A concise review of veterinary forensic medicine in Japan: current status and perspectives

Abstract

Veterinary forensic medicine has received increasing attention in recent years from the perspectives of animal abuse, veterinary malpractice, wildlife protection, and zoonosis. Veterinary forensic medicine, equivalent to human forensic medicine, is a relatively new field. Compared with Europe and the United States of America, Japan currently lags behind in both the education and practice of veterinary forensic medicine. However, the situation regarding animals in Japan has changed dramatically in recent years, and the need for veterinary forensic medicine is increasing. This manuscript provides an overview of veterinary forensic medicine and a brief description of its current status and prospects in Japan.

Introduction

Historically, investigating the cause of animal death has been the primary responsibility of veterinary pathology in veterinary medicine. However, in recent years, a new field of veterinary medicine, forensic veterinary medicine, has emerged and gained worldwide attention. Forensic veterinary medicine, equivalent to forensic medicine in human medicine, is a branch of veterinary medicine. Although it is still a developing field, several textbooks have already been published in Europe and the United States of America (USA), and some veterinary colleges have even incorporated it into their educational programs^{1, 2, 3, 4}. In addition to veterinary colleges, several nonprofit organizations exist, such as the Royal Society for the Prevention of Cruelty to Animals (RSPCA) in the United Kingdom and the American Society for the Prevention of Cruelty to Animals (ASPCA) in the USA. The RSPCA and ASPCA, which have existed for more than 150 years, work alongside law enforcement agencies to prevent animal cruelty in various ways^{5, 6}. The recent focus on forensic veterinary medicine is likely due to stricter global regulations concerning animal welfare and the importance of this field from the perspective of preventing harm to humans. This is based on the concept of “link”, which suggests that animal abuse is associated with interpersonal violence^{7, 8, 9}. Although the definition and role of forensic medicine in human medicine may change over time, it encompasses a wide range of medical problems related to the law, makes medical decisions based on these problems, and is applied in the fields of criminal justice, civil justice, public health, and social welfare^{10, 11}. The role of veterinary forensic medicine may be considered similar to that of human forensic medicine, including investigating the causes of death, investigating crimes, and improving public health and social welfare. However, a major difference between veterinary and human forensic medicine is that veterinary forensic medicine involves a wide variety of animal species, including companion animals, farm animals, laboratory animals, and wild animals. Therefore, it is expected to address an extremely wide range of issues, including not only the investigation of the causes of death and animal abuse but also animal health, public health, improvements in animal welfare and human welfare, food safety, prevention of harm to humans, preservation of species, and environmental issues¹².

However, veterinary forensic medicine has not yet been established as a discipline and is still being practiced in an exploratory manner, especially in Japan. This review provides a brief overview of veterinary forensic medicine and discusses its potential applications in veterinary and toxicological pathologies.

Turning Point for Veterinary Forensic Medicine in Japan

In Japan, the Act on the Protection and Management of Animals (Act No. 105 of October 1, 1973) was enacted in 1973, and for the first time, the prevention of cruelty to animals and proper handling of animals was clearly stated in the law. In 1999, the law was renamed the Act on Welfare and Management of Animals, and was further amended in 2005, 2012, and 2019, expanding legal adaptations, tightening regulations, and increasing penalties for animal welfare. The 2019 revision of the law marked a major turning point in the field of veterinary forensic medicine in Japan. The 2019 amendment to the law made it mandatory for veterinarians to report cases of animal abuse or suspected animal abuse to relevant authorities without delay. However, before this amendment, such reporting was only encouraged as an effort requirement. The increasing need to substantiate animal cruelty cases with each amendment to the law, combined with the proliferation of social media that has exposed the inappropriate treatment of animals, has marked the starting point for a major focus on veterinary forensic medicine. According to data on arrests for lifestyle and economic crimes compiled by the National Police Agency¹³, the number of arrests for animal abuse related to violations of Article 44 of the Act on Welfare and Management of Animals in Japan has been steadily increasing each year (Fig. 1). Notably, there was an increase of approximately 70 animal cruelty cases from 2020 to 2021 following the 2019 revision of the law. In addition to animal abuse, veterinary malpractice has increased in recent years as veterinary medicine has become more sophisticated, and forensic veterinary medicine is now required even for veterinary lawsuits¹⁴. Furthermore, the demand for veterinary forensic medicine has grown in recent years due to issues such as illegal wildlife trade and zoonoses, as governed by the Convention on International Trade in Endangered Species of Wild Fauna and Flora and the Act on Conservation of Endangered Species of Wild Fauna and Flora¹⁵. Since veterinary forensic medicine requires legal responses and handles a variety of animals, the laws related to veterinary forensic medicine in Japan are summarized in Table 1.

