoning of an animal in their animal protection statutes (although one of these, South Carolina, did mention that it was illegal to poison a police dog or police horse). It could be argued that poisoning is implicitly covered by the terms “injury” or “harm” in many of these statutes; however, it could be argued that the omission of poisoning leaves a loophole in the laws. In some states, it is unlawful to poison an animal belonging to someone else; does this imply that it is legal to poison one’s own animal? If the law states specifically that it is illegal to poison cats and dogs, does that make it legal to poison horses? Certainly, standardization of state laws would enable more consistent enforcement and better protection of animals from would-be poisoners.

Despite the laws, animal poisonings rarely meet the criteria for criminal cases unless they are part of a larger criminal prosecution, such as federal investigation of a dogfighting ring. Intentional poisoning of food animals with the intent to adulterate the food supply may result in prosecution under chemical terrorism statutes. However, the majority of animal poisoning cases are relegated to civil court, with one party seeking damages from a second party whom they hold responsible for the poisoning (Desta et al., 2011) (Box 14.1 and Figure 14.1). In many jurisdictions, the standards for evidence admissibility and burden of persuasion for civil cases are not as rigorous as in criminal court. Many civil cases are ultimately settled out of court and it is frequently the quality of evidence on one side or the other that can sway one side or the other to settle (Murphy, 2012).