Fig. 1.

Number of animal cruelty arrests based on statistical data from the National Police Agency in Japan.

Table 1. Summary of National Laws in Japan Related to Veterinary Forensic Medicine.

Differences between Veterinary Pathology and Veterinary Forensic Medicine

Diagnostic and forensic autopsies have clearly differentiated roles in human medicine, being performed by pathologists and forensic pathologists, respectively. However, this difference is currently unclear in veterinary medicine. Forensic necropsies are not yet common in veterinary medicine, particularly in Japan. In some cases, clinical veterinarians perform forensic necropsies at the request of the police or government, or veterinary pathologists perform them at the request of the police, government, or clinical veterinarians. Both diagnostic and forensic necropsies are similar in that the cause of death is determined by observing the lesions. While diagnostic necropsies focus on clarifying the pathological mechanism, such as determining the validity of the clinical diagnosis and the effectiveness of treatment, forensic necropsies focus on determining the cause of death from the perspectives of criminal investigations and trials, public health, and animal health, as well as documentation of examinations and the collection of evidence^{3, 4}. There are no major differences in the basic necropsy procedures and techniques between diagnostic and forensic necropsies. However, even the slightest changes cannot be overlooked in forensic necropsies, which require more detailed observation and careful recording. This is because, unlike diagnostic necropsies, forensic necropsies must be performed under conditions of an overwhelming lack of antemortem information, and the evidence needed for legal decisions must be collected and documented. For example, the date and time of death are often unknown during a forensic necropsy. However, for legal verification, it is often necessary to estimate the time since death based on postmortem changes and conditions at the time the body was found. Differentiating postmortem changes from lesions is important, as it estimates the age of the animal. In diagnostic necropsies, only minimal skin peeling is performed. However, in forensic necropsies, it is necessary to peel the entire skin and observe the subcutaneous condition to find evidence. In addition, if external injuries are observed, careful measurement and recording are required in forensic necropsy to determine whether the injury occurred before or after death, or to determine the cause of the injury. For internal organs, not only must the gross findings of each organ be noted, but the weight of the organ must also be measured. The organ must be properly sampled and preserved for the verification and preservation of evidence. These are the same requirements for diagnostic necropsies. However, forensic necropsies require more thorough recording and preservation^{1, 2, 3, 4}.

Comparing veterinary pathology and veterinary forensic medicine, veterinary forensic medicine is a fairly interdisciplinary field, and veterinary forensic pathology is only one component of veterinary forensic medicine¹⁶. For example, veterinary forensic imaging, known in human medicine as autopsy imaging, is a useful tool that complements forensic necropsies in determining the cause of death in animals^{17, 18}. For poisoned animals, toxicological analysis by a veterinary toxicologist and pathological examination are essential, requiring veterinary forensic toxicology¹⁹. Additionally, there is a field of forensic entomology that applies entomology to estimate the time since death and the cause of death, along with knowledge of various other fields, such as veterinary genetics, veterinary dentistry, and clinical veterinary medicine, all of which are required to practice veterinary forensic medicine^{2, 3, 4, 20}. In light of the above, veterinary pathology needs to play a key role in providing evidence to determine animal abuse, accidental death, disease, and natural death in veterinary forensic medicine and to collaborate with experts in various fields. In veterinary forensic medicine, clinical veterinarians or veterinary pathologists are required to provide the necessary veterinary findings to consider the pathology and cause of death of the animal, whereas the role of proving the crime and finding the culprit lies solely with the police, prosecutors, and other judicial officials.

Investigating the Cause of Animal Death in Veterinary Forensic Medicine

Animal cadavers requested for necropsy in veterinary forensic medicine include various animal species, with diverse causes of death. There are two causes of death: intrinsic death, caused by disease, and extrinsic death, caused by external factors other than disease, such as accidents or other illnesses. Veterinary forensic medicine often requires determining the causes of death, especially to prove animal cruelty. Among the external causes of death, animal abuse is further subdivided into neglect, non-accidental injury (NAI), and sexual abuse. This includes not only direct violence, such as punching and kicking, but also attacks with weapons and poisoning by toxic substances^{1, 2, 3, 4}.

A retrospective study based on dog and cat necropsy records from a single facility in the United States reported that of 13,322 dog and cat necropsy cases, 119 (0.89%) were suspected of abuse²¹. Of the 119 reported cases, 73 (61.3%) involved dogs, 46 (38.7%) involved cats, and 62 (52.1%) demonstrated findings consistent with neglect. Findings suggestive of neglect included starvation, pica, dehydration, ecto-and endoparasites, and a lack of general or medical care. Of the 119 patients, 71 (59.7%) had lesions suggestive of NAI, including blunt force trauma, gunshot wounds, suspected intoxication, drowning, burns, strangulation, and asphyxiation²¹. Although the actual situation in Japan is unknown due to the lack of reported data, severe emaciation, dehydration, depletion of adipose tissue, and serous atrophy of epicardial fat due to neglect are frequently observed as major lesions in animal abuse cases, even in necropsy cases. A case of rickets was occasionally diagnosed due to feeding a dog an extremely unbalanced and inappropriate diet, which would also be considered as neglect in some cases. The case presented in Fig. 2 is that of a four-month-old female beagle, bred as a hunting dog, who developed an abnormal gait and difficulty standing from about three months of age. She gradually developed swollen joints in all four limbs and severe pain, and died at the age of four months. In this case, a necropsy was requested to prove a causal relationship with the vaccine, as the owner noted that the symptoms began after the vaccination. However, necropsy revealed enlarged growth plates in the long bones of the extremities and a rachitic rosary at the costochondral articulation, with histological evidence of physeal chondrodysplasia, leading to the diagnosis of rickets (Fig. 2). This case of rickets was caused by an extremely unbalanced diet of ramen noodles, boiled venison, and vegetables, where the owner’s ignorance led to the development of the disease.

Fig. 2.

The distal end of the humerus in a 4-month-old beagle dog diagnosed with rickets. A: Irregular thickening of growth plates. B: High magnification of A, showing disorganized arrangement of chondrocytes in the hypertrophic zone. C: High magnification of A, showing increased osteoid in trabecular bone. Bars: A=5 mm, B=50 μm, C=100 μm.

In contrast, a similar retrospective study conducted at an institution in Portugal reported that, among 160 dogs and cats subjected to forensic necropsy, animal abuse was suspected in 38 cases (24%), with blunt force trauma being the most common cause of death²². Similarly, a Spanish study reported blunt force trauma as the most common cause of animal abuse²³. NAI, including blunt force trauma, is caused by intentional abuse and is one of the most common causes of death from animal abuse, along with neglect. Although fractures have been observed in several cases of NAI, Tong reported five characteristics that distinguish fractures caused by NAI from those caused by accidents: multiple fractures, fractures occurring in more than one region of the body, transverse fractures, fractures presenting at a later stage of healing, and multiple fractures at different stages of healing²⁴. In contrast, the dog with multiple rib fractures and suspected NAI was diagnosed with fibrous osteodystrophy and multiple pathological fractures caused by chronic interstitial nephritis and renal hyperparathyroidism²⁵. Therefore, caution should be exercised when considering accidents, diseases, or NAI in cases of suspected animal abuse.

The percentage of poisoning in animal abuse cases varies widely, with a Canadian study reporting that 4.8% and a Portuguese study reporting 27% of cases were due to poisoning^{22, 26}. Dog poisoning cases in Portugal reported the breakdown of carbamates (45%), followed by rodenticides (33.0%), organophosphates (11.0%), and cyanides (11.0%)²². Although Gwaltney-Brant’s review suggests that most animal poisonings are due to unintentional accidents, and only a small percentage are intentional abuses, it is still reported that the actual number of poisoning cases may be higher than what is currently known¹⁹. Considering that acute poisoning often results in sudden death or nonspecific symptoms, and that there is an overwhelming lack of information before death, it is important to suspect all types of poisoning and conduct appropriate sampling. In addition, the amount of sample required to detect the causative agent of poisoning must be available, properly stored, and pretreated. Furthermore, the appropriate analytical methods must be selected by experienced toxicologists, particularly in Japan. Currently, only a few toxicologists meet several requirements, and few laboratories are capable of analyzing intoxicating substances. It is often difficult to prove poisoning, even in cases where it is strongly suspected. A case of suspected rodenticide poisoning was encountered in a miniature pet pig that suddenly died of systemic hemorrhage. This six-month-old female miniature pig developed numerous petechiae on the systemic skin, presented with hematuria, and died a few days later. The miniature pig had been kept in a garden and had no prior health problems. A postmortem examination was requested by the owner, who suspected possible intentional or accidental poisoning. Necropsy revealed severe systemic hemorrhage in the heart, brain, bladder, tongue, abdominal wall, diaphragm, stomach, intestine, liver, kidneys, and skin. Histopathological examination revealed multiple fresh hemorrhagic foci in these organs (Fig. 3). Rodenticide poisoning was suspected in this case because there were no findings suggestive of an infectious disease, and the animal died from systemic hemorrhage. An attempt was also made to detect rodenticides in the liver and muscle using high-performance liquid chromatography (HPLC); however, this was unsuccessful. In cases of animal poisoning in veterinary forensic medicine, in addition to lesions, information on the surrounding environment at the time of death is often important. For example, in cases of poisoning with mesomil, a carbamate insecticide mixed with food, unnatural blue-colored food or containers may be found around the scene, and the stomach contents may be blue-colored, and the mesomil-contaminated contents may have a weak sulfur odor². However, because the time of ingestion is often unknown and many chemicals can cause poisoning, even in small amounts, it is often difficult to find traces of poisoning. The sampling and preservation methods for poisoning cases have been described in detail in several veterinary forensic texts and articles^{1, 2, 3, 4, 19}. The key point is to consider the possibility of poisoning in all cases, excluding those in which the death is due to obvious trauma or other illnesses. To diagnose poisoning, it is necessary to gather clues from all sources, including the species, age, sex, weight, and clinical symptoms of the animal, as well as the circumstances of death and the surrounding environment. For toxicity testing, all major organs should be fixed in 10% neutral-buffered formalin, with some organs frozen and some refrigerated. In particular, 300 g of the liver, kidneys, adipose tissue, and brain should be retained as fresh material, and as much stomach contents, feces, urine, blood, and hair as possible should also be collected. Sampling is important not only to prove poisoning but also to preserve evidence. In addition to tissue samples, sampling of food, water, surrounding soil, plants, insects, etc., should also be considered. In recent years, component analysis techniques that combine HPLC or gas chromatography with mass spectrometry have rapidly advanced; however, there is still no analytical system capable of comprehensively screening for all toxic substances. Therefore, clinical findings, pathological findings, and environmental surveys must be comprehensively evaluated to determine which poison should be suspected and which analytical method to select.

Fig. 3.

Gross and histopathological lesions in a pet miniature pig suspected of rodenticide poisoning. A: Multiple hemorrhages in the colon (black arrow), peritoneum (red arrow), and bladder (arrowhead). B: Subarachnoid hemorrhage in the left hemisphere. C: Severe submucosal hemorrhage of the colon. D: Severe suburothelial hemorrhage of the bladder. Bars: A=3 cm, B=2 cm, C=100 μm, D=50 μm.

Potential Applications of Veterinary Forensic Medicine in Veterinary Pathology and Toxicologic Pathology

In veterinary forensic medicine, it is vital to document and provide objective evidence to make legal decisions regarding animal abuse and veterinary malpractice. Veterinary forensic scientists are responsible for providing objective findings, whereas the police and government are tasked with proving crimes and determining abuse. In veterinary forensic necropsies of animals in veterinary forensic medicine, the majority of cases involve investigating the cause of death in the absence of background information about the animal. Therefore, it is necessary to document lesions thoroughly without overlooking slight changes. Pathology is a tool in veterinary forensic medicine, and cooperation with a wide range of specialists, including clinical veterinary medicine, molecular biology, toxicology, microbiology, osteology, and entomology, is essential. Subsequently, it is necessary to consider the type of lesions formed, the mechanisms involved, and the cause of death in animals. In this regard, the importance of observation without preconceptions in veterinary and toxicological pathology, for which information is available in advance, and the importance of cooperation with other disciplines, will be reaffirmed. Furthermore, in several veterinary forensic medicine situations, veterinary findings must be explained to non-veterinary medical personnel. This ability to clearly explain findings is critical and is considered necessary for veterinary and toxicological pathologists.

Since careful recording of pathological findings by veterinary pathologists is crucial in determining criminal cases and veterinary malpractice, they are expected to play a major role in veterinary forensic medicine. Additionally, in cases of poisoning in veterinary forensic medicine, the observation of lesions in target organs is vital for elucidating the mechanism of toxicity and identifying toxic substances. Therefore, toxicological pathologists, who are familiar not only with pathological observations, but also toxicokinetics and toxicodynamics, will play a significant role. For example, in several cases of poisoning where there are few traces of stomach contents, pathological findings are important for diagnosis, such as acute hepatic failure caused by acetaminophen, acute kidney injury caused by ethylene glycol or lily poisoning, oral ulcers, and pulmonary fibrosis caused by paraquat. Therefore, there are high expectations for veterinary and toxicological pathologists in cases of poisoning^{4, 19}. Even in the United States and Europe, where veterinary forensic medicine is widely practiced, toxicological pathologists are currently less involved. However, considering that poisons affect both humans and animals and that the number of poisoning cases is expected to increase in the future, there will be great expectations for toxicological pathologists, especially given the difficultly in identifying the cause in most poisoning cases.

Conclusion

Veterinary forensic medicine is still in its early stages, particularly in Japan, where it has yet to be systematized, and there is a lack of case studies and research. As a result, the field is still being explored by individual researchers seeking solutions. Current challenges in veterinary forensic medicine include insufficient cooperation between veterinarians, the police, and the government; a shortage of facilities for conducting necropsies; and a lack of veterinarians with expertise in forensic medicine due to the absence of an established educational system. Veterinary forensic medicine may share similarities with veterinary and toxicological pathology in that it identifies abnormal findings from an objective viewpoint and determines the circumstances leading to death and the cause of death from the viewpoint of veterinary medicine. Therefore, cooperation between veterinary and toxicological pathology is expected in the future for the development of veterinary forensic medicine.

Disclosure of Potential Conflict of Interest

The author declares no conflicts of interest.